67 TTL Prism

ColColt · Jun 29, 2016

Does anyone know if the Pentax 67 TTL Prism fit the older 6x7MLU camera as well?

Poisson Du Jour · Jun 29, 2016

Yes. They are forward/back interchangeable. But it's best to match the meter to the body.The meters come in either the old Asahi Pentax model or the newer (1991 onward) PENTAX TTL prisms (with revised metering circuit). The now very old (and frequently bashed) Asahi Pentax TTL meters benefit from a check of the meter for accuracy, drift and 'spikes' (e.g. moving the aperture and/or shutter speed resulting in the viewfinder needle charging either up or down before steadying).

MLU or non-MLU does not matter.

ColColt · Jun 30, 2016

This was just to be a spare as I have one on the camera that came with it and works fine. Knowing they're not making these anymore I got this one that was rated by KEH as EX+ and thought I've best jump on it.

DREW WILEY · Jun 30, 2016

Generally KEH stuff sold EX+ is in exceptionally good condition. That doesn't mean the meter has been tested or re-calibrated, but working. And sometimes old light seals needs replacement.

ColColt · Jun 30, 2016

True-I'll put it though the paces when it gets here. seems to me, without checking the manual, you have to take the lens off before taking the meter off or chance breaking the chain.

Poisson Du Jour · Jun 30, 2016

That's correct.
If a TTL prism is removed while a lens is attached:
Remove the lens, re-mount the TTL prism, and then re-mount the lens.
This procedure removes and resets all tension from the aperture coupling chain -- the well-known weak spot in the older 6x7 bodies (the chain was improved with the release of the 67 bodies in the early 1990s).

DREW WILEY · Jun 30, 2016

That doesn't sound quite right to me. The meter itself just doesn't engage unless you mount the lens afterwards (or partially unlock the lens bayonet
and turn it back). I've never had the chain break; but then, I'm not a Pentax repairman either. I prefer the non-metering prism anyway - a bit less clutter.

ColColt · Jun 30, 2016

Looking at the manual that comes with the prism they say, "The Pentaprism finder can safely be removed from the camera body with the lens on".

Poisson Du Jour · Jun 30, 2016

I have all the manuals too (but read page 6!). You may also notice that nowhere does Pentax tell you in any of the manuals why the chain breaks, and many photographers of the early 6x7 era were none the wiser as to the presence of the chain, what it does and how and why it breaks..

The advisory for the process of removing the TTL prism and lens and replacing came much later, with the release of the improved (a stronger chain) 67.

People are free to mount/dismount in any order they want, and they have done that for decades; it's a risk that has always been there — the body-side coupling is not in the correct position to receive the lens aperture coupling. The chain, by association with the coupling, doesn't break because it's bored, but because it becomes fatigued through stress, and snaps. It is entirely avoidable by reasoned methodology. Actually, I share the view there are lots of places in all of the Pentax 6x7 manuals where advice could be improved with warnings. The manuals are typical of the 1960s — sufficient information to instruct, but a lot left unsaid...

In any case replacement of the chain has become a fairly routine chore. I'm sure Eric the Pentax repairman could tell you that! More people still use published DIY info on the web (e.g. by Bill Peifer).

ColColt · Jun 30, 2016

Well, that settles it. I'll take the lens off before removing the prism. That chain is so tiny and fragile looking anyway.

Poisson Du Jour · Jun 30, 2016

You may also notice the conflict of information in the manual (common throughout all of the 6x7 manuals). On one hand the manual says it's ok to remove the prism and refit it with a lens attached. Later, the manual advised, in point form, of the safe methodology that is the focus of these last few posts! It's this conflict of advice that no doubt confused people and led to them doing as they please (as most would!), with often disastrous results at the least expected time.

ColColt · Jun 30, 2016

You're right, I just re-read it again.

DREW WILEY · Jul 1, 2016

With the ordinary non-metered prism, as well as the folding and chimney finders, there is no integration issue at all, other than the two little pressure springs that keep the device in place.

ColColt · Jul 1, 2016

Exactly. My first 6x7 back in the early 80's had the standard prism and no issues whether I wanted to take the prism off for some reason. This one bought early this year is different since it has the metered prism and I wasn't sure about the sequence.

ColColt · Jul 1, 2016

FedEx delivered the prism today and it's a beauty. Had in been in a box you'd be very hard pressed to tell it from a new one...absolutely perfect. Their rating of EX+ was more like LN+. I've found this to be true with other lens/cameras I've ordered from them in the past. I haven't as yet tried it in lieu of the other meter but will soon. The only difference is this was in newer and just has the Pentax logo on the front whereas my other one is "Asahi Pentax".

ColColt · Jul 1, 2016

Well, wouldn't you know it...it won't fit. It looks just like the other one but will not clamp down easily as the other one.

DREW WILEY · Jul 1, 2016

I was under the impression 67II finders are not interchangeable with previous versions, just the lenses.

ColColt · Jul 1, 2016

This is not the 67II finder but for the 6x7 or 67. It should have fit. Looks like this...

Poisson Du Jour · Jul 1, 2016

What on earth are you doing!? I am confused reading the preceding posts and have not got a clear idea of what prism you have for what camera. FWIW, the 67ii prisms are not interchangeable with either the older 6x7 or the newer 67 bodies. Nor can you put a 6x7/67 prism on a 67ii body. What is it you have/have not??

ColColt · Jul 1, 2016

I have a 6x7 body with an Asahi TTL metering prism. I bought a "Pentax" TTL prism as a spare and it's not fitting. I do not have a 67II body or prism. The only difference between the prism I have and the new one is the nomenclature on the front. One has "Asahi Pentax" and the new one I bought just says "Pentax".

Poisson Du Jour · Jul 2, 2016

ColColt said:
FedEx delivered the prism today and it's a beauty. Had in been in a box you'd be very hard pressed to tell it from a new one...absolutely perfect. Their rating of EX+ was more like LN+. I've found this to be true with other lens/cameras I've ordered from them in the past. I haven't as yet tried it in lieu of the other meter but will soon. The only difference is this was in newer and just has the Pentax logo on the front whereas my other one is "Asahi Pentax".

If it is "LN+", you would not be having trouble fitting this prism! My bet is they didn't check the prism at all.
An up-front point: the prism should easily click into place on any of the 6x7 / 67 cameras. The shape/dimensions never changed from the 60s body to the 1990s body. If it doesn't slot in with consummate ease as the prisms are want to do, it's definitely not "LN+"
Mine was described by the seller (an Estate in VT/USA) as mint (as was the whole camera in toto) and remains so 8 years later. My recently acquired fold-down viewer with hood, with the ancient Asahi-Pentax logo, goes freely in and out.

You should ensure the shutter speed pin on the underside of of the TTL finder matches the slot on the shutter speed dial of the camera. Nothing else I can think of other than some form of damage to the mounting pins or (unlikely) some sort of warpage of the prism body. Send it back.

ColColt · Jul 2, 2016

I sent them an email explaining the problem. It appears I may have to send it back, reluctantly, as it looks so good but, if it doesn't fit-it's useless.

ColColt · Jul 2, 2016

I think I've discovered the problem. The foam on the underneath side is twice as thick as one the old prism and perhaps is causing this. I looked both prisms over top to bottom and that's the only thing that stands out. I tried pushing the prism on a little harder after finding this but it still won't go.

moto-uno · Jul 2, 2016

^Does this sound like someones well intended resealing ( without fully knowing what they're doing ? )
If the foam needs to be compressed on install , then you're probably onto something.
Peter

ColColt · Jul 2, 2016

The foam looks good...as new. I've pushed all the around it and it almost snaps locked but not quite. If I could just shave a minute fraction off it it would go.

67 TTL Prism

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