Sold FS: Pentax 67 metered prism finder

[tpstearns]

Pentax 67 metered prism finder in excellent condition. The meter works, but only in manual metering mode, i.e. you switch the lens to manual and meter with the lens stopped down. This is a known failure mode for these finders - there are two circuits inside, and the "auto" setting circuit is prone to failure. Once you get used to it, you don't really notice, as manual mode works perfectly well. Includes base cap.

$100 net to me - includes USPS Priority Mail shipping.

 

[Poisson Du Jour]

"a known failure"???
Not sure about that. By the sound of what you are describing, the meter coupling chain is more the culprit, not the TTL prism.
However, the Pentax 6x7/Asahi Pentax TTL prisms from 1969 do suffer from derangement, and this is to be expected given their advanced age (along with a litany of other problems that plague the 1969-vintage Pentax 6x7 cameras).

 

[tpstearns]

"a known failure"???
Not sure about that. By the sound of what you are describing, the meter coupling chain is more the culprit, not the TTL prism.
However, the Pentax 6x7/Asahi Pentax TTL prisms from 1969 do suffer from derangement, and this is to be expected given their advanced age (along with a litany of other problems that plague the 1969-vintage Pentax 6x7 cameras).

No, not the chain, although that is definitely the most common mechanical failure on these. It's a dead circuit in the meter, separate from the circuit required to read in "auto" mode. The following is paraphrased from user "mysteryonion" on Flickr:

"The TTL prism has two sides to the meter circuit. One is in the "AUTO" mode, and it takes into account the Aperture (Av) position and the Shutter (Sv) position, along with the light sensor. In the "MAN" mode, the Av input is ignored and the meter reading depends only on the Sv input and the light meter."

He has a circuit diagram of it here: https://www.flickr.com/photos/mysteryonionpatch/27583419787/in/dateposted/

 

[tpstearns]

"The TTL prism has two sides to the meter circuit. One is in the "AUTO" mode, and it takes into account the Aperture (Av) position and the Shutter (Sv) position, along with the light sensor. In the "MAN" mode, the Av input is ignored and the meter reading depends only on the Sv input and the light meter."

By the way, the "auto" vs "man" switching is sensed by the meter from the pressing of a small pin in the lens mount. You can see it on the right side of the mount in the attached picture.

 

[Poisson Du Jour]

Mysteryonion is well known on pentaxforums.com, particularly in the medium format section.
He has also published a number of DIY digests for fixing common problems with the older, often-problematic Pentax 6x7 cameras and individual components, among them loss of accuracy of the shutter speed dial, repatriation of the meter circuit that you have brought up -- and still others. Sasha Kraskov is another luminary known for tearing away at the innards of the Pentax 6x7 in search of the sticky solenoid that causes a fair number of woes when it manifests. All well and good for well equipped enthusiasts with the patience of a Hindu cow, but I think I will leave that sort of disassembly to Eric at pentaxs.com, if it is ever required; I have quite enough trouble replacing a watch battery!!