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Thread: Rear lens component used as long lens

  1. #1

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    Rear lens component used as long lens

    I have an RF5 lomo process lens 450mm f10 that is a symmetrical double gauss design. I was wondering whether I could use the rear element as an ~800mm lens if I stop it all the way down to cover 16x20inch (650mm diagonal) cibachrome that I want to shoot in camera. I am in the process of building a ULF camera and this will help me determine how I construct the camera.
    Cheers Kanga

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    Mark Sawyer's Avatar
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    Re: Rear lens component used as long lens

    The Gauss Lens was originally designed with only two elements (in 1817 as a telescope objective), and later "upgraded" to a Double Gauss with four elements for photography in 1888. (If yours is cemented, that's Zeiss' 1895 refinement.) I believe some Double Gausses were sold as convertibles, so yes, it's possible. That's no guarantee how yours will perform, though.
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

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    Re: Rear lens component used as long lens

    IIRC, you lose about two stops of speed when converting a lens. And the lens then requires a longer extension than the nominal converted F.L. I'd say it's worth exposing a few sheets of film to find out what happens... maybe not 16x20 though.... but how else will you find out?

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    Re: Rear lens component used as long lens

    I have tried using only the rear elements from several of my view camera lenses on my 11x14. Trouble is that when you really stop them down, judging sharpness on the GG, I found hard to do. Eventually just sucked up the film costs and went out and shot a negative with each of the rear elements. Some worked, some didn't. Actually liked the Bokeh on one of them that "didn't work out" as far as being evaluated by overall sharpness across the negative.

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    Mark Sawyer's Avatar
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    Re: Rear lens component used as long lens

    Quote Originally Posted by Greg View Post
    Eventually just sucked up the film costs and went out and shot a negative with each of the rear elements...
    That's where the economy and ease-of-processing makes paper negatives a good option.
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

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    Re: Rear lens component used as long lens

    Quote Originally Posted by Mark Sawyer View Post
    That's where the economy and ease-of-processing makes paper negatives a good option.
    Thankyou all for your comments. Has anybody tried colour with film or paper using the rear lens component?
    Cheers Kanga

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    Re: Rear lens component used as long lens

    Kanga, there's a rule of thumb to the effect that half of a convertible lens covers roughly the same circle as the complete lens. Check carefully before sacrificing a 16x20 Cibachrome sheet. Arne Croell believes that the RF- series of six elements in four groups double Gauss type process lenses cover 45 degrees. If he's right, and he usually is, don't even bother.

    I'm sorry, but there just aren't that many lenses that cover 16x20. If the trick you want to try worked well, it would be well-known.

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    Re: Rear lens component used as long lens

    Quote Originally Posted by peterkinchington View Post
    I have an RF5 lomo process lens 450mm f10 that is a symmetrical double gauss design. I was wondering whether I could use the rear element as an ~800mm lens if I stop it all the way down to cover 16x20inch (650mm diagonal) cibachrome that I want to shoot in camera. I am in the process of building a ULF camera and this will help me determine how I construct the camera.
    Cheers Kanga

    Acording to this info (http://www.arnecroell.com/eastern-bloc-new.pdf) the RF-5 is of APO-Planar type, six elements in four groups.

    In general lenses are not convertible to be used in halves. A convertible lens has rear and front cells individually corrected, while in non convertible lenses the aberrations from the front cell are compensated by the ones in the rear cell, being that the common situation.

    So you should try it, for sure that the rear element alone will form an image, another thing is if the performace is enough for your application or not, at the end you may need only 6 lp/mm on the print, it is possible that even in the case that the lens is not convertible you obtain acceptable results, as you are not to enlarge later, so you may check it on the GG.


    Quote Originally Posted by Mark Sampson View Post
    And the lens then requires a longer extension than the nominal converted
    Not always, if using the front cell alone then you require less bellows than the nominal, for example with the Cooke Triple Convertible or with the Symmar Convertible, in the Symmar case the aperture scale is not shown for the front cell alone, but it also can be used. The early Symmar (Dagor, IIRC) type has the 3 scales...

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    Mark Sawyer's Avatar
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    Re: Rear lens component used as long lens

    Quote Originally Posted by Dan Fromm View Post
    Kanga, there's a rule of thumb to the effect that half of a convertible lens covers roughly the same circle as the complete lens...
    Even though the focal length roughly doubles and the barrel is shorter? How can that be? (Not disagreeing, as Cooke's specifications for the XVA Triple Convertible agree with you.) Is it that the outer image area degrades?
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

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    Re: Rear lens component used as long lens

    Quote Originally Posted by Mark Sawyer View Post
    That's where the economy and ease-of-processing makes paper negatives a good option.
    How about the lower cost and ease of processing of X-ray film?

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