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02-18-2012, 06:14 AM   #1
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Metering issues with Pentax

Most of the time I use FA type lenses with my *ist. Recently, however, I have been trying out some M42 lenses, which obviously lack the aperture pin.That's probably why the camera doesn't meter correctly with manual lenses. I tried compensatig the EV with +1 stop, but the negatives were still underexposed (or maybe underdeveloped).

What I'm wondering is what kind of camera should I get for manual lenses. Can MZ-5n for instance meter correctly or should I be looking for something older like those MF cameras?

02-18-2012, 07:00 AM   #2
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I have used the "Spotmatic F" for metering with M42's. It is a fantastic camera and can be had at a good price just shop carefully. The battery for metering may be hard to find but i think an equivalent can still be had.
02-18-2012, 07:13 AM   #3
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The auto diaphragm on M42 lenses only works on M42 bodies like the Spotmatic. On all Kmount cameras, used with the K adapter, you need to switch the A-M switch to M so the lens stays stopped down (at least for metering and capture).
Best use of M42 lenses is on a Spotmatic (if you want metering in the camera) or earlier SV (non-metered) body.
Any of the Spotmatic series would be a good body to use. The Spotmatic F offers full-aperture metering, but only with the later SMC Takumar lenses that have the extra linkage to tell the body the aperture set. But all M42 lenses work great on the original Spotmatic, SPII, SP1000, etc.
02-18-2012, 07:24 AM   #4
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Actually, all the M42 lenses work fine on the Spotmatic F. It operates just like any other Spotmatic with non-SMC lenses. A standard SR44 type silver oxide battery with an o-ring on it fits in the battery compartment and the bridge circuit in the camera can accommodate the voltage difference with no adjustment in the ISO setting needed.


Last edited by Tom in Delaware; 02-18-2012 at 07:32 AM.
02-18-2012, 08:00 AM   #5
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QuoteOriginally posted by Tom in Delaware Quote
Actually, all the M42 lenses work fine on the Spotmatic F. It operates just like any other Spotmatic with non-SMC lenses. A standard SR44 type silver oxide battery with an o-ring on it fits in the battery compartment and the bridge circuit in the camera can accommodate the voltage difference with no adjustment in the ISO setting needed.
Agreed - but often you pay a premium for the "F" model, and if all your lenses are non-SMC, the F offers no advantage, as you must meter stopped-down anyway.
02-18-2012, 09:48 AM   #6
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Hi

With both my KX and K100 it is necessary to add + 1.7 ev with lenses that don't short out the
camera contacts but my K10 and a Sony A33 it is not needed.
I know it is in the implementation of the allow aperture ring in the firmware, something that
has yet to be reviewed by Pentax but should be.
02-18-2012, 10:22 AM   #7
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QuoteOriginally posted by Jüri Quote
I tried compensatig the EV with +1 stop, but the negatives were still underexposed (or maybe underdeveloped).
You are stopping down to meter, I assume?

It might help if you outline the flow (steps) you use with the M42 lenses.


Steve
02-18-2012, 02:55 PM   #8
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QuoteOriginally posted by stevebrot Quote
You are stopping down to meter, I assume?

It might help if you outline the flow (steps) you use with the M42 lenses.


Steve
I use Av mode and M42 lenses with manual aperture, so the camera should figure the shutter speed, regardless of aperture. I just did some testing and metered same scenes with my K10D and *ist using same ISO and aperture. The *ist seemed to underexpose persistently by 3 stops.

I'm not actually planning to aquire a screwmount camera. I need something with K-mount and preferably AF that unlike the *ist can meter correctly with M42 lenses. Or I can just use the EV compensation if it proves to be a consistent method.

02-18-2012, 05:20 PM - 1 Like   #9
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Sounds like you are managing the gear properly. Normally, stop-down metering is sort of the "gold standard" for light measurement and three stops off is pretty severe. The only possibility that I can think of other than a defective camera, is that you may inadvertently be shooting at the low end of the meter's sensitivity.

Your *ist has great meter sensitivity (EV0-EV21(100)), but EV0(100) at the meter comes quickly at smallish apertures in dim light. Meter linearity can fall off well before the low end of its range resulting in underexposure. Be aware that this characteristic has nothing to do with the supported ISO range. The meter can support ISO 6400 as a setting, but that does not mean that it can see in the dark.

As for measuring against the K10D...be sure and use an "A" contact lens for your measurements. The K10D is legendary for poor meter performance in stop-down mode. It is possible that your *ist suffers from the same issue.

IIIiiirrrcccc... (sound of brain coming to a screeching halt). I just took a wander through the *ist manual (downloaded form pentaxusa.com) and low and behold the lens compatibility matrix has the same sort of caution statement for stop-down metering as for the K10D. Sorry to say, but your body probably is not so good with legacy glass.

As a replacement, I can suggest any of the legions of Av and manual-metered K-mount cameras available from Pentax, Ricoh, Vivitar, Cosina, and others. Even better would be a screw-mount body. In actual operation a M42 body is a lot handier with M42 lenses than an adapted K-mount.


Steve
02-21-2012, 05:46 PM   #10
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I'm wondering if the issue is somewhat related to the issues with the K10/20d and old manual lenses. Some cameras have irregular metering because they need to know the maximum and minimum aperture. Without lens contacts the *istD does not know what is connected
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