Bellows size in relation to focal length

Discussion in 'Large Format' started by steve_levine, Sep 27, 2005.

  1. Whats the longest lens I can use on a bellows that is only 7
    3/4 " ? I want to use a 90mm, but will a 135mm work? I realize that
    135mm (5.5") doubled won't work, but what about focused at infinity?
    This is for landscapes and architecture, not for close up work.
    I suppose I can mount my 135mm on my 16' rail camera, and measure
    how much draw I need?
  2. Lessee, now, total extension film plane to front flange is 7.75" = 197 mm. And if the lens is in shutter and of "normal" construction (not telephoto, not retrofocus) its rear node may sit a little in front of the lens board. At infinity, the lens' rear node is 1.0 focal lengths from the film plane.

    So with 7.75" of extension you can focus a 190 mm lens not quite usefully closer than infinity. What's your problem with a 90 or even a 135?

    Without looking it up or measuring mine, 7.75" smells of 2x3 Crown or Century Graphic. The longest standard issue lens for those cameras was the 250/5.6 TeleOptar, also badged TeleRaptar. This is a telephoto lens, needs less extension, given its focal length, than a normal lens.
  3. Actually Im a low budget LF shooter(aren't we all?). So I'm looking at a Calumet wide angle body with a 7 3/4" bellows. The 90mm is also yet to be purchased.

    I already own 2 Calumet bodies, and 2 lenses on their boards. So buying their WA body makes sense.
  4. Steve, I have a Calumet wide body and the 135mm is the lens I probably use most. I have also used a 210mm which is the limit on mine. The thing I like about the wide body is you can go down to a 65mm lens on a flat lens board.
  5. A rough rule of thumb is that to focus on typical distances (but not closeups) the camera extension needs to be about 20% longer than the focal length of the lens. (This rule is for regular, non-telephoto lenses.) So for the camera with 7 3/4 inch extension = 200 mm, a 165 mm lens would work pretty well.

    The exact equations are given near the top of the Lens Tutorial, . One trick to using the equation is that image distance Si should be measured to the rear principal plane. For LF lenses, this is typically in the shutter, and, as Dan says, a little forward of the lens board. So maybe you would have 210 mm of useful extension, which would allow a hypothetical 165 mm lens to focus as close as So = 770 mm = 30 inches.

    Don says that a 210 mm lens is the limit with this camera -- the equations, with my guess for the largest value of Si, say that a 210 mm lens could only be focused on infinity. Since Don says that the lens is usable, probably my guess for Si is a few mm small, but still don't expect to do portraits with this lens.

    At Si = 200 mm, your 135 mm lens will give magnification M = 0.48, so a half lifesize image.

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