Focusing 50mm lens on R2A

[domagojs]

I've been getting hit and miss results with focusing jupiter-8 on my bessa r2a. Of course, I'm talking minimum distance (1m, 1.2m) and wide(ish) open lens (f/2, f/2.8). I don't have any issues with getting the focus right with m-rokkor 40mm.

Now, if my jupiter-8 was constantly back-focusing I could assign it to the different registration distance (if that's the correct term) and be done with it. However, more often than not, I nail the focus just fine. I tried focusing on some objects some 1.2m away today and I kept getting different readings every time I focused.

So, I wanted to ask about other people experiences with focusing true 50mm M lenses on R2A? Do you guys have problems getting the focus right with your lenses? Would a CLA of my jupiter maybe bring something?

 

[RomanV]

The biggets issues around fsu lenses is the quality of the lens alignment. The working distance ( if I'm not mistaken with the correct term in English) could be a bit different, then the distance between the lens mount and the film base.

If you use it on the camera with the adapter - try it with another adapter first.

If you wanna try to collimate it by your own - the best point to start is http://www.pentax-manuals.com/repairs/j8service.pdf
If not - Don from DAG could do it, but I suppose the cost of it will be around the cost of the lens🙂

 

[domagojs]

Hi Roman, thanks for your help. Chinese adapter was a good hint which made me test the Jupiter on the Zorki 4 it came with. Result was that the focus was still changing with every try. :-( After that I tried focusing Yashica Electro GSN in the same way, as well as M-Rokkor 40mm on the Bessa, and both setups showed exactly the same results on the scale. I put Jupiter with the adapter back on the Bessa and every focusing try showed different reading on the scale. :-( So, based on this it's safe to say that both VF and RF on the Bessa are functioning fine. Since the lens displays the same behavior on the Zorki (w/o adapter) and on the Bessa (with adapter) it's not the adapter either. That leaves me the lens itself...

I must add, there's a certain jerk when focusing the lens between 1m, 1.5m, so that might also be the cause for this behavior.

I'm in Croatia, so sending it to DAG would cost much more than what I paid for it. ;-) And this is my 3rd Jupiter (I love it's old Sonnar look, what can I say) and I like pics with this one the best of the three, so I think I'll ask around if there's a way to CLA it locally...

Damn, I really love it's pics when it hits...

 

[ottluuk]

Take the adapter off, turn the focusing ring and inspect the moving cam closely. Does it move in and out evenly across the focus range? Does it have any play in any position? It's possible that the helical is damaged from a fall or heavy bump.

If you have another similar (there were a few different versions as you probably know) Jupiter-8 with good mechanics, it's possible to transplant the good optics block to the good barrel. But in all probability the lens would have to be reshimmed to focus correctly, so not a trivial DIY job. Or you could just try your luck with the next one.