Underexposure vs raising ISO, a practical test

Started 11 months ago | Discussions thread
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hjulenissen
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Underexposure vs raising ISO, a practical test
11 months ago

Screenshot of RawDigger, Image taken at ISO100, f/7.1, 0.3s (approx 4 stops underexposed according to camera metering )

Screenshot of RawDigger, Image taken at ISO1600, f/7.1, 0.3s (approx correctly exposed according to camera metering )

This is a project more about learning things for myself, confirming what some forum heavy-weighters have been saying as it is groundbreaking science. Basically, I want to see how important choosing the "right" ISO is for my Canon 7D. I want to see formyself using a somewhat relevant image, using the tools that I tend to use, not interpreting e.g. DXO plots.

What I would expect from my theoretical understanding (gained mostly from this forum) would be that:

*My 7D benefits from raising ISO to 1600 or 3200 in that noise levels are lowered, although highlight clipping may be a drawback

*My 7D does not benefit from raising ISO above ISO1600/3200, as above that level, my camera applies only digital gain (something that can be offered raw developers)

*"Banding noise" may be a visible factor no matter what measurements of random noise tells us.

*Applying "EC" in raw developers may do something else than what camera nerds might expect or want.

The screenshots of RawDigger tells us (my interpretation) that IMG_1338.cr2 (the underexposed image):

*There are minute differences in the automatic black levels (2048 vs 2046-2047)

*r/g/b values that are not over/under-exposed tends to be about 1/16 that of IMG_1339.cr2 (the raised ISO image), corresponging with [ISO]1600/[ISO]100

*The image is underexposed in 45-60% of the subpixels

*There are no overexposed subpixels

I load the raw files into Lightroom 5.0, apply my default settings (including custom colorchecker profiles made for my camera in "cloudy daylight"), but set sharpening and noise reduction to 0. The two images are exported as JPEG files limited to size<19MB using sRGB color space with no sharpening/scaling and uploaded here.

Image taken at ISO1600, f/7.1, 0.3s (approx correctly exposed according to camera metering ), developed in Lightroom.

Image taken at ISO100, f/7.1, 0.3s (approx 4 stops underexposed according to camera metering ), developed in Lightroom with +4 stop EC

Canon EOS 7D
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