Is the purpose of recessed lens boards to give more play room for the bellows for wide angle lenses? since the bellow is compacted?
what is the purpose of the off center lens board?
Is the purpose of recessed lens boards to give more play room for the bellows for wide angle lenses? since the bellow is compacted?
what is the purpose of the off center lens board?
Recessed lensboards enable you to use lenses with a shorter flange focal length (FFL) than the camera would normally support.
FFL is the distance from the lensboard face to the film face when focused at infinity. It's in the published specs for all modern lenses. It's related to the lens focal length, but not in a predictable manner. For short focal-length lenses, the FFL is usually greater than the focal length by several mm*.
The minimum distance between the lensboard and the film is set by the camera design. (You can only flatten the bellows so much.) That distance is usually published by the camera manufacturer. To be used on a normal lensboard, any lens must have an FFL greater than that minimum distance.
The problem with using short FL lenses on any camera, regardless of the lensboard type, is restricted movements. Since the bellows is compressed significantly, you can't use large front rise/fall/shift movements.
A "bag bellows" is used to permit greater front movement when using short-FL lenses.
Problems with recessed lensboards include restricted access to the shutter controls, and need for a special L-shaped adapter for the cable release.
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I've never understood the reason for offset lensboards. Seems rather stupid to reduce the available rise by that amount.
- Leigh
*nb - slightly OT - For long focal-length lenses the FFL may be shorter than the focal length. With telephotos, it may be shorter by a large amount.
For example, the Fujinon T 600mm lens has an FFL of only 383.9mm, more than 200mm less than the focal length.
my guess is that the offset hole is for better access to shutter controls.
Regarding the reason for offset boards - if you're talking about Linhof Technika boards, the camera was designed so that the lens is centered on the GG when mounted on an offset board, so there is no loss of rise. And as mentioned above, offsetting the shutter in the recessed board's cup makes the shutter controls more accessible.
I've had problems using my 75mm grandagon in a 12mm recessed technica lensboard with an offset hole: The copal 0 shutter bumps up against the edge of the recession and I can't screw the retaining ring in.
Note: my recessed lensboard came from China, and I don't know if the ones sold by Badger might work better.
Actually, it is offset to allow symmetric rise and fall while keeping the standards short for folding/collapsing. If the hole was centered then both the back and front would have be located higher off the camera bed in order to allow fall. Offsetting the hole makes fall easier. Rise can always be accomodated with more play on the front standard. It also reduces the height of the film plane off the bed which allows the camera to be lighter and more compact.Originally Posted by JimL
Of course changing to an offset board on a camera which was not designed for it may not be optimal, but may substitute for a lack of fall in the design, or if flipped will give you additional rise. Some lensboards for press cameras were offset with that in mind.
Linhof made, at the same time, two different standard recessed boards. The 001015 for Compur shutters and the 001016 for Copal shutters. That was because the control layouts and the controls were slightly different and if you used the wrong board the shutter would do exactly what yours is doing.
Apparently whoever made your board copied one of Linhofs and is trying to sell it for both shutters. You just need the correct board for a Copal. Today, from Linhof, that is the new 001015 Comfort board which is made differently then the older Linhof recessed boards. And all operating controls as well as the aperture scale are on the flat portion of the board. No more reaching into the recess to operate the shutter.
Thanks, Bob. Always good to know the whole story.
// Wally
I always thought a purpose of the offset boards was to give you more rise or fall. With a camera with limited movements, like a Tachihara, you could mount the board off center (toward up) when you need more front rise than you could get otherwise.
No, it was to have the optical center of the lens centered on the gg on Linhof cmeras. Since the other boards are copies of the Linhof board this may or may not be the condition on non-Linhof cameras.
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