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Canon 1Ds Mark III Noise and ISO
Why I turned off all those extra ISO settings...
The other day I noticed a post on the FM forum, pointing out that ISO settings for the 1Ds2 and 5D are not all that they may first seem...
'The full stop ISOs ( ISO 100, 200, 400 and 800 ) are implemented with hardware gain settings (in the sensor). But the ones in-between and 50/1600/3200 are implemented through software. The full stop ISO has lower noise than the in-between ones.'
I decided to do a quick test with the 1Ds3...
My suspicion is that this test might show similar results for almost any DSLR (not just Canon)
I noted similar results for the Canon 7D
I've also written a page with comparisons between my 1Ds and 1Ds3, along with my thoughts and impressions about using the 1Ds Mark
Please do let me know if you try this with other cameras? I've seen examples suggsting that the 1D3 does not exhibit the same behaviour
A series of shots were taken with incremental ISO settings:
The camera was set to manual, with a lens cap on and the viewfinder shutter closed. I'm just looking at dark noise here, so any image contant would not be of any use.
Raw images were taken and processed in ACR with no noise reduction and black level set to zero (to show up noise)
An additional set of images was processed at +4 exposure compensation to really show up any noise.
ACR Settings - all default unless shown
The histogram gives an idea of the dark noise levels at each ISO setting - the drop in noise from 160 to 200 is quite noticeable even at the low levels found in this camera.
The next set of shots have had the exposure racked up 4 stops in ACR to show more details of noise
I've included a 100% crop so you can get an idea of what it's actually like when you push images this far
Remember that ISO 50 on the 1Ds3 is an optional setting, since although you have even lower noise in the shadows, you lose dynamic range (at the top end) See the information about L(50) and H(3200) ISO settings in the manual
For normal usage, the default ACR Black level setting of 5 and default colour noise reduction in ACR makes it very difficult to see much image noise in 'real world' photos at ISO 1600
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So there you are...
As far as I'm concerned it was time to turn off 1/3 stop ISO settings on the 1Ds3 :-)
I've seen some mention of the High ISO noise reduction setting available on the 1Ds3 and 1D3 - this affects Jpeg images only, since you can turn it off in DPP (if it affected the raw images you wouldn't be able to undo it) This is not the same as noise reduction at longer exposures using dark frame subtraction.
This is mentioned on page 20 of the Optimising settings PDF available from Canon:
"High ISO images that are predominantly high-key subject matter (example: available-light ice hockey pictures in an arena) will sometimes show more of a “salt and pepper” appearance from remaining luminance noise if the Mark III’s High ISO Noise Reduction is applied. Users should run tests to see whether there’s any negative impact when it’s applied. This is one advantage of shooting RAW files — in either of the two supplied Canon RAW file processing software applications, Digital Photo Professional or RAW Image Task — you can apply or remove High ISO Noise Reduction, making it easy to see the same file “before and after”."
"Finally, High ISO Noise Reduction is completely separate and different from C.Fn II-1 — Long Exposure Noise Reduction. C.Fn II-1-1 applies “dark frame subtraction” noise reduction whenever an exposure with a shutter speed of one second or longer is taken. This is regardless of ISO setting, and indeed regardless of whether High ISO Noise Reduction is active or not. It counters a totally different type of noise, that can occur during long time exposures. The two types of Noise Reduction can be combined, if the photographer desires."
Now I could actually apply some form of statistical analysis to the noise data from my raw files, and produce some fancy graphs, but since I did this to see whether I should turn off 1/3 stop ISO, I consider my original question is answered :-)
If anyone does a really thorough version of this test... please do let me know, and try and get out to take more photos :-)
The views in this article represent those of Keith Cooper.
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