Lens board design theory

Alan Edward Klein · Apr 12, 2023

Don Heisz said:
Frankly, the material you choose for your board depends on the lens you wish to mount. The heavier the lens, the more likely a material such as hardboard, low-grade plywood (lauan), or even plastic is to flex, which will mess up focus. But those materials would be fine for something like an Ektar 127 in a Supermatic shutter.

If you want to mount a heavier lens, particularly if it sticks out more than 2 inches or so, you'll want something stronger. Like aluminum.

Wouldn't that depend on the format? For example 4x5 has a smaller board that seems would be stiffer and stronger than the same heavy lens mounted on an 8x10.

Don_ih · Apr 12, 2023

Alan Edward Klein said:
Wouldn't that depend on the format? For example 4x5 has a smaller board that seems would be stiffer and stronger than the same heavy lens mounted on an 8x10.

Definitely. You can make a lens board for a smaller format Speed Graphic out of hardboard and mount pretty much any lens that will fit on it, it's too small to deflect.

My 4x5 Cambo, though, has a pretty big lens board.

I did make a lens board for a 4x5 Toyo I have out of hardboard. But I only mounted a Kodak lens in shutter from a postcard camera on it. The normal lens boards are pressed steel.

DREW WILEY · Apr 12, 2023

Acrylics bow toward heat, and are dimensionally affected over time by humidity; polycarbonates are a little better, tougher, and more easily machinable. Sintra that thin softens and flexes with heat. Phenolics are as hard as a rock and difficult to mill, but not necessarily free from warpage either. I already mentioned clad PC board, which is thin and stiff.
But in general, I don't see common plastics as a great idea for lensboard use; though people who have scraps of it on hand will no doubt try.

Alan -luan was never used for anything I can recall except dirt cheap wall paneling and moulding. It was popular in the 50's for that reason. Cats love luan moulding as a claw sharpening medium, and tear it all up. It's pretty darn soft. 1/4-inch thick Masonite "hardboard", if smooth and hardened on both sides (Duolux), isn't dimensionally stable, but could be used in a pinch if properly sealed. It cuts fine; but the edges don't otherwise shape well.

Don_ih · Apr 12, 2023

Lauan is what most floor underlay "plywood" is made from. Well, the core of it, anyway. It's also what most cheap paneling was made from - other than the pattern paper on the face. And you used to be able to go buy a residential doorframe made from it. Not for an awful long time, though.

nosmok · Apr 12, 2023

Referring back to my post #8 in this thread, I upscaled the craft-lumber idea for a replacement to the missing lensboard for my 11" x 14" Korona. This is ordinary, crappy 3/16" (I think; it measures 7/32" or so) plywood that I had lying around, assembled exactly the same way as described in that post. The black tape covers an air hose hole I put in the wrong place . It's light-tight and works fine. I'm still refining my ULF technique on the very temperamental Ilford Direct Positive Paper; when I get it dialed in I'll consider a better board (and maybe another film holder). When you're learning to drive, you don't do it in a Ferrari.

DREW WILEY · Apr 12, 2023

Luan underlayment? Never seen that; and I was a buyer in a major construction supplies firm for 40 yrs. Must be a regional thing. Now a lot of waferboard is used, prior to that types of MDF or tongue and groove fir plywood. I've never seen luan core anything; it was used as door-skins, or for front and back facings of chepo decor plys. Fell out of favor around the time the hoola hoop got boring too; after that, only used for repairs of that vintage of home construction. Even the relatively cheap hollow-core mahogany doors, at least the ones we sold, weren't that bad a grade of so-called mahogany. We did sell true mahogany solid wood ones; very pricey, of course. Trying to stain luan to look like real mahogany comes out looking more like rotten moss soaked in rusted radiator water.

Don_ih · Apr 12, 2023

DREW WILEY said:
Luan underlayment? Never seen that; and I was a buyer in a major construction supplies firm for 40 yrs. Must be a regional thing.

It's in a lot of lower-quality plywood. It's got that distinct moldy smell when you cut it. It's usually accompanied by lots of gaps and random delamination.

Those hollow core "mahogany" doors used to be everywhere. That is truly something that fell off the face of the earth.

DREW WILEY · Apr 12, 2023

Interesting. I don't hang out at the cheaper lumberyards or home centers. We catered to the serious types, and sold the better grades of ply. But I got most of my own decor ply due to an inside connection with perhaps the best hardwood dealer in the area. My last job was an African mahog kitchen across the state. But sometimes luck is involved. Who knows how many thousands of sheets of 13/16" maple and birch ply we sold a year to cabinet shops. I wasn't the plywood buyer. But one year exactly three sheets in a row randomly turned up which were true birdseye as well as ribbon-grain maple, and moreover, thick-veneered. You can't find anything like that anywhere, at any price, these days. If you did, it would cost over $500 a sheet. The warehouse guys knew I was looking for something special, so set aside one of the sheets for me, which I got for around $15. It became the top for one of my big desk-height print flat files, to show prints upon. I used a satin hybrid acrylic floor finish with just a little amber tint. I got matching birch pulls for all the drawers. Fun project.

MTGseattle · Apr 12, 2023

Oh boy, let's not head down the path of wacky plywood. During the really crazy material price days ($70 1/2" cdx), I got some "weird" 5/8" stuff for $20 per sheet thinking I could use it for storage projects or anything really. I decided to try and build a sleep platform/drawers for my Land Cruiser. It's horrible plywood. It smells like Eucalyptus when you cut it, no voids are filled, and the veneer layer while looking nice is about 1/16" thick. Needless to say, I consider what I built to be a rough test of concept and not much more.

I've got 1 lens mounted in what I will call MG lens board 3.0. It's 2 thinner layers of the Acrylic or whatever I have epoxied together so that I have my "light trap" rabbet around the edge. I've run some book binders tape around the inside of the rabbet to shim me up to a nice snug fit, and added some of the same tape to the inner surface to combat reflections. It's more rigid than the lens board that shipped with the camera by far.

The other acrylic stuff I have is actually about 1/32" thicker than the Aluminum and is a real tight fit into the front standard. This would be a ridiculously easy thing to surmount had I a router table. The only router table I'd be willing to pay retail for right now would cost as much as another box of film and 3 lens boards from ebay. Not today.

Here's where everything came to a stuttering halt today; the copal 3 shutter aperture stop. It is proud of the mounting surface by a millimeter or 2. I did some measuring and drilled a hole for that pin/screw to rest in.

The Copal 3s shutter I have does not have the same pin/screw. Ah, the glorious realm of shutter variations.

DREW WILEY · Apr 12, 2023

Actual acrylic is miserable to try to rout. It melts, you need a special kind of carbide (unless just squaring edges already cut - a Formica router bit will do that), and a wet lubricant is often needed, making the whole process unsafe with a typical router. What you want is polycarbonate, which behaves fairly well with woodworking style tools.
And any router table that costs only as much as another box of film and 3 lens boards is a flimsy piece of trash, and probably dangerous too. You could probably build a better one yourself. Those sure like nibbling off fingers if they're not properly designed and operated. Few things in the shop are scarier than a cheap router table which vibrates.

MTGseattle · Apr 12, 2023

Here's the inner side of the lens board I mounted the 240mm onto, and a picture of the aforementioned aperture stop. I may be wrong as to its function though. I'll see what I can dig up re; Copal shutters. I have a Copal 3s that doesn't have the little brass stop, and the aperture selection is nice and smooth and stops where it should.

Drew. yeah, I'm still in portability mode, and not dedicated space/cabinet mode. I have plans for a kick-butt router cabinet/station in my file cabinet. Someday. You should see what my patio and yard look like when I do any welding at home.

Apparently a Copal 3s is just "small." Lens cell mount threads are smaller than on a 3. Otherwise they should be the same which has me wondering if the 3s is missing a part?

reddesert · Apr 13, 2023

That's usually an anti-rotation pin, not an aperture stop. It is a feature, not a bug, if you can drill a small hole to match it. You can often take them out with a screwdriver and many people do and then misplace them.

Don_ih · Apr 13, 2023

Yup, that pin is to keep the shutter itself from spinning around. So you did need a shallow hole for it to sit in.

A router table is easily made by just screwing the router to the underside of a sheet of plywood. That's all I used for years - I wouldn't waste more than 2 square feet on a router table. The best place to put one permanently would be in either an outfeed extension for a tablesaw - a much better use of a few square feet - or the side extension, where you could also use the table saw's fence.

DREW WILEY · Apr 13, 2023

Some table saw wings once came with a router mounting hole position in them so you could use the standard saw fence itself like a router table fence, at least in certain applications. But US law stipulates that any router table, or anything obviously meant to optionally become that, must have a built-in finger guard system. So that kind of saw wing option became illegal to import.

I've sold all kind of router table systems. For some reason, they tend to be more popular than shapers in this area, even among pros, while the big shops might have extremely expensive industrial moulders. My own router table is built like a tank and a joy to work with. It's equipped with a large Festool router - relatively quiet, superb dust extraction, powerful and precise as heck - but that was just one of the perks of being their key distributor in the western half of the continent, making sure I had certain things for personal use so that I could commend them to others. Now I mostly use that setup for hardwood picture frame fabrication. A lesser router would just chew things up unless a firm power feeder were added. But just the convenience of spending far less time cleaning up dust makes it worth it. I also use their rails saws - will cut more delicate sheeting better than most programmed panel saws - as well as their sanders, etc. A long long ways from my first little $25 Black and Decker 1/4"router.

Roger Thoms · Apr 13, 2023

DREW WILEY said:
A long long ways from my first little $25 Black and Decker 1/4"router.

I cut my teeth with a Sears Craftsman router and a set of their HSS bits, we’ve certainly come a long ways haven’t we.

Roger

Don_ih · Apr 13, 2023

Roger Thoms said:
Sears Craftsman router and a set of their HSS bits,

Nothing wrong with a Craftsman router - but HSS bits are for people who like to be punished.

DREW WILEY · Apr 13, 2023

Craftsman had some of their routers made by Singer, later, other models by Bosch, after Bosch bought the US Stanley power tool plant, back when Stanley still implied tools rather than toys. Gosh knows how many Porter Cable routers I sold in my younger years. The first really good table ones were Fein; but Festool pretty much makes everything else look primitive now. Even the big cabinet shops with fully mechanized hundred thousand dollar line bore machines would use Festool plunge routers and their own line bore accessories for prototyping and location work. It's like having a cabinet shop in the back of a van. They no longer sell their own router bits in this country except those dedicated to certain of their tools, but the quality of carbide is utterly top notch. Even their steel drill bits last about 50 times longer than the retail store variety. Often what is most expensive to buy up front turns out to be the cheapest and most efficient to use in the long run.

And when it came to making a lot of my own darkroom fixtures, and even that damn heavy as a rhinoceros thick phenolic additive colorhead housing, don't know what I would have done without the system. Throw in all my slot print washers too, custom large trays, even precision registration punch frames .... But if I had to start over again, I'd also acquire a "hobby"milling machine - a scaled-down one like Jet offers. I had to make do with an old industrial floor-standing drill press, conveniently parked in my shop by a friend who didn't have room for it himself.

Roger Thoms · Apr 13, 2023

Not sure who made the Craftsman router, but I do remember the first time I used a Porter Cable with a carbide tipped bite. It was in a Corian Shop, wow what a revelation, the carbide specifically. Not too long ago I was in a cabinet shop that supplied the mill work for a commercial project we did. The owner was showing me the diamond bits they use in the CNC equipment, at 7-8 hundred dollar each. I'm retired now and planning building a shop/studio at our place outside of Flagstaff Az. We are off grid so it should be interesting.

Roger

DREW WILEY · Apr 13, 2023

Corian and synthetic countertop materials require their own special kind of carbide and rake angles. Granite and other types of stone involves expensive diamond router bits and water-fed routers specially GFI'd and UL certified; they're expensive. Jerks sometimes try to attach water hoses to ordinary big routers, and then hire some ignorant illegal worker to run it. One of those messed up his big Makita plunge router doing that, and brought it to our repair dept. He never got it back. We refused to return it. In fact, it would against the law to return it. He screamed and complained; and we simply told him the facts, along with, we don't want your kind of business anyway - why do we want to get sued too if someone gets electrocuted, or charged with negligent manslaughter?

We used to machine a lot of a super-hard phenolic composite countertop material called Benelex for the Navy in our big shop. Some of my older punch and register darkroom gear is made of that too. It also required diamond tooling.

MTGseattle · Apr 14, 2023

Thank you for the heads up regarding the anti rotation pin.
Lens board version 3.1 is quite a bit stiffer than version 3.0 I used a square of the thickest plastic backed by a piece of the thinner. (I'm just going to call it plastic for now. I would need to stop back into TAP Plastics with a chunk to find out exactly what it is) Due to the extra stiffness, I'll probably switch the Caltar S-II 240mm over to the thick board and mount the Osaka 300mm in the thinner board since the 240 is the heavier lens.

@Roger Thoms There's an old documentary floating around called Bens Mill. If you can get a water wheel going at your off-grid place, you could build anything. I have no idea how scarce belt driven mill tools are though.

MTGseattle · Apr 16, 2023

It would appear one also needs to check the depth? height? of the actual mounting threads on the shutter. I cannot mount the 240mm on the thicker board as the retention ring will not grab any threads on the shutter. Oh well. I think I am going to steer towards standardizing around Technika boards. I can get out and shoot with what I have so far (although it's pissing rain today) but I'll continue to scan various places for bits and bobs as needed.

Don_ih · Apr 17, 2023

MTGseattle said:
It would appear one also needs to check the depth? height? of the actual mounting threads on the shutter. I cannot mount the 240mm on the thicker board as the retention ring will not grab any threads on the shutter. Oh well. I think I am going to steer towards standardizing around Technika boards. I can get out and shoot with what I have so far (although it's pissing rain today) but I'll continue to scan various places for bits and bobs as needed.

Depending on material, you could route a recess around the mounting hole to allow the retaining ring to catch the threads. You could also use sheet metal (18 gauge or thicker) to make a mounting flange for the lens, which you could then attach to the thicker material.

The best material will always be metal. The problem will always be making it match the board-mounting system of the camera and the light trap (if there is one).

MTGseattle · Apr 17, 2023

The Caltar 240mm actually has a spacer involved in the mounting hardware. The closest non-photography example I can think of is a bicycle headset spacer. same basic thing, just at copal 3 diameter. A thinner spacer would allow me to mount the lens as it is. I can photograph with what I currently have. Technically, my camera can take the 140x140mm Sinar lens boards. Luland makes a decent Sinar to Technika adapter. Throwing money at a problem is an ok strategy sometimes I guess.

xkaes · Apr 19, 2023

Alan Edward Klein said:
Wouldn't the offset also reduce the amount of tilt and fall since the image circle is in another area rather than centered?

I bought a couple of lenses with the offset and replaced them with a center hole board from Chamonix just to standardize. It made me feel more comfortable even though people said it doesn't matter, much.

Not using the correct placement of the hole can impact tilt & swing (depending on the extension & lens), but more likely will impact shift & rise/fall -- especially with lenses with small image circles. There are lots of lenses that just barely cover the film, and if you are "off-centered" even just a little -- even without any movement -- you won't have coverage (or quality) in the corners.

_T_ · May 15, 2023

I know you're pretty deep into the diy route already, and I don't mean to harsh you on that, but do you have a camera repair shop nearby? Some of the better equipped have a machine shop and they will usually have all the correct tools to make a lens board for you for less than it would cost for you to make one yourself.

Lens board design theory

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Lens board design theory

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