Problems with stop down pin from Adaptall2-M42-EOS

I have broken my Tamron SP 90/2.5 52B (I am gutted) by trying to lock

the stop down lever in the tamron adaptall by simply modifying the m42

mount will a length of insulation tape rolled up to about 5mm diameter

to hold the adaptall lever down. When I was setting the aperture dial

it then ceased to stop down at all, now stuck at 2.5. It seems the

lever in adaptall 2's has a diferent action height for each aperture

setting and i think i have pushed the mechanism beyond the correct

height and broken it.

 

What is the better way to handle the stop down pin from

adaptall-m42-eos without causing damage to lens mechanics?

I use an Adaptall 2 to M42 adapter in a M42 to EOS adapter with my Tamron SP 300/5.6 with no problems. I 'fixed' the Tamron A2/M42 adapter for manual metering by setting the lens aperture to its smallest opening (f/32), then depressing the adapter's pin to close the aperture, and then applying a few drops of crazy glue. Works every time.

 

<p> There is an important difference between the two common types of M42/EF adapters. The most simple "Type A" has an external flange with the EF bayonet mount and internal M42 threads to accept the M42 lens (or adapted lens). The "Type B" adapter has the same exterior EF flange and internal threads, but it also has an internal flange ring about 4mm wide which "caps off" the end of the threads at the camera-end of the M42/EF adapter. This internal flange depresses the M42 aperture control pin on the lens (or adapter) and provides manual aperture control of an auto-aperture M42 lens on the EOS body. This internal flange actually interferes with the aperture-position tab on the newer (old) Pentax Spotmatic lenses, such as SMC Super-Macro-Takumar 50/4, and SMC Takumars 85/1.8 and 135/2.5. You can read a lot more about M42 mount evolution <a href="http://www.aohc.it/tak00e.htm">here</a>.

 

<p> If you want to use a lens with active M42 auto-aperture control (such as your 90/2.5) on an EOS body with the Type A adapter, then you have to modify something to hold down the aperture control mechanism on the lens or adapter - you padded something and I glued something else. If you want to use a Type B adapter, then you have to check for possible interference between the internal flange and the aperture position tab. All of my SMC Taks (listed above) have this interference, where the butt end of the tab grinds against the surface of the flange as you rotate the aperture ring (also, it may prevent the lens from screwing all the way in and so affect infinity-focus). Of course, while writing this response, I just noticed that my SP 300/5.6 with Tamron brand A2/M42 adapter is actually in a Type B adapter which does not interfere with the aperture position tab (it is a micro-tad offset compared to the Taks and it fits just inside the adapter's flange). No worries, I've done considerably worse (such as playing air-ball with my EF 100/2.8 Macro USM).

 

<p> Don't panic - the Adaptall 2 adapter can be fickle. I've found that it sometimes takes more than one try to get it on the lens and have the aperture control work properly, especially the AE on a mechanical AE body (such as the pre-ist Pentax bodies: maybe that should read purist Pentax bodies, but that's a different story). It stands to reason that you might have depressed something too far, but it may return to its proper position if you take the adapter off and fart around with it and the lens a while. Good luck.

I have M42 adapters and M42 lenses.<BR>

Almost all my lens have a "manual" switch, which allows you to play with the diaphragm whatever the position of the pin. The only lens I have without this switch is a Zenitar 16mm f/2.8. I opened the rear of the lens, removed the pin mechanism, screwed everything, and I don't worry anymore about this pin.<BR>

The lens works exactly like with the pin permanently pushed in.

For EOS system, the best way to stop down Adaptall lens is not to use a M42 adapter. The M42 adapter was the best, as the adapter is less then $20. Nikon to EOS adapter has gone from $180 to less then $30 these days. The best bet is use a Nikon Adaptall (cheaper than M42 Adaptall) and use a Nikon to EOS adapter.

I think that Mr. Colwell's solution is best for M42 lenses without a stop down lever. Just remember to use the minimum amount of super glue. A tiny drop of acetone reverses the process easily.

What I did was really easy. I removed the last rear element of the lens: 3 screws. The pin lever was attached with 2 tiny screws: removed. I screwed the rear element back, nothing needing special care for centering. Maximum 5 minutes. The M42->Nikon+Nikon-> EOS solution might not leave you infinity focus with any lens.

What is mentioned is is not M42->Nikon+Nikon-> EOS (M42-Nikon has a lens inside) but Adaptall->Nikon+Nikon->EOS

Thanks Guys, I cracked open the 90/2.5 and bypassed the lever from inside (the jammed up aperture released itself), it seems that this problem is just with 90/2.5 as i was able to lock my other lenses (28/2.5, 135/2.5, 28-80/3.5...)by fixing the lever down but 90/2.5 has some kind of varying action height going on which settles at different levels as you turn the dial, when you take it from one end to the other it wont return to fully open when locked. thanks for ad2-nikon-eos tip, many thanks, JR