Lens with small scratches on the front element - how do they affect IQ?

Question

I am looking to buy a CANON 28mm 1.8 EF lens. I found an offer, significantly discounted, of a lens with small scratches on the front element.

The offer is very tempting. Here is a photo posted by the seller:

The scratches will probably affect my photos a bit. But how much exactly? Does anyone have experience with a similarly scratched lens?

I am an amateur and hobbyist, and I don't make money from my photography. I would use this lens as a 'normal' on my 60D, mostly for taking portrait photos of my family. I am getting this one because of the aperture (1.8), and I would be using it wide open most of the time.

Itai · Accepted Answer

Scratches in general have very little effect on image quality. You may have zones of slightly lower contrast due to the scratches and these areas may be slightly more prone to flare since its the lens coating which is most damaged.

The effect of scratches is inversely proportional to focus distance. The farther you focus, the more out of focus the ill-effects would be. Check out this extreme example. Using the aperture wide-open will blur-out the scratch more too but you may get more flaring.

Eric · Answer

You may improve the lens performance by taking a black sharpie and filling in the scratches. This will help reduce glare from the scratches, and it won't noticeably change the effective f-stop of the lens.

Answered by Eric on May 28, 2021

Michael Nielsen · Answer

Here are two lenses I got off Ebay - they look pretty nice on images. The Canon 85mm 1.8 does have marks visible to the naked eye on the front element but they are very small. The Helios looked perfect on front and back but on an internal glass there is some dust particles.

Canon 85mm 1.8:

Helios 44-2 58mm F2:

[image examples from two lenses I got from ebay]

Here are two shots with them, with wide apertures:

Canon85mm

Helios

Confirms that "dust inside" or "scratches in front" doesn't affect IQ.

But then I noticed spots when stopped down:

I used Helios when taking a macro of a brie and I needed to stop with to F16 to get just a little bit DOF - the black speckles are dust particles:

But this turned out to be on the sensor, because the spots were the exact some place as the 85mm stopped down. I cleaned the sensor and it is fine now! Yeah :)

Lens with small scratches on the front element - how do they affect IQ?

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