Coats Optional?

[Bosun Higgs]

Has anyone ever seen lenses where only some of the elements are coated?

A while ago I noticed that only one element in my 4:4 Petzval Optical Proiectar 120mm lens was coated (both faces), this was the second element in the front air-spaced pair.

The coating was the early very light blue type and was in poor condition, but definitely there. Given the poor condition, I wondered if the coating on the other elements had simply been completely worn away be whatever process damaged the coating I could see.

Now, I have just got a 140mm lens from the same series and all of the elements have intact coating, except the front one.

This is not a case of it being polished off, as the inner surface of the element is also uncoated. The front doublet is an air spaced pair with no spacer ring, and the two elements are in such close contact you can see Newton's Rings. The coating on the second element that is in close contact with the front element is pristine.

As the number of the coated/uncoated elements differ in the two lenses I do not think that including uncoated elements was intentional, I suspect that Optical had a shortage of coated elements and just used whatever they had available.

I have never seen anything like this before, but honestly, with projection lenses you never know what you are going to find inside the tin.

Has anyone seen a similar mixture of coated/uncoated elements in pukka taking lenses?

 

[simple-joy]

Has anyone ever seen lenses where only some of the elements are coated?

A while ago I noticed that only one element in my 4:4 Petzval Optical Proiectar 120mm lens was coated (both faces), this was the second element in the front air-spaced pair.

The coating was the early very light blue type and was in poor condition, but definitely there. Given the poor condition, I wondered if the coating on the other elements had simply been completely worn away be whatever process damaged the coating I could see.

Now, I have just got a 140mm lens from the same series and all of the elements have intact coating, except the front one.

This is not a case of it being polished off, as the inner surface of the element is also uncoated. The front doublet is an air spaced pair with no spacer ring, and the two elements are in such close contact you can see Newton's Rings. The coating on the second element that is in close contact with the front element is pristine.

As the number of the coated/uncoated elements differ in the two lenses I do not think that including uncoated elements was intentional, I suspect that Optical had a shortage of coated elements and just used whatever they had available.

I have never seen anything like this before, but honestly, with projection lenses you never know what you are going to find inside the tin.

Has anyone seen a similar mixture of coated/uncoated elements in pukka taking lenses?

That's very interesting. I've not noticed this in any of my lenses but will keep it in mind... perhaps I just didn't notice it before. I would have guessed companies might have tried to at least provide coating for the front and rear element, even if there was a shortage.

But as you've stated: if they had to mix coated and uncoated elements it might have been impossible to account for that in advance.

What I've noticed in general about early coatings: French lenses (incl. Optical, which had a french parent company) do seem to have very soft coating a lot of the time, extremely sensitive to scratches. I've rarely seen the same amount of tiny scratches (likely from cleaning) in any other lens, than in french ones. Could also be the glass of course, but I suspect the coating plays a role as well, if it's that common.

 

[Bosun Higgs]

What I've noticed in general about early coatings: French lenses (incl. Optical, which had a french parent company) do seem to have very soft coating a lot of the time, extremely sensitive to scratches. I've rarely seen the same amount of tiny scratches (likely from cleaning) in any other lens, than in french ones. Could also be the glass of course, but I suspect the coating plays a role as well, if it's that common.

That may answer another puzzle. I have noticed that the "white curse" layer affects Benoist Berthiot, Optical, and Officine Galileo lenses very much more than any other makes.

Now we know at least two these, Optical and Benoist, are linked. It may be just coincidence, but perhaps Benoist shared their coating tech with OG too?