Jupiter-9 close focus modification?

[principe azul]

I've a J-9 that, from memory, seems to focus correctly on a Leica. But I've hardly used it because the focus is stiff.

I've unscrewed the lens cell (optical unit) and the focus ring. I don't want to get bogged down with helixes, so I'm just racking the focus to and fro and cleaning up the gunk that works its way out.

The ring with the DOF markings on it has a cutaway taking up about 210 degrees of the circumference. The ring behind it (this ring is the one the focus ring screw onto) has a set screw limiting its travel. Sorry I can't provide pictures, but the screw stops against each end of the cutaway.

I've removed this screw and find that the screw doesn't limit travel that much, and the ring can move a little in either direction before the ring naturally stops. It can overshoot infinity by about 5mm of travel and overshoot the J-9's minimum focus of 1.15m by about 50mm, which appears to get the focus down to 0.8m.

So, my question. Any reason I should replace the limiting screw, and would the J-9 focus accurately (if I remember right that it focused accurately before) at its new close focus distance?

 

[Gabriel M.A.]

Any reason I should replace the limiting screw, and would the J-9 focus accurately (if I remember right that it focused accurately before) at its new close focus distance?

I've always wondered about this. This is assuming that the whatever-you-call it is machined properly to move the focusing lever for the rangefinder on the camera accordingly. The drawback would be that you'll have a 360 rotating lens, right?

I'd ask Brian Sweeney.

 

[principe azul]

Hi gabrielma,

It rotates 330 degrees, so not quite full circle. It naturally stops for some reason, but I don't want to disassemble any more to find out why.

My guess of 0.8m was about right. I don't have a tape measure, but I checked it against a Nikon. On the RF cam, ground glass at the film plane looks okay at 0.8m. But I need a 10x or 20x linen checker to confirm.

My precision methods ;-) are as good as what I paid for them. A J-3 that looked to fcous accurately by this method gives slightly off results on film.

 

[Hamster]

J-9 of recent manufacture in M42 mount are able to focus down to 0.8m, and I have had good results with it at said distance with a spotmatic.

Additionally, the recent J-9 are multi coated, and as I have seen on a lens hacking site, the optical block also screws out from the front in the same fashion as older J-9 in Kiev or Leica mount. I am not sure if they were still using the same thread.

As far as I can see with my M42 J-9, the displacement between 0.8-0.9 is quite far, about the same distance as infinity - 5m.

Anyhow good luck with your hack, would really like to know how far FSU gear can used creatively.

 

[principe azul]

Thanks, Hamster, that's useful info. I'm looking forward to shooting with the J-9 again.