What are these Spots I'm seeing at f/22

Wildkits · Oct 10, 2022

I'm not technically a beginner, but this is an area that I know little about, so hopefully it qualifies.

I was in Vail last week to see the aspen trees. It was morning, and I wanted to experiment with sunbursts. I set the aperture to f/22 (Canon R5, RF 14-35L lens). I got the sunbursts that I was looking for, but I noticed a lot of dark spots in the bright blue sky. Note that I only see these spots at a very small aperture and only in the blue. I suspect that they appear elsewhere, but the different colors conceal them. Here is an example.

and a blowup of the affected area.

Is this simply a sensor or lens that needs cleaning? If not, what is causing these spots to appear?

Mark S Abeln · Oct 10, 2022

That’s dust on the sensor. Presumably, your camera is set up to automatically do a dust removal upon power-up, but double check to make sure.

Using a blower, brush, or wet swab to remove dust is a standard practice. Maybe a local camera store can do it for you.

ccarrier · Oct 10, 2022

Hi,

It is dust on your sensor. You will have to clean it or have it cleaned.

Dust is more visible at small aperture (for example f22) that's why you are seeing it more on those pictures.

pmgnut · Oct 10, 2022

Definitely sensor dust. If a blower does not remove it, a wet cleaning will be necessary.

Wildkits · Oct 10, 2022

It's good to hear that it's not major.

I almost never shoot at f/22--rarely as small as f/14--so I'd never seen this before.

The Canon does an automatic cleaning when turned off, but apparently it needs some help. I'll probably do a wet cleaning. I had to do that frequently with my Sony Alpha camera. I never noticed it before with the Canon. I haven't cleaned it yet in two years of usage, so it's time.

JohnSil · Oct 10, 2022

Wildkits said:
I'm not technically a beginner, but this is an area that I know little about, so hopefully it qualifies.

I was in Vail last week to see the aspen trees. It was morning, and I wanted to experiment with sunbursts. I set the aperture to f/22 (Canon R5, RF 14-35L lens). I got the sunbursts that I was looking for, but I noticed a lot of dark spots in the bright blue sky. Note that I only see these spots at a very small aperture and only in the blue. I suspect that they appear elsewhere, but the different colors conceal them. Here is an example.

and a blowup of the affected area.

Is this simply a sensor or lens that needs cleaning? If not, what is causing these spots to appear?

Wild, I don't see anything. I think you've got tons of floaters in your eyes!

Hey just kidding. It's either a large flock of starlings heading back to their roosting grounds or you have the worlds dirtiest sensor. My money's on the starlings!!!

John

LynniePad · Oct 10, 2022

Wildkits said:
I'm not technically a beginner, but this is an area that I know little about, so hopefully it qualifies.

I was in Vail last week to see the aspen trees. It was morning, and I wanted to experiment with sunbursts. I set the aperture to f/22 (Canon R5, RF 14-35L lens). I got the sunbursts that I was looking for, but I noticed a lot of dark spots in the bright blue sky. Note that I only see these spots at a very small aperture and only in the blue.

Is this simply a sensor or lens that needs cleaning? If not, what is causing these spots to appear?

You can be sure that it’s nothing to do with the lens, as only dirty lenses with the shortest focal length are likely to affect the image, and then only when grossly contaminated and stopped down to f/22, with the DOF extending from near the front lens surface to infinity.

You can easily confirm this by deliberately adding “spots” to a filter on the front of your lenses. Also consider the relatively large mirror that’s right in the middle of the optical path of catadioptric lenses or Newtonian telescopes. Newton didn’t care about bokeh, but he knew his optics!

John Sheehy · Oct 10, 2022

LynniePad said:
You can be sure that it’s nothing to do with the lens, as only dirty lenses with the shortest focal length are likely to affect the image, and then only when grossly contaminated and stopped down to f/22, with the DOF extending from near the front lens surface to infinity.

That's been my general experience; except for a screw-on Sony Fish-eye adapter for my F707, which sharply imaged things on the front element, the only time I've even seen those dark spots was when the dirt was on the sensor itself. However, I had it happen with a Canon RF TC recently; a smudge on the camera side of the TC recorded quite visibly at f/22.

LynniePad · Oct 10, 2022

John Sheehy said:
LynniePad said:

You can be sure that it’s nothing to do with the lens, as only dirty lenses with the shortest focal length are likely to affect the image, and then only when grossly contaminated and stopped down to f/22, with the DOF extending from near the front lens surface to infinity.

Click to expand...

That's been my general experience; except for a screw-on Sony Fish-eye adapter for my F707, which sharply imaged things on the front element, the only time I've even seen those dark spots was when the dirt was on the sensor itself. However, I had it happen with a Canon RF TC recently; a smudge on the camera side of the TC recorded quite visibly at f/22.

As a test, I put a 5mm piece of sticky paper on the filter of my 16-35mm zoom. At 16mm and f/22 the blob was quite visible in the image, but by f/5.6 it was barely noticeable.

Obviously, I didn’t try it on the actual lens surface where the effect would have been greater. And yes, the mildly sticky paper (a piece of self-adhesive postage stamp) pealed off without leaving a trace on the filter.

Chris R-UK · Oct 11, 2022

Wildkits said:
It's good to hear that it's not major.

I almost never shoot at f/22--rarely as small as f/14--so I'd never seen this before.

The Canon does an automatic cleaning when turned off, but apparently it needs some help. I'll probably do a wet cleaning. I had to do that frequently with my Sony Alpha camera. I never noticed it before with the Canon. I haven't cleaned it yet in two years of usage, so it's time.

I only clean my sensors when I see dust spots in a normal image. Since I haven't seen any such dust spots since I bought my first camera with auto sensor cleaning in 2009, I haven't had to clean any sensor in 13 years.

If you live or shoot frequently in a dusty environment, YMMV.

Mark S Abeln · Oct 11, 2022

Chris R-UK said:
I only clean my sensors when I see dust spots in a normal image. Since I haven't seen any such dust spots since I bought my first camera with auto sensor cleaning in 2009, I haven't had to clean any sensor in 13 years.

That's a great advantage of Micro 4/3rds systems. By design they have a thicker cover glass than other competing system (4 mm versus 2 mm), and so dust is generally more out of focus.

VLP Bob · Oct 12, 2022

looks a lot like the condensation spots I get time to time but more spread out. Cleaning your sensor and taking a photo into the blue sky is a good first step to problem solve. IDK how you are not a beginner and haven't don't this already unless you are just very admirably cautious with your gear and elements.

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