topic Re: Artifacts from RF15-35mm F2.8 L IS USM in EF & RF Lenses

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

JoshZielinski — Sun, 22 Feb 2026 02:15:43 GMT

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?

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

rs-eos — Sun, 22 Feb 2026 02:55:03 GMT

Scenes such as this are not really capturable in a single photo due to the very high dynamic range. If you have a tripod, you could take at least two, maybe three images at different exposures (expose for cave, expose for sky, maybe expose in between). Then blend the images.

Same thing will happen when shooting a portrait against a white background where too much light is added to the background. Details around the edges of the person (e.g. hair) will lose detail and/or be completely blown out.

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

JoshZielinski — Sun, 22 Feb 2026 12:04:28 GMT

That's correct. This image is the final in a bracketed series of five. One balanced exposure, two underexposed, and two overexposed. The other exposures exhibit the same artifact. I featured this exposure since it is most visible. When I merge these photos to make an HDR composite and lighten the shadows to recover detail in the rockface, the artifact becomes obvious.

This overexposed image would be one of two photos used specifically for the rockface in such a composite, so to have the artifact obvious here presents a problem. If I only exposed for the sky and left the rockface as a silhouette, the artifact would not be visible, but that's not the goal. That's why I'm wondering what else might be the problem, or perhaps this is just an innate limitation of the lens.

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

SignifDigits — Sun, 22 Feb 2026 12:26:10 GMT

First, it would be helpful to know shutter speed, f-stops and ISO. Is that the sun in the upper right corner? It appears that there is radial prismatic diffraction from that spot in the shot from the aperture blades. If you are shooting at or about f22 you might want to dial that back and increase shutter speed. I have certainly experienced diffraction and loss of sharpness due to diffraction at f22 with my version of that lens, but I consider that normal behavior for any lens.

Sorry if I'm missing the point, but I'm not quite 100% certain what I'm looking at and what I'm supposed to be looking for. To me it looks like a shot with the sun in the upper right hand corner stopped down too much and not behaving atypically, but without more data it's impossible to say.

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

JoshZielinski — Sun, 22 Feb 2026 12:51:28 GMT

I should've thought to add the exposure info. It is:
30 seconds
f/16
ISO 100.

The sun is behind a layer of clouds, but I believe it was behind me, so not visible in this frame. I circled the particular area I was referencing. Rather than a more natural grade from light to dark along the rockface, there are streaks and circles of brightness, which I figure is from the lens.

I will try to find another example or see if there's a different way to show it. It's very possible the lens is acting as normal. I just have found the affect very disruptive on quite a few occasions, so I wondered if it wasn't normal.

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

johnrmoyer — Sun, 22 Feb 2026 13:05:25 GMT

I did not notice what software you are using, but metadata seems to say "Adobe Photoshop Lightroom Classic 15.1.1 (Windows)". Below are my guesses, but I hope they might be helpful anyway.

I might guess that the artifacts come from either lack of hood or from lens correction in software. If there is no hood, then light can enter the lens at an angle and reflect. If the hood is optimized for the narrower focal length and not the wider, then there are more likely to be reflections at the wider angle.

Are you doing the HDR composite after lens distortion correction? or before?

If your camera can save DPRAW files, there is a ghosting correction in the DPRAW tools of Canon DPP software and this might be worth trying on each of the raw images before compositing. The 16 bit TIFF files saved from DPP work reasonably well in other software.

I do not have that lens, but use the less expensive EF16-35mm f/4L IS USM. It seems to me that this lens does a little better not wide open and at a little less than the widest angle focal length. This image was not HDR and has less contrast than yours, but I used the "digital lens optimizer" in Canon DPP to sharpen foreground and background details and used the distortion correction and peripheral illumination correction in DPP. I used the DPRAW tool microfocus adjustment to adjust the focus zero front/back with a strength of 8 which seemed to help the edges. https://www.rsok.com/~jrm/2024Feb09_SaltPlainsNWR/2024feb09_reflections_IMG_8919c.html

Reflections in marsh at Salt Plains National Wildlife Refuge in Alfalfa County, Oklahoma, United States on February 9, 2024 ; EOS R5 ; F Number 4.5 ; ISO 100 ; Shutter speed 1/400 ; Focal Length 20mm ; EF16-35mm f/4L IS USM

100% crop showing contrast (unsharp masking appears excessive at 100%)

100% crop in DPP to show contrast at edges

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

rs-eos — Sun, 22 Feb 2026 13:20:01 GMT

Double-checking your shutter of 30 seconds. Were you using an ND filter? Or was this supposed to be 1/30 seconds?

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

SignifDigits — Sun, 22 Feb 2026 13:38:14 GMT

Good point on the hood John. I hadn't thought about that. To me it appears radial which is consistent with aperture blade "stars" of diffraction rather than a "glass element" concern. But it could be one or both I suppose. It's snowing out so I can't go out and take a pic at f16 to try to reproduce the effect and do a hood on and off comparison.

Did you say what Camera?

What was your zoom - looks like 35mm to me, but that's just a guess. IS on or off? AF or MF? If AF settings? Tripod or hand-held? At 1/30 you IS and IBIS systems might be at work. Do you see the same thing at faster shutter speeds? Any and all information you can provide could be useful. Thanks.

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

johnrmoyer — Sun, 22 Feb 2026 13:40:35 GMT

At F/16, there will be a lot of small aperture diffraction blur, spreading across several pixels with your camera. At F/7.1 the small aperture diffraction blur is not likely to be noticed. The "digital lens optimizer" in Canon DPP or the "capture sharpening" in Rawtherapee free software will do a Richardson/Lucy deconvolution to remove some of the diffraction blur. At ISO 100, this works very well because there is little noise.

If you are using the widest angle, then a hood intended for a fixed focal length of 15 mm might fix it if you can find one that will fit.

https://en.wikipedia.org/wiki/Richardson%E2%80%93Lucy_deconvolution

https://snapshot.asia.canon/en/article/lens-faq-4-what-is-ghosting-and-flaring

https://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

https://snapshot.asia.canon/en/article/eos-5d-mark-iv-tips-3-handy-new-dpp-features-for-correcting-dpraw-images

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

JoshZielinski — Sun, 22 Feb 2026 13:58:09 GMT

Yep, it's 30 seconds. This was taken shortly before sunset. I had no ND filter on the lens.

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

JoshZielinski — Sun, 22 Feb 2026 13:39:08 GMT

I do have a lens hood on the lens, and I am doing lens correction before merging as HDR in Adobe Lightroom. The affect is the same even without lens correction applied.

I will have to look into the Canon DPP software for ghosting correction.

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

JoshZielinski — Sun, 22 Feb 2026 13:44:07 GMT

Here is another image from the same outing. Hopefully this might help. I merged one of my brackets of five exposures and briefly edited the shadows, highlights, etc. so things appear balanced. See the irregular bright blotches along the rim of the recess cave? Exposure info:
Various shutter speeds for the five exposures between 2 seconds and 30 seconds.
f/16
ISO 100

I had a lens hood on and I believe the sun had just set by this point, so the light source is only the dim, very diffuse light visible through the cloud cover.

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

JoshZielinski — Sun, 22 Feb 2026 13:56:48 GMT

Ok! I do wonder if small aperture diffraction blur could be the problem. My understanding of diffraction blur is it more so creates a loss of detail, not a lighting/discoloration artifact, but my understanding of it could well be incomplete.

A lens hood designed specifically for 15mm is an interesting idea. That could certainly help. I regret not seeing if the affect is the same at a tighter focal length, like 35mm, so I will have to test that in the future.

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

Waddizzle — Sun, 22 Feb 2026 15:49:30 GMT

I cannot think of any valid reason to use such a small aperture or a 30 second exposure with a wide angle lens.

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

ebiggs1 — Sun, 22 Feb 2026 15:30:11 GMT

"I had no ND filter on the lens."

Do you have any filter attached to the lens if so remove it.

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

ebiggs1 — Sun, 22 Feb 2026 15:30:50 GMT

It looks like moiré. Moiré happens when a high resolution, repetitive pattern interferes with the sensor creating the unwanted, wavy, and rainbow looking patterns. It could be as easy as changing the angle of the shot. Lightroom has a moiré slider to correct for this very easy to do.

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

JoshZielinski — Sun, 22 Feb 2026 16:06:18 GMT

No, there are no attachments on the lens besides the lens hood.

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

JoshZielinski — Sun, 22 Feb 2026 16:08:28 GMT

Ok! I could see that potentially being the issue. I wasn’t aware of a moiré slider in Lightroom, at least not in Classic. I’ll look into it. Maybe my usage of a tight aperture is expounding such an affect.

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

JoshZielinski — Sun, 22 Feb 2026 16:13:43 GMT

The small aperture is perhaps unwarranted. It is habit from shooting often with my 24mm TS-E and other lenses in which I achieve optimal sharpness throughout the image at ~f/16, or at least I perceive it that way. It’s possible the affect wouldn’t be as bad at a wider aperture. Something for me to test.

There’s certainly valid reasons for both (close foreground, astrophotography), but I agree it may be overkill with my specific scenario here.

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

ebiggs1 — Sun, 22 Feb 2026 16:26:10 GMT

"Maybe my usage of a tight aperture is expounding such an affect."

I rather doubt it.

"I cannot think of any valid reason to use such a small aperture ..."

Don't know where or why he is going with that. Perhaps he will expand on it. I would ignore it.

But small apertures can cause diffraction. And diffraction can soften the image and reduce the IQ. I doubt it caused your issue. Diffraction is worse with shorter FL than with longer tele lenses because the aperture is smaller in shorter lenses. This is easy enough to prove shoot it again with different apertures and see which you like the most. You really need to get into the habit of doing that on shoots anyway.