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Why do full frames have shallower DOF?

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tzakielmuto says:

Why do full frame sensors provide a shallower DOF and more isolation? What is the technical or physical reason for this?
4:52PM, 14 August 2008 PDT (permalink)

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ryanthejones says:

I think if you read this article: en.wikipedia.org/wiki/Depth_of_field
it might make more sense. You kind of have to explain DoF graphically for it to be absolutely clear. I believe it has to do with the "circle of confusion" but the layman's explanation is that the bigger sensor allows the light to spread out more. Does any of that make sense?
69 months ago (permalink)

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brnpttmn says:

The short answer is that you have to use longer focal lengths to get the same field of view. Longer lenses produce shallower DoF.
69 months ago (permalink)

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Andrew Ball says:

your using the whole image circle. where on APS cameras its only the center of the image on full frame lenses. so your getting all the fall off and everything that the lenses produce which gives the feeling of shallower depth of field. having a good idea of focal plane and such when your shooting will help you.

i recognize this from film and it just taking some getting use to.
69 months ago (permalink)

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Dan Hershman says:

what cosmic_jeebus! said.....
69 months ago (permalink)

Uneppe [deleted] says:

FF cameras have shallower DOF also with same equivalent focal lenghts than DX. I think Ryan is right: larger circles of confusion give shallower DOF.
69 months ago (permalink)

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scott*eric says:

Or here's another good way to look at it: if you cropped the image you took at 50mm with FX with the same 1.5 crop of the DX, the DoF would look nearly the same as if you took it with that same 50mm on the DX. I believe it was Thom Hogan that put it that way.
Originally posted 69 months ago. (permalink)
scott*eric edited this topic 69 months ago.

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brnpttmn says:

FF cameras have shallower DOF also with same equivalent focal lenghts than DX...larger circles of confusion give shallower DOF. .
The opposite is actually true. Larger CoC will effectively give you more DoF. If you're not worried about equal FoV, the same lens at the same aperture and focus distance will give more DoF on FX then it will on DX.
Example:
On a D3, 50mm @ F5.6 focused to 10ft = 4.25ft
On a D300, 50mm @ F5.6 focused to 10ft = 2.76ft
www.dofmaster.com/dofjs.html
69 months ago (permalink)

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Dustin Diaz says:

Remember that there is also three ways to effect dof aside from the size of your sensor.

1) (easiest) aperture. Simply use a higher aperture for more shallow depth, and a lower aperture for greater depth.

2) Zoom (second easiest). That's right, just zoom in on that subject. You will have more shallow depth if you back up, and then zoomed in (for the same subject area). This technique does not apply for prime fixed lenses.

3) Distance from camera to object (least easiest). It's least easiest (but still easy) since it might not always be an option in some scenarios where you must stay put (like how a sports photographer has to sit on the sidelines). Nevertheless, get your camera closer to the object and you'll get more shallower depth (this is why macros often have much more shallow depth).
69 months ago (permalink)

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SuperFriend says:

The physical distance from the image plane to the lens mount is farther away. The longer this distance, the greater ability to delineate the point of focus from background and foreground. This is why medium and large formats have can isolate subjects in complete sharpness while backgrounds go very soft. I love this effect, even just comparing FX full frame 35mm DSLR's like the D700 to an APS-C DSLR like the D300. The difference is substantial and adds greatly to the creative process, especially in portraiture.

The picture below was shot with a D700, Tamron 28-75mm f/2.8AF, f/4 @ 1/125 sec @ ISO 3200. On my D300, using my Tamron 17-50mm f/2.8AF at the same exposure values, the background elements would have been much sharper, competing with Kate for interest in the frame.

This depth of field difference alone was enough for me to justify replacing my D300 with a D700.

Halloween-1.jpg
66 months ago (permalink)

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brnpttmn says:

The physical distance from the image plane to the lens mount is farther away.
Nope. All F-Mounts are 46.5mm from mount to film/sensor.


Once again, the main difference between DX and FX in regards to DoF is that you have to use longer focal lengths to get the same FoV. It's that easy.
66 months ago (permalink)

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SuperFriend says:

cosmic is right. I stand corrected and apologize for spreading disinformation - something that I detest....
66 months ago (permalink)

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Mathew With One T says:

Not completely right. If you compute DoF and adjust for focal length you still get different answers -- CoC playing a role.

Example:
D300, f/5.6, 200mm, subject at 20 ft = .67 feet
D700, f/5.6, 300mm, subject at 20 ft = .44 feet

Also happens if you keep the same focal length and change the subject distance by the correct factor.

www.dofmaster.com/dofjs.html
66 months ago (permalink)

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_JDT0505 says:

Maybe we should ask Ken Rockwell...
66 months ago (permalink)

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mm_rivrep says:

Try this.
Shoot a subject on a tripod with a medium tele like a 105mm at a set aperture (say 4). Then shoot the same subject from the same spot with a wide angle (say a 20mm) at that aperture. In both cases focus directly on the subject And frame it in the centre. Then crop the 20mm shot to have the same FoV as the 105mm shot. I reckon that the DoF will look the same because DoF, like distance compression, is essentially a function of distance from the subject, focus point and aperture, rather than focal length.

Now try this.
Frame a subject right in the centre and shoot it with a 105mm (or another) at f4 on a DX camera. Then shoot it with an FX camera with the same lens and aperture. Then crop the FX shot to DX size so the FoV is the same as the first shot. There shouldn't be a difference in the DoF.

I think you'll find that the illusion of shallower DoF in FX format when using an identical lens and aperture comes from the fact that there is more around the edges to be out of focus because the FoV is wider.

Am I wrong?
Originally posted 66 months ago. (permalink)
mm_rivrep edited this topic 66 months ago.

tomnorth [deleted] says:

The DOF of the Nikon D700 is greater than a D300, not less. This is due to the larger CoC for the D700. Crop factor has nothing to do with DOF. All you're doing is taking a crop from the middle of a full-frame image. You are not changing the focal length. Focal length has a huge impact on DOF. A D700 has a DOF of 35 ft. at f/8 and 50mm focused at an object 20 feet away. Keeping everything else the same but moving to 200mm the DOF goes to 1.42 ft.
66 months ago (permalink)

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Borneo Pilot says:

"Crop factor has nothing to do with DOF."

This is incorrect. Crop factor is directly related to CoC. That is why when you go to www.dofmaster.com it asks you for your camera type (how big a sensor do you have?). You correctly point out that the D700 technically has more DOF than a DX D300 because of the larger CoC, but this is only if you hold all other factors the same, like focal length, aperture, and distance to subject (as Cosmic already pointed out). The problem is that if you do that the D300 image would be cropped in more, making it appear closer. So to get the equivalent FOV you have to back up the D300 which gives it more DOF.

So yes, technically a D700 has more DOF than a DX camera because of larger CoC, but in practice a D300 has more DOF because we generally care much more about the FOV. Cosmic Jeebus already correctly pointed this out.
66 months ago (permalink)

tomnorth [deleted] says:

The Canon 1D Mark III is a full-frame camera but it has a CoC of .023 vs. .03 for the D3/D700 and .02 for the D300. My point is that there is no direct correlation between crop factor and DOF.

In the FAQ section on dofmaster.com they mention that you should use the actual focal length when calculating DOF, not the 35mm equivalent with the crop factor applied. I have quoted this website below. How can you measure DOF without holding all other factors constant? If you don't you do not have an apples-to-apples comparison.

"Do I use the ACTUAL FOCAL LENGTH or the 35MM EQUIVALENT FOCAL LENGTH for depth of field calculations?

Always use the ACTUAL focal length when calculating depth of field.

Usually, the actual focal length is printed on the front of a lens' barrel. Sometimes the length is printed on a digital camera body. The actual focal lengths of many digital camera lenses are listed here.

DO NOT use the 35mm equivalent focal length for depth of field calculations.

Be sure to use the appropriate circle of confusion for your camera."

It is true that for the same FOV a DX format camera will have a greater DOF because you have to shoot at a shorter focal length to get the same FOV as an FX format camera. That does not mean that a DX format camera has a greater DOF than an FX format camera. It just means that shorter focal lengths have greater DOF. That's it. I am trying to be responsive to the original question posed, specifically, why is it that FX format cameras have a shallower DOF. The answer is they don't. The D700 and D3 have a greater DOF than a D300.
66 months ago (permalink)

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Borneo Pilot says:

"The Canon 1D Mark III is a full-frame camera but it has a CoC of .023 vs. .03 for the D3/D700 and .02 for the D300. My point is that there is no direct correlation between crop factor and DOF."

The 1D Mark III is NOT FX. It has a crop factor of 1.3x FX, whereas Nikon's DX line has a crop factor of 1.5x. The 5D and 1Ds lines are both FX and have the same CoC as the D3 (.030). Keep in mind that these are subjective numbers too. But I reiterate that the size of your sensor is directly related to CoC!. All of the FX cameras have a CoC of approximately .030, according to www.dofmaster.com.
66 months ago (permalink)

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Franky2step says:

Will the real answer please stand up?
65 months ago (permalink)

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LebronPhoto says:

I also agree with Cosmic.

75mm lens has a shallower DOF than a 50mm lens. Yet put the 75mm on an FX camera and the 50mm on a DX camera and both will have the same FOV, but the FX camera will have shallower DOF because the lens is more telephoto. Wider lenses provide greater DOF.
65 months ago (permalink)

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StarInnovative says:

very interesting discussion going on...Thanks for starting it tzakielmuto...

I was playing with the idea of buying a DX camera to support with D700...Idea is to use 85mm 1.4 lens on DX camera so that I can shoot from long distance (assuming I move back wih D300 to cover the same frame) and get better boken...

My understanding is with DX am shooting @ longer distance (130mm) from subject compared to FF (85mm) with the same lens and that produce better bokeh...

Based on the discussion above it seems thats not the case and FF will get better bokeh nonethless????

Please somebody clarify?
60 months ago (permalink)

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xyzE27 says:

Here is a link that uses simple photos to show FOV and DOF at the same distance to subject with FX and DX cams (and Canon cams at that!). Some may be surprised at the results - others not.

www.have-camera-will-travel.com/field_reports/full_frame_...
60 months ago (permalink)

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cliffmarck says:

THIS is what i was looking for... thank you... although it seemed like cosmic jeebus was right... and everytime i do the "calculations" the come up this way... it's quite the opposite....

when someone stated above that... the depth of field created by any lens at the same aperture will look smaller on a full frame camera than aps-c camera... they were exactly right...

it's essentially the exact same dof but just looks more shallow on fx... but if you shot in dx mode on an fx body.. it'd be exactly the same as the aps-c body... the full frame just extends the frame and creates the illusion of shallower dof....

this goes against any mathematical dof calculator.... but... it seems right in practice....
60 months ago (permalink)

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xyzE27 says:

no prob - all that math was giving me a headache ;-D
60 months ago (permalink)

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StarInnovative says:

Quotes from the link xyzE27 posted...
-------------------------
The wishful belief that my 500mm lens somehow magically becomes 800mm on my 30D sounds impressive, but in truth, it's still a 500mm lens with a large portion of the image missing from my view and my print. To make up for my discomfort, they cram more mega pixels into a smaller area, which also tends to make people feel warm and fuzzy.
-------------------------

Is this true?? if yes than buying second camera as DX is not useful if you are looking for that extra reach??
60 months ago (permalink)

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cliffmarck says:

it's true in the sense that there is relatively more pixels in a smaller space.. say the d300 12.3mp and d700 12.0? or 12.1.. whatever.. relatively the same amount of pixels but on a smaller sensor... this will effect the noise in the image and smoothness i'd say... but as for overall resolution... you'd still get more detail from the d300 using the 500mm than you would using a d700 dx mode... (cropped) ..so you're still gaining the extra reach... the quality is just not the exact same...

so to answer your question... dx is useful for that extra reach! just generally at a lower quality... at todays techonology at least... maybe not tomorrows....
Originally posted 60 months ago. (permalink)
cliffmarck edited this topic 60 months ago.

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StarInnovative says:

So if I am shooting with 85 1.4 in DX mode FOV, its exactly equalant to d300 + 85mm?
60 months ago (permalink)

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StarInnovative says:

So if I am shooting with 85 1.4 on d700 in DX mode FOV, its exactly equalant to DX + 85mm?

So except megapixel benifit there is no other benifit DX provide?
60 months ago (permalink)

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cliffmarck says:

yes... the frame should be EXACTLY the same after you click the shutter.... but you will have more resolution (megapixels) in the d300 file over the dx mode d700 file.... doing this... you might as well shoot the full fx frame and make your desired crop in post...

so if you're shooting sports or wildlife and like to make prints... you're probably still better off with the extra reach of the d300 than the low noise and better overall IQ of the d700 because of the wider frame...

note that this is getting a little off topic from the depth of field the original poster was referring to though...
60 months ago (permalink)

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Daniel_Beaman_Photo_Media says:

light and falloff comes in threw a circular lens and goes onto a rectangular capture plate or Sensor, should not we invent a circular sensor as to encompass all the light transferring like the DX lens effect already mimics on FX 35mm sensor body's..?
60 months ago (permalink)

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digitalscribbler says:

Not many people would buy such a camera -- it would be too expensive. They'd probably just buy a Hasselblad H3DII-50 instead.
60 months ago (permalink)

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LanceRiley says:

if you use a FF cam. you'll be closer to the subject compared to an APS-C sized sensor cam taking the same picture frame.

nearer to subject lesser DOF.

farther to subject greater DOF

Basing on the position of the FF cam. the APS-C cam is approximately 1.5x further
49 months ago (permalink)

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LanceSpring says:

Try shooting wide open at f/2.8 on a point and shoot camera with a small sensor, and you will see that its even smaller sensor will give you a tremendous depth of field at f2.8

For example, I shot this photo at f/2.8 with my Canon G10 Point and Shoot, which has quite a small sensor. Yet take a look at it at 100%. and see how in focus it is. It has a wonderful depth of field.

Carousel Horse in Salem, OR
49 months ago (permalink)

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Joe Longobardi Photography says:

xyz-Thanks! This is what I've known to be correct. And to simulate the FOV of the FF, you would have to pull back on the APS-C camera thus increasing DOF. Lance I see points this out as well. Then factor in minimum focusing distance of a particular lens and the math gets a little more involved.
49 months ago (permalink)

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sunnyUK says:

if you use a FF cam. you'll be closer to the subject compared to an APS-C sized sensor cam taking the same picture frame.

Not so. If I stand 30 feet from a subject and reach for my camera, I will not automatically and magically be teleported closer if I happen to reach for a full frame camera.
49 months ago (permalink)

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Hal. says:

sunnyUK: Wow, way to show your lack of knowledge while also being inflammatory. The post you quoted is exactly correct, one of the few posts in here that has their information right.

To get the same framing, a 50mm lens on a DX (APS-C) sensor must be moved further from the subject. Because the view is cropped, to obtain the wider view of the same lens on an FX (Full-frame) camera, a DX camera must be moved back.

Because the smaller sensor must be farther from the subject for the same framing, the DoF is much wider, as the lens must be focused closer to infinity.
This is one factor that makes the DoF look thinner on a full-frame camera.
Originally posted 49 months ago. (permalink)
Hal. edited this topic 49 months ago.

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sunnyUK says:

Hal I beg you pardon? I was a little tongue-in-cheek, but I don't see anything inflammatory. Maybe you want to re-read things?

The quoted post says that I'll be closer to the subject when using FX. Nope. I might instead chose different lens. Or a different field of view. The post simply claims that people shooting FX will be closer to the subject than people shooting DX, and that, my dear friend, is not true.
49 months ago (permalink)

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Hal. says:

The post was talking about the same framing. "compared to an APS-C sized sensor cam taking the same picture frame."

To get the same framing with the same focal length lens, then yes, you'll have to get closer with an FX camera.
They weren't saying you'd magically teleport closer with the camera. That was you being smart.
49 months ago (permalink)

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sunnyUK says:

I don't really want to get into a long debate, Hal, but there was no mentioning of focal length. There was just a (wrong) assertion that FX people are closer than DX peeps. You may well cheer for your homeboy, and that's cool by me. But it was a half-arsed truth at best, and a smart-arsed reply felt appropriate. You don't think it was nice. I think it was at more nice than you saying "way to show your lack of knowledge while also being inflammatory". What say you? Shall we just leave it and stop the argument?
49 months ago (permalink)

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chimphappyhour says:

Pssst! You dug up a thread that is over a year old.
35 months ago (permalink)

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Yavuz Cayir says:

I think the best answer is in this link

dofmaster.com/dof_dslr.html
Originally posted 35 months ago. (permalink)
Yavuz Cayir edited this topic 35 months ago.

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Bogrod says:

Newbie here, but I couldn't help but see the mis-information in this thread about focal length affecting depth of field. Simply put, it does not. The only factors that change with depth of field, regardless of focal length used, are two factors:

Aperture used .
Distance from camera to subject.
35 months ago (permalink)

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MrDAT says:

Bogrod said:

The only factors that change with depth of field, regardless of focal length used, are two factors:

Aperture used .
Distance from camera to subject.


PPPFTTTTHAHAHAHAHAHHAHAHA.

Really? <-- sarcastic

www.dofmaster.com/dofjs.html
Originally posted 35 months ago. (permalink)
MrDAT edited this topic 35 months ago.

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Nick McDonald says:

I think the problem in this thread is people are using depth of field and bokeh interchangeably. And they are NOT the same thing.

Depth of field and bokeh is a function of focal length, aperture and distance to subject.

If you take a series of images at f/2 with a subject from 2 feet to 20 feet and vary the focal length so the subject fills the exact same amount of the frame in each frame. You will in effect have an identical depth of field in every image. The issue is the background blur will be very different in each. At 2 feet you should be able to make out the entire background. While at 20 feet you'll have a nice creamy bokeh background.

I like to explain this effect as zooming in on the bokeh.

As for the whole full frame argument. Yes you get shallower depth of field. But that is because you either need to move closer or use a higher focal length to fit the subject in the frame equal to a crop sensor.
Originally posted 35 months ago. (permalink)
Nick McDonald edited this topic 35 months ago.

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beachwalker2008 says:

MrDAT wrote

Bogrod said:
The only factors that change with depth of field, regardless of focal length used, are two factors:

Aperture used .
Distance from camera to subject.


PPPFTTTTHAHAHAHAHAHHAHAHA.

Really?

www.dofmaster.com/dofjs.html

Nothing to laugh about actually but it isn't correct either:

Focal length and focus distance are NOT the parameters that control DOF - as many textbooks and online calculators make you believe. They can be made to show up in the formulas but as variables that appear to influence the outcome even though they are not the controlling variable of interest.

The correct variable is magnification - and the other two are sensor size (enters as circle of confusion) and f-stop.

Might be worthwhile to remember/ponder this:

A rule of thumb for depth of field is:

Depth of field is the same for all lenses when the image size is constant and the same f-stop is used.


This rule of thumb is approximately true when the focus distance for the shortest lens is less than about 1/4 of the hyperfocal distance for that lens.

Question: which DOF is larger - Nikon 18-200 at 200mm and closest focus distance (50cm) or Nikon 35/2 at closest focus distance (25cm), both at f8 on the same size sensor camera?
Originally posted 35 months ago. (permalink)
beachwalker2008 edited this topic 31 months ago.

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fotosniper says:

im confused.
35 months ago (permalink)

NikOvation [deleted] says:

I think this may help those who cannot agree on what happens to the depth of field as you go from FX to DX etc.

en.wikipedia.org/wiki/Depth_of_field

scroll down to the DOF vs. format size.

Regards,

Stephen
35 months ago (permalink)

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Nick McDonald says:

Hey beachwalker2008, you do realize that the focal length designation on lenses is a function of the lens magnification and sensor size, right?

en.wikipedia.org/wiki/Focal_length

Your rule of thumb is referring to the image size as projected onto the sensor. Which is exactly what I already said.

You're arguing the same answer already provided here.
Originally posted 35 months ago. (permalink)
Nick McDonald edited this topic 35 months ago.

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beachwalker2008 says:

fotosniper wrote

im confused.

Join the circle...

Nick McDonald wrote
bokeh is a function of focal length, aperture and distance to subject
Not true, bokeh is a lens property - two lenses of the same focal length can have totally different bokeh depending on their design.

35 months ago (permalink)

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beachwalker2008 says:

Nick McDonald wrote

the focal length designation on lenses is a function of the lens magnification and sensor size, right?

Focal length is a lens property and has nothing to do with what size medium you have in the camera behind it. A 50mm lens is 50mm, period.
What changes with the image format is the field of view.

And I am not arguing anything - I just provide the facts - plain and simple. DOF is given by f-stop, CoC, and magnification - it is that simple. The one thing that one needs to remember is that CoC is commonly referenced to "8x10 print viewed at arms length".

Magnification is a function of focal length and focus distance - and hence has is dimensionless - which should show that it is the correct variable to use. If you know focal length and focus distance, you can use the formulas in the various online calculations - the problem is that often you don't know the focal length (the one given on the lens is for a focus distance of infinity) and at closer distance, you may have a totally different value. You can always determine magnification without knowing focal length - just measure.
Originally posted 35 months ago. (permalink)
beachwalker2008 edited this topic 35 months ago.

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Nick McDonald says:

Yes, but the 50mm designation is referring to a 35mm sensor. You cannot calculate a lens focal length without knowing the sensor size.
Originally posted 35 months ago. (permalink)
Nick McDonald edited this topic 35 months ago.

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beachwalker2008 says:

Nick McDonald wrote

Yes, but the 50mm designation is referring to a 35mm sensor. You cannot calculate a lens focal length without knowing the sensor size.

Wrong. The 50mm focal length is referring to the lens having a focal length of 50mm - it has that focal length even without a camera anywhere near it.
35 months ago (permalink)

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Nick McDonald says:

What focal length does a Nikon 50mm f/1.8 have on a DX body? What focal length would the same lens have on a 1/3" sensor?
Originally posted 35 months ago. (permalink)
Nick McDonald edited this topic 35 months ago.

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beachwalker2008 says:

Nick McDonald wrote

What focal length does a Nikon 50mm f/1.8 have a DX body?

As I already stated several times, 50mm. Focal length is a lens property and has nothing to do with the camera. What you are thinking of is field of view or angle of view - a 50mm lens on a DX sensor will have a FOV equivalent to that of a 75mm lens on FX. The focal length does not change, the field of view and angle of view do.

You are getting confused because on the internet many use this crop factor to multiply the focal length - which is wrong as it does not change

If you envision the image circle a lens creates falling on an FX sensor and on an DX sensor, then the meaning of crop will become clear. The DX sensor is smaller and utilizes a smaller part of the image circle than the FX sensor does - hence one talks about the crop the smaller sensor creates. That's all there is to it.

crop factor
green frame: 1.3x
red: 1.5x
blue: 1.6x
All the same focal length lens but different field of view. And the only reason DOF would be different is because to get to a 8x10 print, the different images have to be magnified differently - and that's what the CoC accounts for.
Originally posted 35 months ago. (permalink)
beachwalker2008 edited this topic 35 months ago.

NikOvation [deleted] says:

Read this and it straightens out the focal length issue;

en.wikipedia.org/wiki/Focal_length

focal length of a lens is technically defined here with no correlation to format size - however, the field of view is correlated to format size.

I am a science teacher and photography teacher and this discussion always intrigues me.

Please feel free to email me if you want to ask a question without being ridiculed by onlookers.

Regards,

Stephen
35 months ago (permalink)

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beachwalker2008 says:

Stephen Chandler Photography Are you talking to me? I believe I have these things straight and it seems to me that we are stating the same thing.
Originally posted 35 months ago. (permalink)
beachwalker2008 edited this topic 35 months ago.

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Nick McDonald says:

I'm not getting confused. To calculate depth of field, the effective focal length of a lens is a perfectly valid value to use in the equation. You're arguing things with me that I have tested and proven to be true. Did you even try what I suggested originally?

I was also not referring to the quality of the bokeh as you so elegantly argued about. I was referring to the quantity (or smoothness) of it.
35 months ago (permalink)

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beachwalker2008 says:

Nick McDonald Bokeh is the quality of the out-of-focus blur - there is no quantity to it.

As to your original post - you may not realize it but you are agreeing with me - same subject size means same magnification and hence identical DOF. You are just making the mistake of calling that difference in bokeh, which it is not. It's a common misuse of the term. All you are seeing is the effect of perspective changes because you change the distance to your subject and hence are getting different amounts of background in the frame.
Doing your experiment with two different lenses of the same focal length will create different bokeh for each - depending on their design. A lens with a bad bokeh will render that background harsh while one with a good bokeh will render it smooth as silk.
Originally posted 35 months ago. (permalink)
beachwalker2008 edited this topic 35 months ago.

NikOvation [deleted] says:

No beach I was just chipping in for anyone to read I try to avoid siding up with anyone.

Here is an interesting read on photographic lenses too

en.wikipedia.org/wiki/Camera_lens

I spend a lot of my time translating technical descriptions into everyday language, just thought I may be of use to anyone here :)
35 months ago (permalink)

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beachwalker2008 says:

Stephen Chandler Photography wrote

I spend a lot of my time translating technical descriptions into everyday language, just thought I may be of use to anyone here :)

A truly worthy cause - unfortunately, the internet (and many textbooks) are full of misinformation - and that information gets rehashed over and over again. Only few bother to check the facts....

Unfortunately, the often cited dofmaster fails to provide a page with the definitions used in the equations and calculations. And by trying to restrict themselves to parameters a user would know, they are making a mistake in assuming that the focal length is something the user would know - so everyone plugs in the number from the lens without realizing that it might only be valid at infinity focus distance.
Originally posted 35 months ago. (permalink)
beachwalker2008 edited this topic 35 months ago.

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Nick McDonald says:

What's that saying about arguing with people on the internet?

As long as you come to the same conclusion I have tested and proven beach, then I'm happy we can agree to disagree about method of achieving it.

Btw, beach, you really need to quite editing your posts. It makes it very difficult to form a coherent reply. As I said, I am referring to the smoothness of it. Obviously there is no quantitative value to it.

Excuse me if I am being a bit short. Take a little break from programming and look what it get's me. Ah well, back to work.
Originally posted 35 months ago. (permalink)
Nick McDonald edited this topic 35 months ago.

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MrDAT says:

What Wikipedia says:

Same focal length for both formats
Many small-format digital SLR camera systems allow using many of the same lenses on both full-frame and “cropped format” cameras. If the subject distance is adjusted to provide the same field of view at the subject, at the same f-number and final-image size, the smaller format has more DOF, as with the “same picture” comparison above. But the pictures from the two formats will differ because of the different angles of view and the different viewpoints.

en.wikipedia.org/wiki/Depth_of_field#DOF_vs._format_size

Of course, it's a "Wiki". But this is what I've heard too.
Originally posted 35 months ago. (permalink)
MrDAT edited this topic 35 months ago.

NikOvation [deleted] says:

Yes you're right in that respect beach. The internet is awesome for the kind of reference information it can provide although this is often open to interpretation and when key information if left out for simplicity, it results in misinformation being spread and people forming opinions rather than concluding a fact.

I must add this isn't entirely the reader's fault since they haven't been given the full picture to begin with.

MrDAT good spot there, that's the one I refered to earlier - I think wiki is quiet reliable this time.
35 months ago (permalink)

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beachwalker2008 says:

Stephen Chandler Photography wrote

I must add this isn't entirely the reader's fault since they haven't been given the full picture to begin with.

As a science teacher you are very likely aware of always questioning the source of information - and the information itself. Unfortunately, few have the necessary background to dig through the formulas and be able to make sense of them. Even those who do often find that it isn't entirely clear how certain simplifications that are being made (often without mentioning) affect the interpretation.
35 months ago (permalink)

NikOvation [deleted] says:

beach, you can imagine asking 15 year olds who aren't really interested in science to research something like how smoking affects their health and then quote and evaluate their sources!
35 months ago (permalink)

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beachwalker2008 says:

Stephen Chandler Photography
Ignorance never settles a question.-Benjamin Disraeli
It is the supreme art of the teacher to awaken joy in creative expression and knowledge. -Albert Einstein
Originally posted 35 months ago. (permalink)
beachwalker2008 edited this topic 35 months ago.

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MrDAT says:

*grabs popcorn*
35 months ago (permalink)

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beachwalker2008 says:

MrDAT wrote

*grabs popcorn*
show is over
35 months ago (permalink)

NikOvation [deleted] says:

I read lots of discussions for research into how people interact especially how two people can use the same source to support opposing arguments :)

MrDAT - share!
35 months ago (permalink)

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tracer.ca is a group administrator tracer.ca says:

@Beachwalker2008

Do you mind providing a concise answer to the original question? Also a link to some further reading that you believe is correct? I'll put it in the FAQ

(from my understanding, your description of DOF was most accurate here)
35 months ago (permalink)

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Bogrod says:

"PPPFTTTTHAHAHAHAHAHHAHAHA.

Really?"

Yes, Mr.DAT. Really! :)

But don't feel bad. It's a common misconception. Others have clarified it more exactly, but - yes - magnification/aperture is another way of looking at it.

Case in point: Most people think that they are going to get more depth of field with a 60mm macro lens, versus a 200mm macro lens. Not true, if using the same magnification ratio & aperture. Same thing, even with non-macros. Same mag & aperture will produce the same depth of field.
Originally posted 35 months ago. (permalink)
Bogrod edited this topic 35 months ago.

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MrDAT says:

Bogrod, but that's not what you said above:

The only factors that change with depth of field, regardless of focal length used, are two factors:

Aperture used .
Distance from camera to subject.


You only said Aperture and Distance. So lets say I keep the the aperture and distance the same, and change from 50mm to a 85mm at the same aperture, by your statement above, the DOF should be the same. How can that be?
35 months ago (permalink)

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sunnyUK says:

MrDat, I think (hope!) Bogrod was referring to the actual, physical aperture size (let's call it the size of the entry pupil measured in mm, just for argument's sake), rather than the numeric value of the f-stop (which as we all know is the ratio between the lens' focal length and the physical size of the aperture).

So whereas you think of e.g. f/4 being the the thing you'd keep constant in your 50mm-to-85mm scenario, he would argue that a constant aperture means a 12.5mm diameter (= f/4 at 50mm and f/6.8 at 85mm). And by that pysical-size aperture definition, the DOF would be the same as long as you maintain the distance to subject, and aperture size, regardless of the focal length of the lens.

Ignoring the CoC, which (despite all the references to sensor size and 60 degree field of view and 25 cm viewing distance) is a function of how much you intend to enlarge the captured image, rather than a function of the lens or the camera, he is absolutely right. As long as you can agree on what "aperture" means and what "f-stop" means.
35 months ago (permalink)

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MrDAT says:

Yes, I think you're right. Aperture size, not f-stop.

When people ask me why those items control DOF, I tell them.... "Physics".
Originally posted 35 months ago. (permalink)
MrDAT edited this topic 35 months ago.

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dtmateojr says:

you could just take great photos and forget about DoF differences :)
35 months ago (permalink)

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beachwalker2008 says:

Well, it is my understanding that strictly speaking one would need to account for the pupil magnification factor which is the ratio of exit pupil diameter to entrance pupil diameter. For a symmetrical lens, that factor is one, but not so for the much more common asymmetrical lens.
35 months ago (permalink)

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James Windsor says:

The answer to this is actually very simple:

A cropped senor camera makes everything about your shot appear magnified (because it's cropped). This includes the area that is in focus.
31 months ago (permalink)

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MrDAT says:

=/ ?
31 months ago (permalink)

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John the Photographer says:

A cropped senor camera makes everything about your shot appear magnified (because it's cropped). This includes the area that is in focus.

Whilst this is true, Magnification due to smaller DX sensor size doesn't change the DOF.
Originally posted 31 months ago. (permalink)
John the Photographer edited this topic 31 months ago.

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Jeremy Weatherly says:

After much research and explaining the whole FF vs Crop factor to my friends I have narrowed it down to an answer everyone can actually understand.


The conception that FF cameras provide a shallower depth of field literally comes down to:

The wider FOV allows you to get closer to your subject = focusing closer = shallower depth of field. Think about this, macro vs house across the street, the closer you focus, the shallower the DOF.


(sorry for digging this post up, Its one of the top finds from Google and I still didn't find anything that would make sense to one of my family members.)
28 months ago (permalink)

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flipperkoning says:

The cropfactor makes a 35mm lens on a DX camera look like a 50mm on a FX camera, this 35mm lens has a greater depth of field then the 50mm on the same distance. This makes the difference, put the 50mm on the DX and you see it has the same depth of field as it would have on the FX camera!
28 months ago (permalink)

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H@shim A ™ says:

Why do full frames have shallower DOF?

than DX i'm assuming.

or more like - why does the nikon D700 (fx) have shallower DOF than a nikon D200 (dx)?

fx doesn't have a more shallow DOF than dx (assuming everything else is equal)- it only appears that way because the fx sensor captures everything that the cropped, dx sensor doesn't. the larger field of view of the fx makes the depth of field appear more shallow in an image.

the graphic from beachwalker2008 really does say it all.
28 months ago (permalink)

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GranDadWoof says:

my stock answer is "that's just the way it is, now get yer kit off"




one on these days it might even work
Originally posted 28 months ago. (permalink)
GranDadWoof edited this topic 28 months ago.

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Alexander van den Bosch says:

FF cameras don't have a bigger DoF. They rather have the option to have a bigger DoF.

If you'd equalise the angle of view, perspective, (hence the framing and composition,) and focus distance, there is not much that technically stops you from applying a bigger f-number on the bigger camera to equalise the DoF as well. In that case you'd equalise the respective physical aperture diameters, and you'd use exactly the same light rays in both cameras to 'graph the photo'. The projections in both cameras would then be perfectly the same, except for the fact that the one in the smaller camera would be more bundled. As an aside, this explains why different sensor formats have different CoC criteria. It is also the reason why you'd have to multiply the ISO of the bigger camera by the square of the crop factor of the smaller one in order to, in this specific comparison, also reach the same final image brightness at the same shutter speed (i.e. motion blur).

Despite the usually much better ISO performance of bigger sensors, in practice you might have reasons not to bump the ISO on the bigger camera, and instead equalise the f-numbers to make up for the reduced image brightness at equal shutter speed. Doing this you'd increase the absolute aperture size and you'd let in more light rays, rays that were formerly hitting the aperture blades. It can be shown that these extra rays further blur the OOF areas, which is basically everything in a photo that is not in 'perfect' focus, this way resulting in a reduced DoF.

Whether you prefer to 'sacrifice' certain ISO and f-number combinations on a bigger camera format to reach a certain DoF or the other way round, is up to you. This is why I for one prefer to see a shallower DoF as an option instead of a characteristic of FF cameras.

Sorry for kicking this thread in a group I might not even be supposed to be a member of. In any case I hope that to some this contribution could be an interesting alternative way of approaching the question at hand.
26 months ago (permalink)

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GranDadWoof says:

" fx doesn't have a more shallow DOF than dx (assuming everything else is equal)- it only appears that way because the fx sensor captures everything that the cropped, dx sensor doesn't. the larger field of view of the fx makes the depth of field appear more shallow in an image."

Not sure how you reach that conclusion. For the Fx sensor to "capture everything that the cropped, Dx sensor doesn't", you would be taking the image from the same viewpoint so that the wider AoV of the Fx sensor would include more of the surroundings. In that situation, the DoF would be greater on Fx than Dx

If you step forward with Fx to get the same FoV as Dx, then the DoF would be shallower.

Do some sums here www.dofmaster.com/dofjs.html
Originally posted 26 months ago. (permalink)
GranDadWoof edited this topic 26 months ago.

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GranDadWoof says:

"If you'd equalise the angle of view, perspective, (hence the framing and composition,) and focus distance, there is not much that technically stops you from applying a bigger f-number on the bigger camera to equalise the DoF as well"

How can you equalise AoV, perspective and focus distance when Fx and Dx have a different inherent AoV?

The only way to match AoV is to use different focal lengths, and that means a different perspective.
26 months ago (permalink)

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Alexander van den Bosch says:

"The only way to match AoV is to use different focal lengths, ..."
Yes.

"...and that means a different perspective."
No. Perspective only depends on standpoint. My comparison assumes the same position for both camera formats.
26 months ago (permalink)

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stvjackson says:

We may be running into issues of semantics here. Since we're cramming three dimensions into two, focal length does have a perceptual effect on the position of objects relative to each other. If I keep my camera in the same position relative to the subject, and I change from 24 mm to 50 mm to 105 mm to 200 mm. The longer the focal length, the more the image compresses, and the appearance of lines (particularly at the edges of frames) changes. I suspect this is what GranDadWoof is referencing regarding perspective.

If you shoot at the same focal length at the same subject distance, you're correct that in most cases there is no appreciable difference in DOF (relative to DX and FX differences; bigger sensor/film size differences would present a different story). However, that scenario is extremely unlikely, as the additional AoV on the FX sensor is going to push most photographers to move closer to their subject, as they're going to want their subject to fill the frame in effectively equal proportions in most cases. Since one of the key variables of DoF is distance to subject, the practical effect is that, yes, shooting in FX results in shallower DoF.
25 months ago (permalink)

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f3poweruser_ky says:

way back up the discussion the question was answered....to get the same field of view a larger sensor camera needs a longer focal length lens....which at the same aperture gives a shallower depth of field....it's a lens "thing" not a sensor "thing".....
25 months ago (permalink)

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Alexander van den Bosch says:

,

"If I keep my camera in the same position relative to the subject, and I change from 24 mm to 50 mm to 105 mm to 200 mm. The longer the focal length, the more the image compresses, and the appearance of lines (particularly at the edges of frames) changes."

You say 'the image', but there is no 'the image'. In your comparison, at best there is the 200mm image that can be cropped out of the others, to be layed side by side and compared. That 200mm image and the three crops will look exactly the same with regards to perspective compression. This is because you didn't move your feet.

Please allow me to encourage you to leave the idea behind that focal length changes perspective. This is really not the case. It is you giving in to the urge to move forward or backwards to get more or less the same framing, that will give you a different perspective with a different focal length on the same camera. The focal length only changes the angle of view. It is the different position that changes the perspective.

"If you shoot at the same focal length at the same subject distance, you're correct that in most cases there is no appreciable difference in DOF (relative to DX and FX differences; bigger sensor/film size differences would present a different story)."

For the record, my comparison assumes different focal lengths and equal camera positions. This is to be sure to be comparing pictures that are equivalent in as many ways possible except the one we are discussing: DoF. A comparison with different sensor sizes but equal focal lengths has so many changing variables that it becomes very hard, at least for me, not to be comparing apples to oranges. YMMV of course.

,

"way back up the discussion the question was answered....to get the same field of view a larger sensor camera needs a longer focal length lens....which at the same aperture gives a shallower depth of field"

If this is true I apologise for having missed that one. I did see the second answer in this thread, but to me the key is this 'at the same aperture'. Assuming this means 'at the same f-number', we are 100% on the same page.
25 months ago (permalink)

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