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Biotar 75mm F1.5 advice
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PostPosted: Wed Oct 18, 2017 1:30 pm    Post subject: Biotar 75mm F1.5 advice Reply with quote

Hello all,

I have a Biotar 75mm F1.5 with serial number 4910651 (estimative manufacture year 1957-1958).

I dismount the lens for cleaning, lubricate and fungus removal.

The job is almost done, but i don't know how to remove lenses no. 2 and no. 3 from drawings bellow (the fungus is between them)



If somebody know, please post here.

Thank you


PostPosted: Wed Oct 18, 2017 2:11 pm    Post subject: Re: Biotar 75mm F1.5 advice Reply with quote

Welcome here!

Your posting will show now, anti spam measure

IF the fungus is between lens element 2 + 3 this would be rather bad, as this is a cemented (glued) lens group from what I know (as is 4+5)


Last edited by kds315* on Thu Oct 19, 2017 7:13 am; edited 2 times in total


PostPosted: Wed Oct 18, 2017 4:14 pm    Post subject: Reply with quote

So, there is no solution for detach those lenses? (lenses 4 and 5 are ok, without fungus).
Please note that the fungus between lenses 2 and 3 is not bad. There are few fungus and only at the lens edge.


PostPosted: Wed Oct 18, 2017 5:58 pm    Post subject: Reply with quote

andreiul wrote:
So, there is no solution for detach those lenses? (lenses 4 and 5 are ok, without fungus).
Please note that the fungus between lenses 2 and 3 is not bad. There are few fungus and only at the lens edge.


I would not worry and take the lens apart, so will not be able to see it in the resulting images, but you may lose optical centering / collimation Wink


PostPosted: Wed Oct 18, 2017 7:22 pm    Post subject: Reply with quote

Ok then; i already ordered a ring adapter for Canon EOS from aliexpress. After receive, i will take some test pictures. Then i will see if it is mandatory to dismount those 2 and 3 lenses.

Thank you very much for support!!


PostPosted: Wed Oct 18, 2017 10:20 pm    Post subject: Reply with quote

andreiul wrote:
Ok then; i already ordered a ring adapter for Canon EOS from aliexpress. After receive, i will take some test pictures. Then i will see if it is mandatory to dismount those 2 and 3 lenses.

Thank you very much for support!!


The worst it can happen is a slight loss of contrast which can always be corrected in post processing Wink
It will never affect the sharpness...

Wishing you best of luck! Great lens it is....


Last edited by kds315* on Thu Oct 19, 2017 7:11 am; edited 1 time in total


PostPosted: Wed Oct 18, 2017 10:43 pm    Post subject: Reply with quote

Welcome andreiul

Congratulations on your lens.

Yes, cleaning between cemented elements is not so simple with out tools and skills. First determine cement used to know solvent, and, to know if a substitute with similar index of refraction is available. Next clean, if possible. Then accurately align (colliminate) the elements while new cement cures. Cements can range from tree sap to uv-cured epoxy. If you are know you are capable, there should be no problems.


PostPosted: Thu Oct 19, 2017 8:16 am    Post subject: Reply with quote

Hello guys,

Thank you for advice, but i am still not able to understand now to remove the leses and also in which direction do i have to push.

Another question: the lenses 2 and 3 are glued one to another (on the surface) - i don't think so - or are glued to a metalic support (glued only on the edges)?

Perhaps i have to take some pictures of the actual stage of work.

The lens was in pretty bad condition. I mean it was very dirty and also the mechanism was almost stucked (because of the very old grease).

That's why i choose to dismount the lens until the last screw.

First i triyed to clean the mechanical parts and covers with dish soap. But after drying i saw that the old grease was still there. Then i tryied with isopropyl alcohol. Same result, unable to clean the grease.

Finally, i tryied with nitro diluent (for nitro paint) and finally, i was able to clean the old grease.

After that, i clean all the parts again with dish soap and then with isopropyl alcohol. Then dry with high pressure compressed air for cleaning the possible impurities.

After that all the components was sealed into a hermetic container with silicate gel, avoiding the water perspiration.

The last component is the front assembly (the one with the lens 2 and 3), which remain on the desk for trying to dismount those 2 lenses with fungus.

PS: In the meantime i finish to clean and grease last night a CZJ Tiotar 135 F4 (aprox manufacture year 1954), but this one has no fungus at all. Lucky me!


PostPosted: Thu Oct 19, 2017 5:59 pm    Post subject: Reply with quote

cementing lenses means glueing them together surface to surface using either canada balsam or UV hardened lens cement

***over-and-out***


PostPosted: Thu Nov 02, 2017 9:46 am    Post subject: Reply with quote

My advice: leave that group as it is at least until you test the lens (or did you tried it already?). I hardly think it's fungus what you see between those elements. I rather believe it's deteriorated canada balsam and regluing it at home it's not an easy task and it implies heating, some nasty solvents for cleaning and fresh canada balsam.Also you have to recenter the elements.

Just try the lens as is and then if you still want to fix the problem just let a professional camera repairman to deal with it, although, depending on your location it could be hard to find one that works on 60 years old lenses.