Bringing the Film Age to Digital (AKA, Not The Kind of Lens Mount Adapter You'd Expect)

November 15, 2019
Bringing the Film Age to Digital (AKA, Not The Kind of Lens Mount Adapter You'd Expect)

Years ago, before Fotodiox, I had a part time job in a darkroom. There was a lot to be found in a traditional darkroom: comfort, a place to nap, and the familiar smell of stop bath. A darkroom comes to life when it’s busy, with the many bodies bustling between enlargers and the sinks of chemicals, the rustling of paper and negatives, and the click that comes with the enlarger’s light coming on.

Unfortunately, as the years have gone by, darkrooms have become less busy, and eventually that same darkroom needed to be downsized. As I moved enlargers out of their bays, and into an area designated for the dumpster, I asked if I could salvage some of the lenses, hoping I could find a new home for them, or make them useful somehow.

Enter Fotodiox and the present day. Right off the bat, there are a few challenges presented to me:

1) The lenses don’t have a standard mount, only 40.5mm filter threads on the front side. Automatically, that means there isn’t a direct adapter for them, so I have to be creative by reverse-mounting the lens.

2) The lenses don’t have a focusing mechanism. The only real solution for a fixed-focus lens is to put it on a bellows system, or a focus helicoid.

3) The focal flange distance is unknown. Even if I have reverse-mounting solutions, as well as bellows or focus helicoids, I’ll need the focal flange distance to know if the lens is even usable as a standard lens with infinity focus.

This is really the only hard step for the entire process, so I got it out of the way first. As this video shows, you can find how much space a lens needs by projecting onto a surface, and measuring the distance between the lens and the surface.

With the lenses we see here, the 50mm f/2.8 had a focal flange distance of 24mm, and the 75mm f/4 had a focal flange distance of 60mm.

Since I already figured out the focal flange distances for the lenses in picture 1, I’ll use the Sony E-mount for my baseline. We have to subtract the Sony E-mount’s focal flange distance to see what’s left. With Sony E having a focal flange distance of 18mm, the 50mm lens has 6mm left for an adapter (not really a lot, if you ask me), and the 75mm lens has 42mm left for an adapter.

To solve our helicoid issue, we just had to pick from any of our adapters compatible with the Sony E-mount that also had some sort of focus helicoid. I ended up choosing our M42 to Sony E Macro Adapter, since it was relatively slim to start with, while also offering a good maximum extension. Getting the M42 female threads to a 40.5 female threads isn’t necessarily hard, but it did take quite a few step-rings to work out:

  • 39mm to 42mm step-up ring
  • 39mm-55mm step-up ring
  • 55mm-52mm macro reverse ring
  • a 40.5mm-52mm step-up ring

After the amalgamation of these products, our DIY adapter ended up being 38.75mm thick, which was just under what we needed for the 75mm lens. From the thickness of the adapter alone, we know the 75mm should have infinity focus, but the 50mm lens will really only be able to be used as a macro lens.

Let’s see some images:

Right off the bat, the lenses are fairly prone to haze, but this is fixable if you block the light (I used my hands to accomplish this)

As mentioned above, the 50mm f/2.8 is really only viable as a macro lens, so we focused on extreme close-ups

While not the sharpest lenses in the bag, the lenses are a lot of fun. The helicoid has a pretty long throw, so nailing focus can take time, but it’s good to slow down and think. It should be noted that the further you extend the lens, the more light loss you are likely to experience, so macro shots will likely need a tripod of some sort.

Adapting lenses isn't always as straightforward, but there's something satisfying about creating your own solution when you know a direct one doesn't exist.

1 comment

Nov 26, 2019
Rick Boden

Great tip. I have some enlarging lenses and projections lenses I wouldn’t mind trying this on. I hope Fotodiox expands its adapter line up for the Canon EF-M mount as I don’t see a helicoid option…wouldn’t mind a shift adapter too.

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