reddtekk Offline Upload & Sell: Off
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Greetings folks,
I've decided to do a quick write-up on my project of adapting my Tair-11 133mm f2.8 lens to be used on my Canon camera body.
m39 lenses are easy to fit to the m42 adapters commonly available on eBay using an m39-m42 threaded adapter ring. The issue is that the focal plane (at least in the case of my lens) is slightly closer on the m39 lens than standard Pentax m42 lenses. This results in a slight miss of infinity focus.
I obtained a reasonably good copy of the Tair-11 lens (occasionally referred to by some folks as the "bokeh monster") from an eBay seller in Bulgaria. I was intrigued by the bright nickel plating on the lens and the 20 blade aperture (which forms a near perfect circle from f/2.8 through to f/22). It's a beautiful prime, tack sharp through all aperture settings, fast enough to use handheld in many conditions, and a great focal length for stealth portraits, where you're so far from your subject that they don't realize that you're taking their picture. I put the lens on a Canon crop body (initially a 350D and now a 650D) using the m39-m42 adapter that the seller supplied with the lens and a cheap chipless m42 adapter. That infinity focus issue nagged at me though, and I quickly desired a solution.
So I did some searching. Somewhere on some forum (a couple years ago) I found a thread indicating what the focal plane of that lens was. It wasn't far off from the m42 focal plane and was still further than the Canon EOS focal plane so I decided to take the adapter to the metal lathe. Simply facing off a patch near the center of the m42 adapter ring provided the desired results, and I'm proud to say that I can now achieve infinity focus using this great lens.
Measurements are as follows:
I spot-faced the adapter down 0.030" from the original surface. Since there is a 2.122" diameter step in the Canon adapter on the opposite (male Canon EF mount) side, I kept as far as possible to the inside of the step to avoid making too thin a section. I made this diameter JUST big enough to clear my lens barrel, which was 2.055". Even if you over-step this or face the whole thing down to accommodate a larger OD lens, the adapter is 0.052" thick so you'll have 0.022" of flange thickness left. I'd be a little worried about distorting it if the lens were heavier, but my example is pretty small so I'm not concerned about it.
Overall I'm very happy with this. The lens is a little flare-prone since my example has a little bubble in the glass of the front element, but I'm really happy with the appearance of the photos I've gotten with it.
Hope I have been able to help someone.
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