I'm just getting into cameras again--for painting. I have a Canon Rebel T3 EOS 1100D. I'm mainly wanting to know if it is true about this “digital pull” thing and if I can use the concept on my camera. My native ISO settings are 100, 200, 400, 800, 1600, 3200. The magic digital pull settings on a better camera are 160, 320, 640, 1250, 2500, 5000. Since I don't have these magic numbers on my camera to play with, I want to try something else. Can I just reduce the ISO setting by one-third of a stop to achieve the benefit of the digital pull to the sensor to get the least amount of noise/grain? Like from 200 to 100? I prefer to add the noise/grain in my photo-editing software if I need it. I understand that all of the noise/grain can't be removed from the raw file once it's there. However, after having thought about it, this might change the dynamic range of light to dark intensities. There is something about this theory that doesn't set well with me. Why would I set up my shot in manual mode then deliberately move my ISO setting down a notch and throw everything off? Have any of you camera buffs heard of this? Thank you.
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Plus everything else Kingston said. ESPECIALLY ABOUT SHOOTING RAW.
Also, just as with aperture and focal length, ISO scales with crop factor, but since surface area is an geometric measurement (power of 2), you need to scale ISO with the square of the crop factor. (e.g. a micro 4/3 camera has a crop factor of 2, so the best ISO you can achieve on most 4/3 cameras is ISO 100 and roughly equivalent to 400 ISO on a full frame sensor camera . ISO 200 is roughly equivalent to ISO 800 on a full frame camera, and so on.)
This is a little technical and not that important. Just remember that the bigger the sensor, the more light you get to keep, and the better results you'll get in less than perfect lighting. This is especially important if you print large prints. If you have a poor camera (e.g. with a very small sensor), shooting in RAW isn't going to help with this, though it will help you get the most out of what ever your camera did happen to capture.
YES! Noise applies equally to stills. If you examine the lab tests of cameras, one of the carefully examined attributes is the noise distortion at higher ISO levels. I becomes evident at the boundaries of say, a roof and a blue sky and shows edge breakup and color bleed, more insidiously it can introduce granularity in surfaces where there is none.
For our purposes though noise at high ISO is both easily avoided or ignored.
I could post some links but take my word for it, these lab tests are a good nights sleep on every page.
Denis
There are efforts to standardize different aspects of photography across chemical and digital realms, including things like low light performance, but most of those efforts are still in the discussion phases. In the digital realm, what camera makers refer to as ISO is indeed an equation, not a standard.
Josh
With a still image you can't run an analysis like this, however noise is also less noticeable because it's one set of noise, not lots of sets changing every fraction of a second. And noise is easier to avoid, even in low light, with certain types of still shots (any situation where you can set your ISO low by setting shutter speed to be slow and/or the aperture to be wide). With video you're usually stuck with a certain shutter-speed/frame-rate combination, so you only have aperture to play with, so it's more likely you will have to shoot with the ISO up.
Anyway, don't overthink it unless you get a job as a video camera operator or something. Just do what I mention in the guide — take lots of shots, check the ISOs used, establish how much is too much for your purposes, and keep your ISO below that when you have a choice. When possible, keep the ISO as low as you can, but don't compromise shutter speed or aperture for it, ISO is the least important for the purposes of getting good source material to paint from unless it's truly excessive.