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Modifying the Tokina EL 28mm/2.8 M42 for manual aperture
Posted By: sterretje, 11-07-2010, 10:03 AM

// EDIT 2012/03/23:
This modification, for some reason, results in heavy vignetting up to f/8. I've undone the modification and used a Q-tip to preload the lever which solves the issue. But I don't understand why !

The procedure is to move the lever in the second image completely to the left (while mounted). This allows to take the pin out and slide a Q-tip over it. Next place the pin back.

// ORIGINAL POST
A while ago I bought some old M42 gear and and one of the lenses was the Tokina EL28/2.8 M42. As I don't have anything below 55mm for M42, I was determined to get this lens going.

This lens only has an automatic aperture (no manual position) which implies that measures must be taken to push the aperture activator pin in to close the aperture when using it on a dSLR.

I was a bit nervous as this was the first lens that I would disassemble and I did not know what to expect. After removing the 3 small philips screws at the back of the lens, the back comes off.

The below photo shows that the aperture is closed to the position that is selected on the aperture ring instead of wide open when the back of the lens is removed. Exactly what I wanted / is needed.



The next photo shows the back with the aperture activation lever (copper) and the M42 pin (silver, at the bottom) that activates that lever.



A small spring (fixed to the lever, so no risk of it jumping away) holds the lever in the shown position. In this position, the lever pushes the aperture open! So by removing this mechanism (the 2 visible small screws) the lens will become a manual aperture lens. I did this and there were no parts flying through the room
After that, I put the back part back on and screwed it all together. The lever, pin and screws went in a little ziplock bag.

How the mechanism further works:
Pushing the standard aperture activation pin of a M42 lens will move the lever to the left 'releasing' the aperture to its selected setting.

Not sure of the quality as the weather is not to bright over here at the moment, but at f/5.6 it looks quite sharp. Need to do some tests with a tripod one day.

Hope this helps people with the same lens. No need to glue the M42 pin or use of Q-tips.

Last edited by sterretje; 03-23-2012 at 06:39 AM.
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03-24-2012, 03:49 AM   #2
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After the Q-tip modification, it was time to check it all out. Attached are a number of shots, taken with the K10D. At this stage I do not really have any primes to compare this lens against (OK, FA31Ltd excluded); sometimes I think it could be a bit sharper but that might just as well be user error. It hardly gives problems when shooting straight into the sun. Purple fringing seems to be non-existing unless one really forces it. All images taken without lens hood.

f/2.8


f/8


f/2.8


f/8


f/5.6

This is a shot that the FA31Ltd has serious problems with if one does not get the exposure exactly right. This Tokina has far less problems.

f/5.6

Draw your own conclusions; seems a bit harsh, but I like it (and that's what counts )

f/5.6

This rose bush is always willing to pose and those young leaves always come out nice

f/5.6


Note:
I paid around US$40 for a Yashica TL Electro camera with a Yashinon DS 50/1.9 and an old flash, a S-M-C Tak 135/3.5 and this lens. I basically wanted this kit for the lens hood for the Tak as mine was missing and for this lens. All in all, I'm reasonable happy with it (and for the price very happy). Hope to be able to compare it against a Tak one day.

Last edited by sterretje; 03-24-2012 at 08:51 AM.
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