Making Waterhouse stops DIY?

[PHOTOTONE]

I have several brass LF lenses that I want to use. All are missing their Waterhouse stops. Is there a DIY reference somewhere on how to calculate the aperture and how to construct the stops? Of course the lenses don't mention their speed anywhere on the barrel, unlike more modern lenses.

 

[N O Mennescio]

There's a thread about this over at LF Forum.
http://www.largeformatphotography.info/forum/showthread.php?t=23346

 

[Harrigan]

What I do is first cut a piece of chip board to the correct width of the waterhouse stop on the lens barrel. I leave the end square and hold the piece of board against the lens barrel and trace the inside profile of the barrel onto the piece. Then cut the traced line off and slide it into the slot creating the proper curve to the bottom of the stop. You want to check the shape and make sure it follows the exact curve of the inside lens barrel. Then insert the stop into the waterhouse slot in the barrel and carefully trace the inside of the top lens barrel onto the stop. From this mark you can measure the center of the stop and mark it with a pinhole.

From this template you can make all your other waterhouse stops according to the aperture sizes required. I make the final waterhouse stops from aluminum of whatever thickness can fit into the slot in the lens barrel. Finally prime with metal primer and follow that with a coat of flat black spray paint. Of course anodizing the alum would be the best choice but black spray paint works ok.

You also want to make sure that no light leaks around the waterhouse stops at the bottom or sides of the interior lens barrel. Sometimes this requires inserting some black felt strips into the barrel to keep any stray light from sneaking around the stops and degrading the image.

 

[phfitz]

Hi there,

What Harrigan said. To find focal length just focus at inf. and measure from GG to waterhouse slot, then divide by front lens dia. to find their speed.

Figuring the size of the aperture is a bit more tricky because of the optical illusion in the lens, it usually changes the apparent size of the stop OR just make the stops to physical size and change your lightmeter setting for that lens.

Have fun with it

 

[Christopher D. Keth]

It's not the front lens diameter that you need to measure. Put it on your camera and focus to infinity. Then put a card over the groundglass that has a small hole in the center. This should technically be a pinhole (to mimic a focused point at infinity) but a 1/8 inch hole will do fine and be brighter to measure properly in the next step. Shine a bright light through this card so it projects a beam out the front of the lens. Measure the diameter of this beam. That will be the size of the entrance pupil. This is what actually determines the speed of a lens.

This is also the method you should use to determine stops. In reality, you can do this once for the largest standard stop and then derive all others from that one with close-enough accuracy.

 

[Christopher D. Keth]

An addition to my last post. Once you do that once, you can calculate a magnification or reduction value for the physical size of the stop and the effective optical size. That will allow you to figure out the physical size needed to achieve a proper f22, f45, et cetera.

 

[Phillip P. Dimor]

Awesome thread, I favor black matte phenolic plastic. Easy to work with.