Old elmar 5cm f3.5 ltm in two parts

[begona]

my friend anscrew elmar˙s bottom ring,one with f/ numbers for depth of field, that is going on camera`s 39mm screw. Now I wish to screw lens on it and I can not do it...

Anyone can help?

Thanks

 

[Landshark]

I don't have an Elmar to look at but if it has interrupted threads( a helical) it can be ummm, interesting.

Helical threads are pretty thick when you look at them and from the end will look as though there are several threads at the base of the lens or mount.
Since it's separated it's going to be a bit harder than if you had the chance to mark it taking it apart.
Has the focusing stop fallen off the lens? That's what holds the front section on.

Anyway. I've found it easiest to set the mount section on a flat surface and place the focus assembly on it.
Rotate the focus assy anti clockwise until you hear or feel a slight "click" then turn it clockwise and the two should be joined(ha!) Sometimes it seems that something is bent, but usually isn't the threads just don't want to mesh.
If they do mesh, you have to be able to check the focus. This is done by holding a ground glass on the film rails and checking the focus with a magnifier.
Since there are five or six threads on each piece. The odds are against your getting it right the first time. That means take it apart again and find a different start point.
If you have an ltm camera I don't know how you could check focus since you can't see a ground glass on the rails.

It's a wonderful(not!) experience in patience. Call it meditation, that helps(NOT!)

 

[dubya]

If it is the focus mount that has come unscrewed, that would mean that this stop screw-post is missing:

Below is a Summitar but the basics are the same... these are the focus helix threads, you can see that there is more than one "start" point. If the two parts of the infinity lock hit before the two halves are threaded completely together, unscrew it and back up a thread or two and try again. If the threads bottom out before the infinity locks come together, unscrew and go forward a thread or two and try again. In short, only one start point will end up with the infinity latch catching just as the two pieces are threaded completely together.

I know you probably don't have access to something like this but this is the homemade device I use to check infinity focus on M39 lenses..

That, along with a tripod, a loupe and chunk of ground glass that is.

Hope this helps,

Wade

edit: If the focus mount coming unthreaded is the only thing that happened and nothing else has been done to the lens, you shouldn't really need to check infinity focus since that is adjusted by moving elements in the barrel... so if it was good before, it still is. Once it goes back together with the infinity lock ending up in the correct position everything should be good to go... except the missing stop screw.

Now is a good time to clean and lube that focus mount too, if needs be.


W