Multicoating on a lens

[trragan]

Hello Everyone, I'm new to LF photography and have a question regarding the multicoating on a Nikkor 75MM lens. I purchased this off of Ebay and the lens has two smallish spots where the coating has rubbed off. Is it likely that this will cause an issue with its shooting quality? The spots are probably a third of the way into the middle of the lens. I appreciate any help you can provide.

[Andy Eads]

Small marks on a lens are usually a very small percentage of the lens area. The closer to the center of the lens the more harm they will do to the image. Most coating marks I've encountered are not wear marks but damage from a fluid that affected the lens. I taught high school photography and had many coating spots due to cola splashing onto the lens without being cleaned immediately. I don't recall ever seeing a bad effect from those sorts of marks. If the mark is constrained to the coating layer and did not damage the underlying glass, it is unlikely to cause significant image degradation. However, depending on your need for perfection, any mark may be a show stopper.

[revdoc]

The coatings just reduce the amount of light reflected from the glass surface, so if it's just a spot with no coating on the front of the lens, you'll get slightly less light passing through the lens. (I would stress "slightly"; it would be too little to notice.)

Coating loss inside the lens is a little different. That can increase internal reflections and decrease contrast, but again, not enough to notice.

[lassethomas]

As long as the damage is on the front element there is absolutly nothing to worry about. There will be no visible effect at all.
If you don't believe me have a look at this post from lens rentals regarding scratches on the front element :)

https://www.lensrentals.com/blog/2008/10/front-element-scratches/

[trragan]

Thanks everyone, this is extremely helpful!

[alt.kafka]

As long as the damage is on the front element there is absolutly nothing to worry about. There will be no visible effect at all.
If you don't believe me have a look at this post from lens rentals regarding scratches on the front element :)

https://www.lensrentals.com/blog/2008/10/front-element-scratches/

Sorry to ask such a newbie question, but what about the back element?

[Mark Sawyer]

It's the internal air-glass surfaces that are most critical. Missing some coating on the front element means a bit of light will reflect back outwards into the world, have very little effect. On the back element, the very small amount of light that passes through the lens, reflects off the film back to the lens and then back to the film again is again very, very small. On the internal air-glass surfaces, the light can start bouncing back and forth, lowering the contrast a little and increasing lens flare.

But remember, all the photos made with lenses from before WWII were made with uncoated lenses. Don't worry about it! :)