This month I was testing reduced analog gains on 5d2 while everyday shooting and results look great. In short: it looks like we can pull down iso100 to something about
iso20-25 (upd: lets's say about 50) still having full dynamic range (up to 11.6).
Setup.Reddeercity’s builds for 5d2 + raw_diag.mo
As Alex once reported, it’s reasonable to pull these DFE values from 48x down to 250 – until vertical banding becomes very noticeable. I’ve tried lower values and subtracted darkframes in post. Luckily vertical banding stays constant for the same ISO and DFE values. I don’t know whether it is important or not, but I used CMOS[0]=0x200, 0x204, 0x208 to get the darkframes (for iso 100, 200 and 400 respectively). Either it’s some physically stable bias (hard to believe that) or just the factory calibration playing against us. I keep just 3 master-darks, they work without a problem. Final images after subtraction show no FPN and very low random noise (reason 1 - analog amplifiers may generate a lot of noise themselves; reason 2 – longer exposure gives larger number of photons).
At DFE values about 100 raw_diag reports worse DR. We can see shadow clipping (posterised green shadows) in post. 111 was just my safe random choice. It turns selecting of iso 100-200-400 to something about iso 20-40-80. All look unbelievably clean. Iso800 is out of use here (it’s produced with DFE values 0x8xx). Iso1600 is a digital push.
SHAD_GAIN (c0f08030) set to 0xfff disables digital push for wide apertures. Not a great change, but still useful.
Attaching 2 samples of processed images (shadows lifted a lot) and some raws to play with. “-df” in filenames means that I’ve already subtracted blacks with Pixelfixer (I like its CR2-IN > CR2-OUT approach).
Known problems. The only way to see overexposure is looking for pink highlights. Auto-ETTR can’t catch it but raw_diag.mo works perfectly.
Low analog gains may be used with Dual-ISO module (or simply patching CMOS[0]=0x343 for iso100/400). But final images are not always recognized by cr2hdr-20bit. Using
–force gives processed images with striped lights. Attaching samples, didn’t tried it much.
Works also with Reddeercity’s video hacks (14bit raw, don’t forget darkframes) but adtg_gui.mo is an overkill here – it takes a lot of resources (and power?) and a lot of time for setup. No way to save its settings. Not a run-and-gun tool. What we need to emploi low iso range is a tiny separate module, patching DFE values at start. Maybe just on/of and a choice of value for them. Unfortunately I’m not the one to write it.
Checked the same approach with 600d. It gives something, but nothing groundbreaking yet.
Test raw files -
https://app.box.com/s/d7i3qj09pc300ffb73sgrtnj7totjc7i
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