Large Format Adapter for Your Mirrorless Camera




About: I'm an Electrical and Computer Engineering Professor at the University of Kentucky. I'm probably best known for things I've done involving Linux PC cluster supercomputing; I built the world's first back in ...

Modern digital cameras are impressively small, but sometimes big is beautiful. Large format film cameras, most often designed to accept 4"x5" cut sheet film, have a certain charm. It isn't just because the big film is cool, but also because of features like very flexible tilt and shift. Features that ought to be able to work with your mirrorless camera body....

This instructable is about building your own adapter to mount your mirrorless camera in place of film.

This isn't the first digital sensor mount I've made for a large-format camera; in I describe how I packaged the sensor from a cheap webcam so it could be used in place of a 4x5 film holder. It was way back in the late 1970s that I built a back to mount my Minolta SRT101 film SLR on the very same 4x5 camera. In fact, on eBay for between $150 and $200, there are now various sellers offering similar backs with the additional feature that you can slide your DSLR horizontally in order to create stitched panoramas. They don't seem to come with mounts for mirrorless cameras, but you can always just stick an adapter on the DSLR mount to convert it to your mirrorless mount. Sounds pretty good, right? So why build your own?

Well, first off, the unit described in this instructable costs more like $10 to build. No, the digital camera can't slide for panoramas -- but that's ok, because most large format cameras allow the lens and/or the entire back to do that, giving exactly the same functionality! In fact, the lens can shift in both the horizontal and vertical directions, giving better functionality. However, the primary motivation is more subtle and more important: the mounts of necessity force a DSLR to be quite far behind the original film plane (unless you can push your DSLR partly inside the open back of the camera, as in, making it impossible to reach infinity focus with some lenses. The shorter flange distance on mirrorless cameras, combined with the lack of front-facing protrusions, allows them to come much closer to aligning with the intended film plane of the large format camera... so infinity focus is much more likely to be feasible and lens tilt and shift features are less likely to be impeded by mechanical obstructions.

Step 1: Stuff You'll Need

There are lots of options for parts, materials, and tools in this project. Read the whole instructable through to make sure you have everything you need before you get started making. Here's a rough list of stuff you'll need:
  • A mirrorless camera (which should not be harmed by any of this)
  • A large-format camera (which should not be harmed by any of this)
  • A cheap extension tube set -- the kind with front, back, and three screw-threaded in-between segments
  • Any tools required for removing the large-format back (typically a screwdriver)
  • Material for the board; probably either scant board or plywood
  • A saw 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
  • Glue for setting the extension tube in the board hole
  • Electrical tape or other light-sealing material (e.g., black paint)
  • Thin metal/plastic and craft foam to make flat springs to hold the back in place

There is a good chance you have pretty much all the above -- except the 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.

Step 2: Back Where It Belongs

Although large format backs are partially standardized, they do differ somewhat. In any case, your mirrorless camera is probably not thin enough to fit where a 4x5 cut film holder would go. You're probably going to have to take the spring clamp and ground glass assembly off.

I think my 4x5 B&J is fairly typical. The spring clips -- and everything -- is held on by just two screws: one above and one below. Removing those screws exposes the metal bed upon which a cut film holder would be held. That bed defines the size and shape of the board we'll have to cut for our new back.

Measure the bed and cut a rectangular piece of material to fit. The easiest materials are either plywood or scant board. I used scant board because I like how it looks and I had some scrap that had been sitting for years. Beware using "new" scant board; plywood is more more dimensionally stable unless the scant board is well dried, and it is easier to find plywood in various thicknesses.

Step 3: There's a Hole

After cutting the board, sand it lightly and wipe-off the dust... you don't need that getting all over the inside of your camera! Now it's time to mark and cut the hole for the extension tube that you'll be using to mount your camera.

Take the board and hold it in place on the back. Open the front of your camera and remove the lensboard. Reach in and mark the corners of the film opening on your board.

Take the board out and flip it over to the side with the corner marks. We're going to use those marks to find the center of the lens -- which is also what you want to be the center of your extension tube. Use a straight edge to draw lines connecting opposite corners. Where the lines intersect is the center of the lens. Note that it probably isn't the center of your board because one side of the bed is open, and your board probably extends further past the imaging area on that side.

Now you're ready to drill that hole... but read the next step for that.

Step 4: Holey Precision, Batman!

Ok, that's a really dumb title for this step. Sorry.

The problem is that hole needs to be very precise in order to hold the extension tube, and your mirrorless camera body, in place. Drilling a hole with a very precise diameter is easy if you have a drill bit that size, but trust me -- you don't. The good folks in China who make those extension tubes don't want to waste any material, so the extension tubes are made precisely the diameter that's cheapest to fit to that particular lens mount, which is generally some random diameter in mm.

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 the portion of the extension tube that will go inside it, but a little play is ok.

I used a drill press to drill the hole centered in the position marked in the previous step, 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: Paint

If you're ever gonna paint this, now's the time.

I like natural wood finishes, so I gave the outside and edges two coats of clear, semi-gloss, polyurethane.

After that dried, I gave the inside two coats of flat black latex enamel. Shiny light wood isn't good in the light path.

Step 6: Which Way Is Up?

The cheap extension tubes use a screw thread... which is fine, except for the fact that the rotational position at which the thread stops is not consistent from one tube to another.

For most lenses, it really doesn't matter if the lens is sitting a bit rotated on the camera. It just makes it harder to read the distance scale on the lens. However, if the thread doesn't stop in the "up" position for your mount here, the mirrorless camera will be tilted when the large-format camera it is riding on is level on a tripod. That's not ok.

Put the tubes you're going to use together and place a bit of masking tape inside to mark where the top should be when the tubes are mounted on your mirrorless camera.

Step 7: Glue, Baby, Glue!

Now that the tube has been marked with which way is up, the issue is simply how to connect it to the board. The trick here is that you need high precision in connecting it perpendicular to the film plane, not tilted. Here's how I did it.

Take a piece of aluminum foil and place the board on top of it on a flat table.

Take whatever glue you're going to use and line the inside of the hole with it. I used a hot glue gun, which works very well, but requires that you work very quickly before the glue sets. Gorilla glue would be a potentially better choice, but you would need to clamp the board and the tube firmly for the complete drying time.

Orient the tube so that the alignment mark you made in the previous step is at the top. While pressing the board flat black side down, push the extension tube into the hole and flat against the aluminum foil on the table. This will ensure that the mount is perpendicular to the film plane as the glue sets.

After the glue has dried, simply peel-off the aluminum foil that stuck to the excess glue.

Step 8: Yet Another Inappropriate Use of Electrical Tape

Remember how we were saying precision of that hole was an issue? The way the glue was used, the extension tube should be solidly fixed in the right position, but there are probably minor light leaks around it unless you were more precise than I was.

Little pieces of black electrical tape over the seam ensure a good light seal no matter how sloppy the hole fit was. Actually, after using electrical tape, I realized that the precision of my cut was high enough that I could just fill the minor gaps with a little flat black paint. Just do anything that will work; I could even see packing a little wood filler into the gaps if they were really big... or perhaps just lay a bit more glue over the seam if your glue isn't translucent like standard hot glue.

Step 9: Spring Clamps?

Well, the real back is attached via two screws and two flat steel springs... we need something like that.

Not having any flat springs, I faked it. I used two pieces of plastic (separators for a little parts cabinet). These do not flex like metal springs, but were easy to drill holes in. Screwed-into the holes on the back, they overhang just above the board we just made. I used a little piece of craft foam glued to these to serve as the spring. I'm not sure it will hold-up well, but it appears to work very well.

Ah, but shortly after posting this Instructable I found a better answer than the clear plastic parts: use a sample piece of countertop laminate! Free samples are available in many colors and textures, and this material is stiffer than the clear plastic and machines very nicely -- provided you put masking tape over it to prevent chipping when cutting. The laminate is still backed by a little piece of craft foam to serve as the spring. The extra photos added to this step should make it obvious....

Step 10: Conclusions (and Future Work?)

Not only does the NEX-5 have a very short flange-to-sensor distance, but the grip doesn't stick-out too far in the front. So, this means that it's pretty easy to focus close-up or all the way to infinity even with a relatively short-back-focus lens -- like the 127mm Kodak Ektar that I usually have on my B&J 4x5 press view. Compared to use of the ground glass for composition, the NEX-5's tilting LCD with focus peaking is an absolute joy to use... although this isn't a system to use for grabbing quick snapshots....

In case you've been wondering how you use the shutters built-into these large-format cameras and lenses, the answer is you don't. There is generally a "T" exposure setting which locks the shutter open until the shutter is triggered a second time. Simply set the shutter on "T", fire it, and use the shutter in your mirrorless camera for the actual exposures. There is generally no harm in leaving the shutter open in "T" for extended periods of time -- that's how you would have set it while composing images on the ground glass.

One more operating note: without electronics in the lens, mirrorless cameras will not even know you have a lens attached. Many will not allow you to fire the shutter without a lens attached unless you set some option buried deep inside the menus on your camera. You've been warned. Obviously, you don't get autofocus or electronic control of the aperture of the lens mounted on the large-format camera, so you'll generally be stuck with M or A mode (manual or aperture-priority auto exposure).

Take a look at the images here. The first two were shot with the 127mm, the third with a 19in, and the fourth is a crop from the third. I know Instructables doesn't allow very high image quality, but they look good, right? It may surprise you that the resolution per mm of lenses for large format cameras is virtually identical to that of lenses for 35mm cameras: usually about 50 line pairs per mm. That's partly because these lenses span a relatively narrow focal length range in which very simple designs perform quite well. In any case, resolution is unlikely to be a problem. Contrast is another issue; even coated large-format optics tend to be rather low in contrast, although that is easily corrected in digital post processing.

It is also worth noting that you can use the other end of the extension tube set to make a lensboard that has the mirrorless mount on it (e.g., E-mount) so you can use any of those lenses on the large-format camera. They will not focus to infinity, but they will focus very close and still be able to use the tilt and shift features of your large format camera -- these lenses might even cover 4x5 film or larger in the macro focus range. You'd build a lensboard for mounting smaller-format lenses pretty much the same way we built this back! Simply use the other end of the extension tube set with the #1 section. The lensboard usually needs to be thinner, and typically is held by something other than spring clamps, but it is otherwise the same construction. Not clear? Well, I've done an Instructable on that now too:


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    25 Discussions

    Thanks. Only one tube (the #2) is permanently attached. The body-end tube is screwed-into the fixed tube for use. The NEX body then bayonet mounts on/off as if the 4x5 were an ordinary, if rather large, E-mount lens. ;)

    For really long lenses and/or high-magnification macros, you can even push the NEX further back by simply screwing more tubes between the fixed tube and the body-end tube. I actually had to do that to get infinity focus on the Goerz lens, which has a back focus longer than the bellows. Of course, the "tunnel" created by extra tubes limits how much you can shift the lens before vignetting.


    Reply 4 years ago on Introduction

    Great project - am just getting into large format in order to perfect some still life shots that need to use camera movements - you can get some great very good value 5 x 4's on ebay but the issue is digital backs that start at $10,000 for 22mp. Did you get anywhere with your lower cost digital back? I find it hard to understand how Canon can produce a mirror-less 18mp camera for $300 when the nearest medium format back is so expensive. If you could produce an affordable digital back sure there would be a big market for it - I would be first in the que! - let me know if you are still working on the project?


    5 years ago on Introduction

    Hi, We may be distant cousins, (I'm a Dietz from a line in the central New York area immigrated Germany from the 1690's). Anyway, to my question, I have a Busch Pressman "D" that's back doesn't come off easily, but it stretches wide enough for a grafmatic, I was thinking about mounting the first section (#2) of the extension tubes to the center of a film sheet holder, Taking the center piece and the glass off is easy, perhaps I could slip the first part of my film holder device under the spring back, screw the second section in when I've slide the film holder in and then mount the camera. What do you think, I'm thinking it should work, especially if I replace the center piece with a thin piece of wood or metal. I'd like to know what you think. Thanks Thomas

    1 reply

    Reply 5 years ago on Introduction

    I didn't notice your comment until now (had a major research exhibit at the IEEE/ACM Supercomputing conference last month).... Good chance we are related; my family is from NY.

    Anyway, it's unfortunate the back doesn't come off your Pressman, but using the back to hold your mount as you describe sounds reasonable. If I understand you, with the glass removed there is still structure there that would hold the mount in place under the spring back, and having the extension tubes screw-in through the back sounds fine. I wouldn't use a real sheet film holder -- it's easy enough to make a dummy, and you might even be able to put a plate on it to align it with the hole where the glass would have been, thus making it a little thicker and very stable. I wouldn't do anything that isn't reversible to the Pressman.

    I've 3D printed a lot of camera parts lately (including lens mounts) on a MakerGear M2, and it's quite easy to print a sheet film holder shape with the appropriate mount rather than attaching an extension tube. I did this to make a shiftable back for E-mount to a "little" B&J Watson. I even made the retaining springs as an integrated part of the 3D print. You could certainly do something like that. The catch is that now I can literally 3D print a custom lens mount with tilt, shift, and focus so there isn't much advantage to using the large-format frame. I've been busy with other things, but will eventually get around to posting all the 3D-printed camera parts on Thingiverse if not here. I have a few camera parts up at Thingiverse, but nothing posted yet for large format cameras.


    6 years ago on Introduction

    This is a great idea indeed.
    However, a large format camera has, well, a large film/sensor to capture images.

    At best, a compact mirrorless camera will have an APS-C size sensor, which will be 0.8625" wide. This means a x5.8 ratio as comparing sensors.

    The whole point of medium and large format cameras is exactly working with a much bigger sensor size, which will produce much better image quality.

    I don't mean to be offensive at all... maybe I'm missing something?

    9 replies

    Reply 6 years ago on Introduction

    In my research, I'm working on a new technology aimed at producing a cheap 4x5 sensor with at least 500MP. The claim has been made that existing large-format lenses cannot resolve sufficiently well for that to make sense. However, the NEX-5 happens to have the same pixel size, so I now have proof that there are large-format lenses up to the task.

    I have many goodies I can put in front of my NEX cameras: over 100 lenses, a tilt adapter, bellows, etc. The tilt/shift abilities of my old 4x5, plus the huge extension of the bellows, can do things none of my other equipment can. Also, the "look" of the large-format lens images is surprisingly different and desirable.

    Of course, it'll be more impressive with a 500MP 4x5 sensor. ;)


    Reply 6 years ago on Introduction

    500MP... and half of the storage and computing power available at University to store/process the images! :)

    Again, it's a great idea :)


    Reply 6 years ago on Introduction

    Did I mention I'm a parallel supercomputing guy? Here are the toys in my primary machine room:

    I guess it would be too scary for me to mention that I want the sensor to be capable of high-speed video at 500MP.... :)


    Reply 6 years ago on Introduction

    Impressive lab...

    Now... 500Mp at 60fps (not very high speed anyway) would mean 90GBPS transfer speed...

    Not meaning to sound pedantic, but... I don't know of any storage capable of registering 90Gb is a second... not too sure about any suitable size electronics capable of such transfers... I might be behind the times now though.


    Reply 6 years ago on Introduction

    Actually, my research is targeting at least 1000FPS -- equivalent to 1TB/s of raw data, but processed using a massively-parallel nanocontroller array. This is neither the time nor place to discuss details of this research....


    Reply 6 years ago on Introduction

    Ahh, but Prof, you've given us such a fine teaser with the bandwidth goal statement!

    I'll be looking forward to future announcements in that area.  :)

    Thanks for this very interesting instructable, it's got my mental gears turning.


    Reply 6 years ago on Introduction

    I been looking how to do this;

    I had a long message but the instructables robot said my session expired. so I lost everything.


    Reply 6 years ago on Introduction

    I think the idea is that the digital camera samples a small portion of the field of the large format image. This eliminates/minimizes errors like distortion, intensity falloff towards the edges that one would get with the camera's own lens system. The example photos at the end should convince one of it superior quality.


    6 years ago on Introduction

    I just added a better way to make the springs that hold the back in place: using a free laminate sample chip. It's stronger and prettier. I've added photos and text explaining this to Step 9.