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07-10-2009, 07:16 PM   #1
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Using the K-m light meter - if it has one

I want to use on my K-m an m42 lens (Chinon 1:1.4/55) from my film camera. I have the adaptor and the lens does fit, and I can focus with it. I cannot determine a standard routine for getting the 'correct' exposure. It can be wildly off in all directions!

My film camera had an internal light meter. I could either set the shutter speed and adjust the aperture until the meter indicated correct exposure. Or I could set the aperture and adjust the shutter speed until the correct exposure was indicated.

How do I do that with the K-m? I would think that after entering the correct focal length for SR (55mm), and with 'Using Apperture Ring' set to permitted, I should be able to be in Manual mode, set the shutter speed, and then adjust the aperture on the lens until the 'correct' exposure is indicated. But how would it be indicated?

I appreciate that DSLR mechanical design does not put a shutter speed control on the top panel (which could be adjusted while looking though the viewfinder), so I have to enter that before using the viewfinder. But the aperture control on the lens can be adjusted while looking through the viewfinder.

The lens has a manual/automatic slider, and of course I have to set it to manual so the aperture closes and opens as I adjust it.

Can't the K-m measure the light coming in to the camera and indicate if I'm over or under exposing?

I thought I'd ask this question now while I'm waiting for my 3-month old K-m to come back from the second warranty repair.
...Chris

07-10-2009, 07:40 PM   #2
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Unfortunately, this is normal. Pentax cameras don't meter well with pre-A lenses (which includes all m42 lenses). There are several workarounds: installing a different focusing screen, using exposure compensation (which works for some lenses), or using an external meter. What I do is guess exposure--usually aided by the green button--take an exposure using the preview switch, and adjust exposure based on the histogram. Lots of information around for the reading--just use the forum search.

The only upside is that your camera can be expected to meter light just fine with any recent (Pentax-A or newer) lenses. Most of my lenses are m42, but I keep several newer ones handy when I need quick shots or just convenience.
07-10-2009, 09:36 PM   #3
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First, use the switch on the lens in "manual" position.
Then use Av mode - and the camera will adjust shutter speed automatically. Or, use "green" button in manual mode (or "?" button on K2000? I'm not sure about that one - help button is supposed to be programmable; so just let it change your shutter speed settings to program line - I can explain that further if needed)
Also, as JonPB said, there might be some errors in meter's readings - usually overexposure on smaller apertures (f/8 and smaller) - but they are correctable either by looking at results and changing exposure compensation, or using a different focusing screen - but K2000 is *supposedly* not screen-interchangeable (as opposed to K10D/K20D).

Hope it helps,
Bo.
07-10-2009, 09:41 PM   #4
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Oh, and one more thing. I don't think you can let K-m tell you if you are over/under exposing, because your power switch only has 2 positions (on/off). The other Pentax cameras have the third position - which stops down manual lenses and fires up the meter. I just looked at some pics of K2000 and I don't see that third position. Compare these two:
K-m:

K200D:


Thus, I'm pretty sure you're stuck with the "?" button reprogrammed for program line.

07-11-2009, 05:40 AM   #5
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Yep, page 119 of the manual explains how to use the "?" button for digital preview. You can use it to check depth of field, exposure, composition and focus. If you want a histogram and a warning for bright and dark areas, and you can prgram it to display that as well.

Once you assign the preview funtion to the "?" button, simply press that button whenever you want to access digital preveiw. Great use for that button IMHO!
07-11-2009, 07:04 AM   #6
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QuoteOriginally posted by Sew-Classic Quote
Yep, page 119 of the manual explains how to use the "?" button for digital preview. You can use it to check depth of field, exposure, composition and focus. If you want a histogram and a warning for bright and dark areas, and you can prgram it to display that as well.

Once you assign the preview funtion to the "?" button, simply press that button whenever you want to access digital preveiw. Great use for that button IMHO!
Thank you, sew-classic. I know about the 'preview' function and don't think it has any value. I can check depth of field, exposure, composition and focus, and display a histogram and a warning for bright and dark areas for each photo I take - it's a lot faster than preview etc. If you read my question, I wanted to know if there is a real-time method of getting a useable exposure, before I take the shot, as one does with a film camera.
07-11-2009, 07:11 AM   #7
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Use full manual mode (M) and press +/- (Av) button to set the shutter speed. It it mostly consitent. You can also shoot in Av mode if you short the data pin on mount, but I recommend shooting in M mode, checking exposure with digital preview and fixing it if it's way off.
07-11-2009, 07:12 AM   #8
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QuoteOriginally posted by kitkat Quote
Thank you, sew-classic. I know about the 'preview' function and don't think it has any value. I can check depth of field, exposure, composition and focus, and display a histogram and a warning for bright and dark areas for each photo I take - it's a lot faster than preview etc. If you read my question, I wanted to know if there is a real-time method of getting a useable exposure, before I take the shot, as one does with a film camera.
Yes, JonPB's post answered that question quite well:
QuoteQuote:
Unfortunately, this is normal. Pentax cameras don't meter well with pre-A lenses (which includes all m42 lenses). There are several workarounds: installing a different focusing screen, using exposure compensation (which works for some lenses), or using an external meter. What I do is guess exposure--usually aided by the green button--take an exposure using the preview switch, and adjust exposure based on the histogram. Lots of information around for the reading--just use the forum search.
Dummy me was just trying to help with the workaround. Sorry about that.

07-11-2009, 07:45 AM   #9
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Summarizing:

- With an M42 lens in "manual" mode, you can use Av mode normally. set an aperture, camera sets shutter speed. Drawback is that it stops down immediately as you turn the aperture ring, so the viewfinder dims.

- With K-mount lenses, or with an M42 lens in "auto" mode, you have to use "M" mode, but a magic button will cause the camera to temporarily stop down, take a meter reading, and set a shutter speed. The magic button differs from model to model. On the K2000 I think itis +/-, but see the sticky thread in the beginner forum on using manul lenses (or check the manual).

- With models *other* than the K2000, you can use the optical DOF preview to get the camera to stop down for as long you want and actually *display* a meter reading as you play with aperture and shutter speed. K2000 lacks this ability.
07-11-2009, 08:27 AM   #10
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QuoteOriginally posted by pbo Quote
Oh, and one more thing. I don't think you can let K-m tell you if you are over/under exposing, because your power switch only has 2 positions (on/off). The other Pentax cameras have the third position - which stops down manual lenses and fires up the meter. I just looked at some pics of K2000 and I don't see that third position. Compare these two:
K-m:

K200D:


Thus, I'm pretty sure you're stuck with the "?" button reprogrammed for program line.
That's irrelevant for M42 lenses as there is no mechanical connection between the lens and the camera anyway. Even if the DOF preview switch were present, the aperture actuation thingy inside the camera is designed to work on K-mount lenses. Even on the DSLRs that have the preview switch this is the same.

Since DOF can be checked at anytime on M42 lenses by merely stopping down the aperture no inconvenience arises from this situation.
07-11-2009, 12:44 PM   #11
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QuoteOriginally posted by Marc Sabatella Quote
- With K-mount lenses, or with an M42 lens in "auto" mode, you have to use "M" mode, but a magic button will cause the camera to temporarily stop down, take a meter reading, and set a shutter speed. The magic button differs from model to model. On the K2000 I think itis +/-, but see the sticky thread in the beginner forum on using manul lenses (or check the manual).
This is true with a PK-mount lens, but can't be applied to an M42 lens in "auto" mode.

There is no mechanical linkage between the camera body and the M42 lens to temporarily stop down the lens.

M42 lens in "auto" mode will be in full-aperture, regardless of the setting of the aperture ring.

This is the reason why M42 lens with "auto" only needs to be modified to "manual" only.
07-11-2009, 02:38 PM   #12
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My mistake, - sorry. But - dumb question alter - what is "auto" for, then? Or do other camera bodies provide that linkage?
07-11-2009, 03:21 PM   #13
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I don't thnk you people understood me. I said the lever, when used with m42 lenses, is just for firing up the meter - since it does not show up until you pull the lever! Try it - put on the m42 lens, and switch camera to M mode. Do you see the meter? Nope, just dark space. Now pull the lever - and bingo! - it meters!

And "Auto" mode on those lenses are for older screw mount bodies that had a plate to press that pin every time shutter is fired or DOF preview switch is pushed.
07-11-2009, 05:52 PM   #14
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QuoteOriginally posted by pbo Quote
I don't thnk you people understood me. I said the lever, when used with m42 lenses, is just for firing up the meter - since it does not show up until you pull the lever! Try it - put on the m42 lens, and switch camera to M mode. Do you see the meter? Nope, just dark space. Now pull the lever - and bingo! - it meters!
A light tap on the shutter button in Av mode does the same thing.
07-11-2009, 06:23 PM   #15
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QuoteQuote:
A light tap on the shutter button in Av mode does the same thing.
Yep, I was just explaining about manual mode.
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