The green zone

[ammitsboel]

I saw something green in my M8 shots, so I used an expodisc and captured as many different stops as I could from black to clipping. The white balance was manual in the camera, adjusted with the expodisc at auto exposure.

The zones -3, -4 and -5 was green and noisy, the other zones was fine and very close to perfect gray. I tried this at ISO 160 in Lightroom, C1 and RAW developer.

Have any of you experienced this?

Best Regards
Henrik

[Jamie Roberts]

Um, no...I've done similar tests for profiling neutrals, and didn't see this.

What lens were you using? Is it coded? Oh--and what lighting and target?

PS--my *guess* is you underexposed the shot badly or mis-used the expodisc, which is easy to do with the expodisc on auto. You should be trying to push the expodisc exposure into the mid-upper quartertone, not a midtone (*around* RGB 200 200 200 in sRGB). Much easier to do on manual

[ammitsboel]

Originally Posted by Jamie Roberts

Um, no...I've done similar tests for profiling neutrals, and didn't see this.

What lens were you using? Is it coded? Oh--and what lighting and target?

PS--my *guess* is you underexposed the shot badly or mis-used the expodisc, which is easy to do with the expodisc on auto. You should be trying to push the expodisc exposure into the mid-upper quartertone, not a midtone (*around* RGB 200 200 200 in sRGB). Much easier to do on manual

Thanks, this is what I did.
I put the expodisc in front of the lens, adjusted WB manually with auto exposure.
I then did a series of exposures from -4 to +4 for capturing the full range of the M8.
The lens is a new summilux 35mm with UV/IR. The test was done in a bright sunny day in the shadow.

Did I do something wrong? isn't it valid to determine color cast in the noise this way?

/Henrik

[ammitsboel]

Originally Posted by Jamie Roberts

PS--my *guess* is you underexposed the shot badly or mis-used the expodisc, which is easy to do with the expodisc on auto. You should be trying to push the expodisc exposure into the mid-upper quartertone, not a midtone (*around* RGB 200 200 200 in sRGB). Much easier to do on manual

Aha!
So the expodisc might not be valid at RGB 1 to around 100?

[Jamie Roberts]

Originally Posted by ammitsboel

Aha!
So the expodisc might not be valid at RGB 1 to around 100?

Exactly... I would expect it to yeild some rather poor results in the shadows with that kind of exposure (which is what you got ) Try it with a higher level of exposure on the expodisc.

[ammitsboel]

Originally Posted by Jamie Roberts

Exactly... I would expect it to yeild some rather poor results in the shadows with that kind of exposure (which is what you got ) Try it with a higher level of exposure on the expodisc.

Thanks Jamie, the idea was to capture the different zones to get some kind of idea of the tone curve in different raw converters and maybe do some calculations to make a linear one. But I guess I'll have to use something else than the expodisc for this.

I tried shooting a scene in -5 stop and bossting it to see if I could see any green, and nothing appeared so I guess I'm ok.

Best Regards
Henrik