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11-09-2010, 05:15 PM   #1
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Auto Lenses on Pentax Kx..stop down metering..HELP

Hey everyone..Pentax Kx users..need help if you can please, I have a 28mm Auto lens screw mount and I use the adapter & Also a 35 mm k mount...I cannot figure how to do the stop down metering with the lenses...could they be broken or am I doing something wrong!? I have a 50mm k mount that I use and works fine..I have my Green Button set to open & close when I hold it & I also have a 135mm, 300mm, and 75-200mm that all work fine(screw mounts) I am not sure what is wrong...any advice, help..anything..thank you Pentax users

11-09-2010, 05:48 PM   #2
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Here's how it's done, step-by-step: https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-manua...7-k-x-etc.html

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11-09-2010, 05:54 PM   #3
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QuoteOriginally posted by CLYNN0928 Quote
...I have a 28mm Auto lens screw mount... I cannot figure how to do the stop down metering with the lenses...
Is there a switch "auto - manual" on the lens? If not, your 28 mm screwmount lens is "auto-only." Read this thread.
11-09-2010, 08:48 PM   #4
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QuoteOriginally posted by SOldBear Quote
Is there a switch "auto - manual" on the lens? If not, your 28 mm screwmount lens is "auto-only." Read this thread.
To add, you will not be able to do stop down metering with the M42 lenses as you can with your K mount lenses. That is, you need a lens that can be set to M (as suggested above), and the lens aperture will not move by any action of the camera. You Can do the stop down procedure to get/set your shutter speed. There is no mechanism in the camera to operate the aperture.



11-09-2010, 09:24 PM   #5
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QuoteOriginally posted by JeffJS Quote
To add, you will not be able to do stop down metering with the M42 lenses as you can with your K mount lenses. That is, you need a lens that can be set to M (as suggested above), and the lens aperture will not move by any action of the camera. You Can do the stop down procedure to get/set your shutter speed. There is no mechanism in the camera to operate the aperture.

This makes me confused about what stop down metering exactly is. The bold text can be read in two ways
1)
you can't do stop down metering with M42 lenses
2)
you can use stop down metering but it works different from K mount lenses

Without wanting to hijack the thread, can you explain or give a definition.

For me, it is
"closing the aperture to the intended 'value' and letting the camera determine the other variables for correct exposure."


It's what I do with M42 lenses in either Av mode or M mode with the green button.

PS
I only have M42 lenses, no manual K-mount lenses.
11-09-2010, 09:33 PM   #6
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QuoteOriginally posted by sterretje Quote
"closing the aperture to the intended 'value' and letting the camera determine the other variables for correct exposure."
That is correct. Again I will refer you to the link in post #2, as that article explains everything that there is to know (except for that fact that apparent some 3rd party lenses don't have the auto/manual clutch. If that's the case, then you can't stop the lens down on a DSLR, and thus can't use stop-down metering).

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11-09-2010, 09:41 PM   #7
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QuoteOriginally posted by sterretje Quote
This makes me confused about what stop down metering exactly is. The bold text can be read in two ways
1)
you can't do stop down metering with M42 lenses
2)
you can use stop down metering but it works different from K mount lenses

Without wanting to hijack the thread, can you explain or give a definition.

For me, it is
"closing the aperture to the intended 'value' and letting the camera determine the other variables for correct exposure."


It's what I do with M42 lenses in either Av mode or M mode with the green button.

PS
I only have M42 lenses, no manual K-mount lenses.
#2.

Perhaps we define it a little differently. To me, and this may just be MY definition, Stop down metering is setting the camera to exactly how you intend to shoot by setting the exposure manually with the meter. With M42 lenses, as you know, the dSLR camera cannot control the aperture so we need to use lenses that have the A/M switch so we can control the aperture (preset lenses aside). With the caveat that I've never used a camera that does not have 2 e-dials, this is how I go about it with K mounts (K/M).

1. M mode (rear e-dial set for shutter speed, Preview set for Optical)
2. Focus
3. Adjust aperture as desired
4. Pull Preview lever (this both shows DOF preview and activates the meter)
5. Adjust shutter speed as needed to center the meter.
6. Shoot.

With this method, the K/M lenses stay wide open until step 4. With M42 lenses (set to M) it works the same way except the camera is not stopping the aperture down, you are. While the meter is active in either case you can both turn the aperture ring and/or dial the shutter speed to get your desired meter reading. Steps 4 and 5 do this automatically (on the K10/20/7/5) by pressing the green button but it Centers the meter and that's not always where I want it.

With an A type (k mount) lens set on A in M mode, the preview lever will Not activate but a half shutter button press will. At that point set your shutter speed and aperture. Once set, if you half press the shutter release while changing either the aperture or shutter speed, the other will adjust to keep the same exposure. It works this way with A/F/FA lenses. I see no reason why it wouldn't be the same with DA/DA* lenses as well.

Hope that explains it..

11-10-2010, 03:54 AM   #8
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using M42 lenses the easiest way is to use Av mode.

the camera will adjust the shutter speed to match the light thelens passes.

assuming all settings are set (use Aperture ring etc) the process is as follows

leave the lens in Manual mode, this will let the aperture follow the aperture ring.

With the aperture wide open, focus and compose your shot

then stop the lens down to the desired aperture, and press the shutter

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