Issues with dust at smaller apertures

Hey all - been really struggling with white dust spots in my DSLR scans. I was noticing a repeating pattern of spots in the same exact place even in a batch where I was using two different cameras. So I was sure it wasn’t my film cameras, and it wasn’t my developing because those spots are not visible on the negatives.

I cleaned my lens and even swapped the camera bodies. Turns out it was because I was shooting at f/16 (to try to get the most in focus). I did some tests and reduced to f/8 and then f/5.6 and as I made the aperture larger, the dust spots went away gradually. F/8 had fewer spots, and at f/5.6 there was only one or two that were noticeable that were easy enough to remove in LR.

But I’m also worried that 5.6 might be too open, or is that a concern?

Is there something I can do to be able to shoot at f/8 or higher again or is this something I should just not worry about? When I look through the lens into light I can only see the most miniscule of dust spots, and it’s a relatively brand new modern lens (albiet a 7artisans cheapo one).

Hi @ekimneems and welcome to the forum.

Dust is an everlasting pain with any optical reproduction and macro work accentuates this.

You have changed cameras and negatives and the spots have stayed put. You could now check the backlight and try to clean it and/or move it away from the negative. Also, a minuscule dust spot on or in a lens can lead to undesired effects, which should go away if you use a different lens (if available)…

with f16 you will hit diffraction which will create sharpness problem. It is much better to deal with dust and shoot at 5.6 or 8 rather than loss of sharpness which you can’t recover.

I was under the impression reading other guides that I want to shoot at “at maximum f/8” to ensure everything is sharp incase the negs aren’t perfectly flat. Is that not true?

My issue is that at the higher my f-stop number, the more dust I’m seeing. So if f/5.6 is fine for sharpness, then I’m good because I’m not seeing much dust at that aperture.

Each lens has an optimally sharp aperture stop, usually 2 stops less than the max opening. You need to find out how the sharpness behaves for edges as the center is usually not the concern. If you are using a true macro lens, then it should have a flat field curvature meaning as long as everything is parallel to the sensor, edges will be nearly as sharp as the center. If you pass the optimally sharp aperture, with any lens in the world, you will start the diffraction problem which will unsharp the image gradually.

Fatih Ayoglu

I had this problem. It was when I was using a bellows and slide copier to make scans. Dust on the white diffusion glass was coming though if the separation distance between the film and the white glass was too small. it was worse at small apertures like you mention. I fixed by increasing that separation layer and keeping all surfaces clean. . I have found no matter what scanning method I use I need to pay attention to those distances - film to white diffusion layer and diffusion to light source. I’m currently using a essential film holder so you can picture what I’m referring to.

I’m using a Skier Copy Box v3 - I’m pretty sure it’s a dust issue at the lens though because if I clean the lens with one of those lens brushes, it moves the tiny dust particles around and they end up on different (but still repeating) parts of the images.

I’m using a brand new 7artisans 60mm macro so maybe because it’s cheap it allows too much dust. Maybe I should just spring for a Fujifilm X macro

Sounds like your being pretty systematic about this so you may be right. Do you have a UV filter on the lens? That would get the dust farther towards the film. I have never observed dust on the glass of my macros to be in focus - nikkors - but I never looked for it either…