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04-22-2013, 09:31 PM   #1
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Metering with M lenses on K-x

So I have a SMC-M 1.7, trying to make it work with a K-x.

Did my homework, read the stickies, got it to work maybe 80 percent of times.

My problem is that every so often (maybe like twice out of 10 tries) the reading from metering with the green button is off the charts...majorly so. Most times it works ok: let's say I'm focusing on a light bulb and it gives me shutter 1/4000 at f1.7, and as I stop down and keep metering the shutter decreases like it should, and I end up with let's say 1/10 at f22 it all makes sense and it's normal. But sometimes the reading is just nuts, like half a second at 1.7 on the same focus point, same light conditions. The kind of reading that if you follow it you end up with either a full white or full black image. Is this supposed to happen? Is the green button a compromise that only works sometimes, or is it supposed to be bulletproof?

Second question: when I'm in Av with the same manual lens, I understand the green button is useless and the metering is done automatically wide open. Is this correct? Let's say you only want to shoot wide open, is it ok to leave it Av, in terms of metering?

Third thing: setting up the green button in M mode I have the following options - P-line, Tv shift, Av shift, or off. Which one do I chose? I'm a bit lost there...

And last, what does the exposure compensation button do when in manual mode with manual lens? Seems to me it acts just like the green button, metering, but the reading is totally different...lost again.

Thanks in advance. Yes, I will read the manual, I know, shouldn't even be asking all this stuff. Maybe one of the geniuses is up and bored? Thanks guys.


Last edited by steppenfuchs; 04-22-2013 at 09:38 PM.
04-22-2013, 09:47 PM   #2
dms
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As regards your first question--I use same lens with Kx (and K20D) and never noticed anything odd--except if the lens aperture (on stopping down) results in a light level below the ability of the light meter. This can happen as the lens is not metering with open aperture--as it would with an A lens (if set to A).
04-22-2013, 10:01 PM   #3
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Well I am still up so a few more ...

Second question: when I'm in Av with the same manual lens, I understand the green button is useless and the metering is done automatically wide open. Is this correct? Let's say you only want to shoot wide open, is it ok to leave it Av, in terms of metering?

(Answer) Yes. Although you can meter and the make mental adjustments--as an example so little light that only full open is enough for the light meter.

Third thing: setting up the green button in M mode I have the following options - P-line, Tv shift, Av shift, or off. Which one do I chose? I'm a bit lost there...

(No Help There--I only know about manual and AV--Old School)

And last, what does the exposure compensation button do when in manual mode with manual lens? Seems to me it acts just like the green button, metering, but the reading is totally different...lost again.

(Answer) Unfortunately the Kx does not apply exposure adjustment in M mode. Which my K20D does. Thjs is a major issue for me--and I don't know why reviews (any of them) of the Kx don't point this out (yes--after buying it I read the manual!).
04-22-2013, 10:04 PM   #4
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QuoteOriginally posted by dms Quote
As regards your first question--I use same lens with Kx (and K20D) and never noticed anything odd--except if the lens aperture (on stopping down) results in a light level below the ability of the light meter. This can happen as the lens is not metering with open aperture--as it would with an A lens (if set to A).
I got it. Does it work the other way as well? If the light level is OVER the limit of the light meter? Like needing 1/8000 (which the K-x can't do) and then the reading gets screwed up?

04-22-2013, 10:16 PM   #5
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Yes--if you look at the camera spec there is a maximum and minimum.

As a matter of practicality the maximum isn't generally a problem once you are aware of it--as you can stop the lens down--and take it off A setting if need be--although not sure what you do for a lens w/o aperture ring.
04-22-2013, 11:06 PM   #6
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I occasionally see this wildly off metering occuring using M lenses using M mode on my K-x. Not often, though - much less frequently than what the OP reports - maybe 1-2% of uses of the Green button. In aggregate, I would have taken approx 2000+ shots with M lenses, so have a pretty extensive sample set here. No idea why this is so (maybe variability in the mount's electrical contacts ability to stay in contact with the M lens' metal bayonet plate??). I either press the Green button a few more times and it gets its act together, or I cycle the camera off and then on again, and then the problem is gone for some time. It's not a metering range issue - typically I am well within tolerance - eg using F4 - F8 on a sunny day when the odd results occur. Likewise, the erroneous setting can go either low or high in terms of shutter speed set. I note though that the M 50/1.7 wide open can go out of range on a really bright scene.

From memory (camera not with me), I have the Green button programmed as TAv when in Manual Mode. I use fixed ISO settings if that's relevant - I don't commonly use auto-ISO ranges.

AFAIK, its does not appear that any exposure compensation can be set when using manual lenses in M mode with the K-x. For me, the compensation button seems to act just like the Green button. To vary exposure away from the metered setting determined by the Green button, I vary either shutter speed or aperture after the act of metering (generally vary the shutter speed so I keep the desired DOF). I find the camera under-meters about 2/3rds stop commonly with the M lenses, so two clicks on the rear wheel immediately after pressing the Green button is near automatic for me (and checking the histogram after the shot to confirm the desired outcome was achieved).

I dont use the Av mode, but I believe your understanding is broadly correct. Green button probably acts like it does in other modes and returns the camera to a 'correct' metering, but doesn't need to be touched to take a photo.

Last edited by southlander; 04-22-2013 at 11:15 PM.
04-23-2013, 12:34 AM   #7
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Thanks southlander, you actually really answered part of my issues, and I'm happy I'm not the only one with this bug, so I'm cool with it. I only started playing with manual lenses today and I'm pretty sure in real day-to-day usage the issue won't be an issue at all.

I still don't know what the exposure comp button does in manual mode with manual lenses. Is it maybe some kind of DoF preview I don't get? The readings I get from that button and the Green button are something like 1/3 EV apart usually, excpt for when they both go berserk.
04-23-2013, 01:57 AM   #8
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80% of the time I use MF lenses, not M or K lenses but converted Contax lenses. These can be used in M- and Av-mode (in Av-mode with Auto ISO).

On the K5 the EV compensation works in M-mode. There are two ways of metering, Green button and DOF preview on the ON/OFF switch. I have moved the Tv to the back e-dail so I can change the Tv setting with my thumb while holding the switch with the index finger. I do not know if the K-x can do the same thing.

QuoteOriginally posted by steppenfuchs Quote
Third thing: setting up the green button in M mode I have the following options - P-line, Tv shift, Av shift, or off. Which one do I chose? I'm a bit lost there...
Set the Green Button to Tv shift, that is the only thing you can shift with an M lens.

I do not recommend using Av with an M lens.

I have never experienced the Green Button to meter wrong but I do compensate some, when using my 1,4/50.

04-23-2013, 03:56 AM   #9
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The metering could be off because of sticky aperture blades. If the camera doesn't stop down correctly before metering. Sometimes the metering will also be off because the light reflects in some way or there is a highlight. In that case, the metering isn't wrong, its just done according to camera logic, which isn't necessarily as good as yours.
I suggest you just meter less. You can meter when the light scene changes and then just change according to that. When I use M lenses I meter and then just set the ISO high enough to keep the shutter that I want (1/(2*focal length), usually) and then move the aperture depending on whether the light is brighter or darker than when I metered.
Oh and btw, I noticed my K-r's metering is sometimes different in live view than it is is during regular metering. So the camera is using some algorithms to meter and they might not be perfect.
04-23-2013, 06:07 AM   #10
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QuoteOriginally posted by steppenfuchs Quote
Third thing: setting up the green button in M mode I have the following options - P-line, Tv shift, Av shift, or off. Which one do I chose? I'm a bit lost there...
On K- and M-series lenses you always get Tv-shift no matter what this option is set to.

On A-series or newer lenses the camera can change apeture, so then you can use the other two options (if aperure ring on the lens is set on A-position).
04-23-2013, 07:46 AM   #11
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I have a lens with sometimes-sticky aperture blades, and this gives me bad metering. If it sticks when I press the green button, the shot is under exposed. If it sticks on the shutter button, over exposure. I usually press the green button a couple of times to make sure I get the same reading, and fire off two shots, and I seem to get one right most of the time.
04-23-2013, 11:23 AM   #12
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Lens is perfect, no sticky blades.

From what I've seen so far it only happens when I'm out of range, too dark or too bright. Like Southlander said, cycling the camera on and off solves the problem.
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