Separating optical block from focussing assembly?

[Spyderman]

Hi

I have a 'tight' problem:

My Jupiter-8 is way off, so needs adjusting shims. But the optical block is screwed in too tight and I can't unscrew it fromn the focusing assembly... 🙁

Any tips what to do? 😕

 

[Ash]

the old, 'heat it up' idea? maybe placing it next to a very warm source (but not too warm - ie next to the oven not IN it) will cause the metal to expand? maybe that will help with the screws... or else, get a hammer

 

[rxmd]

Get a good grip on it with a pair of pliers with rubberized jaws. If you don't have those, you can use a heat shrink hose to pad your existing pliers. If that doesn't work, you could drill small holes in it from either side and use a spanner wrench. The holes won't hurt, there should be some in already for the set screws.

Philipp

 

[ZorkiKat]

No Pliers!

No Pliers!

Never use pliers on that J-8. Those black model (and likely, all) J-8 were made of rather soft aluminium. Gripping the sides of the lens filter mount with the intent of loosening them with pliers (with or without rubber lining) will cause the rim to deform. I believe any form of pliers, even plastic ones, will deform the lens.

Drilling on the "sides" (likely the ID ring) isn't likely a good idea too.

You could try using rubber mats. The material from an auto tyre's inner tube is very suitable. Take two sheets, about 10x10cm square. Lay one flat on the table, and put the lens on it, face (front part) down. Then use another sheet
to grip the lens by its barrel. Apply a bit of downward force -gently, and as strong as what you'd give when you try to open a tight jar lid- and turn. Chances are, the optical block will unscrew. This trick worked for me all the time.

BTW, placing shims (does the lens really need it?) between the optical block and the barrel mount will cause the optical block to be reoriented when it's replaced. The index marks for distance, aperture, or DOF may no longer align properly after shimming.

Jay

PS I assumed that the J-8 in question is the one shown in your avatar.

 

[rxmd]

Get a good grip on it with a pair of pliers with rubberized jaws.

Never use pliers on that J-8. Those black model (and likely, all) J-8 were made of rather soft aluminium. Gripping the sides of the lens filter mount with the intent of loosening them with pliers (with or without rubber lining) will cause the rim to deform. I believe any form of pliers, even plastic ones, will deform the lens.

Ha, it's good to have a word of warning before following any idiot's advice on the Internet 😉

Philipp (whose J-8 was deformed to begin with...)

 

[Spyderman]

Thank you guys. I will probably try o heat it up.

And yes, it's the black J-8 in my avatar.

And yes, it needs shimming. It focusses at infinity when the ring is set to 20m.

 

[JonP]

Do you mean the lens is focused at infinity (on a ground glass screen) when the scale reads 20m. Is the r/f aligned at infinity then? If th r/f and focus are both at infinity, why noy just loosen the scale ring realign it to infinity and retighten?
Or am I being thick/misunderstanding the problem?

 

[comp_wiz101]

Are you sure the focussing helical has been lined up properly?

 

[colyn]

Hi

I have a 'tight' problem:

My Jupiter-8 is way off, so needs adjusting shims. But the optical block is screwed in too tight and I can't unscrew it fromn the focusing assembly... 🙁

Any tips what to do? 😕

Did you loosen the grub screw??

Near the base is a tiny grub screw that prevents the unit from unscrewing. You will need to loosen it a bit.

 

[Spyderman]

Well done.

I put the lens in an oven, heated at about 50-60°C. Then I took a bag of frozen vegetables and placed the lens on the bag to shrink the front part. And it worked. I managed to loosen it!

I added a paper shim and the lens is fine now.

PS: How I found that it needs shimming? the answer is "2-camera-collimation-test". The RF coupling was good, but the focus on film was off. Adding a shim solved it. Now when the RF patch is focussed at infinity, the scale reads infinity and also the inňmage on film plane is in focus.

Thanks for the heating suggestion.