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      10-25-2012, 12:22 PM   #1
ddk632
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ISO 50 on Digital Cameras (Canon)

I have a curiosity, given that I have no real experience with modern DSLR's yet. I understand that the 5D and 1D series, maybe some others, have ISO 50 as an "L" option.

Does anyone use this?

Coming from film prior to my XTi my mindset is lower ISO = best quality / least noise.

However, some people have mentioned that ISO 50 is not a "real" ISO, but that it's ISO 100 "pulled" via software/firmware to adjust for what the sensitivity would be at ISO 50.

So my questions are:

1) Does anyone use ISO 50 on their camera?
2) Has anyone compared ISO 50 vs. ISO 100 shots and see any difference?
3) Does this even matter in the DSLR world?
4) Can anyone comment on the pulled ISO 100 comment vs. actual sensor sensitivity for ISO 50, or point me to any technical articles or whitepapers on the subject?

I am really interested in the actual sensor tech behind this, so I'm not being a smart ass in question #4 I am also very interested in the potential effect on IQ of a "true" ISO 50 vs. a software emulated ISO 50.

Keep in mind this is coming from someone who's shot film, and a 6 year old Rebel XTi which has ISO 100 - 1600 only, and I shoot lower ISO's due to old habits and the fact that my XTi high ISO performance sucks even if you nail the exposure - and REALLY sucks if you underexpose even slightly.

I shoot mostly landscapes, getting into shooting motorcycles (but this is still sort of landscapes), night shots, etc. I've noticed even night shots, I do at ISO 100 and long exposure, in order to minimize noise.

What are your thoughts on the topic? Are my views obsolete or valid?
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      10-25-2012, 05:25 PM   #2
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so basically, digital sensors have a base ISO, where image quality is optimum. moving away from this base ISO brings about noise and reduced dynamic range the further away you go from the base number. So, with today's sensors, being one or two stops away from the base ISO is not going to hurt you much.

I shot a D3 for several years, 200 was its base ISO and if I needed to shoot at 100, I would without hesitation.

as far as how it's done, it's pretty much a negative gain on the sensor. where increasing the ISO is "overcranking" the gain / sensitivity of the sensor.

make sense? it's not really a push/pull of the metadata via firmware/software, as it happens before the image and stays with the image whether you shot RAW or not (as opposed to a metadata function like white balance).
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      10-25-2012, 08:15 PM   #3
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Ok that makes sense - it's a function of the hardware light sensitivity (I.e, how fast light fills photosites) of the sensor itself, so if a sensor's base ISO is 200 and you shoot at 100, the camera has to de-amplify the analog data of the actual photons received at the photosites.

So shooting below base ISO doesn't make a lot of sense, then, in terms of IQ, and possibly DR, because you might clip highlights sooner at an ISO that's less than base. But in practice, perhaps this is not noticeable.

Thanks - you've pointed me in the right direction to do some more research.

Found an interesting discussion or two here:
http://www.cameralabs.com/forum/viewtopic.php?t=4503
http://photo.stackexchange.com/quest...mera/6622#6622

Which led me here:
http://photo.stackexchange.com/quest...igital-cameras

And here...
http://photo.net/learn/dark_noise/



I am a software guy so I love the technical details. I also have a need to better understand sensor tech, as well as LCD tech, for a project I'm working on, not photography related.
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      10-25-2012, 09:42 PM   #4
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glad you found some answers.

honestly, you're not going to notice a difference. this is even more true with current generation sensors.
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      10-30-2012, 12:54 AM   #5
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Just as an update, in case anyone is reading this thread or may be interested, I found and read through this most interesting paper on image quality, photon and read noise, and other various factors that generally contribute to image quality in digital photography.

If you have some time and find this subject interesting, I recommend to check out the paper.

http://theory.uchicago.edu/%7Eejm/pi....html#bitdepth
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      10-31-2012, 10:07 AM   #6
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ISO L which is 50 will not give as good IQ as ISO 100. I shoot a 1D4, 1D3, 5D2 and 7D and never use L.
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      11-01-2012, 04:17 PM   #7
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Thanks for sharing, I was always curious if the L and H modes get used that much.

I gathered as much regarding lower IQ at ISO 50 from the articles I've read and posted above, since essentially the camera sensor will always receive the same amount of light, and changing ISO value results in amplifying the analog data prior to readout (or maybe during, I suppose), so in the case of L mode, you're essentially overexposed by default and can risk blowing highlights, causing the de-amplified signal conversion to potentially be lacking in highlight detail (and therefore reduced DR) even though it is a lower ISO.

Man, that was a long sentence

Makes perfect sense, once I got over the fact that ISO on film and digital work in completely different ways.
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      11-01-2012, 05:24 PM   #8
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it's the same penalty as shooting at a higher ISO - neither of which are going to show much difference in the real world.
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