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11-19-2009, 08:37 PM   #1
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K-x Stop-down metering with m-42 lenses

Hi everyone-

I love my new K-x like everyone else seems to, but I'm just having some problems getting stop-down metering to work with my Takumars and I would appreciate any advice that you might have. I'm not new to stop-down metering, having used it with my Takumars on my K100d for about two years. However when I put the Takumars on the K-x and press the green button, nothing happens. No sound of aperture blades, no metering. What is particularly odd is that when I mount an "M" lens on the K-x, the green button does work, performing the stop-down metering as it should.

Am I missing something obvious here? Is there a particular way that the green button has to be configured for m-42 lenses? Or, god forbid, does the K-x not meter with m-42s?

I should note that the Takumars I've tried are the SMC 50 1.4 and the SMC 28 3.5, both of which have quite narrow mounts that don't fully cover the electrical contact points on the camera body. Maybe that's a factor.

Thanks for any suggestions.


Bazwell

11-19-2009, 09:27 PM   #2
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M42 lenses need to be manually stopped down on DSLRs. The body cannot do it.
11-19-2009, 09:34 PM   #3
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Yep, as said above.

The good thing is it manuals without pushing the green button or +/-. So the meter should be reading. You can also set the green button for program mode, so it gives you recommendations, AND Av mode will work (you stop down the lens and it will select a shutter speed and ISO for you).

For this reason, some people prefer m42 lenses.
11-19-2009, 09:48 PM   #4
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QuoteOriginally posted by Bazwell Quote
What is particularly odd is that when I mount an "M" lens on the K-x, the green button does work, performing the stop-down metering as it should.
I was looking through the manual(PDF) and I too wondered if this was possible because I did not see a manual metering option in contrast to our K20/200 camera's

Though I know you could get away with Av mode, it sort of defies the entire purpose if you can't fine tune your settings after an initial reading

QuoteQuote:
narrow mounts that don't fully cover the electrical contact points on the camera body. Maybe that's a factor.
To my knowledge the contact don't affect green button reading, though it does affect in focus trap(doesn't work). Other than that, most other functions should work.

Though I do hope this is just a setting or something. Because I've been working out a plan to add a K-x to our kit specifically to take advantage of the higher sensitivities with some of our manual lenses. However, with disadvantages such as these, I don't see much use coming from that body in our case.

11-20-2009, 06:25 AM   #5
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Thanks for your responses. I should have clarified a couple of things about my experience with the camera. I realize that I can use Av mode and the camera will meter. That does work on my K-x, with the usual necessity for dialing up various amounts of of +/- to compensate for changing levels of underexposure throughout the lens's aperture range. But I find it awkward because of the guesswork involved in figuring out how much compensating overexposure to dial in for each aperture.

On my K100d I have preferred to use the M mode and just press the AE-L button to get a suggested Tv value for the particular aperture I've selected, the same as one does with K and M-mount lenses. That part is what doesn't seem to work on my K-x. I have the Green Button set to P-Line in the "Action in M Mode" setting. With an M or K lens, the Green Button does cause the camera to take a meter reading--accompanied by the usual swishing sound as the lens is stopped down--and to give a suggested shutter speed for the aperture value I've chosen on the lens. But when I mount a Takumar and try the same thing in M mode, it doesn't work. This is different from what happens on my K100d, where the K, M and M-42 lenses all work the same way in M mode: pressing the AE-L button (precursor to the Green Button) gives you a meter reading with a suggested shutter speed to match your chosen aperture value.

So, my K-x definitely does meter in Av mode, which a lot of people seem to prefer with m-42 lenses anyway. But in M mode, which I preferred on the K100d because of the more reliable meter readings, I can't get the K-x to give me any meter reading at all. Can't find anything in the K-x manual about this either. I know I can get accustomed to using the Av mode if necessary but I would really like to continue using M if possible. This is certainly not a proverbial deal-breaker for me with this camera which has so many other fantastic features (the Takumars also work great in video mode which is fabulous b/c of their smooth focusing). But I'm still hoping that I have just got some setting wrong and once that is fixed I'll be able to continue using the M mode with my Takumars...

Thanks for any other advice you might have on this.
11-20-2009, 06:44 AM   #6
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Hey-- it does work after all!

After an hour of switching lenses back and forth between cameras and peering into them while pressing green buttons and ae-l buttons, I discover that the K-x DOES meter in M mode as long as you ensure that Green Button is set to P-line. I had it on one of the other settings last night. One thing that threw me off is that the K-x doesn't make that swishing sound (aperture stopping down on the M and K lenses) when you press the green button, though it is still making the meter reading. The K100d still did make that sound even though the aperture was already manually stopped down. So this is actually better than the old way.

So, the good new is that the K-x works with Takumars basically the same way as other Pentax DSLRs. Sorry to have caused doubts on this issue! I had a feeling it was some stupid thing I was doing, which turned out to be true. Not the first time.

Thanks again for your responses.
11-20-2009, 07:17 AM - 1 Like   #7
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just a few points to clarify here.

Regardless of what the green button functionality is set to, with any manual lens, i.e. K mount or M42, it will default to aperture priority, and set the shutter speed based on the light that comes through the lens because it does not know any aperture information to follow a program line.

pressing the green button will take a meter reading, but the reason you do not hear any "swish" of the aperture blades on M42 lenses is because there is no aperture coupling for M42 lenses. You stop them down manually.

In Av mode, there is no need to make compensations for every f stop you select, generally only one compensation for the lens, and the camera will meter that ever light comes through the lens and do the appropriate setting of shutter speed. (note on the K10D and K20D this is not quite true because the metering is not linear but that is a different issue)

With a K mount lens, regardless of where you set aperture in Av mode, the camera will always shoot wide open. Again yoou do nothing but point and shoot.

The bottom line is that for M42 lenses the best mode, unless you deliberately want to under or over expose is Av mode

For K mount lenses the best mode is Manual.
11-20-2009, 11:02 AM   #8
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QuoteOriginally posted by Lowell Goudge Quote

The bottom line is that for M42 lenses the best mode, unless you deliberately want to under or over expose is Av mode

For K mount lenses the best mode is Manual.
For an M42 lens, doesn't Av mode work similar to P mode?

11-20-2009, 12:57 PM   #9
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QuoteOriginally posted by dragonfly Quote
For an M42 lens, doesn't Av mode work similar to P mode?
More or less - you don't need to change any settings on the camera to adjust exposure, just use the aperture ring on the lens to adjust that and the camera will take care of the rest.

One thing that I didn't see mentioned (unless I overlooked it) is to make sure that your M42 lenses are set to "M" or "Manual", not "A" or "Auto". (This threw me for a little while until I realized it.) Auto mode only works on actual M42 cameras that can press the pin on the back of the lens. On a DSLR, leaving it in Auto mode will mean that you'll shoot at maximum aperture all the time, no matter where you turn the aperture ring.

I tend to prefer M42s to Pentax-M lenses. In Av mode, they behave very much like a modern lens, but the "M" lenses require you to do the extra step of stopping down before each exposure, unless you are shooting wide open in which case you can also use Av mode.
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