Shiming a Jupter-8

[Red Robin]

Don't know if this the right place to ask but here goes. I have just gotten an Jupiter-8 lens I have heard people say they "shimmed " it to have it work correctly. How is this done, is it a DIY job? If it is shimmed for one camera or camera body. That is, switch bodies and shim again? Thanks Red Robin

 

[Sonnar Brian]

The FSU lenses are made to a slightly longer focal length than a Leica RF is calibrated for. This means that many FSU lenses will focus slightly behind what the RF indicates, especially wide-open and close-up. Removing the optics module and thickening the shim by ~0.1mm usually takes care of the error. The worst part is undoing the three set screws for the aperture ring and repositioning it if the shim has to be changed.

I would try the lens out first, with a few test shots done wide-open and close-up. That will indicate if you need to adjust the lens.

Several RFF members have done this job themselves, a jeweler's screwdriver is required for the very small set screws on the aperture ring, and aluminum foil works for shim material.

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

Kim Coxon hosts several repair articles, including the J-8 and J-3.

 

[Red Robin]

shiming a J-8

shiming a J-8

Brain, Thanks for the post . I'll try it out first and also, thanks for the tip on tinfoil, I was wondering. Red Robin

 

[Red Robin]

J-8 pre-shim tryout roll

J-8 pre-shim tryout roll

Well it's taken a bit to finish 24 on the Canon VI-T with a j8 lens . I didn't want to expose it to the local humidity. Now it's off to Walgreen's . Also there's trouble here in river city. Looking at my canon 50 mm 1:1.8 the shutter blades are a nice shiny black- - All over . Looks like another money maker for someone. I don't even see how this baby opens. Maybe a good thing!

 

[Sonnar Brian]

Is it the Chrome Canon 50/1.8 or the Black Canon 50/1.8?

I've taken apart the chrome lens, and RFF member "JLW" posted instructions on the Black lens.

See this old thread:

http://www.rangefinderforum.com/forums/showthread.php?t=10141&highlight=canon+disassemble+rear

 

[Red Robin]

jupiter rebuild/lube/adj.

jupiter rebuild/lube/adj.

Brian, I will be picking up my test roll this AM. I have the chrome one, also how does one know how much to shim?

 

[Sonnar Brian]

If you do a test picture with a ruler or something that you can measure the exact distance that the lens is off, you can use the formula for focus vs focal length to determine the required change in shim.

1/s1+1/s2= 1/f

see:

http://en.wikipedia.org/wiki/Lens_(optics)