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Vadim Joy

How to clean Foton 37-140mm?

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Guys I need help cleaning glass on Foton 37-140mm zoom. It has some fungus, almost invisible but still. How do I dissemble this lens and put it back together?

Any help would be appreciated. Thank you.

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Are you sure you want to tackle it yourself? It's very easy for inexperienced people to cause damage or misalignment to a lens that will degrade the image quality much more than anything the original problem might have caused. Especially anamorphic lenses, where the horizontal alignment of the cylindrical elements is crucial to the performance.

 

The difficulty of the job depends largely on where the fungus is located. It's relatively straightforward to remove the front element, it's just held by the front frame with 4 screws. But the glass itself will probably be wedged in place with thin metal strips, which will also be positioning the optical centre of the element (hopefully) in the centre of the lens axis. So make sure to note where those spacing strips are, and which way up the element is. Try to avoid accidently scraping off any of the black paint masking the element edges, as that will show up dramatically through the front, and add internal reflections.

 

If the fungus is not accessible with the front element removed, I would honestly recommend giving it to a professional, or leaving it be. A day in the sun should retard the fungus growth, and make sure not to store the lens in a dank or humid environment.

 

Old Russian stuff is very often hand assembled and tweaked, with what can appear to be rather agricultural construction. A lot of technicians refuse to work on the stuff because it's so easy to strip screws or lose an alignment that was held in place with bits of scrap metal, or depended on how tightly a screw was done up.

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I have dissembled one of these things and it was not that big of a deal. Main thing is never remove or adjust the rear most element since it will require expert adjustment if you do. I don't recall exactly how I did it but I started by removing the mount which is interchangeable on this lens. Then removed the aperture ring and scale, then the zoom ring and scale. Next remove the front silver ring where the lens cap would screw in and focus scale. Once you get it to a point you can adjust focus and the front element will unscrew out as you do. For the next elements they are held in place by plastic pieces that slide in channels as you adjust zoom. From there you can remove the aperture components. Clean and lube everything that needs it re-assemble. Take it slow and take note of how it goes back together. All the glass elements will have there own metal housings and there should be no reason to remove them from it. Again if you do the lens will need expert service. I went through this process to remove the aperture blades on mine when they self destructed and everything worked out fine. Good luck.

Edited by David Hessel

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Main thing is never remove or adjust the rear most element since it will require expert adjustment if you do.

Are you talking about rear ring with screw on it? Rear focal length adjustment if that's how it's called.

Edited by Vadim Joy

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Ah ok. I'm asking because I had an issue with this lens yesterday, for some reason it wouldn't focus at 1.6m. I adjusted rear focal length of the lens to my camera and it works great now. Although many people said it has to be done in a lab.

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Sorry, I was assuming you were asking about the square-fronted anamorphic Foton 37-140, different lens.

As far as I know it's the same lens, only with anamorphic square adapter attached. Isn't it?

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Hi guys.

Foton 37-140 mm do not complex zoom lens from outside view, but, do not simply lens iniside.

to viisit of my web page

 

https://sites.google.com/site/olexservicelenses/home/spherical-zoom-lenses/37-140-mm-f3-5-foton

 

Foton included a few finished and adjusted optical components.

All this components have factury assembling and collimating and do not need touch of this optical components

All other lens housing parts can be take to pieces, but, you must be sure, what you do, because, any oprtaion will destroy a zoom lens collimating.

You can see a test pictures from Foton zoom lens at process of collimating and after collimating.

 

Foton do not have technical possiblity to adjust of variator and compensator positions, but, rear optical block adjustable and front focus block adjustable too.

Do not need forgey about standard procedure of flange focal distance collimating after assembling.

If you have do not quality-critical condition of fungus, i recommed do not touch of zoom lens.

Because, you will have high probability do not clean fungus, to receive a MC coating destroy after cleaning.

The glue layer exfoliation of clued glass component can show like fungus.

 

I will be very happy, if you see a oil dirt and oil can be clean.

But, any full service of Foton and other lens ask of detailed collimating.

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