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I didn't know that! Did you?
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An unexpected side benefit of my recent new hobby of photography is the great people you meet along the way. Certainly, I mean all the folks in this forum and the DPS forums, but I also mean other photogs one runs into out in the field.
I had a great day Friday shooting pictures at a rodeo and not only did I learn a lot about rodeo while I was there, but I met a fellow shutterbug to talk shop with while we passed the time between events.
OK, so I will get to the point.
He was a Canon shooter and he had recently dropped some cash on an 'L Series" lens which is the equivalent of our "G Series."
He asked me what ISO I was shooting at, and since we were at about the same shutter speed and aperture, I thought he was shooting 400 like me. HE WAS SHOOTING 200!
He explained to me that better glass not only gives a sharper image (I thought that was the main advantage), but it also takes in more light so that it is also faster!
Is this so? I didn't know that.
Originally posted at 9:15PM, 12 April 2009 PDT
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e.b. image edited this topic 38 months ago.
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deleted deleted [deleted] says:
yep
a good example is the famous beercan
when you zoom in using your kit lens you are using an aperture of maybe f/5.6, but using the beercan you can zoom in and use an aperture of f/4.
this doesn't sound much difference, but it means you can take the same photo in half the light it took for the kit lens to take it :]
real expensive zoom lenses might have an aperture of f/2.8 which really lets a lot of light in - you can use a lens like this to take wildlife shots in poor light for example
the ultimate tho are fixed lenses, like a 50mm which can have an aperture of f/1.4. as many people have found you can get some great indoor low light portraits with such a lens
Posted 38 months ago.
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No, I don't think we are talking about the same thing. I know that the aperture is larger on expensive glass, but he says that at the same aperture, good glass works the same at half the ISO.
For example, he was shooting at 500 hundreths a second at 5.6, and I was shooting at 500 hundreths of a sec at 5.6, but he could do it at 200 and I had to do it at 400 ISO.
Originally posted 38 months ago.
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e.b. image edited this topic 38 months ago.
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deleted deleted [deleted] says:
just ignore the bit in itallics heheh ;]
well, regardless of the individual lens' performance, the f/numbers are still a mathematical ratio
the ISO is the sensor sensitivity, and like f/numbers should be standard across cameras
if he was using ISO200 to your 400, then his pixels were half as sensitive to light, meaning he would need twice as much light as you to make the shot
that's why we have the f/number and ISO system - ISO being named after the standards body that manages the numbers
to save confusion all cameras follow the ISO system and all lenses conform to the f/number system. better lenses then just have better numbers rather than somehow doing more with the same numbers
there may be factors to expensive lenses that let them work better in the conditions you describe, but in this instance i have to go with the numbers - half the ISO means half the light, and since all lenses are made to standard f/numbers half the light means a darker photo unless you change those f/numbers
is there a chance he had some exposure compensation dialled in? or a filter of some kind attached? (or did you?) is it also possible that canon and sony ISO numbers do not correspond perfectly? i don't mean to be contrary, i simply understand photography in terms of light and numbers - not great for artistry i know, but it helps sometimes :P
edit - although your f-numbers give the area of the aperture opening, the amount of light transmission will be affected by the quality of the lens. there are a number of factors tho - expensive lenses have more elements and more coatings, but at the same time a cheap plastic lens could offer different ISO performance than a glass lens.
so now i am hedging my bets :P
does anyone have a g-lens and a few minutes for testing?
ok - it is my week for being wrong, but thanks to that i have learned a lot :)
you are absolutely right. if you and your mate have the same f/number, the same shutter speed, AND the same ISO, the only thing left that can make a difference is the quality of the lens.
lenses are made of many different individual glass (or plastic or even liquid!) elements. let's say there are 14 elements in your zoom lens. glass both allows light to travel through it AND reflects some back.
if all 14 elements reflected even a small percentage of the light back again you would not get any to reach your sensor :(
for this reason the lens elements are coated with a transparent layer which helps to eliminate reflection. expensive lenses are multi coated to more effectively eliminate reflection, and this light then makes it to your sensor
so... properly coated lenses and quality glass components mean that for the same aperture and shutter speed you get more light, and you can use a smaller ISO number
thanks for pointing this out - i got there in the end :P
my problem was confusing the f/number for a light transmission constant when it is just an expression of area - but after three hours of reading i feel i understand lenses a lot better thanks to your thread :D
Originally posted 38 months ago.
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deleted deleted edited this topic 38 months ago.
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deleted deleted [deleted] says:
i'ma cry :[
if anyone can spot the obvious flaw in my explanation they can have a virtual hug :P
Posted 38 months ago.
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i don't think he is right. he may have been underexposing for saturation purposes or something. one may have been spot metering and the other matrix metering, but iso is a set standard and so is exposure. If this weren't the case light meters wouldn't work.
Good glass can speed up auto focus, add clarity and sharpness, but it can not increase the amount of light being reflected off of a subject.
Posted 38 months ago.
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deleted deleted [deleted] says:
ah! you are thinking like i was at first.....
although ISO is a standard, the exposure values you mean of f/numbers are purely to express the area of the aperture opening.
let's say for example you have an aperture of f/5.6, speed 1/500th and ISO 200 like the example above.
if you take the G lens it will have very high quality, low dispersion glass inside. glass reflects a small amount of light but the most of the light is directed at the sensor.
however the cheap lens will have plastic elements, cheaper glass and worse coatings. this is like taking the G lens and adding a few layers of goo to it :P
also, the glass itself if not high quality will scatter some of the light inside the lens. this can lead to flare and also lessens the light that hits your sensor
this could easily add up to the one stop difference experienced
this doesn't mean an expensive lens will definitely work in lower ISO but many of them will, although the difference may not be as much as a full stop
in response to your light meter point - lightmeters still sometimes require you to set the exposure compensation on your camera. this is quite normal - many people who use Aperture priority mode also find it necessary to dial in some exposure compensation, and now i think that might be in part due to the differences between lenses
my mistake was that the anti-reflection coatings do not let more light in, they simply cancel out the light that is already reflected. the difference between lenses then is simply the quality of the glass. here are some websites that explain these ideas a bit further ;]
www.madehow.com/Volume-2/Camera-Lens.html
www.cctv-information.co.uk/i/Light_Transmission_Through_L...
www.cybercollege.com/tvp014.htm
rick_oleson.tripod.com/index-166.html
Originally posted 38 months ago.
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deleted deleted edited this topic 38 months ago.
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There is one other thing that could come into play. Different cameras have different measured ISO than the setting states. Some cameras are as much as 3/4 of a stop different. So you may set your camera to ISO200, but in reality the camera is operating at ISO140. If this is the case, then the difference in the lense doesn't have to be as large as a full stop.
Posted 38 months ago.
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I think this is a simple case of his glass was faster. What I mean is if he is shooting: 70-200 F2.8 and your shooting with say a beercan 70-200 F4 hes gonna be able to shoot at speed a couple of stops quicker. So hes partially right by saying he gets more light. So the only way for you to really know if your shooting similar to him is to match his aperture. Then match his iso. All things being equal the shutter speeds should then match.
As for your last statement about cameras having different ISO, I cannot believe that to be true. ISO is a mathimatical calculation and is not a manufacturer variable. Heres a link to the math if you like.
[http://en.wikipedia.org/wiki/Film_speed#Measurements_and_calculations]
The one thing to note is that the camera may not DISPLAY the actual correct ISO on the screen, that doesn't the camera isn't shooting the correct number.
Posted 38 months ago.
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The article I read this on was on Adorama's website. It had the title "ISO Lies: When ISO 100 is really 72"
They had graphs of measured ISOs for all the major cameras including Sony.
Some were off more than others, but almost all of them showed a deviation between what ISO was selected to shoot with and what the measured ISO was of the photograph. They still show the article on the front page of the learning center. www.adorama.com/learn but when I try to click on the link it shows invalid url.
Originally posted 38 months ago.
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Michael McGaha (a group admin) edited this topic 38 months ago.
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deleted deleted [deleted] says:
we discounted the idea of it being a different aperture way back at the start :p
take a look through the links above to do with the transmission properties of glass, it's interesting stuff - and means that different lenses can and do allow different amounts of light through despite having the same aperture value
as for the ISO, digital camera manufacturers take a value that corresponds roughly to the same value on film. here is what wiki says...
"In digital camera systems, an arbitrary relationship between exposure and sensor data values can be achieved by setting the signal gain of the sensor. The relationship between the sensor data values and the lightness of the finished image is also arbitrary, depending on the parameters chosen for the interpretation of the sensor data into an image color space such as sRGB.
For digital photo cameras ("digital still cameras"), an exposure index (EI) rating—commonly called ISO setting—is specified by the manufacturer such that the sRGB image files produced by the camera will have a lightness similar to what would be obtained with film of the same EI rating at the same exposure. The usual design is that the camera's parameters for interpreting the sensor data values into sRGB values are fixed, and a number of different EI choices are accommodated by varying the sensor's signal gain in the analog realm, prior to conversion to digital. Some camera designs provide at least some EI choices by adjusting the sensor's signal gain in the digital realm. A few camera designs also provide EI adjustment through a choice of lightness parameters for the interpretation of sensor data values into sRGB; this variation allows different tradeoffs between the range of highlights that can be captured and the amount of noise introduced into the shadow areas of the photo"
maybe a simpler way to put it - a better lens focusses the light more effectively on the sensor. less flare, less scattering, less in the way of the light. the better lens doesn't add any light, it just doesn't take as much away as a cheaper lens.
Posted 38 months ago.
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There is obviously a lot of truth in the better glass argument, however, Canon are well renowed for twisting their ISO figures to give a 'lower' ISO impression than other manufacturers. So a combination of better glass and a false ISO figure will allow the Con-on, sorry, Canon to give a lower figure. Yes ISO is supposed to be standard but like many things in life the 'standard' gets stretch to suit a manufacturers needs. Whether that's a full stop, I don't know but it wouldn't be the first time Canon have been sussed for it.
Originally posted 38 months ago.
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Th'Owdhamer edited this topic 38 months ago.
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deleted deleted [deleted] says:
if you read the wiki article on standards it says "The choices are based solely on the manufacturer’s opinion "
opinions vary :P
Posted 38 months ago.
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Ok, this is fun! I definitely think it calls for an experiment. Will someone please get a G Series and test it against a kit lens with all other factors being the same?
I don't have access to such a lens, but someone out there does. We eagerly await your results.
I also started the same discussion over at DPS and you can get their opinions here:
digital-photography-school.com/forum/showthread.php?t=54856
As of yet, no one over there has come up with Manimal's explanation.
Posted 38 months ago.
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deleted deleted [deleted] says:
heheh, yeah those guys are making the same mistake i did - f/numbers are a ratio that means an area - it's related to the total amount possible, but the glass you use can cut that by a few percent for good glass, or loads for bad glass
and i am sure michael is right about the dodgy ISO standards also!
Posted 38 months ago.
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deleted deleted [deleted] says:
here ya go - wiki says it quite clear in their lens section
"The introduction many years ago of optical coatings, and advances in coating technology over the years, have resulted in major improvements, and modern high-quality zoom lenses give images of quite acceptable contrast, although zoom lenses with many elements will transmit less light than lenses made with fewer elements (all other factors such as aperture, focal length, and coatings being equal)"
Your lens design affects the amount of light you get, even if the aperture value is the same as another lens of different quality.
en.wikipedia.org/wiki/Photographic_lens
ps each element in the lens reflects 4% of the light it receives, that is why they have to be coated in the first place :] that's a lot of lost light for a multi element lens!
Originally posted 38 months ago.
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deleted deleted edited this topic 38 months ago.
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I don't buy the Canon guys explanation. Sounds bogus to me. There might be a number of other factors determining the ISO he was using including his opinion on whats a properly exposed picture and the metering mode, exposure mode etc etc. I doubt very much that the Exposure triangle of ISO, Aperture and Shutter speed will be in question based on the quality of glass. The relationship between the three parameters are fixed irregardless of the equipment AFAIK.
Agreed that there might be a small variation in light, but I doubt there is a big enough difference to step from ISO 400 to 200 based on optical coatings alone.
Originally posted 38 months ago.
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jilgiljongiljing edited this topic 38 months ago.
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I can't get that original article I read to come back up. But I remember they said they could only test cameras that shot in raw format. I'm not sure how they were measuring the ISO of the photo from the raw file, but I remember that they said that even on film, the ISO could deviate from the standard. I really wish that article would load for me so i could read it again.
Posted 38 months ago.
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So, manimal, which lens would have more elements, the cheapo or the good one? Sounds to me like you are saying that a multi-element lens is the cheap one and that the G Series would have fewer elements. If that is the case, wouldn't the one that has more elements cost more to produce?
Posted 38 months ago.
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deleted deleted [deleted] says:
i dunno, i'll check - i was thinking more of a prime 50mm for example, which can have as few as three or four elements (Tessar lenses have four) and a zoom lens which can have 14 elements
4% light loss per lens element remember......
anyone still in doubt check out the wiki page on lenses and it's references - this IS a numbers question, you just gotta know the right numbers to use :]
Posted 38 months ago.
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deleted deleted [deleted] says:
well, your kit lens has 15 elements. the carl zeiss version has 14 elements. so the number of elements alone is not the main issue, although already you see there is a 4% difference in the amount of light between these two lenses even at the same aperture value
start adding in other factors mentioned above and one full stop is not out of reach
Posted 38 months ago.
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deleted deleted [deleted] says:
"... Maxxum/Dynax 5D ...
... Before the company left the camera business, Konica Minolta produced a pair of innovative DSLRs, but ISO accuracy was not the strong suit of the second model, the 5D. Measured ISO was as much as 1/2-2/3 stop higher than the listed one, although accuracy improved at the highest speeds. At ISO 100, measured ISO was 178. At ISO 200, it was 328. At ISO 400, it was 654. At ISO 800, it was 1113. At ISO 1600, it was 2021, but at ISO 3200, it was extremely accurate at ISO 3180 ...
... Maxxum/Dynax 7D ...
... As with the 5D, the 7D's exposure accuracy varied greatly. At ISO 100, the measured ISO was 173. At ISO 200, it was 294. At ISO 400, it was 576. At ISO 800, it was 1010. At ISO 1600, it was accurate with an measured ISO of 1595, but was slightly lower at ISO 3200 (measured: 2798) ..."
Posted 38 months ago.
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deleted deleted [deleted] says:
and here is that pesky lost link ;]
www.adorama.com/catalog.tpl?article=020109&op=academy...
the canon undervalues ISO - the sony overvalues it :D
Originally posted 38 months ago.
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deleted deleted edited this topic 38 months ago.
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