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04-25-2013, 12:02 PM   #1
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Pentax K1000 Light Meter Issues with M42 lense

I'm having an issue when I use a Takumar 1:3.5 28mm M42 lense on my Pentax K1000. The light meter stays in the (+) position until the shutter speed is switched to the (B) position. Then it starts reacting to aperture adjustment. When I switch the lense back to my 50mm K-mount lense, everything works just fine.

Any ideas?

04-25-2013, 12:11 PM   #2
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Hi,
I think that lens has an Auto/Manual Switch at the back of the lens. This should be set to Manual. The K1000 has no auto setting.
d
04-25-2013, 12:17 PM   #3
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QuoteOriginally posted by dermc Quote
Hi,
I think that lens has an Auto/Manual Switch at the back of the lens. This should be set to Manual. The K1000 has no auto setting.
d
The issue persists even when the Manual selection is on.
04-25-2013, 12:43 PM   #4
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Are you sure the lens aperture is working?

Set to Man (or to Auto and pressing the actuator on the back of the lens) should result in opening/closing the aperture if you change the setting on the lens.

If this works, the light meter of the body should react. Of course, if you are not pointing the camera directly to the sun or a very strong light bulb.

04-25-2013, 12:49 PM   #5
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I read both your postings again carefully.

What you describe seems to be technically impossible.
At least I cannot think of an error which could lead to such a behaviour.

Maybe your description is not complete?
04-25-2013, 01:02 PM   #6
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What adapter are you using? Does it screw in completely and click firmly inside the K-mount?
04-25-2013, 01:27 PM   #7
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QuoteOriginally posted by kcobain1992 Quote
What adapter are you using? Does it screw in completely and click firmly inside the K-mount?
The adapter that I'm using is a genuine Pentax adapter. Would the adapter not being attached just right cause a problem with the light meter?
04-25-2013, 01:32 PM   #8
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@kcobain1992
This should not make any difference.
The K1000 has no means to detect the aperture setting of a M42 lens.

Whether it is correctly fitted, loose, or no lens attached at all, it shouldn't change anything.
The body would always "think" a lens with fully open aperture is attached.

EDIT:
The late Takumars had a linkage to allow for open aperture measurement with the Spotmatic SP/F, ES, ES II.
But as far as I know, the K1000 with M42 adapter has no means to detect the offered lens state information, so any defect in this mechanic should not cause the described error.


Last edited by RKKS08; 04-25-2013 at 01:51 PM.
04-26-2013, 11:32 AM   #9
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QuoteOriginally posted by RKKS08 Quote
@kcobain1992
This should not make any difference.
The K1000 has no means to detect the aperture setting of a M42 lens.

Whether it is correctly fitted, loose, or no lens attached at all, it shouldn't change anything.
The body would always "think" a lens with fully open aperture is attached.

EDIT:
The late Takumars had a linkage to allow for open aperture measurement with the Spotmatic SP/F, ES, ES II.
But as far as I know, the K1000 with M42 adapter has no means to detect the offered lens state information, so any defect in this mechanic should not cause the described error.
Yeah I've been messing with it a bit more, it seems that this its extremely sensitive to light with that lense on though. Today it's mostly sunny and I've got it set to f/16 and even at 1/500 or 1/1000 I can barely get the light meter to a good exposure.

I'm new to 28mm lenses, so maybe that's the way it's suppose to be.
04-26-2013, 11:38 AM   #10
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QuoteOriginally posted by RKKS08 Quote
...
This is not correct.
If you have a non-crippled Pentax camera handy, take the lens off, locate the aperture detecting lever (on the right hand side while looking at it), then look through the viewfinder and watch the exposure go up and down as you slide that lever.
04-26-2013, 11:49 AM   #11
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QuoteOriginally posted by kcobain1992 Quote
This is not correct.
If you have a non-crippled Pentax camera handy, take the lens off, locate the aperture detecting lever (on the right hand side while looking at it), then look through the viewfinder and watch the exposure go up and down as you slide that lever.
Alright I'll try that. The weird thing is that when I attach my 50mm lense everything works just fine.
04-26-2013, 12:03 PM   #12
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Well, that's because I only told half of the story, because I forgot where I started from, lol
If you look closely at an M42 adapter, you will see that the aperture detecting lever is dragged all the way down by a hole in that adapter, the same hole that serves no purpose in a crippled (digital) K-mount. You may be experiencing problems because of not screwing the adapter all the way, hence resulting in wrong exposures with the M42 lens. There really should be no other reason.
04-26-2013, 01:06 PM   #13
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...and the next question is (again)...

With the Auto/Manual switch in the manual position, is the diaphragm actually stopped down when on the camera and the aperture ring moved to other than full open. The diaphragm action should be visible looking into the front of the lens and should also be evidenced by a significant dimming of the viewfinder.


Steve
04-26-2013, 01:18 PM   #14
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QuoteOriginally posted by stevebrot Quote
...and the next question is (again)...

With the Auto/Manual switch in the manual position, is the diaphragm actually stopped down when on the camera and the aperture ring moved to other than full open. The diaphragm action should be visible looking into the front of the lens and should also be evidenced by a significant dimming of the viewfinder.


Steve
Yes when looking through the viewfinder, it does get dimmer. It actually gets really dim at some points. Is this what's suppose to happen?
04-26-2013, 02:50 PM   #15
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The K1000 light meter is an analog computer! (I am old enough to think that's cool.) There are several variable resistors in the camera, controlling how much electricity gets from the battery to the needle in the viewfinder. The resistors are the cell that measures the light, the shutter speed dial, the ASA dial, and the aperture detecting lever in the lens mount. That lever moves in an arc on the right side (camera facing you with no lens on it). It's spring loaded to stay up until pushed down. A K-mount lens has a slot for this lever. Turning the aperture ring on the lens when it's mounted moves the lever, so the light meter can account for you adjusting the ring.

As mentioned above, an M42 lens doesn't have the mechanics for that lever. The adapter has to move it into a position where the analog computer doesn't factor in that lever at all. It can still account for the other settings on the camera (shutter speed and ASA) and the light coming into the lens. When you put the M42 lens into Manual mode and turn the aperture ring, the blades stop down, less light gets to the light cell and the meter can adjust. If the adapter ring doesn't catch that lever properly, the lever position confuses all the other inputs to the meter.
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