RB67 ProS not getting infinite focus?

Discussion in 'Medium Format Cameras and Accessories' started by Athiril, May 30, 2013.

  1. Athiril

    Athiril Subscriber

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    So normally I use the 180mm Sekor C and do portraits for quite some time, haven't shot landscapes in ages.

    I own the 50 C with floating element, 90 C and 180 C.

    I decide I would test the lenses and check everything out.


    I decided I would photograph a test chart about 10m away.

    The 50mm couldn't focus that far away, it looked, it is not the viewfinder/screen/etc (using WLF), as the bellows were racked all the way back and can't go back any further. The focus in the image (Developed neg) looks at about 3m at the infinite focus setting. In the viewfinder I think it did look further down, very close to my subject, but just shy of it -I think-.

    The 90mm looked a lot better, but also focused it at minimum bellows (couldn't go back any further again). The test chart is outside the DoF, so it's out of focus, but maybe by about a metre or less?

    My focus with the 180mm was -just- off, I did have to use a very small amount of bellows extension to focus it, so that seems normal. And the focus error may simply be my error.


    Now I don't think it's the mirror/screen/viewfinder etc being out, because being racked to infinite with my object at ~10m, but having focus closer than that indicates the lens needs to be closer to the film.

    I don't think it's the back because I saw I couldn't quite focus properly in the viewfinder.


    Now I don't think all the lenses (or at least the 50 and 90) are both somehow out (moved elements somewhere?) as that seems very unlikely.


    But there is nothing obscuring the bellows from closing to minimum extension, and it sits flush at the bottom where it touches the camera body when closed, so I dont think its possible for the bellows aren't being drawn all the way in.


    I think the lens mount itself is protuding/extended as that doesn't look possible for it to happen.


    When I mount the lenses they are secure and there is no play at all.



    Any suggestions? Kind of puzzled.

    Body is ProS not ProSD, lenses are Sekor C's, backs are Pro backs, (ProS back bunged out on me a while back)





    Given the fact it didnt seem to focus pin sharp in the VF, close but not quite, but that I think its focused closer than it is in the viewfinder, I think both the lens is not sitting close enough in somehow, and the film is also too far out.

    Now the back I used put some foam seals in it myself (inc the revolving back). I didn't do the best job, but it seemed to be fine at the time, so I'm wondering if I'm pushing the back or part of the back out a little to throw the film plane off (as well as the lenses/mount being out somehow)



    I'll attach some pics of that.
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  2. MattKing

    MattKing Subscriber

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    The foam in the channels on the rotating adapter does look fairly high.
     
  3. cramej

    cramej Subscriber

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    Why are you trying to focus at infinity when your target is only 10m?? It will be out of focus no matter what.

    Your viewfinder is not set at the proper height. There are 4 adjustment screws underneath the ground glass that you can use to set it correctly. Use another ground glass or tracing paper at the film plane with the film back on the camera, open the shutter and focus to infinity - as in something at least 100m away. Make sure that the image is in focus at the film plane first, then drop the mirror and check focus in the viewfinder using a loupe or the magnifier. Adjust as needed. Test all your lenses at different focus points after infinity is set. Focus errors at close distances with the 180 are more critical than far distances with the 50. I noticed my RB was focusing about 6 inches in front of my subject so I had to do this. Once done, everything looked as it should with every lens.
     
  4. John Koehrer

    John Koehrer Subscriber

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    Photographic infinity for most purposes is 500X focal length of the lens. Beyond that is still infinity but consider 500X the closest infinity. :wink:.

    Additional thickness of the foam shouldn't matter unless it interferes with installing the back. You could(if you had another back) measure from the lens flange to the film plane to verify your accuracy.
     
  5. Athiril

    Athiril Subscriber

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    Because I was focussing at infinite as moving the bellows out more focussing closer brought the focus closer. The focus was already too close in the VF with the bellows set to infinite.

    Yes it should be out of focus, but the focus should be further than the object not closer as it was in the developed neg.



    I shoot close with the 180 a lot, it makes sense that the back or revolving back is set too far away (foam seals) + viewfinder being out too.. focusing closer due to VF error and back being too far out compensating for that in some cases.

    I'll try to see if I can find a piece of ground glass


    edit: it appears I brought the other back with me today which has a roll of unfinished roll of Tri-X in it.. damnit. I'll finish it off and try it with that one anyway. IF it is indeed the revolving back it'll happen on both backs.
     
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  6. Athiril

    Athiril Subscriber

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    I assume you mean the screws with two holes in them, and not the philips head screws?

    How do you adjust those? As in, looks like a special driver to do it.

    I cant find something that small, we have a tool like this but it just doesn't fit.
     
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  7. polyglot

    polyglot Member

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    When you shoot close up with the 180, are the shots well-focused on the neg compared to the viewfinder? If so, then your back and viewfinder are in registration with each other at least.

    Either the lens mount is bad, or maybe the back is defective and someone has shimmed up the viewfinder to match?
     
  8. Athiril

    Athiril Subscriber

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    They're not in registration as the focus was different to the viewfinder, they would have been much closer with the 180 and close shots.

    Fixed the back issue I think, was the foam around the revolving back. VF seems pretty close with it now, but dont think it's 100% focused at infinite, looks pretty close though, I need a sharper ground glass than my make shift one to tell though (Even with the loupe it was hard).
     
  9. polyglot

    polyglot Member

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    Ah, well you possibly have any number of alignment problems then. Do your alignment checking work with your shortest lens of course.
     
  10. paul ron

    paul ron Member

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    Before you start playing with adjsuting the screen or anything.. take the lens off the camera.. now look at a white backgound in your VF.. how sharp are the lines n grainof the screen? If it;s out of focus you need a diopter!

    To adjsut lenses for infinity... You need to use a colimeter not a target for infinity focusing. There are ways to make shift a colimeter using another camera and a tele lens. Look it up on the net?

    Also if you are going to mess with the spanner screws (large flat head with 2 holes) you should make a small reference scratch on each head to teh body so if you have to go back you can undo your screw ups.

    Also when checking focus film to lens you have to use a ground glass on the film plane to compare the VF to it. Doing it by eye is playing a dangerous game.

    Your foam seals wil not effect the focusing as much as you think.. the difference is so small nad the way it locks it will force it to the minumum thickness or it will not lock!

    .
     
  11. cramej

    cramej Subscriber

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    Yes, I believe so. I haven't looked at it in a while. A couple metal tip mechanical pencils or maybe even paperclips would work. I usually use a couple metal pointed picks.
     
  12. paul ron

    paul ron Member

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    The spanner is very common and sold in Home Depot.. spanner drivers.. come in tips for magnetic holders and also in sets for security screws.
     
  13. Athiril

    Athiril Subscriber

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    I ended up having to raise the screen with blue tac on the shims/screws.. because they wont go that high (probably). Which is a problem, its well out of infinite focus, at least on the shorter lenses.

    And the film plane agrees with this adjustment, and I put a roll through and used the 90mm wide open and focused closer than 1m and focus seems pretty spot on on an actual roll run through it.


    Not sure now.. obviously this is wrong, but the focus is at least in agreement with each other so I can shoot (portraits at least).