Why are the holes in some lens boards offset and others are central. Does it make any difference ?
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Why are the holes in some lens boards offset and others are central. Does it make any difference ?
An offset hole allows larger decentering movements (rise/fall, right shift/left shift) than the camera's front standard offers.
Thank you
In the case of Linhof Technica boards the position of the hole allows the lens to be centered on the film when all controls are set at the zero position.
Ian,
It depends on the camera you have. Most cameras designed to take Linhof Technika lensboards are designed to take a lensboard with an off-center hole. As Bob relates above, this is part of the design of the camera and centers the optical center of the lens on the film when the camera is in zero position.
For other cameras, especially those with square lens boards, mounting a lens off-center will mis-align the lens when in zero position, but, as Dan mentions, allow you to get more rise/fall or shift depending on how you mount the lens on the camera. This is particularly helpful with cameras that have limited movements that you tend to use a lot.
I have Wista DX cameras that were designed for the off-center Technika board. I use these in the city a lot for architectural shots and often need more front rise than the camera provides. I have mounted my 135mm and 90mm lenses on boards with centered holes, which locates the lens a bit higher than center when the camera is zeroed (I can always compensate with fall if needed), but gives me that extra bit of elevation when the lens standard is at the top of the front rise. This little bit is often all I need and saves me a bunch of time not having to use the point-and-tilt-parallel method to get more rise.
Best,
Doremus
Thanks for the replies. The camera I have is a Chamonix 4x5, does anyone know if using an offset board will cause any issues
If you have an axis-tilt FS, the lens should be centered on the pivot axis points...
Steve K
I usually center the hole on the lensboard so the image circle is in the center of the negative when the camera's detents or 'centering marks' are centered. However, sometimes the lensboard hole has to be placed so the shutter can clear the lensboard locking mechanism, as in the case of this Copal 3. This camera has detents for axial tilt and base tilt, but uses marks for rise, shift and swing.Quote:
Originally Posted by IanBarber
If the lens isn't centered with the marks or detents, I use the clipped corners of the GG to center the lens, and ignore the marks, when the lens needs to be centered. That would be the case with my 125mm and 180mm lenses which give best results when centered perfectly.
I don't pay much attention to lens centering with respect to axial tilt because, my lenses almost never have the node in the tilt axis.
Attachment 155956
Ian,
You're making this way too complicated. Just set up your camera in "zero-position," set the front standard very close to the ground glass, mount a lens and look to see if whatever lensboard you have centers the lens on the ground glass. If the center-drilled board centers the lens, then that's the board the camera was designed for. If it's the off-center board that does the job, then so be it. Heck, you don't even have to have both types of board. It should be readily apparent if the one you have centers the lens in zero-position or not.
And, if you have the "wrong" board, you can always center it easily with a little rise or fall (put a sticker on the lensboard with an arrow pointing to a landmark on the front standard if you want quick alignment).
To answer you question: If your Chamonix is designed to take a board with a center hole and you use an offset board, i.e., with the hole lower than center, you will automatically have a little lens fall built in "zero-position." This is the only "issue." You may not want this. Keep in mind, lens position relative to the film determines where the optical center of the photo will be. If the lens is lower than center, the optical center of the photo will be higher than center and vice-versa. See my post to your other thread about "elevated perspective," (which really is just front rise). And, if you have a lens with limited coverage, then it would possibly vignette if not aligned with the center of the film. But, as mentioned already, you can easily center the lens with a bit of front rise.
Also you will not be able to get as much front rise with an offset board as with a board with the centered hole. This may make you work harder for shots that need a lot of front rise unless you can mount the offset board upside-down, effectively offsetting the hole higher instead of lower. I use this trick to get more rise out of one camera I own all the time.
Best,
Doremus