Author Topic: Moving front element  (Read 175 times)

Zang

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Moving front element
« on: July 30, 2022, 16:04:49 »
Hey all,

I am overhauling Contax Zeiss 85mm f2.8, initially wanted only to remove internal dust and regrease the helicoids. When I took the lens apart, I notice that the very front element is rattling a bit when I shake the front assembly. It is not too bad but it is definitely rattling. Now, I am very sure it has been like that since it left the factory. There was no indication that anyone opened the lens up. Of course, I want to tighten the element. However, the front assembly housing is so difficult to unscrew. My question is, could it be a serious optical issue if I leave it as is?

I will still try opening it, but it seems to be next to impossible :(

Cheers,
Zang

Zang

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Re: Moving front element
« Reply #1 on: July 30, 2022, 17:32:30 »
Nail polish remover + patience did the job! Chemical nor patience alone will not work :D We need both.

I have learned one thing working with lenses, never lose the hope :)

Toby

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    • Toby Marshall
Re: Moving front element
« Reply #2 on: August 01, 2022, 12:12:11 »
Hey all,

I am overhauling Contax Zeiss 85mm f2.8, initially wanted only to remove internal dust and regrease the helicoids. When I took the lens apart, I notice that the very front element is rattling a bit when I shake the front assembly. It is not too bad but it is definitely rattling. Now, I am very sure it has been like that since it left the factory. There was no indication that anyone opened the lens up. Of course, I want to tighten the element. However, the front assembly housing is so difficult to unscrew. My question is, could it be a serious optical issue if I leave it as is?

I will still try opening it, but it seems to be next to impossible :(

Cheers,
Zang

Lens elements are very precisely placed to achieve the designers' aims. It certainly will decrease performance, but how much is another question. I have, as an experiment, increased element spacing in some old vintage lenses by partially unscrewing front or rear element groups. A small amount will probably not be noticeable, but it depends on the design of the lens. In my experiments I noticed a definite increase in spherical aberration when spacing was increased.

Zang

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Re: Moving front element
« Reply #3 on: August 01, 2022, 14:23:26 »
Thanks Toby,

That was my feeling too, thus my question. In my previous lens (Canon 135mm f3.5), I had a moving element that I identified fixed at the end, but before I found that, test pictures look more than OK.

Luckily, I was able to open up the front assembly of Zeiss 85mm, clean up all the thread lock and assemble everything back again. Now I feel I can tighten the casing nicely with consistent but not too hard resistance. I think the way the spacers and barrels were designed ensures the glass elements to be well aligned when sited firmly in their slots so I am pretty sure they are OK now.