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02-12-2011, 04:07 AM   #1
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Another K7 metering problem?

A few weeks ago I traded in my much-loved K100DS for a K7 and I'm beginning to regret it. I just can't get consistent metering from this thing. Here's the results of a simple test I've just done to check out the meter mode switch. The camera is on a tripod, focused on a radio on my desk, with strong desklamp lighting. Over a period of about ten minutes I set the camera to Av and respectively to ISO 400, 800 and 1600 and f4.5, f5.6 and f8 in turn. I took readings and noted that the shutter speeds were all over the place. Then I went back and did it all again a few minutes later and in some cases got a different set of shutter speeds, even though I hadn't moved the camera or tripod at all. Here are the readings (and sorry if this is a bit long, but I'm on the verge of quitting this camera and I'd really appreciate some help before I do anything daft). The figures in parentheses are the ones I took second time round.
ISO 400:
f4.5 f5.6 f8
1/20th - pattern mode (1/20) 1/15 (1/15) 1/8 (1/8)
1/15th - centre-weighted (1/15) 1/13 (1/15) 1/6 (1/6)
1/13th - spot (1/10) 1/8 (1/8) 1/4 (1/4) So far so reasonable.

ISO 800:
f.4.5 f5.6 f8
1/50th - pattern (1/40) 1/30 (1/30) 1/15 (1/15)
1/40th - centre (1/30) 1/40 (1/25) 1/20 (1/13)
1/30th - spot (1/20) 1/60th(!) (1/15) 1/30 (1/8)

ISO 1600 was OK both times. Go figure.
[Sorry, I tried to set this out as a table but it wouldn't let me. Hope you can figure it out]

I'm tearing out what little hair I have left on two counts. Firstly, why such a wide discrepancy between the three different modes? I'd expect some, but this seems a bit much and results in colour inconsistencies too. Secondly why did I get a different set of readings in some instances but not others the second time around when absolutely nothing, including the lighting, had changed? Did I buy a dud or is this perfectly normal? Any sage advice, words of comfort, relaxation tapes, banana cake would be gratefully received.

02-12-2011, 05:54 AM   #2
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images would be nice.

also can you describe the lighting better.

You will note that metering depending on spot, multi segment or average will meter differently for the same scene.

also note that lights may be very inconsistent in terms of output as a functio of time they are on, while they reach temperature stability.

Aside from that, you may be getting issues with light entering the viewfinder from the eye peice, and your approach to the camera could be part of the issue, as well as your shadow.

to test metering, the only true way is to take a shot of a block wall, and measure greyscale. or to take actual photos with the set up you are using, and measure the greyscale of the shots and other parameters, but be aware of light entering the eye peice
02-12-2011, 06:16 AM   #3
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Thanks, Lowell. Yes, I've begun to think that light entering the viewfinder could be part of the problem. I'm usually pretty careful with that, but this is a new camera and clearly a lot more skittish and thoroughbred than my old Clydesdale of a K100DS. I've also been reading a bit more about WB fine tuning with the K7, which could also be part of the problem. I'm quite willing (hoping, really) to admit that it's me and not the camera. It's just that the K100 was stone axe reliable, predictable and utterly consistent and I'm not getting that same experience with the K7 so far.

The lighting is a desklamp with a non-tungsten long-life bulb. It sheds plenty of warm but not yellow light - enough to register a reasonable set of shutter speeds at the apertures chosen. The room is otherwise quite well lit with two overhead lights of the same type (tungsten lights are no longer available in Australia). And by the way it's getting on for midnight. Speaking of which...
Tomorrow morning I'll tear out the 18% grey sheet at the back of Scott Kelby's book and do some more testing. Thanks for the response.

Last edited by Wombat; 02-12-2011 at 06:25 AM.
02-17-2011, 02:00 AM   #4
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Did you end up sorting it out , mate? Is the meterimg now doing what you expect it to?

The K-7 has a pretty decent metering system, but each mode is suited to different subject and lighting setups.

02-17-2011, 03:26 PM   #5
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QuoteOriginally posted by Wombat Quote
non-tungsten long-life bulb. It sheds plenty of warm but not yellow light
This may be out of date info but, Don't fluorescent bulbs (both compact and tubes) cycle? We used to have to occasionally deal with this when I shot video professionally a few years back. All fluorescent lights "cycle" through various levels of temp. (degrees Kelvin) and therefore do not give a constant color temperature.
So maybe using AWB instead of a preset (sunny, cloudy, shade, etc.) affects the exposure.(?)

Again, this may be old info. I'm sure someone will correct me if I'm wrong!
02-17-2011, 06:06 PM   #6
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QuoteOriginally posted by Wombat Quote
A few weeks ago I traded in my much-loved K100DS for a K7 and I'm beginning to regret it. I just can't get consistent metering from this thing. Here's the results of a simple test I've just done to check out the meter mode switch. The camera is on a tripod, focused on a radio on my desk, with strong desklamp lighting. Over a period of about ten minutes I set the camera to Av and respectively to ISO 400, 800 and 1600 and f4.5, f5.6 and f8 in turn. I took readings and noted that the shutter speeds were all over the place. Then I went back and did it all again a few minutes later and in some cases got a different set of shutter speeds, even though I hadn't moved the camera or tripod at all. Here are the readings (and sorry if this is a bit long, but I'm on the verge of quitting this camera and I'd really appreciate some help before I do anything daft). The figures in parentheses are the ones I took second time round.
ISO 400:
f4.5 f5.6 f8
1/20th - pattern mode (1/20) 1/15 (1/15) 1/8 (1/8)
1/15th - centre-weighted (1/15) 1/13 (1/15) 1/6 (1/6)
1/13th - spot (1/10) 1/8 (1/8) 1/4 (1/4) So far so reasonable.

ISO 800:
f.4.5 f5.6 f8
1/50th - pattern (1/40) 1/30 (1/30) 1/15 (1/15)
1/40th - centre (1/30) 1/40 (1/25) 1/20 (1/13)
1/30th - spot (1/20) 1/60th(!) (1/15) 1/30 (1/8)

ISO 1600 was OK both times. Go figure.
[Sorry, I tried to set this out as a table but it wouldn't let me. Hope you can figure it out]

I'm tearing out what little hair I have left on two counts. Firstly, why such a wide discrepancy between the three different modes? I'd expect some, but this seems a bit much and results in colour inconsistencies too. Secondly why did I get a different set of readings in some instances but not others the second time around when absolutely nothing, including the lighting, had changed? Did I buy a dud or is this perfectly normal? Any sage advice, words of comfort, relaxation tapes, banana cake would be gratefully received.

Check your menu to ensure you have multi-exposure setting "OFF", also in drive mode make sure you have bracketing "OFF".
02-17-2011, 07:38 PM   #7
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QuoteOriginally posted by K(s)evin Quote
This may be out of date info but, Don't fluorescent bulbs (both compact and tubes) cycle? We used to have to occasionally deal with this when I shot video professionally a few years back. All fluorescent lights "cycle" through various levels of temp. (degrees Kelvin) and therefore do not give a constant color temperature.
So maybe using AWB instead of a preset (sunny, cloudy, shade, etc.) affects the exposure.(?)

Again, this may be old info. I'm sure someone will correct me if I'm wrong!
although the phosphors are pretty goo they still cycle

I shot a tube at 1/250 th and diagonally across the frame so that the shutter slit moved along the tube as a function of time. You can see a different color at one end to the other. Slower speeds will show less
02-17-2011, 09:02 PM   #8
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QuoteOriginally posted by Ash Quote
each mode is suited to different subject and lighting setups.
Thanks everybody for your kind help. I think I've got my head sorted out now and that comment, Ash, is kind of the clincher. The leap from the K100 to the K7 really threw me for six and I went into a bit of a panic with all the choices and decisions to make. I've since read more widely and also have updated the firmware from 1.0 to 1.11, which seems to have settled things down really well. One thing I've discovered is that this camera needs at least +1.00 Ev for many shots. I thought there must be something wrong, because the most I ever had to correct the K100 was +0.3, but it seems +1.00 is not unusual for the K7. Is that your experience?
So yes, I can now get consistent shots if I take careful note of every mode, every button and every setting I'm in. M mode seems to be the easiest for me to work with but P and TAv are useful and fun at times. It's all settling down nicely, I've apologized to the camera and thanks to all your suggestions and encouragement I feel a lot more confident with it. All my old manual primes at last have something to bite on and are coming into their own.
Thanks again, gents. Pentax forum does it again.

---------- Post added 02-18-11 at 02:36 PM ----------

QuoteOriginally posted by Lowell Goudge Quote
although the phosphors are pretty goo they still cycle

I shot a tube at 1/250 th and diagonally across the frame so that the shutter slit moved along the tube as a function of time. You can see a different color at one end to the other. Slower speeds will show less
Are you a scientist, Lowell? You constantly amaze me with all this stuff! I'd love to have that sort of knowledge.

Les

02-17-2011, 09:46 PM   #9
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Little pic for you of appreciation (somewhat oversharpened - I'll fix it later. And yes, the sky's blown out, but I like it like that...). Couple of local kangaroos at sunrise.
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