Glass Dressing or coating for old lenses

[Drew Bedo]

Several years ago I asked if there was a finish coating I could apply to the exterior elements of an old lens. Now I am moving forward with a project lens and want to get some.

My recollection is that there were several suggestions, but I have no rtecord here at home of what that was.

Can't find search terms on this forum that work.

Anyone remembe?

[Jim Noel]

This isn't a suggestion as to what to do but the first coated lenses came about because a photographer or photographers in the late 19th century noticed that lenses that had been used a lot in a smoke filled studio had a light film on them and seemed to produce a sharper image. After cleaning this additional sharpness was lost.
Is this true? I'm not sure but I've heard it for at least 75 years, and it makes sense.

[Mark Sawyer]

This isn't a suggestion as to what to do but the first coated lenses came about because a photographer or photographers in the late 19th century noticed that lenses that had been used a lot in a smoke filled studio had a light film on them and seemed to produce a sharper image. After cleaning this additional sharpness was lost.
Is this true? I'm not sure but I've heard it for at least 75 years, and it makes sense.

I doubt it. Coatings are for reducing reflections within the lens, thus increasing contrast and reducing flare, but they don't affect resolution.

[reddesert]

There is a kernel of truth to the serendipitous origin story of optical coatings, although it's not about a photographer, cigarette smoke, or resolution; but respectively Lord Rayleigh, tarnish, and transmission. From wikipedia, https://en.wikipedia.org/wiki/Anti-reflective_coating

"The simplest form of anti-reflective coating was discovered by Lord Rayleigh in 1886. The optical glass available at the time tended to develop a tarnish on its surface with age, due to chemical reactions with the environment. Rayleigh tested some old, slightly tarnished pieces of glass, and found to his surprise that they transmitted more light than new, clean pieces. The tarnish replaces the air-glass interface with two interfaces: an air-tarnish interface and a tarnish-glass interface. Because the tarnish has a refractive index between those of glass and air, each of these interfaces exhibits less reflection than the air-glass interface did."

I don't know of any simple techniques for home-coating a lens: an AR coating has to be very even and very thin, it's not something you can paint on. Questions would include, what do you want to achieve, protection or decreased reflection/increased transmission? And, is increased flare part of the character of an old lens anyway?

[Vaidotas]

https://www.largeformatphotography.i...-What-is-bloom

[Mark J]

I remember years ago reading an article on a novel telescope design, by Donald Dilworth ( a notable figure in optics, he wrote a lens design program ) . He made the optics himself, and a couple of internal lenses were of a high-index lead flint glass, which he dipped in dilute acid for a specified time, to form a basic AR coating.

[GoodOldNorm]

Would it not be easier to fit a coated lens filter?

[Drew Bedo]

This is a 150year old brass barreled Petzval. I will be using it with a Packard Ideal pneumatic shutter as a shooter and want to retain a "period correct" look.

I had thought that a few years ago, there was a discussion here on a glass dressing that sort of protected the ouer surface, a bit like waxing a car (not a good analogy).

[Tin Can]

Very glad you are going to use a Packard

[Mark Sawyer]

Would it not be easier to fit a coated lens filter?

Coatings on the filter would reduce reflections from the filter surfaces. AR lens coatings are for reducing reflections from surfaces inside the lens itself. Those are the culprits behind flare and reduced contrast.