Significance of tiny blemishes in lens coating of front element

[timothy_pia]

Hello all,

 

Just aquired a Canon FD20mm f2.8 wide angle off of ebay. Lens appears to be in

excellent condition mechanically as well as finish wise. I discovered however

that the front lens element has two minute blemishes about the size of a tiny

grain of sand in the coating. At first glance you wouldn't even notice them

since they are so subtle, but you can see them if you hold the lens into the

sunlight or under a lamp. You really need a magnifying glass to see exactly

what they are. I don't beleive that the lens needs cleaning since the rest of

the glass including the rear element are extremely clean and clear with no

cleaning marks. The dealer had a 100% feedback rating and he said I could

simply get a full refund if I wish and that he appologized for his tech

overlooking this. I have yet to shoot a role of film. I'll do that this

weekend. I've read extensively that with wide angle lenses, this can be more

of a concern expecially if the lens is stopped down. Just looking for advice.

I don't really mind the minute blemishes if they don't make a diffence on the

photos. I got the lens with the BW-72 hood and original caps to go with it.

It is otherwise in beautiful condition. Your input is welcome. Thanks.

 

Tim Pia

Davis, CA

[j._scott_schrader]

In my experience they will have virtually no effect on image quality. I have had a lens or two

over the years that had the coating "problems" that you described. Both were purchased new.

One was a large format aspherical lens, and one was a 35mm lens L series lens. Neither had

any perceptible degradation of quality. I looked long and hard and ran many tests to make

sure the image quality did not suffer as a result of these "blemishes" it simply didn't degrade

the image quality. Also, it in no way affected the resale price when I sold one on e-bay.

[bobatkins]

It's very likely that the blemishes will have absolutely no visible effect on the image quality.

 

They might reduce resale value, but if you got a good deal on the lens, I'd keep it.

[phyrpowr]

Never seen a lens that didn't look like it had "something" floating in there, the final print is the test

[yellowwoodguiding]

In direct light I have had glare from minor blemishes on the glass which have ruined landscape shots. Assuming your not shooting into the sun the images should be fine.

[walang_pangalan]

<i>I discovered however that the front lens element has two minute blemishes about the size of a tiny grain of sand in the coating.</i>

 

<p>If they are causing problems when the lens surface is illuminated directly by the Sun (or similar), just cover them up with some ink. Otherwise, this kind of micro-obstruction will have basically no visible effect on your images. Indeed, big-time macro-obstructions that cover a third of the objective on mirror lenses or large reflecting telescopes have no effect but for the notorious "donut bokeh".

[anish]

I agree with all of the above. i got my 24mm on ebay, and it has a small scratch on the front glass. i couldn't find its effect on my pictures even if i tried. don't even worry about, your lens is fine...

 

Anish

[timothy_pia]

Hello again,

 

Just wanted to thank you guys for the input. Got a chance to test the Canon FD 20mm lens over the weekend. You guys were right about these minute blemishes in the coating not being of serious concern. I could not see anything detectable on the prints at all. A wonderful lens. Now I can say I'm completely satisfied with my purchase and call it a keeper. Hope this post is of help to anyone else out there that may have the same concerns. Now time to get out there and take some more photos. Thanks again to all who answered.

 

Tim Pia