stubborn lens threads

pstake · Feb 27, 2014

I'm in the middle of taking apart my first lens to clean out some light fungus. It's a cheap lens and I'm okay with this being a complete failure; I'm mostly interested in learning to do this.

I'm using SK Grimes spanners. The problem is that the ring/thread (what is this called?) that holds in the center elements will not budge; same for the one hold in the center elements from the back.

Is there any kind of "liquid wrench" type product I can use to loosen it? Is it by chance a backward thread? I couldn't get it to move either way...

Any help is appreciated!

Cheers,
Phil

shutterfinger · Feb 27, 2014

It will help to know what lens.
Common things are some type of thread locker was used during assembly. Element spacing is critical.
Nail polish remover, acetone, might work for dissolving the thread locker but it might harm the lens coatings so save it for a last resort.
Turn your oven on and let it heat up to its minimum setting. Once the oven has reached temperature, turn it off and put the lens in the center of the oven and let it sit for 30 minutes.
Remove the lens and try to unscrew the retainer(s) while the lens is warm.
Another possibility is that holding the lens barrel is causing it to deform slightly resulting in the retainer being jammed.
Clamp the lens barrel so that pressure is applied evenly when trying to unscrew the retainer, too tight clamping may cause the problem also.

Tom1956 · Feb 27, 2014

Typically any ring I've ever come across was standard right-hand thread. Use of a wee dab of penetrating oil is OK, but once you use it, you're committed to doing the job. Your biggest enemy of course is slipping and scratching the lens or ruining your slot, making the job impossible and the lens into junk. Always a risk. Be sure to keep downward pressure as strong as you can push, to keep the tool from jumping the slot. Yes, some rings are impossible. But since it's a junk lens anyway, good one to learn on. A lot of times you need a helper to hold the lens.

gone · Feb 28, 2014

Good advice here. You might also put some ice in a washcloth, then in a baggie, and set it on the ring to help get it out. You could try heating the lens body to expand it, but you're getting into dangerous territory if you overdo it. Just setting it in a pan on the stove and watching the temp will work, but do not get it much above 110 - 115 degrees or so, and only for a short while. Sometimes a few judicious taps w/ a hammer and a wood dowel on the ring will free things up. I've often had to resort to placing a small screwdriver in one of the ring slots and giving it a few gentle taps w/ a bit of wood in a counter clock wise direction too. You may not have room for this if you're working in the middle of a small lens. Again, do not overdo anything. As mentioned, it's often easier to clamp your tool and twist the lens rather than the other way around. You will need a bench vise to do this properly.

Xmas · Feb 28, 2014

The lens spanners are pretty but you may need to make up a tool for each ring. The factories had special tools.
Id not recommend heat or solvents myself.
You need to be careful with a vice the lens is easy to damage.
My current problem is an EGerman lens where the factory has penned the threads using a pin punch.
Thinking about the problem never hurts the lens.
I've drilled out the punch mark but...
Some rings will loosen off a dab of nail varnish after tightening in bright orange is all you need apply with darning needle.

richard ide · Feb 28, 2014

Some lenses will not unscrew because there is one or more very small set screws which prevent the ring from loosening.

pstake · Feb 28, 2014

Thank you everyone. I'm going to order a set of the rubber lens-ring tools from micro-tools and give those a go, first. Will keep you all updated.

For info, this is a 35mm lens, an m42 Fujinon 55 1.6, which has the fungus and which I got cheap, locally. I imagine it was built to last.

Tom1956 · Feb 28, 2014

richard ide said:
Some lenses will not unscrew because there is one or more very small set screws which prevent the ring from loosening.

!!! What he said. Look for teeny invisible set screws.

pstake · Feb 28, 2014

Tom1956 said:
!!! What he said. Look for teeny invisible set screws.

I did. I have removed 9 (maybe more. I'm not looking at it right now) screws so far, and I have the whole thing taken apart and bare metal exposed on the helical. Everything is apart except for the elements inside, and the aperture blades in between them.

There are no screws left within my reach until i get past where I'm at.

I'll post pictures tonight.

stubborn lens threads

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