pentax 6x7 - loose seating of ttl prisms?

Having recently purchased my first pentax 6x7 MLU with a ttl prism

(both quite old but in well looked after condition) I have found that

the prsim actually seems to fit quite loosely on the body even though

there are no real signs of wear on the retaining clips. This seems to

cause power to the metering system to be very intermittent because

the spring loaded electrical contact pins at the back of the prism

loose connection with the body so easily (eg. tilting the camera

forward at say 45 degrees is enough to break the contact). This is

particularly bad when doing verticals and I find myself having to

press down on the prism to ensure getting meter readings (where's

that third hand when you need it). I'm a little surprised since I

haven't seen comments about this in the archives. Everything looks

straight and shows few signs of wear and as far as I can see the foam

under the prism looks ok. I'm looking for feedback on other users'

experiences regarding this - is it common to see this rather loose

fit between the two? Is there a fix? Is it also another reason for

dumping a beanbag on top of the prism (for horizontals at least) to

reduce image blur due to additional vibrations?

Richard, it could just be down to poor quality control by Pentax. I'm on my 4th

Pentax 67, a 67II model this time and before that I had an early 6 x 7 and two

new 67 models. I tried on two occasions to buy a used TTL prism to use with

my previous camera bodies and each time I had to return the prisms because

of problems.

 

The first prism was reading consistently about 2 stops out from my own hand

held light meter, although it seemed to fit quite well on the camera. The

second prism ( late model with Pentax in white letters on prism ) wouldn't sit

properly on the camera body, even with both the side locking pins clicked into

position, the prism could rock back and forwards and I could see that there

was a large gap between the camera body and the base of the prism!

Needless to say the meter wasn't able to work with such a loose connection to

the camera body, it flickered once or twice and that was all that I could

persuade it to do.

 

I can only assume that the manufacturing tolerances used by Pentax were not

as tight as they should have been. If you were able to test out a broad sample

of similar TTL prisms, you would probably find that some would fit slightly

better than others on your camera body. There really isn't very much that you

can do wrong when fitting a prism on to a Pentax 67; so I would tend to blame

the prism rather than your own technique. I have heard this problem

mentioned before, you've probably just been unlucky I am afraid.

thanks Allan, I actually played around with placing an extra strip of self-adhesive foam on the body under the front of the prism last night (taking care not to obscure the aperture link gap). The seems to have done the trick as far as stability goes - it forces the back of the prism to push down a little harder on the electrical contacts so it doesn't rock anymore. It still sits pretty level with the camera base as far as I can tell so I'm hoping I haven't changed the view through the finder by doing this, but time will tell. I guess this may indicate that the foam on the prism may have flattened out over time and needs replacing after all even though it looked in ok condition.

FYI,Pentax in Colorado will fix any camera regardless of age.Ive had an old P67 rebuilt to new by them!And they warantee the repairs for 6 mos.