Is rail length required to focus a lens the same for any lens. If so is there a math formula to find out how long the rails need to be to focus at X distance with Y sized lens? In my case I have a 210mm Symmar S on a 4x5 Sinar F and I would like to focus at about 2-3 feet. I could just get an 18" rail ext but I dont really want to have to deal with that poking out. But im not sure a 6" or 8" is enough.
Ryan Mills
Not necessarily. It depends on if the lens design. A telephoto design requires less rail and bellows then a non-telephoto design. Telephoto in this context is the design of the lens, not just a long lens.
Also, a 210mm Symmar was never designed to perform optimally at 2 to 3 feet. That is where a macro lens would perform best. But at infinity down to about 1:20 the Symmar would perform better then a macro lens.
yea the 2-3 feet is a worst case, just wish I had a way to know how much good a 6" will do or will add.
Ryan Mills
m = (v/f)-1 = f/(u-f)
where 'v' is the lens or bellows extension, 'u' is the lens to subject distance, and 'f' is the focal length.
One man's Mede is another man's Persian.
what unit of measure would "u" be in?Originally Posted by E. von Hoegh
Ryan Mills
Depending on lens design.
For instance:
FFL for Schneider 250mm Apo Tele Arton = 206.5mm. For 240mm Apo Symmar = 238.5mm
FFL for Rodenstock 23mm HR Digaron-S = 44.8mm. For Schneider 24mm Apo Digitar = 26.4mm
It doesn't matter as long as you use the same units consistently. I'd suggest metric units.
One man's Mede is another man's Persian.
Yes, Bob. The OP has indicated he's using a 210 Symmar.
One man's Mede is another man's Persian.
But the formula works for some lenses and not for others. It is not an all purpose one. And the OP might think otherwise.
So Ryan needs about 13 inches of bellows for focusing at 2ft with a 210mm lens?
"It's the way to educate your eyes. Stare. Pry, listen, eavesdrop. Die knowing something. You are not here long." - Walker Evans
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