Specs for Calumet 4x4 lensboard

[Don Wilkes]

Can anyone point me to the proper specs for a 4x4 Calumet (old style) lens board? I have a new lens to mount, and I'm finding it hard to determine the proper thickness at the edges from my old, somewhat chewed-up board (made by some previous owner). The new lens is mounted in a Copal 0, which has a much shorter flange for the retaining ring than the old Compound shutter, so I couldn't mount it on the old board even if the holes were the same size (which they are not, although close). Also, any construction tips would be most welcome! I got some thin (about 1/8") plywood last night, and did a bit of experimenting, but soon realized that in rasping down the edge so it'll fit into the bottom slot, it makes for a dangerously thin bit of plywood. Would I be better off using solid hardwood, or a glue-up of two layers of plastic (say opaque plexi)?

The hole drilling also has me concerned... I have some hole bits, but doubt very much if one will be exactly the size for a Copal #0... Again, advice on this would be much appreciated.

[Nick_3536]

Solid wood would be weaker. 1/8" solid wood is basically thick paper. Can you front mount the retaining ring? I did that a few weeks ago. The rear element was big enough to hold the whole thing together. I don't have any real Calumet boards but I just wing it normally. The hole doesn't need to be exact.

Calumet still sold boards last time I checked. Maybe they have a tech department that could find the offical measurements?

[Don Wilkes]

Nick -- The retaining ring is not designed to be screwed down; it's just a thin threaded ring, so front-mounting is not an option.

Calumet still sells the boards, so if all else fails I guess I could contact them about the specs. And if anyone is wondering why I don't just purchase the real thing, it's because of the startling cost of getting stuff up here to Canada. A couple of years ago I ordered a simple ground glass, which was about US$20, from a US supplier. By the time I got it, the shipping, currency exchange, and import duties made it about CDN $60. At this rate, a US$45 lens board would set me back about CDN $135, which is patently ridiculous. Hence my determination to at least have a shot (or two) at making my own...

[Nick_3536]

Avoid UPS. Avoid UPS. How do I know the shipper was UPS? Lets just say I can tell.

I make mine but I really don't measure anything. I just chisel until they fit. I've got three different cameras that use what is supposed to be the same board but all three are a little different. So I've just gotten into the mode of just working the board until it fits. It's not hard.

[Ernest Purdum]

I measured the edges of a Calumet board and, not surprisingly, got slight variations from 0.122 to 1.125 inch. This board was from the original CC-400 series, which I hope is the one you are talking about. Your comment about rasping down the bottom edge makes me think you might be talking about somethiing else. If your plywood is actually 1/8", and the camera a CC-400, it should fit into the bottom groove without needing to be thinned down.



Model shops carry a birch plywood made up of more plies than the common 3-ply. It is much stronger, smoother and comes in useful thicknesses, It is often helpful to glue two or more layers of these together to get the differing thicknesses needed in making a lensboard.



Regarding making the hole, one way that can be laborious, is to use a hole cutter of the next smaller size, then enlarge the hole with a drum sander. Another method is to use a flycutter which adjusts to the exact size. These, however, are rather nasty to use on a home shop drill press. They work great on a milling machine with a super slow power downfeed and the workpiece mounted on seventy-five pounds of vise, but otherwise they want to dig in and spin the workpiece. If you use one, don't drill straight through. Get one side well started, then turn the board over.

[Don Wilkes]

Thanks, Ernest -- that's very helpful. The camera is, indeed, a CC-400. I did my best to measure the bottom slot last night, and it looks to be about 3mm, which is a bit less than an eigth-inch. I'm heading into town on my lunch hour shortly, and will be popping in to a hobby shop to see if they have thin birch ply in stock; here's hoping it isn't ridiculously expensive (as many things are in hobby shops!)

I don't have a drum sander, but should be able to simulate one with the drill press. Otherwise, I guess I'll have a go with the Dremel.

[Ernest Purdum]

Don, I probably should have said sanding drum rather than "drum sander". They are available as accessory items for your drill press and here, at least, are quite inexpensive, as are the abrasive sleeves. It's a lot easier to keep the hole round and regular with one of these than with one of the small diameter Dremel cutters.

[Ralph Barker]

When I needed to make several lensboards for my 8x10 Tachihara, Don, I did a bit of research on hole sizes, and put together a short article for the home page here. See http://www.largeformatphotography.info/lensboard_hole_sizes.html for the results. Where possible, I like using Forstner bits, but the larger sizes usually have to be special ordered. Whether using a Forstner bit, or a hole saw, in a drill press, it's a good idea to clamp the piece to the support base, along with a couple of stop blocks to keep it from spinning.

Whether using solid hardwood or thin furniture-grade hardwood ply, you may find it helpful to laminate at least a couple of thicknesses, crossing the grain, if solid wood. When doing so, however, precut the inside piece to leave a thinner area in the center to accommodate the retainer ring. The inside piece also forms part of the light trap at the edge of the board (just paint the back side flat black with a spray can).

[Nick_3536]

Lee Valley I think stocks Forstner in fairly large sizes. All the way up to 4". But if you only need a few boards drilled it might be cheaper to hire somebody then buy one of the big bits.

[Don Wilkes]

Ernest: I knew what you meant about the sander; I accidently used the same terminology <g>.

Ralph: Many thanks for putting that page together! It looks so useful that I've printed it out for future reference. I believe we have some Forstner bits at home, but it's unlikely we have one that large. I'm hoping I have a hole saw relatively close to 1 3/8 (a faint hope, but a hope nonetheless). If it proves too darn difficult, one of the photo shops in town will machine me a hole for a price ($20, I think).

While in town at lunch, I found some 3/32 birch ply in a hobby store, but not only was it pretty expensive, but the four sheets they had were all warped. More looking will be called for on the weekend. And I did plan on glueing up two layers, just as you suggest -- wouldn't like to risk my glass on a too-flimsy board!

Nick: I think for the price of a special-order Forstner bit, I could buy several boards from Calumet <g>. If I ever do get over to Lee Valley Tools in Vancouver, I plan on taking cash only -- otherwise the credit card would be smokin'...

Cheers