Over the years, through my journey as a photographer, I have come to appreciate the idiosyncrasies of different optical systems. Sometimes, it's not always the sharpest lens or the most expensive camera that takes the best photo, especially since everyone has their own notion of what 'the best' actually is. Someone once said that the best camera is the one you have at hand. That means that so long as I'm carrying it, any camera can be the best! So, I can feel free to do all sorts of stuff with 10-year-old digital cameras and 70+year-old lenses that haven't been touched in ages.

8mm Film and the D-Mount Lens

In the previous century, film photography and videography really came into their own, spawning several standardized film formats and lens mounts. Some of these mounts were shared across multiple manufacturers, seeing wide-spread use for many years, one of which was the D-mount. Primarily used in 8mm-format and Super8-format film movie cameras, D-mount lenses were once prevalent on the market, sold by a wide variety of manufacturers.

The lenses were relatively easy to produce and simple to design around. The mount system was a simple 5/8ths-inch diameter threaded hole with 32 threads per inch, much easier to make than a locking bayonet-style mount. There was no aperture or focus linkage between camera and lens, which also reduced mechanical complexity. For these reasons, I was attracted to the idea of adapting these antique optics onto a modern camera for a vintage effect and to appreciate what came before me. However, I didn't learn about these lenses until just a few years ago.

A Minor Discovery (for me)

I first discovered the D-mount while I was perusing a local film camera repair shop, and I stumbled across what I thought to be the cutest little lens. Nestled away, ignored, in the back of a plastic storage bin, was a little red clam-shell box. Opening it revealed a velvet-lined cushion with a specially molded indentation, cradling a well-loved cinema lens engraved with the text "WOLLENSAK-REVERE 12½mm 𝑓3.5 VELOSTIGMAT".

It was love at first sight and I had to have the Velostigmat. Luckily, the shop owner, one of my favorite people, wasn't charging an arm and a leg for it since it was for a long-defunct camera ecosystem rarely used anymore. It went home with me that day, and that is how I was first introduced to the D-mount and the world of antique cinema lenses.

I originally bought the Velostigmat just to have a piece of photography's history, and to support a local small business owner. I knew after some precursory research that the little D-mount lens would never be of much use adapted to my daily-driver at the time, a Nikon D3500. Nikon's F-mount system is simply incompatible with D-mount lenses; the flange focal distance is too great.

Adapting Lenses and Mount Systems

While, at a glance, it may seem simple enough to take a lens designed for one system and mount it on a camera designed for another by means of an adaptor ring, optics make it a little more difficult than just changing what the mating surfaces look like to match one another. The primary consideration is flange focal distance (FFD). This is basically how far away the camera body holds its lenses from the imaging plane (either film, or an electronic image sensor). Essentially, if the FFD of the camera mount system is greater than that of the lens you wish to use then you will never be able to achieve focus at infinity with that combination of camera and lens, alone. Sometimes, when the FFDs are similar enough, like with Nikon F-mount and the Olympus OM-mount, you can find adaptor rings that contain an extra optical element to correct for the disparity, similar to the way prescription glasses allow myopic individuals to see things that are far away. This is not the case for D-mount.

Lens Mount Compatibility

The D-mount flange focal distance is so much shorter than Nikon F-mount's FFD that many D-mount lenses are unable to render an image at all; the subject would not be in focus even if it were so close to the lens that it was touching the front element. While I love Nikon, their F-mount ecosystem is not good for adapting lenses from other camera systems as the F-mount has one of the largest FFDs of any other mount, excluding medium- and large-format film systems. This seriously inhibits cross-compatibility which may or may not have been an intentional design decision way back when Nikon first conceived the F-mount. Besides, optical mount adaptors add distortion so, no matter how good the lens is, it will be handicapped by whatever additional element you're placing between it and the image plane.

If I ever wanted to get images out of the Velostigmat, I would need a different camera.

The Samsung NXmini

If you just need a camera with a FFD shorter than the lens you're trying to adapt, why not just buy a camera with the shortest FFD there is? That camera turns out to be the Samsung NXmini, a camera released over 10 years ago at the time of writing, of which there was only ever one model released. The NXmini was a slimmed-down version of Samsung's already-established NX series of interchangeable-lens mirrorless pocket cameras. The appeal was an even thinner profile with smaller optics at the cost of a 1-inch sensor instead of an APS-C sensor and some other alterations. It came in black and white variants. All that mattered to me was its miniscule 6.95mm FFD.

Even in 2024, it still remains uncontested as the thinnest mount system, even if that system is small and has died out already. Neither the cameras nor the lenses are still in manufacture, but second-hand units may be attained relatively easily on eBay or wherever else used cameras are sold. While many of the online and wireless features are now defunct, the camera still does a great job at being a camera and taking pictures.

My Custom D-Mount Adaptors

Despite the ease with which D-mount lenses can be adapted to the Samsung NXmini, I suspect that the low manufacturing volume of the camera and an even lower demand for niche adaptors resulted in a commercial product being impossible to find. It isn't that no one is adapting D-mount lenses; adaptor rings for Pentax Q-mount, Fuji X-mount, and others are readily available today. There are even records that show that a D-mount to NXmini-mount (D-NXm) adaptor was once commercially available, though now I find them impossible to track down. Having bought the camera before finding an adaptor ring, I was left with no other choice but to design my own.

I am not new to 3D printing and so set out fairly confident in my ability to reproduce a lens mount adaptor. With nothing but a pair of calipers, some CAD software, a 12-year-old 3D printer, and the Wikipedia article on lens mounts, I was able to fashion almost exactly what I needed. The part came out with a FFD that was slightly too long, and it required quite a bit of sanding to achieve the proper infinity focus I was striving for. But after that, it worked!

I am most satisfied that I was able to accurately reproduce the bayonet mount geometry of the NXmini on my first try which, as I mentioned before, is non-trivial. Measure 10 times, print once. I chalked the FFD discrepancy up to printer accuracy, though it was fortunate the model came out too thick instead of too thin, which would have required shimming. By this point I had already started collecting other D-mount lenses. The lens on the adaptor in the photos above is my "BAUSCH & LOMB 12.7mm 𝑓/2.8 ANIMAR" lens, which I acquired from the same local camera shop as the Velostigmat. The following photos were taken with the above camera, adaptor, and lens combination:

I was pleasantly surprised by the sharpness of these old D-mount cinema lenses, but then of course they would have to be sharp to get any sort of image quality at all out of an 8mm film negative. One thing to note is the intense vignetting around the edges of frames; the 1-inch sensor of the NXmini is much larger than the film that most D-mount lenses were designed for, so their image circles don't always quite consume the entire frame. In some cases, I quite like this, in others, I can crop in (the NXmini has 20.1MP to work with). Depending on the lens, the vignetting can get much worse at higher f-stops, so I often find myself shooting wide open. Here are some photos taken with the Velostigmat, cropped in:

I especially like the swirly bokeh that the Velostigmat and many other D-mount lenses produce when focused on closer subjects. Astigmatism and coma, some of the phenomena responsible for swirly bokeh, are some of my absolute favorite optical aberrations and many D-mount lenses were designed before they were well understood and designed around in many optical formulas. This is huge for me. As optical understanding, manufacturing prowess, and modern computing methods improved, many lens manufacturers sought to eliminate coma and astigmatism from their lenses as they were deemed imperfections. A classic case of industry's trash is my personal treasure.

Dissatisfaction in a Solution

While my first attempt at the adaptor (let's call it V1.0) could be considered a success, I found dissatisfaction in the design and couldn't feel like I could call it a finished product. My main qualm was with feel and build-quality/appearance. I wanted something that would complement both the sleekness of the newer camera and the classic utilitarian beauty of the vintage lenses I would be adapting. Having a rough disk of black plastic between camera and lens would never be attractive, no matter how dialed-in or functional.

Additionally, I had incorporated contacts into the adaptor bayonet mount geometry to bridge two specific pogo-pins on the camera body's mount in order to trick the NXmini into thinking there was a lens attached. Without this electrical connection, the camera would refuse to take photos, claiming the absence of a lens. The plastic part was nonconductive, so I had to add a layer of metal foil tape to the electronic geometry features, a flawed half-solution fraught with frustration, reliability issues and missed shots. The foil tape would come unstuck occasionally and eventually wore out, sporadically locking up the camera in 'Lens Detached' mode.

The aesthetic issues only hurt my sense of style, but I could not abide the functionality flaws. I ended up deciding to refine the outward-facing geometry, leaving mating surfaces unchanged, before sending off to have a new Version 2.0 D-NXm adaptor 3D printed in metal. I also added a little personal branding just to show off how custom the part was, and because I let my hubris get the better of me. Since I only had a Maker Gear M2 FFF printer at the time, I used an online service that offered BJP, a process that allowed the part to be printed directly in metal. The finished part was a gorgeous bronze with a slightly grainy surface finish. I am much happier with this second iteration.

The Version 2.0's full-metal construction fixed many problems but introduced others I had humorously overlooked. For one thing, metal is heckin' heavy! A silly oversight that seems obvious in retrospect; the V2.0 is over 10x heavier than V1.0. Moreover, the new version turned out gorgeous, synergizing much better between camera and lens.

D-NXm Adaptor Comparison

If I were to iterate on my second design, there are a few things I would do differently. I would try to narrow certain geometries and hollow out other volumes to reduce mass and materials cost of the metal-printed part. Also, it turns out that either my math was off again, or my sources were inaccurate, as the FFD was still too long, and the printed model required modification. Given the criticality of the tolerances in optical systems, print inaccuracy might be too variable for a reliable result. It might actually be wisest to always print over-sized so critical mating features can be dialed in with precision. The high machinability of bronze-infiltrated sintered stainless steel made this a breeze on the lathe, however, leaving a gorgeous surface finish. I wish all machining were so easy.

I learned not to trust threads that come out well on an FFF machine to be rendered to the same spec in BJP, since the D-mount threads were unusable straight from the printing house. It was trivial to recut the threads using a 3/8x32 tap (another win for the machinability of this material) since they were luckily undersized on the part. I had originally been too optimistic, having never tried BJP print services before. In the future, I would just print a straight hole and always tap-cut the threads, which I would recommend over printing threads whenever possible.

In any case, I am now satisfied with the current state of this project and have been enjoying my silly old lenses on my silly new-old camera. I look forward to using this piece of kit more in the future, so look forward to related updates. To finish up, please enjoy some of my favorite photos I've taken using this system, so far:

Gallery

Maybe there is something to be said about how the greatness of a camera is measured not by all of the fancy apps and software connectivity features it boasts but by how long it remains capable of that one core functionality essential to all cameras: photography. The Samsung NXmini still takes great photos, and it fills a very niche role in my kit, adapting my D-mount lenses (as well as practically any other lens, for that matter). Additionally, sometimes I feel that striving for 'optical perfection' has led most modern lens manufacturers to converge on uninspiring formulas that all produce images with less character than older lenses did. For these reasons, the diminutive NXmini and imperfect D-mount lenses both remain relevant to me, today, even if others might pass them over.

Thanks for reading,
~Joseph