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10-29-2013, 11:01 AM   #1
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SMC Pentax-M 35mm f/2.8 and light-meter

Hi everyone,

I just purchased a SMC Pentax-M 35mm f/2.8 in good condition, but there is something weird going on with the light meter of my K-1000, it seems to be about 2 stops off compared with when I use the SMC Pentax-A 50mm f/2.0 that came with it. The same thing happens with a RMC Tokina 28mm f/2.8.

Here's what I did:

Mount the 35mm lens, adjust the settings according to the light meter, at f/2.8 I had to set the shutter speed to 1/15. I switch to the 50mm and at f/2.8 and 1/15 the light meter tells me it's overexposed. I mount the 28mm and again the light meter tells me that the exposure is correct.

I use the 50mm all the time, so nothing's wrong with it. A few months back I experimented with the 28mm and decided to not trust the light meter, good hunch.

Is there something to setup to get the light meter to work correctly with those lenses, or can I set the camera to a higher ISO to compensate, that would imply that the difference is linear.

Any suggestions or hints are welcome.

Best

-- Bastien

10-29-2013, 12:25 PM - 1 Like   #2
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Your K1000 meter reads the entire area of the focusing screen equally, a so-called "averaging" pattern.
When you compare readings you may be taking in more bright sky with the wide-angle lens than with your 50mm.
This will tend to inflate your exposure reading.

A simple test would be to point the camera with 50mm lens mounted standing close to a large evenly lit wall uniform in color.
Set aperture and shutter speed to center exposure indicator needle.
Then switch lenses and point it at the same wall. Check the viewfinder to make sure all you see is the wall.
The needle should still be centered, or very close to it. If so I'd say you have no problem. Good luck!

Chris
10-29-2013, 01:23 PM   #3
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Thanks Chris, it seems like a good guess. I falsely assumed it was spot metering.
10-29-2013, 03:10 PM   #4
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Not sure about your camera but most camera have different errors over the exposure range with non A lenses.

Search the threads for metering issues with K10/20 bodies and a post I have made.

The best test is to meter at each aperture setting using the camera to meter, and then plot greyscale value as measured in your photo editor, i use a uniformly lit block wall, or paved road as the target

10-29-2013, 03:25 PM   #5
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QuoteOriginally posted by Bastien Quote
Thanks Chris, it seems like a good guess. I falsely assumed it was spot metering.
A mistake people have made going back to the Spotmatic.

Pentax did not have a camera capable of spot metering until the PZ series.
10-29-2013, 04:41 PM   #6
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QuoteOriginally posted by Lowell Goudge Quote
Not sure about your camera but most camera have different errors over the exposure range with non A lenses.

Search the threads for metering issues with K10/20 bodies and a post I have made.

The best test is to meter at each aperture setting using the camera to meter, and then plot greyscale value as measured in your photo editor, i use a uniformly lit block wall, or paved road as the target
No worries, your K1000 should meter fine with any pre-digital Pentax lens.

Frankly if I'd had to "plot greyscale values in a photo editor" I would never have picked up a camera.
Fortunately learning correct exposure using a film camera's built-in light meter isn't difficult at all.

I consider myself extremely lucky for having learned photography in the film era.

Chris

Last edited by ChrisPlatt; 10-29-2013 at 05:47 PM.
10-29-2013, 08:51 PM   #7
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QuoteOriginally posted by ChrisPlatt Quote
Frankly if I'd had to "plot greyscale values in a photo editor" I would never have picked up a camera.
Fortunately learning correct exposure using a film camera's built-in light meter isn't difficult at all.
You don't need to do scans or even shoot a single photo to evaluate meter readings between lenses. Simply point the camera at an evenly-lit blank wall. You should get similar shutter speed readings across lenses for the same aperture. You can enter the numbers into a spread sheet to plot the values if desired.


Steve
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