Any clue how to disassembly front element from Contax 100/2?

[Giovanni]

Long story short,
I have a bunch of CY lenses from Germany, among them a couple got fungus, the 50/1.7 and 100/2 have very slight traces on the back of the front element, I got the rubber circles to unscrew the front element, I started off the 100/2 as I want to take it with me for a trip but found out that it is a block along with another element and dunno how to unscrew just the front one off the combo, any clue how to try that?

I am waiting to get isopropyl alcool to try and clean it, also have to buy gloves and eventually a market to paint the borders in black as recommended by some tutorials, still if I handle to tear it apart...

The traces of fungus are very very light but I am afraid it will spread and I have tree more lenses who got it, one of them was sent to Nikon very long time ago, they charged a lot and the problem is back so I rather try it myself, nothing to loose on these old lenses and too expensive to send them to a repair (which I did with the Distagon 35/1.4 and Planar 85/1.4).

Thanks for your attention

Giovanni

[kiddo]

Unless having good knowledge on repairing lenses ,I wouldn't learn on a Zeiss 100mm D2 , that's still an expensive lens nowadays ,just like the other mentioned that you have

[caspert79]

If the fungus is there already for a long time, I’m pretty sure it’s dead. I would store it in a non-humid environment.

[kiddo]

do you have pic of how far have you reached to open it? if you already got front group removed, than you might have to deal with some kind of loctite (in yashica ML red one, the worst, but it would work with acetone after multiple attempts) - don´t know if it would be the case for your lens, but as far as i know, some of these blocks (groups) might have a retaining screw, others are glue sealed (loctite or not), others might use some retainers that are visible and worse ones would be the one in a capsule (minolta zoom 35-70mm macro but most of the cases only 2 elements)- i might be missing some other op`tions though -

[Giovanni]

Good morning,

here is a pic of the back and front of the group, behind this there is the diaphragm and then the rear lens, doesn't seem like more than just a veil but still trying to figure how to remove the front retaining ring if that's what keeps them together, the rubber rings I have grip it but it seems not to move

Grazie

[BrianSVP]

Put a few drops of acetone in the seam behind the front bezel of which the front name ring is a part, wait a few seconds for it to soak, then you should be able to rotate the entire bezel off.

As you proceed inward, you'll likely encounter the more traditional notched spanner rings.

The front cell consists of three elements. The rear one is obviously held in by the notched ring seen in your second photo, and the middle one likely removes from the front after you get the frontmost element out.



[quote="Giovanni"]Good morning,

here is a pic of the back and front of the group, behind this there is the diaphragm and then the rear lens, doesn't seem like more than just a veil but still trying to figure how to remove the front retaining ring if that's what keeps them together, the rubber rings I have grip it but it seems not to move

Grazie




#1

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[kiddo]

As Brian mentioned above, acetone is your friend (I found 2 different one on the market, one stronger than the other); I do remember yashica ml 50mm 1.4 had the most stubborn loctite applied (red one) I've ever found in a lens, it didn't work with few drops , I had to put aside that lens multiple times ,until finally it released . I don't know if all these contax lenses would work the same (ml 35mm 2.8 was easier to open) , but sometimes you'll need some more patience.
Take good care of that lens , is a highly desirable one and not cheap at all nowadays.

[BrianSVP]

Ha, I coincidentally have the front group (with rearmost element removed) of that very Yashica lens soaking in a jar of acetone to get the frontmost element out to clean some fungus behind it.

The Yashica threadlocker is indeed pretty bad, but even worse is the stuff used on the EBC-era Fujinons and the vintage Kiron f/2 wide angles. Some of them are virtually impossible to disassemble, even with loads of solvent and heat.

Returning to the subject at hand, this Zeiss definitely uses threadlocker, as you can see some of it on the thread holding the rear element in Giovanni's third picture in the post above.

[kiddo]

[BrianSVP]

The coatings are vapor deposited metal salts and believe it or not actually aren't affected by acetone.

I took the rearmost doublet in the front cell out, as it has a painted edge and is held in by a plastic retainer that I didn't want to melt, and submerged the front side of the cell in acetone overnight. The front two elements don't have painted edges and are mounted solely with metal rings, so nothing for the acetone to attack other than the threadlock.

[stevemark]

@ Brian / kiddo:

Thank you for the additional information - probably quite useful in other "cases" as well

S

[kiddo]

"Removing threadlocker varies depending on the type you’re working with. For Loctite threadlocker blue, simply remove the bolt and nut with normal tools.

Loctite Threadlocker Red 271, is formulated to be a high strength thread locker, meaning it will require the localized heat of a blowtorch to weaken the bond. "

https://www.loctiteproducts.com/ideas/build-things/threadlocker-red-or-blue-which-ones-right-for-you.html

I've read about some people using CRC brake cleaner with success to release the red threadlocker ,depends on the amount used , it would come lose easily or not, as is not the same to release it from screws head or an internal helicoid , reason why Brian already mentioned the need to soak it properly to get it open. The Nikon I've opened , mostly used the blue one, much easier to open .

[BrianSVP]

Most vintage lenses don't actually use Loctite (threadlocker) but rather just a bit of varnish/lacquer.

The most effective thing to loosen nearly all types of threadlocker from lenses is MEK (Methyl Ethyl Ketone), but it's not nearly as safe health-wise as acetone, and it's becoming increasingly harder to find in hardware stores in the U.S. Definitely something you'd want to use outside only.