Artifacts from RF15-35mm F2.8 L IS USM

[JoshZielinski]

Hello,

For a while now, I've had bad artifacts from my RF15-35mm F2.8 L IS USM when photographing scenes in which light meets a sharp edge beyond which the scene is dark. A recent, particularly severe example is attached from underneath a recess cave. I overexposed the image so you can see how the artifact obscures the texture of the sandstone nearest to the edge. I've encountered this effect on many other similar scenes. It frequently renders the images essentially unusable due to the amount of work it would take make the exposure appear natural.

As far as I can tell, the lens is clean on the front and back, so I'm not sure what would be causing this. Any thoughts?

[ebiggs1]

Photography isn't an exact science but it does have some fixed laws.

[ebiggs1]

Here's the deal smaller apertures, your higher f-numbers such as f/16 or f/22 do not make moiré worse if in fact that is what we are seeing. It actually will help reduce it or fully eliminate it. Small apertures increase diffraction but that is not what you are seeing in your examples.
I don't know if he knows this or how experienced he is or whether he is aware of that. He has one point about DOF. Other larger apertures would have had sufficient DOF in that situation if DOF was your concern.
Smaller apertures are used for more than DOF, however.

[JoshZielinski]

Got it. I wasn't aware of moiré (or at least not by name) until you brought it up a few posts ago, so it's nice to have a better understanding of it now and how aperture affects it in case I encounter it in the future. I did test the moiré slider in Lightroom Classic just to see if it would reduce the artifact, which it did not.

f/10 or perhaps even larger would've definitely been sufficient with the two scenes I shared originally. All of the components in the scene were far enough away to make DOF concerns negligible. Anyway, I'll see how a smaller aperture might affect the artifact in the future. Perhaps it's just flare that is innate in any RF15-35mm F2.8 L IS USM.

[ebiggs1]

Keep in mind moiré was just a guess. And it does in fact look like it. I am surprised the LR slider had no effect even if it isn't moiré. You did work on the raw file not a jpg? Not any already processed file? You masked out the area and then adjusted the slider? Develop module>Masking tool>Brush choose Radial or Linear select area and scroll  down to the moiré slider. It should do something even if it isn't what you want.

[JoshZielinski]

Yep, I did it on the RAW file with a radial brush. I may as well try it again, but it didn't seem to reduce the affect when I did it the first time. I should clarify, it did alter the appearance a little, just not in a way that actually reduced the flare/artifact.

[johnrmoyer]

This is just a guess.

If the goal is to recover the existing images, then I might try setting brightness levels above and/or below thresholds to transparent for each image before combining into HDR if your software handles transparency correctly. If transparency does not work, then set above threshold to white and create HDR by darkening when stacking.

I did not notice any moiré. It looked more like flare to me. 

Yet another way to avoid flare would be to use an EF lens with adapter which would lengthen distance between back element of lens and sensor.

It has been decades since I have used any Adobe software, so my image stacking guesses might be meaningless.

[ebiggs1]

Even if it isn’t the LR slider should have done something even if it made it worse. LR has other adjustment sliders that may possibly fix it.