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I've bought a second hand Helios lens online (40 years old). At first sight everything looks fine no fungus haze no dust. Under 45 degree the front element in covered in very very thin scratches like it was cleaned with a T-shirt. I will test it next but I'm on film with no access to digital. Will this affect the photos?

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It takes a LOT of damage from scratches or fairly sizeable obstructions before they become noticeable! These photos from Roger Cicala's blog entry at lensrentals.com illustrate just how far a lens can be damaged or obstructed with very little impact on image quality.

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Although it is true that the coatings on the surfaces of lens elements that face other lens elements are more important because they reduce the amount of flare generated by light bouncing back and forth between those two elements, the coatings on the front of your lens are there for a reason: to increase the amount of light that makes it through your lens to the camera's light box by decreasing the amount of light reflected off the front elements of the lens.

Most minor scratches on lens' have an infinitesimal impact on image quality. They look a lot worse than they are, especially in terms of the front element of a lens. This is because the light from a point source in the scene being photographed is spread over the entire area of the lens as it enters the front element before being focused (hopefully) to a point on the image plane behind the lens.

The cumulative effect of a lot of small scratches will eventually start to affect contrast. If the scratches are fairly evenly distributed over the entire surface of the lens, this can be dealt with to a degree by shooting with a higher contrast film or using Adams' Zone System of adjusting exposure/development times to increase/decrease contrast. If you scan your negatives and do further digital processing or for those who shoot digital, one can add contrast in the processing pipeline, whether than means increasing the camera's contrast setting before shooting for photos shot straight to JPEG, or doing it after the fact for raw image processing.

If the scratches are causing a perceptible effect on your images, then masking them with a very fine (to minimize the size of the mark) black marker can reduce the amount of flare to which the scratches may contribute, but that's usually a way to deal with a few more serious scratches than a lot of light ones.

  • I am shooting film. – Andy Andy Nov 29 '19 at 21:29
  • @AndyAndy Do you scan your negatives and do any digital processing of the results? Are you familiar with Adams' Zone system of adjusting exposure/development times to increase/decrease contrast with a purely analog workflow? You could also consider using a film that has higher contrast at box speed and development times. – Michael C Nov 29 '19 at 21:58
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Many thin scratches will affect the tendency for lens flare and other backlight artifacts and the contrast of the images (since light hitting a scratch gets deflected to a number of unrelated sensor points).

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    I don't see flare an issue for myself, but the contrast will be a potential issues. – Andy Andy Nov 29 '19 at 1:58

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