Have you ever wondered why Holgas, Dianas and the Time Magazine cameras were not made in Germany? Well whatever the reason, German optical companies have have decided that quality is the way to go. Zeiss is among the best optical lens company there is....their motto says it all, "We Make it Visible."

Getting the best optics in the world comes at a hefty price. A Zeiss prime lens for the Cannon EOS system will easily cost $500. Luckily, some older lens designs from a discontinued camera using an obsolete film format can be had for a song.....$12 to be exact [Thank You Surplushed.com].

The Carl Zeiss Tessar we use in this instructable was originally destined for a Contaflex 126 camera. The Tessar design is over 100 years old so it has stood the test of time. In this Instructable, we'll adapt it to fit The Canon EOS system type cameras...35mm, digital or APS types. Since I have all three types...its a win, win, win!

Step 1: Stuff You Will Need

The two significant items in this instructable are the Zeiss Tessar lens and a body cap for the Canon EOS mount (EF mount to be specific). The lens was bought from Suplushed.com for $12 and the body cap was from eBay at $10 for a dozen...so that is $.84 each. With shipping and other miscellaneous supplies, I priced this whole project at $15.

1. Carl Zeiss Tessar 45mm f2.8 lens.

2. One Canon EOS body cap.

3. Rotary Tool with associated bits.

4. Two part epoxy adhesive (I used the 5 minute variety).

5. Flat black paint.

6. Dental floss.

7. Cyanoacrylate glue (super glue).

8. Paper clips.

9. Wire cutters.

10. Two small rare earth magnets.

Step 2: Lens Hacking 101

Lens hacking is putting a lens onto a camera for which is was not designed. Recently, hacking has become depressingly easy with purpose build adapters flowing out of China. Some are very sophisticated with corrective optics and focus confirmation chips built in. Nikon to Canon...not a problem.

However, here we will try to leverage the legendary Zeiss optics into a Canon mount. Through trial and error, I found that this particular lens will work with the EOS camera system due to the similar flange focal distance. More on that here:

http://en.wikipedia.org/wiki/Flange_focal_distance

No math involved in this method, just hold the lens up to the body and look at something at infinity through the viewfinder (something over 50 meters away). Get that image in focus and your lens is at its flange focal distance. Some lenses need to be so close that the mirror would slap the lens when you take a photo. Some are so far away, you would need all sorts of unsightly tubes to mount the lens at the proper distance. Luckliy, this lens sat at almost the correct distance.

One thing we will not preserve with this lens is the ability to focus. Like so many crappy cameras from the 90's...it will be "Focus Free." The lens will be set at infinity so distance shots will be easy. Closer shots will be more difficult. However, we will be able to control the aperture which affects the depth of field. At a small aperture (higher f number) I've found that you can get to about 8~10 feet from your subject...good enough for portraits providing there is plenty of sun or a strobe.

Step 3: Prepare Your Body Cap

1. Cut out the inside of the body cap with a rotary tool. The plastic will melt when you use a grinding bit which is fine for a rough cut.

2. Use a sanding drum to clean up the cut. It will sand away the plastic instead of melting it.

3. For this particular lens, you will need to grind down a millimeter or so to get to the correct flange focal distance. Grind a little and dry fit the assembly and attach it to a camera and look through the viewfinder to judge the infinity focus. If you go too deep, don't worry as you you can shim it up before you make it permanent with epoxy.

Step 4: Prepare Your Lens

Although I'm not building in a way to focus the lens, I still want to preserve the ability to change apertures. To do this, I'll need to be able to control the aperture lever. My solution was to drill a hole in the lens collar so I could feed a string into the assembly to control the aperture.

1. Locate a nice spot on top of the assembly and drill a hole through the collar.

2. Coat the inside of the hole with epoxy so a string can slide easily without fraying.

Step 5: Join Body Cap to Lens

Once you are satisfied with the infinity focus, it is time to join the lens with the body cap...permanently.

1. Fit the body cap to the target camera. Dry fit the lens on the body cap in such a way that the writing on the lens is faced up and readable. After all, you want other photographers jealous of you for using a Zeiss lens!

2. Mark the lens position with a sharpie (magic marker) on the body cap and lens so you can position it exactly for the glue up.

3. Take the body cap off the camera and position the lens with the help of the marks you did with the sharpie. Take care to make sure the lens is level...if not you will have a tilt and shift lens that will have a permanent tilt!

4. Mix up a small amount of epoxy and tack glue the lens to the body cap.

5. Once cured, flow epoxy around the lens.

6. Once cured, flow epoxy around the inside of the lens mount. This bond needs to be rock solid!

Step 6: Black Is the New Black

Time to make the assembly light tight.

1. Use some flat black paint to paint the silver looking pieces inside the assembly. This will cut down on internal reflections and increase contrast of the image. I used some paint designed for refinishing military emblems, however, you can just use flat black spray paint that you spray into a dish or the cap and just apply it with a paintbrush.

2. Cut a piece of electrical tape to cover the slot on the bottom of the assembly. This slot was originally used on the Conaflex lens mount.

Step 7: Add Aperture Function

I'm using a magnet to pull and keep the aperture open... however this whole lens assembly is aluminum, so I had to add some ferrous metal to get the control I wanted.

1. With some wire cutters, cut 4 small sections of paper-clip about .25 inches long.

2. Glue these sections to the outside of the lens assembly with epoxy glue. I used the now obsolete distance scale to space the sections.

3. Once the glue has cured, get some waxed dental floss and tie one end to the aperture lever. Cut off the tail as close to the knot as possible.

4. Reinforce the knot with a drop of cyanoacrylate glue to make it permanent.

5. Thread the floss outside the lens assembly through the hole that was drilled earlier.

6. Use the two rare earth magnets to pin the floss. Adjust the length so you have at least three stops when you pull the string. Trim the excess. The magnets should hold the floss without need for extra glue.

Step 8: Attach to Your Camera

The lens assembly is now ready for use!

1. Simply attach the assembly to the camera as you would any lens.

2. Adjust the aperture with the magnet and string assembly you built.

3. Set your camera to aperture priority mode and begin shooting.

Step 9: Lens Performance

Like most lenses, this one performs best at about 5.6. At that aperture, the focus is about 10-15 feet to infinity. I can get close to 5 feet at f16, but this leads to long shutter times and introduces a lot of motion blur. A trade off to be sure, but since the lens didn't come with its own helicoid focusing system, building one would have been too complex and bulky.

[Update] These low resolution photos are duplicated in the original resolution (that is 3.3 MP of the D30 in JPEG format) here:

http://www.flickr.com/photos/21721108@N00/sets/72157625877439142/

Anyway, enjoy your high quality, genuine "Carl Zeiss" photography lens!