Using convertibles. The glass kind. Not the 'vroom vroom' kind.

Discussion in 'Large Format Cameras and Accessories' started by Robert Kennedy, Aug 12, 2004.

  1. Robert Kennedy

    Robert Kennedy Member

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    So I'm thinking about playing with the convertible aspect of my old Caltar S-series 8 1/2"-14".

    I've used this lens at 8 1/2, and I like it. I just tried some test shots at 14" with the front element removed and have some questions.

    First off - Is 14" practical for much? On my old Calumet 402 I found the bellows REALLY being pushed by this lens. I mean it is a 14" lens. With my two test shots, it seemed difficult to deal with simply because the bellows is way out there. Although I am thinking this could be a good portrait lens.

    Secondly - I wanted to use this for portraits because I could get, I hoped, a softer look once the front was taken off. And it does seem a bit softer. I was stopped down on my test shots, but when I open up I think I will get some real nice softness from this lens. Not "softar" soft, but softer. My concern is that with that front off, I have about an inch of shiny metal all around the lens all of a sudden. I'm thinking this means I will be entering flare city if I am not careful. Any hints on this?

    Thirdly - Since the bellows is out so far, how can I calculate my bellows compensation?
     
  2. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Are you shooting 4x5"? I've used 360mm lenses for landscapes and portraits on 4x5"

    The front element of the lens is still reasonably far in there. If you're getting flare, then shield the lens with a black card or compendium bellows, if you have one that attaches to the camera.

    I like to calculate bellows compensation by magnification. I have a magnification/exposure factor table on the back of each of my cameras, and I either estimate or physically measure the magnification factor by comparing the width of the field of view at the subject position to the width of the film frame. I've posted my magnification table as an MSWord .doc file somewhere around here.
     
  3. steve simmons

    steve simmons Inactive

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    Here is a convenient way to calculate bellows factors.

    For every 25% more than an infinity extension your bellows is extended add one half stop of exposure. For a 50% greater than infinity extension add one stop. This holds true regardless of the focal length(For your 14" lens at 17.5" I would add one half stop of exposure, and at 21" I would add one stop. I carry a cloth tape measure in my camera bag for measurements

    steve simmons
     
  4. PaulH

    PaulH Subscriber

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    If that is the same lens I had, it had 2 aperture scales on it. One scale was for the full lens and the other was for the rear element only. I think the second scale was in another color, maybe orange or red. Hope this helps.
     
  5. jnanian

    jnanian Advertiser Advertiser

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    robert -

    i have a convertable symmar that is not in its original shutter - so it doensn't have the second scale Paul mentions. since it only has one aperture scale i have to remember f8 isn't f8 when the front element is removed it is between f11 & f16. with convertable lenses the f stop is 1 3/4 stops smaller (larger number) when one element is used than it is when both elements are used.

    i hope this helps ...
     
  6. Ole

    Ole Moderator Staff Member Moderator

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    Maybe that explains why I've got THREE shutters with double scales for f:5.6 Symmar 150mm - and only one lens? And I'm trying to sell that one as well...

    Want to swap shutters? :D
     
  7. PaulH

    PaulH Subscriber

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    Robert, if your shutter only has one aperture scale on it, Calumet may be bale ot help you with the second. I don't think the calculations are as straight-forward as bellows extensions.
     
  8. Robert Kennedy

    Robert Kennedy Member

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    Oh, I have both scales. They are on the shutter. Otherwise I would be screwed! :smile:

    Very nicely printed too..... It does get weird though since the 14" starts at f/10.

    My meter does not like that.... :smile:
     
  9. Deckled Edge

    Deckled Edge Member

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    Removing the front element also introduces three new challenges:
    1) a drop in aberrancy correction. This can be countered with a yellow or orange filter--not too helpful for color. I never liked the colors I got from my Symmar with the front element removed.
    2) Introduction of focus shift. You will have to refocus at the working f stop.
    3) Grime. There is now nothing between the shutter and the Real World of wind, dust and blowing crud.

    Wouldn't it be nice if someone made filter rings sized for front threads of common shutters? This would hold a filter and block grime. Speaking of grime, I'm sure SKGrimes could do this on a custom basis, but the price will be steep.

    Any APUGgers know of such an item?
     
  10. Ole

    Ole Moderator Staff Member Moderator

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    Do you mean the Zero-strength Anastigmats included in some of the better casket sets? If so, they do (at least did) exist!

    Quite simplified they are correction lenses with infinite focal length to use in front of the shutter when only one element is in use. Instead of a flat glass (filter) they were finely tuned anastigmats, designed to correct astigmatism, field curvature and colour aberrance, without contributing to the focal length.

    I wish I had one - with a set of Protars... :wink:
     
  11. jnanian

    jnanian Advertiser Advertiser

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    i'd love to, but i am so used to shooting at the wrong f-stop and adjusting in development, i don't know what i would do. i guess it is like asking me if i want to have my shutters calibrated to the correct shutterspeeds on my speed graphic, or all my shuttered lenses for that matter :smile:

    i better not, my negatives, and chromes will suffer when i have to relearn everything ...

     
  12. Deckled Edge

    Deckled Edge Member

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    No. Way over my budget. I'm speaking of a step up ring which would fit a Copal 1 or 3 shutter. This would screw into the threads in place of the front cell. Your standard filter would fit into the ring. The anastigmat will correct all aberrations, but a simple yellow or orange filter will go along way towards correcting a single cell. This was a tip I learned from Ron Wisner, who went on much later to produce just such a casket set as you mention.