Converting a 103-year-old Zeiss lens to autofocus M-Mount

Recently I was rummaging around in a box of old cameras, and I stumbled across a cute little Zeiss lens that I didn’t even know I had.

It was a 5cm (50mm for you youngsters out there) f: 3.5 Carl Zeiss Jena Tessar. I researched its serial number (in the 411,000 range) to discover this little lens was manufactured in 1920, that’s 103 years ago.

Based on the history of the long-manufactured Tessar, I know some of them are pretty good while others offer failure from the day they were made. It is unlikely that a Zeiss Tessar from 1920 was bad, so I mocked up a temporary mount onto my Sony A7 RIII and found that it had excellent color rendition.

That sold me on the idea that I must properly adapt this like gem onto my Sony.

Over the summer I was able to purchase a new Techart PRO Leica M – Sony E Autofocus Adapter (version II), which also referred to as the Techart LM-EA9.

This autofocus adapter is amazing if you know how to use it. More on how to use it later as it was essential in my build.

I took the Zeiss Tessar and sat it next to a couple of my “junk” boxes filled with parts and pieces that I have amassed during my 40-year collision with photography.

I located a Leitz 80mm projection Hektor lens with a Leica Thread Mount tube. I easily removed the optical parts and pieces by taking out a single screw, and I had my mounting tube for the Tessar ready for cutting to the correct length.

I don’t exactly have a large metal working shop, but I am excellent with a Dremel tool. If you are not good with a Dremel do not attempt this next exercise.

I played with the Tessar on my Sony with a discarded toilet paper tube until I pretty much focused the lens at infinity. I marked the length and transferred it to the Leitz tube. I intentionally cut the tube about a quarter-inch too long with a cutting wheel on my Dremel.

I wanted to have extra room to play with, so I left it long. Cutting the Leitz tube with the Dremel took way too long and was too much labor. Truth be told, my garage was such a mess that I couldn’t locate a hacksaw.

Again, I didn’t have a decent belt sander to properly shorten the tube, so I shortened it by hand with a grinding wheel on my Dremel. Do not try this as it is very difficult to keep straight, and it takes a lot of time. After a couple days of careful grinding, I got the length and internal diameter of the tube perfect. It focused to infinity after being placed into a Leica Thread Mount to Leica M-Mount adapter and then onto the Techart LM-EA9.

I never actually measured the required distance needed for the tube to achieve infinity. No, I was lazy and used trial and error, mounting the lens onto my Sony about four times until I reached infinity.

The blessing on the Tessar is that it has a focus helical built in, so I had quite a bit of latitude when determining the distance of the mount.

I was lucky and got it spot on, so now the focus helical becomes a handy macro adjustment.

I took the Tessar assembly in M-Mount and clicked it into the Techart LM-EA9 and I now have a 103-year-old 50mm Leica M-Mount autofocus lens. The new Techart will allow you to make most any Leica mount lens into autofocus and it works well, though focus is not lightning fast.

I sanded and painted the newly modified Leitz barrel before assembly. The darn thing came out beautiful as well as completely functional. It looks like something that Zeiss might have produced in 1920, less the new-fangled Techart adapter. I even found a metal lens shade in another visit to my junk boxes.

Operating the Techart LM-EA9 has a secret and there is a chart necessary to gain proper exposure.

To tell the Sony camera what lens you have mounted onto the Techart, go to the aperture priority setting and dial in the focal length of your lens using the exposure adjustment wheel, which controls the f:stops.

For instance, for this 50mm lens, I dial in the aperture as f:8, and then take two exposures. Then turn the aperture setting back to f:2 and you’re ready to go.

By dialing in this setting, the Sony will properly expose the frame for the proper lens focal length.

The focal length will remain in the aperture priority setting until you switch to a different focal length. You will have to reset it to the new focal length if you change focal length.

You control the actual aperture using the setting on the lens and allow the body to pick the shutter speed using the aperture priority setting. See the chart below for the proper f:stop to focal length translation.

While it may sound complicated, it is quite easy after doing it a few times. I don’t know why the Techart adapter works this way, but I guess they had to have some method to tell the camera what the focal length of the lens is without electronics installed in each lens.

The Techart LM-EA9 works with lenses from 12 to 800mm, but focal lengths under 200mm work better than the longer telephoto ranges (I am told).

For more on the use of the Techart LM-EA9 go to https://phillipreeve.net/blog/review-techart-lm-ea9-leica-m-to-sony-e-autofocus-adapter/

The Motivation

I sat back and asked myself why I even attempted to convert this old 5cm Zeiss Tessar. It’s not like I don’t have a long line of exotic and much faster lenses waiting to be used.

The motivation is clearly one based on history.

The history of the Tessar lens dates back to 1902 and it is an offshoot of the Anastigmat design. The Tessar has an air space between the front two glass elements compared to the cementing of those elements in the Anastigmat.

The air space lessened the amount of spherical aberration of the lens.

The first Tessar had a maximum aperture of just f:6.3. By 1917, the maximum aperture had jumped to f/4.5. My Tessar was rather revolutionary in 1920 with a “fast” aperture of 3.5. Zeiss was breaking a boundary with this little lens at that time.

The reason I took this little lens and remounted it was simply because it was 103 years old, and it had the Zeiss name on it.

I love Zeiss and have adapted no less than 15 Zeiss brand lenses onto my Sony A7RIII and Fuji X-Mount cameras. I don’t normally sell Zeiss glass, unless it is medium or large format, because I want to use it and see what kind of unique image each Zeiss lens design produces.

Usually, I fall in love with the bokeh and image quality of the Zeiss lenses and put them into my personal “keeper” camera bags.

How often do you get a chance to convert a 103-year-old Zeiss lens into an autofocus Leica M-Mount, especially considering that Leica never made an autofocus M-Mount lens or body?

In the Field Tests

I started testing the Tessar right away in my less-than-ideal front yard. It did surprisingly well.

I quickly readied my ebike and headed to the local park. Wow, the little Tessar captured some awesome images of the BMX bike track and the street I live on.

I quickly learned that the lens needed to be stopped down to f:5.6 or 8 to perform well. Wide open it wasn’t very sharp and contrast fell like crazy when wide open.

The aperture dial is nearly impossible for this old man to see in the field, and it doesn’t have clicks, so I guessed at what appeared to be f:5.6 to 8.

I took it on a trip to my favorite camera store, Monument Camera in Tucson.

This meant traveling through the White Mountains, where I live, and into a great section of the Sonora Desert. Unfortunately, it was a gloomy day, meaning the Tessar suffered more contrast issues.

The saving grace of the lens was in macro mode. I extended the focus helical of the old lens out as far as I could go and let the Techart LM-EA9 autofocus from there. Holy smokes, despite the gloomy day, the Tessar was awesome in macro mode as it focused closely on cactus nodules.

I’m sure the Tessar would perform excellent in black and white, but I tested it using a color mode on my Sony A7RIII. It wasn’t perfect but it is 103 years old, and it was a blast to modify, mount and shoot this old piece of history.

This lens goes into my Leica M-Mount bag for more field use in the future.