Tamron M42 User manual

Tamron M42 Adapt a Matic Mount Actuating Pin Assembly Fix

By Wade Spradley

Lens background.

I acquired a few Tamron Adapt-a-Matic mount prime lens for my collection. I was really

interested in the 35mm wideangle which I acquired with a Topcon Adapt-a-Matic mount

for a very reasonable price off the notorious auction site so I could examine it before I

committed myself any further. I determined that the build quality was exceptionable for

the lens for its period. This is one of the few Tamron 35mm wideangle manual focus

prime lenses out there. There is an earlier version that is of a preset design in a T-mount

format. These Adapt-a-Matic lenses were only produced within a 4 year period 1969-

1973 according to http://www.adaptall-2.com. During this time many of these designs

were revised. The 35mm wideangle I acquired is one of the later revisions which

involved redesign of aperture ring and focus grip details. No change to the optical design.

The two 28mm wideangles I also added were one each of the original 62mm optical

format and a later revised 58mm optical redesigned of the lens which respectively

involved redesign of aperture ring and focus grip details as well.

I subsequently purchased another Adapt-a-Matic lens for the M42 mount to use on the

35mm wideangle. The two 28mm lens came with their respective M42 Adapt-a-Matic

mounts. The first one is the P-CS model which seems to be a bit more robust with its

internal aperture actuating assembly compared to the later model. The actuating pins on

both models are swaged so they do not fall out and foul the lens being used. The P-CS

model has a larger flat pin base used to activate the arm in contact with the internal lens

aperture throttle. The notch in the M42 mount fits over a screw to align the mount to the

lens used as you carefully emplace the internal mount lever used to make contact with the

lens aperture assembly throttle. Some resistance may be encountered in the attachment.

The M42 mount is in two separate pieces the silver outer ring is screwed on to secure the

M42 mount section to the lens.

The underside of the P-CS Adapt-a-Matic M42 mount. Notice how the lever arm sits on

the flat actuating pin and its size. There is a slight bend to the actuating arm sitting on the

pin, That is normal. Also note the M42 arm with its roller bearing that contacts the

internal lens aperture throttle.

Next picture is the underside of the "For Pentax II" Adapt-a-Matic M42 mount, second

M42 version. This one has been fixed. Notice the actuating flat pin base is smaller and

there is no bend in the contacting arm sitting close to the center of the actuating pin.

Both of the "For Pentax II" Adapt-a-Matic M42 mounts I acquired originally were

aggressively maladjusted due to not being installed correctly on their originating lens. In

this condition they were non functional unless the original lens A/M switch was used in

the A position.

In the next picture you can see galling marks behind the aperture pin arm and where the

roller pin arm was slammed up against the inside edge in front of the screw holding the

spring.

In this next photo of the second "For Pentax II" Adapt-a-Matic M42 mount (ignore the

fuzzy) you can see the offset pin contact arm how it is sitting on the back rim of the M42

mount and not the flat plate of the actuating pin. As shown in the prior pictures. Even the

internal roller arm has to be re-aligned to sit correctly to actuate the internal aperture

throttle in the lens.

Next is a closeup of the actuating arm. You can see the galling behind the arm next to the

actuating pin and where the roller arm has been wrenched up against rim next to the

screw holding the spring. This was a lot worse than you see here now, since I started

working on it before I realized I wanted to document it...

You can see how tough the metal used in the actuating pin lever and can imagine the

force used to bend it out of place since the M42 mount metal composition gave first. So

you can imagine the force you will need to apply to bend the actuating arm back into

place. You will need to choose your tool(s) carefully.

You will need to bend the rear contact arm back until it contacts the rear actuating pin

base until it looks like it is in the middle of the round pin face just slightly off from

middle as you see here. Be careful on how much force you use so you do not malform the

assembly.

Next you may have to rebend the roller bearing arm so it correctly contacts the internal

aperture throttle of the lens. Using slight downward force to adjust in most cases.

Once you are satisfied with your adjustments reattach mount to your respective Adapt-a-

Matic lens and test the A/M switch function to ensure it engages correctly with the

aperture pin. If the lens is functioning right your are done.

Tamron M42 User manual

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