Jupiter 8 problem

[john341]

I have a mint J8 1955 model but it has some black specs between the glass elements. I cannot remove the optical component (too tight) and I don't want to apply too much pressure to an apparent light aluminium construction. Can I clean the specs away by removing the aperature ring at all? Any information will be gratefully received. Thanks in advance!

 

[Sonnar Brian]

UNDER FRONT ELEMENT: The optics module has to come out to get the front element off. There is a set screw under the aperture ring, not just the outer portion. You have to take the optics module out of the mount, take off the variable stand-off ring, take off the aperture linkage, take off the ring with the chrome trim on it. Then you see the set screws that hold the front retaining ring on.

NEAR THE APERTURE BLADES: If the specks are between the surfaces on each side of the aperture, you can remove the rear optics module from the back to get access.

I've seen a couple of J-8 optics modules cemented into the focus mount. The lens was probably adjusted, and someone skipped using a proper shim.

 

[john341]

Thank you

Thank you

for that Info Brian. As the specs appear to be near the aperature blades I will try going via the rear element as you suggest..strange, this is the first J8 I have had that I had trouble removing the optical component.

 

[Elektrojänis]

Can't get the optics module out

Can't get the optics module out

This thread seems like a good place for more Jupiter-8 questions.

I have one of the newer black Jupiter-8-1 lenses. It was actually sold as new (on ebay) and when it arrived to me it also looked like new.

However the infinity focus seems to be a bit off with my Fed-2 (I checked it with an SLR focus screen placed on the film plane).

The camera should be ok. I shimmed the lens mount myself to the 28.8mm (as good as I could, using only cheapish digital caliper for measuring). Before my adjustments the mount was around 28.6mm from the film plane. After doing that the Industar-26 that came with the camera got just perfect infinity focus (it was off before shimming the camera) so I must have done something right there.

Now... The Jupiter-8-1 is probably not enough off to return it, and I bought it several months ago. It would probably be fine in use, but I would like to try getting it as good as I can. I like to tinker with these anyway.

The problem: I cant get the optic module out of th focus mount. I even made my own tool (sort of collar from a thin sheet of brass with some rubber to get mor friction) to get a better grip from the front part. Is there some special trick to it? I have sort of assumed that the thread are normal so I have mostly tried turning it counter clockwise. Could it be that it has a "left hand threads" or something?

I have tried to read the instructions at pentax-manuals.com carefully...

 

[Sonnar Brian]

I have seen three J-8's first-hand that had the optics module cemented into the mount. Rather than using the proper shim material, whoever worked on the lens just cemented the module into place. Most do not do this, and will come out with a mighty twist. At worst, I've used a rubber mouse pad. On the ones cemented in, they would not budge.

I've had one 5cm f1.5 wartime Sonnar that was frozen into a Contax mount. I used a dremel. Turned out a Set Screw was wedged into place in the threads, and it could not be turned.

 

[Elektrojänis]

Hmmm... Maybe I will give it another try tomorrow.

I take it that the threads should be regular ones (anti-clockwise to open)?

Edit: Actually tried it now and got it out! That mousepad tipwas great! I dont have a rubber mousepad but I used a thick rubber sheet that I pressed the front agaist while twisting.

Thank you very much!

 

[Sonnar Brian]

I'm glad that worked. Let us know how the focus works out. These lenses are easy to adjust. If you do not have shims, you can use aluminum foil or other material like copper tape to build up the shim. Also: for small adjustments, you can use the variable stand-off ring. It is held in by one set screw. Take it out, adjust the standoff. When you have it right, TAP out a new hole for the screw. Otherwise, the ring might be offset and the optics module will go in off-center.

 

[Elektrojänis]

I'm glad that worked.

Me too. 🙂 It just took quite a bit of force... and I think my self made tool thingy was not actually as good as I thought. The rubbed sheet on a table was much better. I actually tried the rubber thing before, but I used a kitchen utensil that is meant for opening stuck jam jars etc. It just didn't have enough friction. This time I tried som thicker rubber sheet I have.

If you do not have shims, you can use aluminum foil or other material like copper tape to build up the shim.

The lens I have has two shims, and the focus at infinity setting is not quite infinity so i think I will try sanding/polishing one of the shims. The variable standoff ring seems to be as much in as it goes.

Another slight problem seems to be that the focus on the lens and the rangefinder on the camera seem to disagree more at close range than on infinity. The rangefinder is tuned for the I-26 that came with the camera. I might try adjusting the focal length too, but it's probably more trouble than it's worth so I will probably settle for adjusting the rangefinder when changing lenses. (I'll probably carry the fed-2 around with only one lens at a time anyway).

 

[Elektrojänis]

I think I have the infinity focus quite good now. There was two shims in my jupiter-8. I took one of them and sanded it from 0,75mm to 0,73mm.

I originally intended to sand it to 0,74mm first and see how much that affected the infinity focus, but first my sanding didn't seem to do much to the thickness and then suddenly it was 0,73mm. And I even measured the thickness from many points around the shim to make sure I got it even.

Anyway... That 0,02mm seemed to take the infinity focus setting from almost infinity to really infinity (or at least as much as I can see with the cheap loupe and cheap focus screen (from some SLR) placed on the film gate of the camera.

After that the 1 meter setting was a bit off when comparing the scale on the lens and what I could observe through the loupe/focus screen. Not much but a bit anyway... Inside the f=2 depth of field marks anyway. (I assume that the scale should mach the distance from the film plane to the target.) I just tuned the rangefinder on the camera to mach the focus observed through the lens (as accurately as I could with the equipment I have). I've haven't shot a test roll yet though, so I can't really be sure about it.

Now the rangefinder on the camera does not quite mach the Industar-26 I have, but I think it is still useable with that too. I might try adjusting the focal length of one lens or the other in future to make the focus on both lenses match each other, especially if I ever get a third lens for the Fed-2 (I think Jupiter-12 might be nice).

Adjusting the lens itself was really not hard (at least when it comes to the focus at infinity). The hard part is measuring/evaluating the focus accuracy.

BTW: On many of the nice guides on www.pentax-manuals.com/repairs.htm -site it is mentioned that the instructions for collimating lenses are another document. Has anyone found that document?

 

[Murray Kelly]

I quickly found one site, and it looks a lot like others I have seen.

http://elekm.net/zeiss-ikon/repair/collimate/

Remove the back of the LSM and mount the lens. Use the SLR (never saw a preference for waist level focusing before) with both on tripods to fix things rigidly and follow instructions.

It's not quite as easy as it sounds but it makes sense. 🙂

Murray

 

[Elektrojänis]

I had my "test roll" developed and I think the lens/camera is probably ok now. I'm not 100% sure yet though... Wide open it seems a bit soft, but I don't really know if it just is that way, or if the focus is a tiny bit off... This is because I did not take that kind of test pictures where that could be easily observed. I was going to, but I ended up just taking pictures as I would on any camera.

Oh well... The next roll is already in the camera.

I quickly found one site, and it looks a lot like others I have seen.

http://elekm.net/zeiss-ikon/repair/collimate/

I think I saw that one too or something with a similar method before I started tuning my jupiter-8. I thought using that method too, but ended up just using the method with an SLR focus screen on the film port of the LSM-camera and viewing some object that's far enough through it.

I do have Nikon F2 and 105/f=2.5 lens that I coud use for that method. It can even be converted to have a kind of waist level finder just by removing the eye level prism finder (as many of you probably know).

(never saw a preference for waist level focusing before)

The waist level finder is probably just because it might give you better working ergonomics, at least if you dont happen to have two tripods that are high enough to get the cameras on the eye level.