Large-format cameras typically allow lenses to be interchanged by mounting each lens on a lensboard. If you have a lot of lenses, you need a lot of lensboards.... Beyond that, if you want to mount any of multiple lenses that have the same screw or bayonet mount, you shouldn't need a lensboard for each -- why not have just one lensboard with the appropriate mounting flange for your lenses?
This Instructable shows how to build your own high-quality wooden lensboards. We'll show a simpler construction that works for some large-format lenses, the standard construction, and a variant of the standard that provides an interchangeable mount accepting any of a wide range of lenses -- without the need to swap lensboards.
This instructable is the logical inverse of https://www.instructables.com/id/Large-Format-Adapter-For-Your-Mirrorless-Camera/ . There, a back was created to allow a mirrorless body to replace the film in a large-format camera. Here, you'll learn how to build a front lensboard, including a special type that allows any lens that could mount on a mirrorless body to mount on your large-format body. Why do this? Well, lenses designed for smaller formats will not cover a large format at infinity, but this adapter will allow you to use them as tilt/shift macro lenses -- and many will cover 4x5 at macro focus.
Step 1: Stuff You'll Need
The next thing you need is an understanding of which of the three types of lensboard is appropriate for the lens(es) you want to use. The photo shows examples of all three types: barrel lens with mounting flange, barrel or shutter mount with rear locking ring, and generic (E-mount) bayonet flange. This is roughly in order of increasing build difficulty, although none is all that hard to make. Step 3 only applies to thick lensboards that must have thin edges. Each of Steps 6-8 is specific to one of the three types of lensboard shown in the photo here.
So, what else will you need? Read the complete Instructable before building anything, but here's a rough list:
- Material for the board; probably scant board (you can get various nicer woods for a few dollars via the Internet)
- A saw, etc., and sandpaper to cut and finish the board to size
- An adjustable hole saw or other device that can make a hole in the board
- Paint and brush or other finishing materials
- A cheap extension tube set -- the kind with front, back, and three screw-threaded in-between segments
- Glue for setting the extension tube in the board hole
Step 2: Cut and Mark the Board
Like it says... cut and mark the board.
For this step, it doesn't matter what thickness the board material is. Simply measure the outside dimensions of your reference lensboard and cut the wood to match. Note that a 4"x4" board is not actually 4"x4", but slightly smaller. It is probably a good idea to wipe the sawdust off and test-fit the board on your camera; nibble a little material off if the size is too large.
Once you've cut the board to size, you can mark the center by finding the intersection of lines linking opposite corners.
Step 3: Route the Edges (for Thick Lensboards Only)
A thicker lensboard is generally stronger, but the lensboard is commonly held by relatively thin edges. Thus, if you're using a relatively thick lensboard, you'll need to shave-down the thickness of the edges.
The right way to do this is using a milling machine, router table, or even nibbling using a table saw. It took a few adjustment tests, but cutting the edge thickness down is quite quick and easy with an appropriate tool. Note that this is the surface that will determine how the lens points, so precision is critical.
If you need a thicker lensboard and cannot figure-out how to do the cuts to make precise thin edges, simply buy wood that is edge thickness. Cut pieces with different dimensions for two pieces: the top and bottom of the lensboard. These are then glued with carpenter's glue and clamped to dry. In fact, the glued-up board might even be stronger and more dimensionally stable than a one-piece board because you can glue with the grain of the two pieces crossed.
Step 4: Make the Mounting Hole
The lensboard needs a mounting hole which is accurately centered and has the appropriate diameter.
If you've got a lathe or a CNC milling machine, feel free to use it now. For the rest of us, it's time to find that adjustable hole cutter you bought when you had to replace the lock set on some door. The cheap hole cutters aren't easy to set very precisely, so I used a few iterations of trial and error to adjust mine testing with a piece of scrap wood. If you have a scroll saw, or even a hand jig saw, you could probably cut the hole with that. You want it to be a firm fit around whatever will be going through the lensboard, but a little play is ok.
I used a drill press to drill the hole centered in the position previously marked, but you can do this with any drill. Just be careful to drill straight down into the wood, Also, don't drill all the way through from one side; drill halfway and then flip the board and drill the rest from the other side, using the center hole as a guide. This will prevent chipping at the edge.
Step 5: Sand and Paint
Lensboards need to be as dimensionally-stable as possible, so leaving the wood unsealed isn't a good idea -- variations in humidity could easily cause the thin areas to warp. You also want the inside to be as non-reflective as possible; black paint or a dark stain will help reduce internal reflections.
Lightly sand the board, especially the thin areas. This is your last chance to improve their flatness....
I like natural wood finishes, so I usually give the outside and edges two coats of clear, semi-gloss, polyurethane. You could really make this any color or pattern: stain it purple, paint a face on it to help your subject smile, etc.
After that dries, I give the inside two coats of flat black latex enamel. The black goes on second because if the wood edges are not sealed first, the black paint can soak into the wood enough to to unevenly tint the edges under the clear coat. Of course, it is perfectly fine to just paint the whole thing flat black or clear-coat over a dark stain.
Step 6: For a Barrel Lens With a Mounting Flange...
Barrel lenses (lenses without shutters) often come with screw-threaded mounting flanges. If that's what you've got, here's what you do....
Barrel lenses with mounting flanges are usually intended for copying flat artwork. The film sizes are often huge, so the coverage, focal length, and weight of the lens all tend to be bigger than usual. This makes solid mounting critical.
The mounting flange typically needs to be screwed-into the lensboard. This is no problem for large lensboards, common on 8x10 and larger format cameras, but 4x5 and smaller often use lensboards that can barely fit the flange for a large lens. The example shown here fit my B&J 4x5, but the screws securing the mounting flange had to point the wrong way, and the lensboard had to be thin, in order for the screws to clear the felt masking in the camera. That's ok: the brass flange is so strong there's no lack of rigidity despite the thin lensboard. Actually, I made this lensboard back in the 1970s out of mahogany which I painted black, and it continues to be perfectly solid despite the rather heavy load it has to bear.
It should be obvious that the paths for the screws to hold the flange need to be drilled (except for very thick lensboards, such as the 3/4" thick one shown here). SImply mark where they need to be by holding the flange in the right place. Most of this type of lens don't have any functionality issues with being mounted in a random rotational orientation, but if there is rectangular masking in the barrel, you need to orient the lens appropriately to avoid potential vignetting. To get the right side up for the lens, you'll need to screw the lens into the flange so that you can find and mark the spot on the flange that should be at the top of the lensboard.
Step 7: For a Lens With a Locking Ring...
Most large-format lenses are designed to have a leaf shutter mechanism installed between the front and rear elements. For such lenses, it is common that the mount is simply a sandwich of the shutter assembly in the front, the lensboard, and the the locking/retaining ring behind. This type of "clamping" attachment method also is used by some barrel lenses -- especially those intended to be used on enlargers.
The key question with such a lens is where does the locking ring go? The locking ring is supposed to clamp against the back side of the lensboard, but that implies that the hole must be sized big enough to let the optical path pass through, yet small enough for the ring to clamp against. It also implies that the thickness of the lensboard is neither too thick nor too thin.
A too-thick lensboard isn't usable -- the retaining ring cannot be threaded, so there's nothing to keep the lens from falling out the front. A too-thin lensboard would naturally leave the shutter and lens assembly loose. However, thickness can be added by simply placing a washer under the retaining ring. A washer made out of neoprene, craft foam, or a similar material can even help in reducing shutter-induced vibration, and one can be cut from readily-available materials.
Step 8: For a "Universal" Lens Mounting Flange...
Suppose what you really want to mount is any old lens from your smaller-format film cameras? Well, this is what mirrorless cameras like the Sony NEX line really shine at. There are cheap E-mount adapters accepting lenses in mounts including Adaptall, C, Canon EOS, Canon FL/FD/FDn, Contax/Yashica, Exakta, Konica AR, Leica L39/M42, Leica M, Leica R, Micro 4/3, Minolta SR/MC/MD, Minolta AF/Sony A, Nikon F/AI/G, Olympus OM, Pentacon Six, Pentax K, and T/T2.
Your large-format camera will not come close to infinity focus with those lenses. Very few would cover 4x5 even if you did manage to get infinity focus. Still, perhaps they'd be nice, fast, macro lenses? Instead of mounting a lens, you can mount a flange that can take adapters for every type of lens you care about!
If all you've got is Nikon glass, feel free to put an F flange on your lensboard, but Olympus/Panasonic micro 4/3 and Sony E-mount have the nice property that there are cheap, glassless, adapters for nearly every lens mount ever made. Adapters for nearly every lens mount are cheap -- often below $10. Ironically, you'll probably never use a native micro 4/3 or E-mount lens on this because native lenses in those mounts require electronic control that this flange will not have.
So, where does one get an E-mount flange? You buy a cheap extension tube set. You can get that on eBay for less than $7 shipped. They're made in China, but you can get them shipped from within the US for about $0.50 more.
First, screw the E-mount lens flange into the #1 segment of the extension tube and determine the rotational position in which the flange must appear in order to have lenses mount right side up. There are many lenses that have rectangular masking in them, so getting this alignment is not just a convenience feature.
The #1 tube is very thin, so not much will stick-out in front if we make the back of the adapter flush with the back of the cabinet. Tack it in position using a hot glue gun.
Now fill-in the glue in the back. I used hot glue for this too, but Gorilla glue is probably a better choice -- if you clamp it so the expanding glue cannot shift the positioning. To ensure the seal would be light-tight, I alternated layers of glue and black paint.
For use, you have to screw the lens flange section of the extension tubes into the permanently-mounted #1 section, but you can still use the flange for other things when you're not using the lensboard. Note also that the extension tube parts used in this Instructable are not the ones used in the https://www.instructables.com/id/Large-Format-Adapter-For-Your-Mirrorless-Camera/ Instructable -- the parts for both can come from the same extension tube set!
Step 9: So, Do These Lensboards Work?
Yes, they do work!
All three types work at least as well as a factory-built wooden lensboard. However, custom building your own lensboard allows you to mount many lenses that a standard lensboard would have trouble with. The third type of custom lensboard is especially unusual in that it provides a bayonet mount permitting lenses to be changed without changing the lensboard. Unfortunately, the third type only works for macros, but it still allows tilt/shift and can take advantage of the longer bellows to get higher magnifications.
As mentioned at the outset, this instructable is the logical inverse of https://www.instructables.com/id/Large-Format-Adapter-For-Your-Mirrorless-Camera/ , in which a back was created to allow a mirrorless body to replace the film in a large-format camera. It is worth noting that, although you can use these lensboards for exposing large-format film, they also work well with a mirrorless camera stuck on the back of the large-format camera. Mix and match. The macro photo shown here is an example of what a NEX-5 on the back of my 4x5 can do with an old 35mm SLR lens mounted in the E-mount lensboard... and the flower was shot with a NEX-7 and a 4x5 enlarger lens.