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Steve
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 14, 2005 - 02:19 pm: | 
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I recently bought an Exakta VX IIb. I found that a far-distance object focuses in the viewfinder (prism type), both on the ground glass and the split-image, with the focus ring at around the 25ft mark. I tried a different lens with the same result. The viewfinder ground glass sits correctly in its position in the camera body (even if it sat a little high, this would reduce the error rather than increase it).
With the shutter open on T, and the camera back removed, I tried placing the viewfinder with its ground glass on the film rails. Holding the camera, adjusting the focus, keeping the viewfinder in position, and peering through the eyepiece proved to be a bit of a juggling act (!) but I am pretty sure the infinity focus is correct at the film plane.
Since the position of the film plane and the viewfinder screen are both fixed, the only thing which could affect the optical relationship between the two is the mirror. Is it adjustable for vertical position? I would very much appreciate any advice, or sources of information on how to deal with the problem. |
rick oleson
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 14, 2005 - 07:23 pm: |
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I don't see any really obvious adjustment, though there must be something. Before going there, though, have you checked that your prism is seated properly? The IIb is unique among Exaktas in lacking a positive latch for the prism and groundglass. |
Steve
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 15, 2005 - 03:04 am: |
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The ground glass screen is definitely seated correctly in the body. If focus is correct on the screen, could the prism affect anything but the position of the frame?
One thing that may be significant or may be a complete red herring: About half an inch in front of the point where the mirror pivots, on each side within the body there is a tapped hole. On the left side the tip of a screw is visible in the hole. On the right side there is no screw and there are signs of the metal having been worked. This camera has definitely been through the hands of Wrong Screwdriver Repair Man. Could some botched repair in this area be the cause of the problem? |
Peter Wallage
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 15, 2005 - 09:02 am: |
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Hi Steve,
I've got a translation of the German factory repair manual for the Varex IIb, which I think is basically the same as a VXIIb for mirror adjustment. Give me a day or two to dig it out and scan in the right part and I'll e-mail it you. If it doesn't apply to your model I can possibly find the info you need.
Peter |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 15, 2005 - 05:20 pm: |
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Steve,
As far as I can remember the only adjustment is the angle of mirror. Just checked on an Ihagee site and they only mention mirror angle and warped/replaced mirror, as source of focus problems.
From use I remember that it was important to only use centre of screen for critical focus. The same site mentions that outer parts of screen can appear out of focus, even if centre is OK.
Screen is located in finder by series of springs made from strip steel. If Multitool Man has been removing dust, check that screen seats properly.
Glenn. |
rao
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 15, 2005 - 07:19 pm: |
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i just got a peek at the adjustment instructions.... they say the way to adjust the mirror position is by BENDING the latch thingie in the left-hand wall of the mirror box: bending it towards the mirror lowers it, and bending it back into the wall raises it. this will not give a lot of adjustment, and it's a very crude way to do it... but that's what it says. |
me again
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, July 15, 2005 - 07:36 pm: |
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oops. think i had the direction backwards on that. well, you get the idea anyway... |
Steve
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 16, 2005 - 06:44 am: |
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It does seem surprisingly crude. I was expecting that the mirror would have to be adjusted vertically at the pivots, and corrected for 45 degree angle, but I suppose that as long as the pivots are set reasonably accurately in manufacture, the only thing that can change is the latching point of the mirror. Even if focus is not exactly right at top and bottom of the viewfinder, nobody is going to focus there.
It looks on my camera as though the mirror angle is set by a bendable tab on the corner of the mirror, which engages with a retaining pawl or hook on the side of the mirror compartment.
I am a bit disappointed that it appears so easy. Was looking forward to a major disassembly job! |
rick oleson
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 16, 2005 - 11:00 am: |
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they're generally adjusted by the position of the stop in the down position... but even the little-respected pentacon has a screw for adjustment.
in the exakta, apparently it's actually the pawl in the side that you bend rather than the tab on the mirror. |
Peter Wallage
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, July 16, 2005 - 05:17 pm: |
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Just discovered that on the later models of Varex IIb, like the one Steve has, the mirror latch was redesigned to hold the mirror at the bottom corner of the mirror tray. The mirror itself has the corner cut off to allow this. This later latch isn't adjustable. The 45 degree angle of the mirror is adjusted by bending the tiny exposed corner of the mirror tray.
Peter |
Steve
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, July 20, 2005 - 03:29 pm: |
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Have now reset the mirror, and all is well. I checked the lens-flange/film-plane distance first which was OK, so the fault was definitely the viewfinder. The bendable tab was not quite as bendable as I expected but I got there without too much difficulty.
Now for a test film!
Thanks for all the help. |
