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11-24-2013, 11:25 AM   #1
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TTL light meter doing weird things

Quick background: I have a pentex 67 camera with a TTL light meter. Currently, there is 100 film loaded. I just changed the battery too.

Problem: The light meter does nothing in auto setting at all. In manual I can get the needle to move but only when lens is wide open and I'm in a pretty bright light and slow speed situation. I have taken the lens off and the meter several times. I did also wipe down the contacts (which were already pretty clean).

What is going on?

11-24-2013, 12:00 PM   #2
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Welcome to the forum!

I had the exact same issue with my 67 & TTL meter.

https://www.pentaxforums.com/forums/48-pentax-645d-medium-format/135245-penta...-metering.html

Eric can probably fix your meter or what I did was use the regular prism and bough a handheld light meter.

Here is a link to Eric's web site:

Pentax Camera Service



The 6x7 and 67 TTL meters are notorious for being flakey. This was fixed with the 67II AE metered prism.

Phil.
11-29-2013, 11:13 AM   #3
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QuoteOriginally posted by gofour3 Quote
Welcome to the forum!

I had the exact same issue with my 67 & TTL meter.

https://www.pentaxforums.com/forums/48-pentax-645d-medium-format/135245-penta...-metering.html
Welcome to the forum.

Thanks gofour3, the link above has just helped me get a newly acquired metered prism working in stop-down mode, thanks for that!

My problem is slightly different, in that the needle is pinned to '+' (overexposure) when not on the camera or without a battery. In open-aperture metering it stays there always. In stop-down metering it works and reads reasonably consistently compared with my other one.

I remember seeing a comment on the web suggesting someone else's meter read from the top, down instead of bottom, up - anybody know if this is related to open-aperture metering not working? My other prism works fine on both bodies, so I can only assume it's a prism thing?

Regards,

John.

Last edited by johnha; 11-29-2013 at 11:34 AM. Reason: Minor change
12-01-2013, 11:16 PM   #4
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Check meter coupling chain. If the TTL prism / lens re-fit process isn't followed correctly, metering will be either erratic or not functional at all.
The procedure is: Freely remove and refit a lens as required. However, if you remove the TTL prism, remove the lens. Then refit the TTL prism and lastly refit the lens. There will be no meter coupling if this procedure isn't followed. It's an idiosyncracy of the 6x7 / 67 and love it or hate it, ignoring it exposes you to the risk of snapping the coupling chain.

12-02-2013, 02:22 PM   #5
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Thanks Silent Street. I'm removing the lens before the prism and installing the prism before the lens. My problem seems more confusing (I need to test more methodically I think). I have two 6x7 'Asahi Pentax' TTL prisms, a 6x7MU body and a 67 body (both chains look fine).
Both prisms appear to read roughly the same exposure as each other and compared to a separate meter:

Prism a) meters upwards from '-' in both stop-down and open-aperture metering on both bodies.
Prism b) meters downwards from '+' but only in stop-down mode on the 6x7MU and doesn't appear to respond in either mode on the 67.

The above doesn't make sense so I'll need to recheck them again more carefully (I may not have ensured the shutter dials on the body & meter were sync'ed up).

How does the prism know whether the lens is set to 'Auto' or 'Man'?

Regards,

John.
12-02-2013, 03:31 PM   #6
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QuoteOriginally posted by johnha Quote
How does the prism know whether the lens is set to 'Auto' or 'Man'?
The lens lock pin... if you look at the lens release button/slider, the pin that it locks the lens in place has a smaller pin at its center. That is the actuator that operates the switch within the camera body just under the lens release slider and it goes from negative to body to the connector under the finder on the advance lever side.

Last edited by MysteryOnion; 12-03-2013 at 07:47 AM.
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