Question for those with S.A 90 F8

Discussion in 'Large Format Cameras and Accessories' started by wiseowl, Aug 14, 2006.

  1. wiseowl

    wiseowl Member

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    I have a super angulon 90 f8 in a synchro compur, I've noticed that the f stop lever moves across 2 more clicks than the f8 mark when fully open, ie to the f5.6 position if it was marked. At one click (f6.8, if it was marked.) down I can start to see the blades and when it is on the f8 mark the aperture blades are clearly visible. The aperture lever does move all the way around to minumum aperture, (f45)

    Is this normal for this lens, or are the aperture marks one stop out? if they are how do I adjust the aperture lever?

    Thanks

    Martin
     
  2. Ole

    Ole Moderator Staff Member Moderator

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    Mine is in a Compur #00, so I can barely see the aperture scale!

    But no, mine is fully open at f:8. Could you be missing the little angled pointer on the aperture lever? Many of these small WA lenses had an "offset" aperture pointer, it looks like exactly the same scale was used for 90/8 and 121/8, with a different pointer!
     
  3. David H. Bebbington

    David H. Bebbington Inactive

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    You should not worry, the marked f8 will be right. The aperture control caters for all the possible lenses that could be mounted in the same #0 shutter, and the lens groups of a 90 f8 SA have a comparatively small diameter on the inside faces, so opening the aperture past a marked f8 will have no effect.

    Regards,

    David
     
  4. wiseowl

    wiseowl Member

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    David, I follow what your saying but at the f8 mark, the lens is apparently stopped down?

    Thanks for the replies

    Martin
     
  5. wiseowl

    wiseowl Member

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    Ole,

    the pointer is a molded plastic knob, not a small angled pointer. There doesn't appear to be any distortion or damage to this.

    Thanks

    Martin
     
  6. Donald Miller

    Donald Miller Member

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    Mine is mounted in a 0 copal. Your lens aperture will be accurate at the Fstop indicated.

    The shutter will be capable, in many cases, of exceeding the advertised and marked Fstops of a given lens. If you wish to use the smaller or larger F stops accurately, you should measure the apparent pupil diameter and compute it against the focal length of the lens.
     
  7. Paul Sorensen

    Paul Sorensen Member

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    I have one also in a Synchro Compur. My aperture have positive click stops and it does not go beyond f/8 at all, however, at f/8 the aperture blades are clearly visible.
     
  8. Ole

    Ole Moderator Staff Member Moderator

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    My 121mm f:8 Super-Angulon is mounted in a Synchro Compur 0 which obviously was intended for a different lens. At f:5.6 (largest opening), the aperture blades are clearly visible. I estimate it as "marked 5.6 = f:10", and expose accordingly. So far even slides have been spot on.

    I repeat: At f:8 setting, the aperture blades on my 90mm f:8 SA, in Synchro Compur 00 shutter, are almost but not quite visible.

    I recommend that you take a few comparison shots with your 90mm and another lens at the same aperture and speed (if the speeds are to be trusted, or can be measured or be made long enough to be timed by a wristwatch). From what you've described, I would not trust it.
     
  9. Donald Miller

    Donald Miller Member

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    There is a way that is a lot quicker and less expensive to determine the validity of the actual Fstops and their corresponding designations.

    At F8 a 90 mm lens would have a apparent pupil size of 11.25 mm. At F32 the apparent pupil diameter would be 2.81 mm. At F45 the apparent pupil diameter would be 2 mm.

    Exposing film is a less definitive way since you have to consider the possible variable of inaccurate shutter speeds.
     
  10. Monophoto

    Monophoto Member

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    I have the Calumet version of the SA 90/8 in the Copal 0 shutter, and it displays the same characteristic that the aperture lever will move past the f8 position with no apparent increase in physical aperture. I suspect that this is merely a personality quirk of that shutter.
     
  11. Ole

    Ole Moderator Staff Member Moderator

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    Donald, that's easy if the opening is approximately round. If the opening is pentagonal, it isn't easy at all.

    Even if the aperture were perfectly round, it's not easy to measure on a 90mm SA. The difference between f:8 (11.25mm) and f:9 (10mm) can be very hard to discern.
     
  12. Donald Miller

    Donald Miller Member

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    I just tried this with my F8 90 and I don't seem to have any difficulty in determining the aperture size.

    However, be that as it may, I stand by my preference to measure the apparent pupil size unless of course the shutter speeds had been checked for accuracy.

    The difference between F8 and F9 represents about 1/3 stop...I tend to believe that an old unproven shutter could be off by that much or more.
     
  13. wiseowl

    wiseowl Member

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    Thanks, how would I measure the apparent aperture, is this what I see through the lens, or what I measure with the rear element removed?

    Thanks,

    Martin
     
  14. Justin Cormack

    Justin Cormack Member

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    Mine (also in Synchro Compur) does not move past f8 and you can see a little of the blades at that, so I would go with David and suggest that the marked apeeds are right, and opening the aperture any more will have no effect as its not in the light path. Quick test is to see if it looks a stop brighter on the ground glass as you open it past f8.
     
  15. wiseowl

    wiseowl Member

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    Yes it does look brighter as I open it up. So there is a problem with the aperture.

    I will now work on the basis that the scale is 1 stop out. Anyone have any ideas how to adjust it?

    Rgds

    Martin
     
  16. argus

    argus Member

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    Martin,

    I have several shutterless lenses where I can open the aperture beyond the marked smallest aperture. There is also a visible change in brightness, but I noticed that the marked aperture seem to be correct to the longer exposure times I have to do (as far as those are exact timings without shutter...).

    Have you noticed an f-stop shift in your exposures? It is the result of the exposure that is important. I have not read it in your postings.

    G
     
    Last edited by a moderator: Aug 20, 2006
  17. David H. Bebbington

    David H. Bebbington Inactive

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    I have just checked the 2 Super Angulons in my possession (90 mm in #0 Copal. 65 mm in #00 Synchro-Compur). In both cases the aperture control will move a long way past the f8 mark and at the f8 mark, the iris blades are just visible. It would appear to me that the "f8" Super Angulon would probably have a true maximum aperture of say f6.3 but that Schneider has chosen to describe it as f8 because it felt that the definition at apertures larger than f8 is not acceptable.

    Before you do anything, make some exposure tests and only send the lens for repair if the marked apertures are not giving correct exposure. I expect you will find that the marked f8 gives correct exposure. It is not uncommon for lenses to be mounted so that the maximum aperture setting does not uncover all of the glass, I expect Ole can give you plenty of examples from his collection of vintage lenses.

    Regards,

    David
     
  18. wiseowl

    wiseowl Member

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    Argus and David,

    thanks for the reply, I have taken a few negs with the aperture set to 1 stop wider than indicated by the meter. I've yet to process them, but will post about the results once done.

    I will say that the blades are very visible at the F8 mark, not a little bit visible. If I had a digi I would have posted an image to illistrate.

    Cheers

    Martin
     
  19. phaedrus

    phaedrus Member

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    Just looked at mine: the f-stop lever doesn't go beyond f/8, but at that aperture there are still aperture leaves visible from the front. The lens ist from 1965.
    FWIW, Christoph