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Today's theme is distance, scale and DOF. After having downloaded a super free application called iSee4K for the iPhone which lets me calculate DOF on the go, I thought I might apply it. So for this set-up, I calculated my height, divided it by the length of the sensor and multiplied it by the focal length of the lens to determine that I would need to stand 5 meters from the (estimated*) central nodal point of the lens in order to fit in frame at a 100mm focal length, and then further calculated that at f/2.8 I would have around 20cm focus either side of me, which is more than sufficient to keep me in focus but also give the background some blurring. I then set the ISO to 50 and bounced an off-camera 580 EXii at half power off the ceiling about two-thirds of the distance from the camera to me. And it worked – hence the smug, but slightly tired look!

 

Wanted to shoot this at 135mm, but my house just wasn't big enough.

 

* As my 100mm is a 1:1 macro, this was a fairly easy task. Simply measure the closest focus distance from the focal plane mark (sic) and then measure 100mm back from there. Ipso facto. This may have no scientific grounding.

 

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  • jamesjustin 6y

    Congratulations on the result. You are far more dedicated than me. I think I would have given up halfway through that exercise. I almost gave up reading your long explanation halfway through ;-)
  • Coal Miki 6y

    Cheers Justin. The calculations only took 10 seconds, but it's been bothering me for a while now – if you wanted to take a straight on portrait so the head just fits in frame at 100mm, at f/5.6 your dof is about 5 centimeters which is barely enough to get the eyes and the whole of the nose in focus. That professionals can get away with it regularly astounds me.
  • pankun 6y

    I had some little charts printed out for DOF calculations using DOFMaster software. www.dofmaster.com/custom.html I just noticed they now have software for the iPhone, might be an excuse to get an iPhone.

    I'm confused about the central nodal point. You measure the focus distance from the focal plane, which is the film back or sensor in dSLRs. This should be marked on the top of your body, or just use the back of the camera - you'll only be out by a few mm.
  • Coal Miki 6y

    Had a look at the DOFMaster app but it costs like 230 Yen. iSee4K is free, and also has field of view and view angle calculations. :-) It's worth getting an iPhone anyway...

    When you're calculating focal distance to set the focus, then you go by the focal plane mark (which should actually be referred to as the image plane mark – the focal plane marks the points where light converges from subjects at infinite distance), but for scale you need the centre nodal point of the lens. Assuming a 1:1 macro of 100mm focal length, the subject would have to be 100 mm from the central nodal point of the lens to appear projected on the image plane at the same scale. Accordingly, a subject at 200mm from the central nodal point will appear at half scale, 400mm at quarter scale etc. With modern camera lenses which are far more complicated than a simple lens in air, you have to estimate where the central nodal point is of course, which messes your calculations up somewhat...
  • pankun 6y

    "for scale you need the centre nodal point ..."

    [vaguely remembers drawing ray paths in physics at university]

    thanks got it, that rings a few bells ...
  • Mike Connolly 6y

    Not to change the topic at all, but while you're talking about cool camera-related software for the iPhone, have you taken a look at the OnOne DSLR camera remote? It'll be my first purchase as soon as I get my hands on an iPhone next month.

    www.ononesoftware.com/detail.php?prodLine_id=38

    Combine your camera in a remote location, do the proper DoF calculations, use OnOne to check the scene via Liveview, and you've got one badass photographer set-up there.
  • Coal Miki 6y

    That does look interesting, though reading through it I see it has to be connected via USB to a laptop for it to work which would somewhat limit its usability – a lot of the functionality can adequately be replicated using the standard IR remote and the bundled EOS Utility software. I guess if you were going to have the laptop with you anyway it could make things more convenient though.

    Now, if they were to sell for around the 10,000 Yen mark a plug-in Wi-Fi adapter (rather than the 100,000 Yen Wi-Fi grip) that could work with OnOne then I would definitely add it to my must have list. :-) Or even better, iPhone software that allows you to connect iPhone to camera using standard iPhone USB cable and use as intervalometer etc., or even use iPhone's Wi-Fi... possibilities endless.
  • Mike Connolly 6y

    It sounds like the software uses the laptops wifi set-up to be accessible by the iPhone, without needing a net-connection. Which would be ideal if you had a compact little net-book. I certainly see your point about the plug-in.

    That is a nice point about the 5DmkII. The 30D I'm using curiously is missing any IR ports. So I've picked up a third party Taiwanese maker's external IR device to trigger my shutter from afar. I still think the OnOne software is pretty cool - but again, can't think of any practical applications except for self-portraits, or when mounting the camera in strange places... which would would require me to invest in a netbook as well. Hmm... Maybe it is more of a gimmick rather than practical software.
  • image-MILL 5y

    what the hell are you talking about??? ;)
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Taken on July 24, 2009
  • EF100mm f/2.8 Macro USM
  • 100.0 mm
  • 50
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