Longer lens and short bellows - Reversing a recessed lens board as solution?

[EdC]

I've been looking at possible solutions for making a longer lens work with my F&S 7x17. The front standard has been modified to take Sinar lens boards. Wouldn't it be possible to take a recessed Sinar lens board and reverse it as a means of allowing a 450mm lens to focus at less than infinity? I would expect that this would have some impact on movements, but I don't think that this would be a major issue. Any downside that I'm missing here?

Thanks,

Ed

[B.S.Kumar]

Many lens boards have machined features which prevent from being mounted the "wrong" way. I can confirm this for Sinar/Horseman, Linhof and Toyo. Perhaps a top-hat lens board would help.

Kumar

[EdC]

Many lens boards have machined features which prevent from being mounted the "wrong" way. I can confirm this for Sinar/Horseman, Linhof and Toyo. Perhaps a top-hat lens board would help.

Kumar

Thanks for the comment. I have looked at Sinar boards, and they do have some grooves along the back edges, which is what I believe that you are referring to. However, the intended use for this board is on a wooden camera with a wooden front standard. As I recall, there is a felt pad running around the entirety of the opening in the front standard where the lens board fits. Given that, would it make any difference if the Sinar board were reversed? I have an existing flat metal Sinar lens board, and could install that backwards in the front standard with some opaque covering over the lens opening. Using a strong flashlight or other light source, if there were no light leaks, I would think that this could work. Again, if I'm overlooking something, let me know.

Ed

[B.S.Kumar]

If the receiver front standard is a simple felt pad and does not have the matching grooves, then there's no issue. Just make sure there's no play, and the board can be locked securely. Note that the machined grooves on the rear of the board may obstruct the sliding lock. You could also make a shallow, open wooden box. Then you would not be restricted by the size of the board's depth - you could make it as deep as you want.

Kumar

[Luis-F-S]

Or you could have a top hat made. L

163134

[Doremus Scudder]

If your Sinar board will mount backwards on your F&S without light leaks and if you can mount the lens to the board reversed without problems, then there's no reason I can see that you can't use a recessed board as a top-hat board. I've done similar with a recessed lensboard fitted, reversed, to an enlarger.

You may not get very much extra extension, though. A top-hat board could be longer. FWIW, I made a top-hat board for my Nikkor M 300mm for use on 4x5 field cameras with only 12" of bellows extension. Total extension is about 3 inches. I used Masonite reinforced with small 1/4" pieces in the corners. Not difficult at all. A top-hat board may limit the front tilts/swings a bit, but they are still usable up to the point where the board itself vignettes the projected image. How much and where this happens depends on the position of the rear element and the depth of the board. Tilt/swing are a bit trickier to apply too, since the nodal point of the lens is positioned forward of the front standard with a top-hat board.

You may be able to purchase a Sinar-compatible top-hat board as well.

Best,

Doremus

[Len Middleton]

Wouldn't it be possible to take a recessed Sinar lens board and reverse it as a means of allowing a 450mm lens to focus at less than infinity? I would expect that this would have some impact on movements, but I don't think that this would be a major issue.

The movements would be similar to using a telephoto lens with the nodal point in front of the lens, in that if you used axis tilts, it would be well off the lens axis. However, it would provide you with the ability to use the lens on that camera, which you would not have otherwise...

[Jim Andrada]

I've made wooden "Top Hat" extenders for my Seneca - it isn't very hard to do.