ISO Noise
ISO is a measurement of your camera’s sensitivity to light; lower numbers are less sensitive, and higher numbers more sensitive (ISO 200 is twice as sensitive to light as ISO 100, for example). However, the more sensitive a camera’s “film stock” — or in this case, the digital equivalent — the more noise in the image. With film stock the relationship between sensitivity and noise is generally linear (more on film speed and its digital equivalents), but Canon’s implementation is somewhat unique.
The 5D and 7D‘s “native” ISO levels are 160, 320, 640, 1250, and 2500 ISO. The following paragraph, it turns out, is not entirely accurate, but I’ll leave it here for posterity’s sake:
While the cameras have dozens more ISO settings, it turns out that settings in between these values are artificially boosting (or lowering) the camera’s exposure compensation; you don’t actually gain any highlight headroom (e.g., ISO 200 is just an exposure-compensated ISO 160). While the difference between “native” and exposure-compensated ISO levels is not drastic by any means, if you’re shooting in a difficult situation without any lighting options it can help to know that a shot at ISO 1250, boosted in post to the same perceived brightness as an ISO 1600 shot, will be cleaner than the native ISO 1600 image. You can see this on a noise levels graph and it also apparent in these 5D highlight tone priority tests.
What is true is that the noise levels at these particular ISO levels are lower. However, as has been pointed out by a couple of helpful commenters, this is actually because the camera is electronically dampening the exposure, giving the image 1/3-less stop of noise whilst also giving 1/3-less stop of dynamic range. Basically: it’s a wash. I’m leaving this section here in case someone read it before and was going out of their way to select 160, 320, 640, etc. — or in case someone read this “native ISO” information elsewhere (as I did originally). Move along, there’s nothing to see here (except a bit less noise and a bit less highlight retention).
14 COMMENTS
-
-
Lee, you’re right, although I was assuming the reader already knows that higher ISO settings generally mean more noise. I should’ve said “a shot at ISO 1250, boosted in post to the same perceived brightness as an ISO 1600 shot, will be cleaner than the native ISO 1600 image.” I’ll clarify the point.
-
-
I’m having trouble setting the proper ISO for filming in Low Light situations. Can you shed some light on your workflow as far a prepping the camera settings before shooting. Thx.
-
-
I haven’t gotten my hands on a T2i yet but if there is a histogram or Zebra function, that will be helpful. I would recommend paying a visit to the forums (cinema5d.com, dvinfo.net) and asking T2i users, as they’ll have more specific advice.
-
@ Stu, I use a T2i and can tell you that with magic lantern firmware, you can expand the capabilities of that small equipment and turn it into a machine of sort. First off, you’ll be able to access the 320, 640, 1250 isos, which gives you cleaner pictures in low light. You’ll also be able to get better sound and control use zebra function.
-
-
-
-
Stu Mannion on 06.5.10 @ 5:30AM
It’s now common knowledge that the 160, 320, 640, 1250 etc ISOs are in fact NOT the native ones but are actually the dampened step down from the native ISOs of 200, 400, 800, 1600. This electronic dampening leads to the lower noise that made many assume they were the native values. The dampening of noise is made at the expense of a small amount of highlight headroom. Whether this is a good compromise depends on what you’re shooting.
-
-
-
Thank you for some other great article. The place else may just anybody get that
type of info in such a perfect way of writing?
I’ve a presentation next week, and I’m on the look for such
information. -
My friend discovered your cool website on the search
engines and we’re glad you had coupons
3 pingbacks
- Magic Lantern for T2i Will Save You $60 | james polits on 03.8.11 @ 11:36PM
- Let’s Settle This: Do Canon DSLRs Perform Best at ISO Multiples of 160? | NoFilmSchool on 05.2.11 @ 4:25PM
- Vincent Laforet’s Tips for Getting Filmic, Gradable, Footage out of Your Canon HDSLR - NoFilmSchool on 03.14.12 @ 8:08PM
The comment . . .
“it can help to know that ISO 1600 is likely to be noisier in post than 1250.”
. . . . misses the whole point of the native ISO noise issue.
It is a commonly held idea that the higher the ISO the higher the noise – and this holds true for most cameras/situations – but the way the 5DmkII fakes it’s non-native ISOs means that it is best to stick to the native ISOs (listed above). It would have been more illuminating were you to have said:
“it can help to know that ISO 1000 is likely to be noisier in post than 1250.”