Jupiter8 doesn't fit in Fed2 and Industar61 doesn't fit in Zorki6

[Repunante]

Hi all, I'm new here, I hope I'm not repeating an existing threat but I couldn't find more info regarding this issue.

So, I got a Zorki6 with Jupiter8, I have been only playing with Fed/Industar combos before (not for a long time though) and I wanted to try something else.

When I tried to fit the Industar61 in the Zorki6 the barrel of the lens was not properly aligned, like it needed an extra twist.
Then I noticed that the Jupiter8 was longer in the back than the industar61 I had. When I tried to put the Jupiter8 in a Fed4 it was difficult because of that back.
The Jupiter8 was not smooth at all, so when I opened it to clean the wax I realised that the extra back was glued (very bad actually). I removed that extra and now the Jupiter fits better in the Fed4, but the barrel is not aligned, like it happened before with the Zorki/Industar combo.

What am I missing? Why my Fed/Industar and Zorki/Jupiter cannot be interchangeable?


Thanks.
Luismi.

 

[wolves3012]

Both lenses should fit both cameras without any problems. I'm not quite following when you say the Jupiter is "longer in the back". Have a look at the articles on this page, you can see what the lenses should look like and what might be wrong:

http://pentax-manuals.com/repairs.htm

By the way, in case you're not used to coupled RF lenses, it's much easier to mount them when they are set to minimum focus because the RF cam doesn't protrude.

 

[Martytoof]

On this note, when I put my I-50 on one of my Zorki 6 cameras, I notice that the centre "3.5" mark of the scale focus markings doesn't end up at the exact top of the lens. I'd say it's about 2 or 3 degrees off centre. Is this a big problem? I can't imagine it will affect the focus if it's just off by those two or three degrees, but I wanted to doublecheck 🙂

 

[wolves3012]

On this note, when I put my I-50 on one of my Zorki 6 cameras, I notice that the centre "3.5" mark of the scale focus markings doesn't end up at the exact top of the lens. I'd say it's about 2 or 3 degrees off centre. Is this a big problem? I can't imagine it will affect the focus if it's just off by those two or three degrees, but I wanted to doublecheck 🙂

Presumably you mean a rigid I-50. It's common for any of the RF lenses to screw up to slightly different positions on different bodies and few of them end up perfectly "upright". That doesn't affect the focus in the slightest, assuming the lens and body are properly adjusted in the first place.

The focus is determined by the lens-helical to lens-body relationship, which is not altered by the lens' actual position on the body. If you want to be super-critical, it does matter just how tight you screw the lens on but in the real world once it's screwed up home and not slack it makes no difference.

 

[Repunante]

Both lenses should fit both cameras without any problems. I'm not quite following when you say the Jupiter is "longer in the back". Have a look at the articles on this page, you can see what the lenses should look like and what might be wrong:

http://pentax-manuals.com/repairs.htm

By the way, in case you're not used to coupled RF lenses, it's much easier to mount them when they are set to minimum focus because the RF cam doesn't protrude.

Awesome link, thanks!

I knew about setting the minimum focus, I was reading quite a lot to find details regarding this issue.
When you set the focus to the minimum you can see that in a normal lens the barrel moves back to match the screw of the lens. In this Jupiter lens after setting the lens to the minimum there was still some of the inner tube out.
Sorry about my terrible explanation, I think I will upload some pics later.

On this note, when I put my I-50 on one of my Zorki 6 cameras, I notice that the centre "3.5" mark of the scale focus markings doesn't end up at the exact top of the lens. I'd say it's about 2 or 3 degrees off centre. Is this a big problem? I can't imagine it will affect the focus if it's just off by those two or three degrees, but I wanted to doublecheck 🙂

Yeah, that's more or less what happens to me.

 

[wolves3012]

Awesome link, thanks!

I knew about setting the minimum focus, I was reading quite a lot to find details regarding this issue.
When you set the focus to the minimum you can see that in a normal lens the barrel moves back to match the screw of the lens. In this Jupiter lens after setting the lens to the minimum there was still some of the inner tube out.
Sorry about my terrible explanation, I think I will upload some pics later.

The tube is the focus coupling cam and it should *almost* be flush at minimum focus on a Jupiter 8. If it's not, maybe someone has made a botch of reassembling the lens. If the cam protrudes too far, that will upset the rangefinder and lead to focus errors, unless the RF has been equally bodged to compensate!

 

[Martytoof]

Thank you wolves. Educational as always 🙂

 

[Repunante]

Yeah, I didn't want to push that Jupiter8 into another of my cameras just in case.
And I think that the Zorki6 is seriously irritated by that modification of the lens.
I will try to repair both, it's going to be a lot of fun.

Thanks for the help, this forum is great.

 

[rxmd]

On this note, when I put my I-50 on one of my Zorki 6 cameras, I notice that the centre "3.5" mark of the scale focus markings doesn't end up at the exact top of the lens. I'd say it's about 2 or 3 degrees off centre. Is this a big problem? I can't imagine it will affect the focus if it's just off by those two or three degrees, but I wanted to doublecheck 🙂

It's no problem at all. Actually it is rather common. The reason is that it's actually quite hard to machine an M39 screw thread with totally precise entry points. If you look at Voigtländer lenses they show similar behaviour.

The good news is that it doesm't affect focus at all unless the focusing cam is sloped, which it isn't on any FSU lens.