Lens board design theory

[MTGseattle]

I was hoping this had already been covered. maybe I didn't search well enough? At any rate, here is where I'm at.
I now have a really nice Osaka (Tachihara) 8x10 field camera. It came with a lens in an abs or some type of plastic lens board that is slightly too thin. The easy/temp fix for this is just a few more strips of book binding tape to get things snug. Problem 1 solved.
Problem 2 is my other lenses.
There looks to be a well-regarded maker of wood lens boards on ebay. I'm guessing it would take a week to ten days for me to get a few boards in hand.

I have some random selections of thin plywood around, so I thought I would try and make a few boards myself. While digging through my materials stash, I happened upon a sheet of aluminum I had forgotten about. It also happens to be the perfect thickness. when I set a piece into the front standard, it locks in nice and tight with no wiggling.

So,

Is the decision to mount the lens off center in the board driven by focal length of lens or camera (bellows shape?) or some of both?

If I have to machine a thinner section around the shutter hole to properly mount the lens (due to mount thread width), I'm not sure how to accomplish that with aluminum and the tools I have at home.

If you think of a traditional wood field camera lens board with its rabbet around the mounting perimeter, is there any problem using a perfectly flat board instead if it sockets in nice and snug?

 

[B.S.Kumar]

I was hoping this had already been covered. maybe I didn't search well enough? At any rate, here is where I'm at.
I now have a really nice Osaka (Tachihara) 8x10 field camera. It came with a lens in an abs or some type of plastic lens board that is slightly too thin. The easy/temp fix for this is just a few more strips of book binding tape to get things snug. Problem 1 solved.
Problem 2 is my other lenses.
There looks to be a well-regarded maker of wood lens boards on ebay. I'm guessing it would take a week to ten days for me to get a few boards in hand.

I have some random selections of thin plywood around, so I thought I would try and make a few boards myself. While digging through my materials stash, I happened upon a sheet of aluminum I had forgotten about. It also happens to be the perfect thickness. when I set a piece into the front standard, it locks in nice and tight with no wiggling.

So,

Is the decision to mount the lens off center in the board driven by focal length of lens or camera (bellows shape?) or some of both?

If I have to machine a thinner section around the shutter hole to properly mount the lens (due to mount thread width), I'm not sure how to accomplish that with aluminum and the tools I have at home.

If you think of a traditional wood field camera lens board with its rabbet around the mounting perimeter, is there any problem using a perfectly flat board instead if it sockets in nice and snug?

Whether a lens is mounted in the center or off center in the board is driven by the design of the camera. Linhof cameras have focusing tracks stacked one upon the other. This raises the lens by 7 or 8mm. To make the lens centered on the focusing screen. the shutter mounting hole must be lowered by the same distance. Check your camera's front and rear centering and drill the hole accordingly.

To avoid machining a thinner section around the hole use a flange like this one: https://www.photrio.com/forum/threads/fs-lens-flanges.198197/

The rabbet around the lens board mounting perimeter matches the inner frame of the lens panel on the standard and acts like a light trap. It may be better to have it to avoid light leaks.

Kumar

 

[MTGseattle]

I'm all hopped up on cold/flu medicine, so thank you for that. Built in light trap. D'oh! Anyway, landing on the "perfect" thickness of aluminum and not having a Bridgeport around doesn't let me get very fancy with metal work.

Thank you for linking your thread regarding the lens flanges. I had seen that when you first posted but it wasn't something I needed at the time.

 

[Jim Jones]

Woodworking power tools often work well enough when machining aluminum. I use a table saw for rough cutting flats like lens boards and a table mounted router for something like rabbets.

 

[MTGseattle]

For sure. I like to have a couple of dedicated blades on hand, but I totally agree with you. The main difference is RPM's, most woodworking tools turn a lot faster than the metal versions. Funily enough, I don't own a router table. My band saw isn't the fancy wood/metal version with the gear reduction, it's just the "wood" version. I used an angle grinder and a rasp to get the first square yesterday.

 

[Doremus Scudder]

Heck, I've dealt with removing thickness on aluminum lens boards with hand files. I scored the border of the area to be removed with a hacksaw blade to the desired depth and then filed the rest by hand, test fitting along the way. Lens boards are not rocket science.

Doremus

 

[DREW WILEY]

My gosh! Trying to kill yourself or get fingers torn off? Aluminum requires a completely different kind of carbide and tooth pattern than wood cutting blades. Same with router tables - different carbide, different bit rake angles (not something you're going find at a neighborhood hardware store or home center), and it's potentially even more dangerous than a table saw. Either way, the aluminum should be securely attached to a lager wooden sled for sake of secure control. No, not rocket science, if you don't mind blowing up yourself with one of those either. Things need to be spelled out for sake of beginner safety. I've seen more than my share of missing fingers, hands, and limbs over the years.

Cutting the lens shutter hole with a hole saw can be even more dangerous to the uninitiated. I tightly affix the lensboard to a large piece of wood, which is turn is securely clamped to the drill-press table, and then a fly cutter used (cleaner cut than a hole saw). Don't try it by hand! And always count your fingers and eyes afterwards, just to keep tally. Blood is a poor cutting lubricant - use official cutting oil, preferably the water-rinsable kind.

All this would be better done on a real milling machine, if you know a machinist. Never attempt aluminum with a saw or router unless practicing first with wood; and then you still need to right kind of blade or bits. Even too high a rake angle on a carbide saw blade can send that carbide tip flying like a bullet, and embedding itself a couple inches deep in a wooden beam fifteen feet away. Seen in happen more than once. Using the wrong blade was grounds for instant firing of the individual in our shop. Losing a hand or eye would shoot the insurance rate through the roof, not to mention the personal connotations of maiming or serious personal injury.

Same applies to mitre saws, and correct usage, though radial arm saws are the most dangerous. The pro aluminum-cutting blade on my own mitre saw cost more than nearly any electric mitre saw itself currently on the market, and is equipped with some exceptionally strong clamps. But for around a hundred bucks you can find a nonferrous materials blade sufficient for aluminum plate. Don't forget the cutting fluid; those blades aren't intended to be used dry.

Wood, thin ply per se, is not dimensionally stable, so not ideal for lens boards, though safer to work with.

 

[nosmok]

I find that if you get some 1/8" basswood craft lumber, and cut a chunk the size of the outside of the LB opening and another the inside, and then glue them together with the grain pattern running at 90 degrees to each other (i.e. one is || and the other = ), it'll be very light and strong. I then use a hole saw to get close and a sanding belt rolled into a cylinder and twisted by hand to bring the hole diameter up to big enough (agree with Drew W that you've got to know how to fix the board prior to hole sawing). It's actually fairly quick to dope out a lensboard this way and it'll get you going until something better comes in the mail.

 

[Alan Edward Klein]

Whether a lens is mounted in the center or off center in the board is driven by the design of the camera. Linhof cameras have focusing tracks stacked one upon the other. This raises the lens by 7 or 8mm. To make the lens centered on the focusing screen. the shutter mounting hole must be lowered by the same distance. Check your camera's front and rear centering and drill the hole accordingly.

To avoid machining a thinner section around the hole use a flange like this one: https://www.photrio.com/forum/threads/fs-lens-flanges.198197/

The rabbet around the lens board mounting perimeter matches the inner frame of the lens panel on the standard and acts like a light trap. It may be better to have it to avoid light leaks.

Kumar

I;ve nought lenses with mounting board so that the lens is lower (not centered) but change it for my Chamonix with a center hole even though I was told it wouldn't matter. That I could use it with the lower lens. Would it have mattered?

 

[Alan Edward Klein]

My Chamonix lens boards are carbon fiber, lined with black velvet on the inside in order to reduce reflection. Has anyone worked with carbon fiber?

Lens Boards — Chamonix View Camera

Continuing to design with the principles of light weight and simple function, Chamonix has developed a carbon fiber lens board, lined with black velvet on the inside in order to reduce reflection. Currently we have Linhof type and Sinar type boards, but we can make any size lens b

www.chamonixviewcamera.com

 

[MTGseattle]

@DREW WILEY I know from some of your other posts that you have a long background in tool sales and likely usage, so I appreciate the points. I am not new to tool usage. If I had a 30x40 steel building, I may not be getting back into photgraphy as much as I would have filled it with tools by now. In my earlier post I said that I keep dedicated blades around for metal. When I say this, we're talking light duty stuff that a typical general contractor and/or cabinet installer may encounter. 1x1 Aluminum "L" and metal closet rod with the occasional Al railing parts. I own a big 14" abrasive saw if things get more serious (I hate the mess associated with them though). To me, the most dangerous thing to do with an angle grinder is to cut flexible stuff. I've had a blade grenade on me before, but I was wearing the appropriate gear.
I've taken a chunk of wood to the gut from the tablesaw before too. It's eye opening and eye watering. We could start a whole new "lounge" thread with tools and use/misuse tales. On one of my first official jobsites, I watched a plumber duct tape 2 A-frame ladders together to get higher.

Aside from Linhof, is there any reason to off-center the shutter hole?

The Chamonix lens boards are really nice.

I'd like to try and make a traditional style board at some point, I've got a random piece of lacewood, some Sapele, some interesting maple. I don't have any cherry on hand to match the camera though.
For me to do any serious work, it needs to be not raining, and I need to setup sawhorse city on our patio.

 

[DREW WILEY]

There are different varieties of carbon fiber, Alan. Some of it's headache to work with compared to aluminum in terms of smooth edges. The thin type used for this kind of project is fairly easy to cut. I prefer working with thin PC board, which has a thin phenolic or fiberglass core sandwiched inside two outer copper layers. It's easy to fabricate with the right blade or scoring device, and stays very flat. It accepts metal primer and paint well. But I personally wanted a cool looking ground glass protective cover for my 8X10, so did a true verdis gris upon copper random swirl effect on it, then sealed over it with acrylic varnish.

MTG - an offset hole can be used to obtain a little more rise to the lens than the front standard would normally allow. But otherwise, I see no sense in having one unless it came free with the lens. All mine are center hole.

What you might be interested in is what I did with maple. I wanted a very solid dual-mounting rail for a big Pentax 300EDIF tele lens, which needs just as much support as my 8X10. Since the tripod involved is my large maple Ries, a real veteran piece of equipment with plenty of battle scars to prove it, after I epoxy laminated a thick piece of maple rail to black Garolite phenolic and installed the stainless thread inserts, I pickled the wood with penetrating epoxy with rust mixed in, to match the weatherbeaten look of the tripod itself. My 8x10 happens to be a Phillips, which was made of custom fiberglass/maple ply treated with marine penetrating epoxy. That has yellowed over time, so I thought it would be fun to cosmetically match everything. Then when it tote that around in a vintage 70's true California-made Kelty external frame pack, I get a lot of compliments.

The only sapele I have on hand is in the form of some Festool Domino mortising tenons. Instead of using these blind, I'll due a through mortise and leave a tenon end exposed, contrasting its deep mahogany color with the blonde maple sheet material itself.

 

[MTGseattle]

OK, we need a picture of that.

 

[DREW WILEY]

Picture of what? Tenons? - well, technically sipo, closely related to sapele, but more machinable, and stronger than mahogany.

 

[mshchem]

Message Zbima1 on Ebay. He makes beautiful wooden lens boards. Very reasonable, he's based in Chicago. Most any wood you want, cuts the hole to fit your lens, finishes the board.

 

[nosmok]

Chiming back in to +1 zbima1 on evilBay. If you want a wooden lens board to match your wooden camera, he's your guy.

 

[Don_ih]

If I have to machine a thinner section around the shutter hole to properly mount the lens (due to mount thread width), I'm not sure how to accomplish that with aluminum and the tools I have at home.

A carbide downspiral cutting bit, put in a drill press, can enlarge a hole. I'd just put a straight double flute cutting bit in a router and do it. Like Jim Jones said above, you can use woodworking tools to machine a piece of aluminum. An extra investment might be needed if you're going to do it repeatedly. Aluminum will clog a circular saw blade quickly. Extra caution needs to be used. You can't aggressively attack aluminum - the cutting has to be done more slowly than with wood.

Plywood is dimensionally stable, assuming you're getting something like Baltic birch and not sheathing plywood. Solid wood, on the other hand, is not dimensionally stable. It will shrink and grow laterally as humidity changes. You could always buy tempered hardboard, which doesn't warp or shrink and is easy to work. Paint it black.

Cutting aluminum on a table saw is a risky venture. Never run the aluminum between the blade and the fence.

 

[Alan Edward Klein]

There are different varieties of carbon fiber, Alan. Some of it's headache to work with compared to aluminum in terms of smooth edges. The thin type used for this kind of project is fairly easy to cut. I prefer working with thin PC board, which has a thin phenolic or fiberglass core sandwiched inside two outer copper layers. It's easy to fabricate with the right blade or scoring device, and stays very flat. It accepts metal primer and paint well. But I personally wanted a cool looking ground glass protective cover for my 8X10, so did a true verdis gris upon copper random swirl effect on it, then sealed over it with acrylic varnish.

MTG - an offset hole can be used to obtain a little more rise to the lens than the front standard would normally allow. But otherwise, I see no sense in having one unless it came free with the lens. All mine are center hole.

What you might be interested in is what I did with maple. I wanted a very solid dual-mounting rail for a big Pentax 300EDIF tele lens, which needs just as much support as my 8X10. Since the tripod involved is my large maple Ries, a real veteran piece of equipment with plenty of battle scars to prove it, after I epoxy laminated a thick piece of maple rail to black Garolite phenolic and installed the stainless thread inserts, I pickled the wood with penetrating epoxy with rust mixed in, to match the weatherbeaten look of the tripod itself. My 8x10 happens to be a Phillips, which was made of custom fiberglass/maple ply treated with marine penetrating epoxy. That has yellowed over time, so I thought it would be fun to cosmetically match everything. Then when it tote that around in a vintage 70's true California-made Kelty external frame pack, I get a lot of compliments.

The only sapele I have on hand is in the form of some Festool Domino mortising tenons. Instead of using these blind, I'll due a through mortise and leave a tenon end exposed, contrasting its deep mahogany color with the blonde maple sheet material itself.

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.

 

[Don_ih]

If the camera would normally use a centred board, having the lens off centre toward the top is like having front rise built into the camera, which could just be for convenience for architecture photography. Yes, it would limit the amount of tilt, since the image circle at the focal plane would be centred higher on the ground glass.

 

[Alan Edward Klein]

If the camera would normally use a centred board, having the lens off centre toward the top is like having front rise built into the camera, which could just be for convenience for architecture photography. Yes, it would limit the amount of tilt, since the image circle at the focal plane would be centred higher on the ground glass.

I didn't realize the implications at the time when I replaced the off centered boards with center openings. But I figured I didn't want to have different types as it might create confusion as I switch from one lens to another. And I'm confused enough with LF photography.

 

[DREW WILEY]

Oh gosh, Don. Would I really want to use a solid carbide down spiral bit in a slow drill press just for a lenboard hole? The damn things are a hundred bucks apiece, and I already chewed up one on a big teak countertop project; but at least there I factored the cost in. For about 30 years we were the biggest Freud carbide bits n' blades dealer in the entire US. And our own shop used even higher quality carbide. Freud is now owned by Bosch; but all along, these larger solid carbide bits were made by a US specialty supplier, Velepec. Love em for hardwood and phenolic applications. And tough as they are, try to pamper em, keep em clean from resin buildup etc. But gosh, some of the hardwoods I've worked with are like rock, high-silica - Ipe, teak, purpleheart, new hybrid varieties which sink in water. Even with my massive discount back then, the carbide cost added up. And ya sure had to avoid the dust and wear gloves; some of those tropical wood oils could be nasty, but my gosh, beautiful too when finished!

Even fin plys are tricky to keep dead flat. I don't have much left anymore in my own shop, and it's a very expensive time to buy, given the short supply. Just like counter-mounting a big picture job using wet glue, so that it won't differentially bend, there is a distinct technique to impregnating ply with penetrating marine epoxy to prevent warpage even in the process itself. But that's nasty stuff, so just using a fast-drying hybrid water-cleanup wood floor finish makes more sense in the short run. In the long run, only metal lensboards make sense to me.

 

[Don_ih]

Plywood flatness is an issue, but not with a lens board that probably will not exceed 8x8 inches. Even the cheaper "Russian" plywood (knock-off baltic birch) will be ok at that size, even with the potential thickness irregularities (one more or one less ply in random locations).

I only suggested the down spiral bit as a sure-fire safe way to get a clean cut. The key would to not be agressive. And aluminum is typically not as hard on carbide as hardwood - definitely not as hard on carbide as sapele is (sand in its grain). I have a mirror frame I made from sapele - that's nasty wood to cut.

 

[DREW WILEY]

The flattest ply I have ever seen was actually Chinese, with extremely thin layers, but hideous red glue than edge-burned; so you have to cap the edges on any cabinet doors etc. What people would most likely use for a lensboard would be hobby plys, though these too differ in quality, depending on source. Russia is (was? - now interdicted) where most ply maple comes from; but the plywood manufacture itself is in China, and in metric thickness.

Carbide - yet again, the rake angle for a nonferrous metal milling machine or router table bit is going to differ from one intended for hardwoods, and the actual carbide itself be somewhat different. What helps extend carbide life when shaping oily dense tropical hardwoods are spray-on teflon coatings, as well as a religious soak of the bit in solvent between jobs. But I miss the lack of some of the especially high quality Austrian and German woodworking carbide which was once briefly available here (Freud is made in Italy;
and Amana is qualitatively equivalent). I'm sure you know a lot of this already, Don, and am just stating it for sake of the thread in general.

But other than picture framing mouldings and some upcoming personal and kitchen bath remodeling, I don't have any place to put completed furniture projects, and only once in awhile do some minor cabinet-shop or restoration task for sake of quick cash. I don't live in a fancy craftsman house like Sam Maloof. His assistants were my equipment customers not so long ago; and I formerly owned a large craftsman-style house, but it wasn't realistic to hold onto that extra maintenance burden going into retirement. Now we basically run a cat hotel, though they're the ones in charge (not welcome in the darkroom, however).

 

[MTGseattle]

Aluminum is out for me currently. I went and bought a couple of items today, and it's still sketchy. I would have felt safer drilling the hole with a hand drill while standing on the aluminum.

That ebay seller mentioned above is who I would source from as well. I'm simply being silly and trying to use up some random materials I have lying around. I also enjoy tinkering.

I also happened to have some scrap from Tap plastics (black acrylic or plexi or something like that) that is the same thickness as the aluminum plate. I've got 2 flat boards cut and drilled, and I'm waiting on adhesives to cure on version 3.0 for myself which is still plastic (of unknown type) but will be 2 layers and look a bit more like a traditional wood board.

@DREW WILEY a picture of the copper ground glass protector you mentioned.

 

[Don_ih]

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.