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08-10-2018, 05:10 PM - 1 Like   #1
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ADVISORY: Pentax 6x7, 67 METER COUPLING CHAIN AND TTL METER PRISM

___________________________________________________________________________________
IMPORTANT INFORMATION FOR NEW USERS OF PENTAX 6X7 CAMERAS FITTED
WITH TTL METER PRISMS

APPLIES TO: HONEYWELL-PENTAX 6X7, ASAHI PENTAX 6X7, PENTAX 6X7, PENTAX 67 CAMERAS
___________________________________________________________________________________


Pentax 6x7 (pre- and post 1969) and Pentax 67 (post-1989) medium format cameras are fitted with a thin copper interweave meter coupling chain that is located in a runner slot along the forward-facing fascia of these cameras, just above the Pentax name plate. In normal use the chain is completely hidden by the TTL meter or normal prism*. The meter coupling chain is the operational link between the aperture lever of the lens and the TTL meter prism. If it breaks, you will only be able to perform stopdown metering with the lens in manual mode.

Incorrect removal and re-assembly of the TTL prism can impart stress on this chain and lead to unexpected breakage.

Chain breakage is not recommended as user-serviceable.

Repair of the chain requires disassembly of the lens mount (and subsequent precise calibration to factory standard) to gain access to the mechanism, and repatriation with a replacement chain sourced from a similar body (new parts are not available). Pentax made small material improvements to the chain in the 1989-release of the Pentax 67, but it remains a fragile, failure-prone component that requires awareness.

*Although all Pentax 6x7 / 67 cameras are fitted with a meter coupling chain, a non-TTL meter prism e.g. chimney finder, waist-level finder, etc., has no operational connection to the chain.
_____________________________________________________________________________________

The lens can be removed and re-mounted freely any time a TTL-meter prism is seated,
however, if the TTL-meter prism is removed or jarred loose:
  • remove the lens;
  • re-mount the TTL-prism, and then—
  • re-mount the lens.

This process resets the meter coupling chain to its neutral position which will match with the nib in the base of the TTL-meter prism.

The meter coupling chain can also break of its own accord due to old age (all of the Pentax 6x7 cameras are now quite old, and a great many have been used decades ago in aggressive professional practice, and the common ingress and accumulation of dust, dirt, rust or foreign bodies in the mechanism.

In the event of in-field breakage of the chain, be assured the camera is not 100% inoperative!
With an inoperative TTL meter prism, stop-down/manual metering (e.g. with a separate light meter) will need to be employed to bypass the failure. For beginners with their first MF camera, this method of metering is potentially problematic and defeating, and this is why an early acquaintance with the Pentax 6x7's proverbial Achilles Heel, the meter coupling chain, is so important! Additionally, basic operational competency in the use of a separate hand-held meter is considered a recommended adjunct to use of most MF cameras today.

This information published here is also found in the original owners manual supplied with Pentax 6x7 / 67 cameras.

___________________________
Gary Higgins
Silent Street Photography | AUS
August 2018


Last edited by Silent Street; 01-22-2019 at 09:08 PM. Reason: clarification [min.ed.]
08-10-2018, 06:02 PM   #2
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Very well written Gary!
08-10-2018, 09:58 PM   #3
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And a replacement chain is no longer available from Pentax. I haven't heard of a replacement.
08-10-2018, 10:17 PM   #4
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QuoteOriginally posted by pentaxus Quote
And a replacement chain is no longer available from Pentax. I haven't heard of a replacement.
As mentioned.
Chains are taken from other Pentax 6x7 /67 camera bodies, typically those no longer operational and assigned for "parts".
Thin, multistrand jewellery beading wire is the usual fix in the absence of a suitable chain from another camera body. This ultra-flexible material (bonus: many colours to choose from! ) is much stronger than the native chain, but does not negate the precision required in disassembly, fitting, reassembly and calibration.

.::GRH


Last edited by Silent Street; 08-11-2018 at 11:23 PM.
08-11-2018, 04:47 AM   #5
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QuoteOriginally posted by Silent Street Quote
[
In the event of in-field breakage of the chain, be assured the camera is not 100% inoperative!
With an inoperative TTL meter prism, stop-down/manual metering (e.g. with a separate light meter) will need to be employed to bypass the failure. For beginners with their first MF camera, this method of metering is potentially problematic and defeating
While I don't want to sound elitist, IMO anyone who takes up medium format film photography in this day and age (and arguably ANY day and age; it was expensive back then) should reasonably be expected to know how to meter manually in the field and have the means to do so (even if it's just a cellphone app).

The PSA is most welcome.
08-11-2018, 07:21 PM - 1 Like   #6
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QuoteOriginally posted by pathdoc Quote
While I don't want to sound elitist, IMO anyone who takes up medium format film photography in this day and age (and arguably ANY day and age; it was expensive back then) should reasonably be expected to know how to meter manually in the field and have the means to do so (even if it's just a cellphone app).
The PSA is most welcome.

Your point is entirely valid.
I too, would strongly suggest that photographers making the move up from the relatively high-levels of automation and 3D metering of 35mm come to an effective operational competency with separate, hand-held incidet/spot metering techniques as an effective standby workaround. Unfortunately, many do not and have no interest in doing so. Many still are completely blithely unaware of the fallability that is the purpose of this sticky!
08-14-2018, 07:44 AM   #7
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QuoteOriginally posted by Silent Street Quote
Unfortunately, many do not and have no interest in doing so.
This is something against which the Angry Photographer on YouTube has posted many rants. On the bright side, Mark Wallace and Gavin Hoey are often seen demonstrating the use of a meter, specifically for studio flash.
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