Scuff mark on 50mm FLE - Suggestions on how to test if detrimental?

[declark]

Just acquired a bargain grade 50mm FLE Hasselblad lens from KEH. The mechanics are quite nice, but I am a bit concerned about a scuff mark in the front element coating that is about 10mm long by 2mm wide arc shape that appears to have happened when a cap was put on crooked. The glass does not look scratched. I am thinking of testing it before returning it, because all else is in very nice shape. My thought is that if this mark causes any effect, it would be at minimum aperture at minimum focus. I plan to run a roll of B&W thru it and enlarge it to see if I can see any detriment. I'm thinking of focusing on a block wall at different distances and apertures/shutter speeds which won't hurt to see if those are consistent or would it be better to point it a cloudless area of sky and just shoot blank frames? Any suggestions?

 

[Tom Nutter]

You're right about when, if ever, the effect with be noticeable. The only other thing is a possibility of lens flare. If you can return it though, why not....but makes sure the scuff won't just wipe off with a littlke lens cleaner. I would say that a scuff on the back element of the lens would be much more troublesome.

 

[Q.G.]

Try it under different light, hitting the lens from different angles.
You need to have detail in your test images to see an effect (if there is one), so a blank sky would not be the best test subject. You need contrast/tone range too, so a uniform brick or block wall (though plenty of fine detail) might not be the best test subject either.

 

[Barry S]

The biggest effect will be on resale value. Think about the size of the imperfection vs. the total area of the front element, and how much damage it takes to actually show up in an image (quite a bit more than you'd expect!). I used to worry about this stuff until I started buying (really) old lenses and was shocked that what looked like major flaws had *zero* effect on the image. Shoot a test roll and I'll bet you anything--no problem is evident.

 

[Voyager13b]

Don't give up an "EX" quality lens that was rated "BGN" by KEH only because it has a minor scuff blemish on the front element. The scuff will not cause flare (doesn't work that way), and most likely will only be detectable if you happen to be looking at front of the camera, and not at the film plane, or captured images.

Forget resale value, as a "BGN" lens from KEH is a steal anyway. All that matters is that it works without issue. If you trade it in for a "BGN" lens that has no glass blemishes at all, you are likely getting a well used lens that had a tough life, countless shutter trips (for shutter equipped lenses), and shows it in terms of look and feel.

Solid mechanical (and electrical if it's the case) condition, along with high optical performance is of primary importance in reality. The scuffed lens that you described here sounds like a winner on all counts to me. Prove it's performance by testing it next to a known premium condition example before you return it if the scuff bothers you that much. Don't just give up a great lens deal out of hand.

 

[suzyj]

Here's a pic of my 55mm f/2.8 Mamiya lens. It had a 1mm chip in the front element, which I simply filled in with black paint to ensure it wouldn't flare. I've seen absolutely no evidence of the chip in photos.

 

[declark]

Thanks for all the tips. I hate to return this lens because it is in very nice shape mechanically and after running a couple of rolls of film thru at diff apertures and focal distances this weekend, I have yet to see anything show up in the negatives. I shot open sky for 6 frames at f32, 22, 16 .... and all look very evenly exposed so the shutter seems to be working very well. I also shot some high contrast images as well and still nothing noticeable. I also ran a similar set of open sky shots on an Excellent grade 150mm at F32, 22, 16 ... and the images don't look as evenly exposed (not bad) but not as good as the bargain grade 50mm.

 

[ic-racer]

My thought is that if this mark causes any effect, it would be at minimum aperture at minimum focus.

Wide open, infinity with light hitting the front element will cause it to have maximum effect. But what are you going to test against unless you have the same lens without the defect?

If the mark is at the periphery of the lens element, light rays may not go through it at macro range (as the angle of view is less in a close up)