What are these tinted rings (low-light E-M5 w/flash)?

Started Mar 20, 2014 | Questions thread
Anders W Forum Pro • Posts: 21,468
Re: What are these tinted rings (low-light E-M5 w/flash)?

texinwien wrote:

Anders W wrote:

texinwien wrote:

Anders W wrote:

texinwien wrote:

Anders W wrote:

My idea for further testing would be to test shoot a white wall or something like that (perhaps even defocused) with severe underexposure. This should make it easier to isolate the culprit. Among those I can think of are the flash, vignetting correction, and distortion correction. So I'd shoot with vignetting correction on as well as off and with two different lenses/FLs, one of which with little or no distortion correction.

Excellent tip. I'll give that a go this evening and see what comes out of it.

When I think about it, an even better solution might be to use the same lens but look at it in a RAW converter where you can turn the distortion correction on and off. That helps keep everything else constant, which is difficult with two different lenses/FLs.

See here: http://www.dpreview.com/forums/post/53347249

I opened it up in Raw Therapee - distortion correction turned off, CA correction turned off, etc., and the bands are still very visible. Here's what it looks like with just their auto exposure adjustments applied:

The bands are super visible (especially in the darker areas) in this uncropped Raw Therapee conversion.

What do you think? Looks too symmetrical and perfectly concentric to be the product of something at all random.

Good. So we can rule out distortion correction. And yes, that certainly doesn't look random. So perhaps the vignetting correction if it is done crudely. I know the E-M5 does that in RAW and if done crudely, rather than by a large set of different multipliers depending on exactly how far from the center a certain pixel is, then it might of course give rise to circular bands. If so, another good reason not to use it. I never do. Far better to do it in PP when/if it is at all needed.

Yeah, crazy. I know to keep it off, and could have sworn it was. Maddening.

Frankly, before seeing this, I would have been very hard pressed to believe that this correction was done quite that crudely. How on earth could they fail to come up with something better than that?

I think I hadn't noticed it before because barely used Olympus lenses before buying my 12-40mm. I used the 45mm relatively often, but my 12-50mm and 40-150mm haven't seen much use in a long time. Since the correction is only applied when an Olympus lens is attached, it just affected me so rarely that I hadn't noticed it.

Glad to have caught it.

Glad that you did and took the time to discuss it here. Valuable to have this problem discovered and documented.

Wish I could remove the Shading Compensation setting from the menu, altogether.

Good idea actually. An option to get rid of certain dangerous and/or superfluous options.

Could of course also be the flash itself but ...

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