Pentacon Six & Biometar 80 focus problem

Discussion in 'Medium Format Cameras and Accessories' started by Tor-Einar Jarnbjo, Sep 11, 2017.

  1. Theo Sulphate

    Theo Sulphate Subscriber

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    There must be a logical reason, even if we have to follow this into the realm of quantum physics.

    Time to test with a second P6 when you have the opportunity.
     
  2. Theo Sulphate

    Theo Sulphate Subscriber

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    Just a thought for a test that completely eliminates all body and mounting issues.

    Can you assemble a fixture where the camera and a lens are separate (i.e. lens is not mounted) but holds both the P6 and the lens perfectly steady and in alignment? I would suggest constructing this fixture, use the old Biometar at infinity (but separated from contact with the body -- it should thus optically behave as a close-focus lens), and then move a focus target progressively closer to this fixture until it is in focus on the groundglass. Make a photo. Then replace the old Biometar with the new one also at infinity. Is it still in focus on the groundglass? Either way, make a photo when it's in focus.

    Or: send the camera and lenses to me and I will keep everyone informed of my tests and progress.
     
  3. rockpowered

    rockpowered Member

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    Now that you've confirmed that the optical path change is incorrect you can tweak the ground glass . It's great that you can in real time monitor what affects focus on the film plane. I would suggest adjusting the ground glass so that you have satisfactory focus with both your older lenses and the new one. The ground glass rests on three set screws that can used to raise or lower to achieve a flat field of focus across the projected image. Rick Oleson has a great set of instructions on how to remove the top plate from the camera. Or alternatively just stop using the newer lenses if you don't like the compromise. If you had a collimator you could have an exact factory reference but I'm guessing it's a bit off and works well enough with the older lenses, but still falls short with the newer ones. The key with focus is it's all based on perception of sharpness which is never an exact thing.

    Here is the link for Rick Oleson reference. You will need to get through step 4 at which point you can lift out the ground glass and adjust the screws. It should take about 1/2 hour for a first timer.

    http://rick_oleson.tripod.com/index-129.html
     
    Last edited: Sep 17, 2017
  4. shutterfinger

    shutterfinger Subscriber

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    Both new versions off the same amount in the same direction= new version not compatible with view screen at old version of lens position, reposition view screen to the new version of the lens.
    New versions have different focus errors= lens incorrectly assembled or an element shifted position.

    Have the lens checked by a ZEISS technician.
     
  5. rockpowered

    rockpowered Member

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    As an extra thought the front adjusting level for the ground glass is visible once the lens is removed if you look directly up toward the the glass from underneath. It looks sort of like of like a wheel projecting out. If it's only slight off you maybe able to teak without any disassembly. The downside is it may have been locked into position with a bit of lacquer to keep it from moving. I can provide a reference image if you like.
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    Have I? If so, why can I focus as expected with the three other lenses I have previously used?
     
  7. Dan Fromm

    Dan Fromm Member

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    I just searched for the word collimate in this tedious thread. It isn't here.

    Tor-Einar, your new lenses need to be collimated. They are out of adjustment. End of discussion. Your camera is fine. Its GG is fine.

    Find a shop that can do the work and have the lenses adjusted to focus properly on your Pentacon Six body.

    ..................

    on reflection, I think my suggestion is off base. Not because lenses have to be collimated but because Tor-Einar seems to have focused them through the lens on his P6 body and on the rigs he used to test.
     
    Last edited: Sep 18, 2017
  8. AgX

    AgX Member

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    We are going circles. A lens does not need to be collimatet to produce a sharp image on the film after focused correctly on the groundglass.
     
  9. Dan Fromm

    Dan Fromm Member

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    Stuff and nonsense. The focusing mount is adjustable. It is out of adjustment.

    I've bought a couple of 12"/4 TTH Telephoto lenses in AGI 139 lens cones. The AGI 139 is an aerial camera. The cones bayonet into it. A lens is locked in position in its cone by nasty little radial set screws that are cemented in place. Both lenses' barrels had many marks from those nasty little set screws. Each had been collimated to a body, and several times.
     
  10. rockpowered

    rockpowered Member

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    You've determined that the GG and film plane focus adjustments are off with the new lenses. At least that's what I understood. You've further determined to your satisfaction that the lenses are not faulty through tests you've conducted off the body. If the only factor that you can control is to adjust the GG why not see if you can obtain a happy medium. Your ground glass may focus correctly using the older lenses as it's within the tolerance of the lenses. However, you've indicated that you believe the newer lenses to be "clearly sharper" so your focus issues may be more apparent. Trying to adjust the ground glass is a method that could reasonably end your search for a solution.

    At least your in Germany so you stand a chance to find a competent tech that can sort this for you if nothing else presents itself. Try that in Canada and see how much luck you have. I service mine myself and would not hesitate to dig in. But that's just me
     
    Last edited: Sep 18, 2017
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    I can't think of a way to do something like that right now, but it is worth a try. I'll try to think of something.

    Thank you very much for your offer. Where are you located? Shipping the camera halfway around the world is probably just as expensive as to buy a second P6 body. I have asked a friend here where I live to also do a round of testing for me and I will give him the camera tomorrow.
     
    Last edited: Sep 18, 2017
  12. OP
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    The new Biometars are clearly sharper than the old Biometar, but not clearly sharper than e.g. the Sonnar 180 I have been using previosuly (with which, just to be precise and repeat myself, have had no focusing problems). The Sonnar 180 is by the way also a relatively new model, produced around the same time as the problematic Biometars in the late 80ies. It is at least obvious to me from the test shots I have posted earlier in the thread, that the focus is so way off with the new Biometars, that your speculation that I always had a focusing issue and simply haven't realized is because the old lenses aren't that sharp and that it is difficult to distinguish a focusing problem from a slightly unsharp lens simply does not hold.

    Sure, if I don't find the solution to the problem, I still even have a competent service technician here in the city I live in.
     
  13. rockpowered

    rockpowered Member

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    Well if anything was going to stress the body resulting in flex or something unintended I would think it would be that beast. I can't imagine bringing that into the field without having an ache at the end of the day. I'm interested in how this plays out as I have a bit of an investment in Pentacon gear myself
     
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    The Sonnar 180 is still just a small beast compared to my Orestegor 500, with which I also have no problems taking in-focus images:

    [​IMG]
     
  16. rockpowered

    rockpowered Member

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    Do you have an update on this. Would love to know what you discovered?
     
  17. OP
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    A friend of mine had the camera for a few weeks to do some extensive tests to make sure that the problem is not my brain. I will get the camera and a series of test images back one of the next days. I will have to develop the films myself to confirm the results, but he believes to have visually seen the same odd behaviour as I do. When comparing the projection on the groundglass with the projection on a piece of opaque tape in the film plane, the focus plane matches when using the old lens, but does not match with the new lenses.
     
  18. OP
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    Today, I have developed the test images taken by my friend and they didn't really bring anything new to solve the problem. When focusing on the groundglass, the pictures he has taken with the new Biometars also show the same front-focus problem.
     
  19. Theo Sulphate

    Theo Sulphate Subscriber

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    To solve this, you will need either the services of a professional optical engineer and a lab or an exorcist - whichever is easier to find.
     
  20. Neil Grant

    Neil Grant Member

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    ...there's an auwful lot to read here, and you have my sympathies. Is it possible that the film is moving as the mirror swings up and causes and very mild vacuum? Is your newer lens better sealed and therefore able to allow a stronger vacuum to be formed? Is there a P6 user group on line somewhere for advice?
     
  21. Theo Sulphate

    Theo Sulphate Subscriber

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    A clever thought - but since the focus with the new lenses falls in front of the subject, the film would have to move further away from the lens.

    Also, I think the problem has been observed with the mirror held up and the back open.

    I'm really curious whether this problem would occur with a different P6 body. However, that's just curiosity. I do believe it's a lens issue.
     
  22. Neil Grant

    Neil Grant Member

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    ...we really need to know the answer to this problem (if there ever is one) in case we com across something similar.
     
  23. OP
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    The film is at least held tight around the edges of the exposed area, and since the focus problem is consistent across the frame, it does not sound reasonable that the film is moving.

    I will try to take the question to a German forum (APHOG) and see if anyone there is more familiar with any known peculiarities of the P6 system.
     
  24. AgX

    AgX Member

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    My long time quest at Apug is for a forum that handles the unexplainable artefacts...
     
  25. OP
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    Tor-Einar Jarnbjo

    Tor-Einar Jarnbjo Member

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    Just an update and a summary from the thread I started in the German APHOG forum last week: For the most, the same issues we have already discussed here were reiterated without anyone coming up with something new. One of the readers came up with a new tests to verify once more that the new lens does not impact the position of the mirror during focusing. With the old lens, I pointed the camera to an object, which I placed in the centre of the groundscreen, released the shutter, cocked the shutter and checked that the position is the same. Then, without moving the camera, I changed to the new lens and verified that the object is projected onto the groundscreen in exactly the same position, once again release and cocked the shutter and checked for a last time, that the projection on the groundscreen remained the same. That was the case. If the new lens had somehow prevented the mirror to rest in the intended position, the previously centered object would have been moved up or down on the groundscreen.

    After reading about the new 6,500$ edition of the Leica Thambar, I wonder if I should just try to market the Biometar focus error as a design feature for a dreamy and artistic look and sell the lenses for a lot more than I bought them. Some of the Thambar example images have very much in common with the out-of-focus pictures I have unintentionally made with the new Biometars.
     
  26. Patrick Robert James

    Patrick Robert James Subscriber

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    I am not going back to read this whole thing, but what kind of ground glass do you have? If you have a fresnel between the lens and the actual focusing surface that could account for the focus shift. I'd check that. The preferred arrangement would be lens/ground glass/fresnel. The fresnel could be incorporated in the screen as well, so make sure the screen isn't in upside down.
     
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