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01-18-2008, 01:35 PM   #1
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K10D low light metering

symptom:

with lens cap on and in manual mode it is possible to have the metering bar competly
on the right side (overexposure) with 3.5 aperture and a 25 seconds exposure time.

putting the exposure time down to 6 seconds, the metering bar is middle (correct exposure?)
exposure and aperture values blinking.

how is that possible? there is no light, the lens cap is on - why does the metering bar can be
on overexposure side, or why are exposure and aperture values blinking with metering
bar in the middle?

firmware 1.3, tamron 18-250

01-18-2008, 01:50 PM   #2
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Unless you like to shoot pictures of the backside of your lens cap, who cares? So the lens cap screws up the metering. Do you see any problems when using the lens the way you are supposed to?
01-18-2008, 01:53 PM   #3
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Light entering viewfinder..
01-18-2008, 01:58 PM   #4
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Two things come to mind. 1) I don't believe the lens cap keeps 100% of the light out, and 2) if you were not in a completely darkened room, light can enter from the viewfinder. Could that have an impact on the results?

01-18-2008, 02:02 PM   #5
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i just tried to pull down the problem to a reproducable situation.

yes - in very low light situations i suppose at least the manual metering bar to tell me *some* truth. sign of overexposure is not the thing i expected with lens cap on.

without lens cap (supposed usage?) i encounter the same problems in very low light situations - it is of cause possible then to have a "worth" picture by completley ignoring the metering bar and the blinking values - setting everything to something reasonable.

is your k10d acting the same way in such situations? (that was my intentional question)

01-18-2008, 02:07 PM   #6
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light entering the viewfinder is not the case - happens also in complete dark room.
01-18-2008, 03:10 PM   #7
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I'm guessing the camera *thinks* that is what would be necessary to turn a largely black frame to 18% grey. Of course with no actual light it won't succeed and will stay black.
01-18-2008, 03:34 PM   #8
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QuoteOriginally posted by mc5 Quote
symptom: with lens cap on and in manual mode it is possible to have the metering bar competly on the right side (overexposure) with 3.5 aperture and a 25 seconds exposure time.

putting the exposure time down to 6 seconds, the metering bar is middle (correct exposure?)exposure and aperture values blinking.

how is that possible? there is no light, the lens cap is on - why does the metering bar can be on overexposure side, or why are exposure and aperture values blinking with metering bar in the middle? (snip)

Your thread title is wrong. You're talking about no light, not low light. Anyway, in virtual total darkness with long exposure times, the image sensor itself will, at a certain point, generate enough noise to actually impact the final exposure value of the image. In other words, your "symptom," as you put it, is entirely normal. However, this is also not something most would experience in the real world since even those who shoot at night would have at least some existing light for the image sensor to work with. Everyone else would likely choose to add lighting to the scene long before this became an issue.

stewart

01-18-2008, 04:09 PM   #9
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QuoteOriginally posted by stewart_photo Quote
Your thread title is wrong. You're talking about no light, not low light. Anyway, in virtual total darkness with long exposure times, the image sensor itself will, at a certain point, generate enough noise to actually impact the final exposure value of the image. In other words, your "symptom," as you put it, is entirely normal. However, this is also not something most would experience in the real world since even those who shoot at night would have at least some existing light for the image sensor to work with. Everyone else would likely choose to add lighting to the scene long before this became an issue.

stewart
i'm not talking about 'no' light - perhaps about *very* low light.

again:

QuoteOriginally posted by mc5:
without lens cap (supposed usage?) i encounter the same problems in very low light situations - it is of cause possible then to have a "worth" picture by completley ignoring the metering bar and the blinking values - setting everything to something reasonable.
perhaps i'm just missinterpreting the metering bar in manual mode. i supposed it to work
somehow like on the rollei sl35 i had - if it's in the middle - ok - if it's on the right - too much light, decrease shutter speed or/and increase aperture value.

is the metering bar working different in such *very* low light situations, or is just my camera broken?

edit: if it's the sensor noise affecting the metering - why is that sensor noise not seen in the picture in the meaning of 'exposure' then?
01-18-2008, 06:13 PM   #10
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QuoteOriginally posted by mc5 Quote
(snip) or is just my camera broken?

I don't believe there is anything wrong with your camera, my friend. No camera in existance was designed to take images with the lens cap on, so by all means take that lens cap off and shoot some images in normal light. If you see problems there, then perhaps you have something truly worthy of your concern. But, quite honestly, worrying about camera/metering behavior with the lens cap attached is just plain silly.


QuoteQuote:
edit: if it's the sensor noise affecting the metering - why is that sensor noise not seen in the picture in the meaning of 'exposure' then?

Read the owners manual (pages 34 & 159). The K10D, like virtually every other DSLR, has noise reduction software built-in to reduce image noise. That software works best at removing noise from images containing little or no detail (the type of images one might get with the lens cap on) and less so with images containing considerable detail (designed that way to lessen impact on wanted image detail).

stewart
01-18-2008, 06:54 PM   #11
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pardon me, but i expect the metering bar working as printed in the handbook page 157 (german edition).

to get the right exposure adjust shutter speed, aperture and iso values so the bar is in the middle / same way as it works since ever.

btw.: light metering has nothing to do with sensor noise, nor with noise reduction.

i'm doing some further tests and will send the camera in for adjustments if it turns out to be a metering problem in other complicated light situations also.
01-18-2008, 07:21 PM   #12
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QuoteOriginally posted by mc5 Quote
pardon me, but i expect the metering bar working as printed in the handbook page 157 (german edition).

to get the right exposure adjust shutter speed, aperture and iso values so the bar is in the middle / same way as it works since ever.

btw.: light metering has nothing to do with sensor noise, nor with noise reduction.

i'm doing some further tests and will send the camera in for adjustments if it turns out to be a metering problem in other complicated light situations also.
With the lens cap on. Huh. Good luck with that.
01-18-2008, 07:49 PM   #13
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QuoteOriginally posted by mc5 Quote
symptom:

with lens cap on and in manual mode it is possible to have the metering bar competly
on the right side (overexposure) with 3.5 aperture and a 25 seconds exposure time.

putting the exposure time down to 6 seconds, the metering bar is middle (correct exposure?)
exposure and aperture values blinking.

how is that possible? there is no light, the lens cap is on - why does the metering bar can be
on overexposure side, or why are exposure and aperture values blinking with metering
bar in the middle?

firmware 1.3, tamron 18-250
The metering system has a lower limit on the amount of light that can be measured for exposure purposes. Anything below that level and the metering system can not give you any meaningful readout.

K10D Metering Range -EV1 to +EV21.5 (At ISO 200 with 50mm f1.4 lens)
01-18-2008, 08:15 PM   #14
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Rickster has it right - the light metering system is spec by Pentax (according to my manual) to operate for EV 0 to EV 21, f/1.4 lens at ISO 100. Outside this range, all bets are off. Playing with my K10D and f/1.4 lens just now, I could easily replicate the "over-exposure reading on the meter, but the aperture and shutter speed readouts were both blinking, which I take to mean "Out of range, do not believe!" Now, somewhere in Pentax software-land I'd suspect that a systems engineer did not fully spec what was to happen when an "out of range" condition was encountered (beyond blinking the readout), so a software engineer wrote some code that does what we might call 'strange things' like indicate an over-exposure condition, instead of just blinking the whole exposure scale. Irritating, maybe, and probably fixable in a software update, but not a sign of anything basically out of adjustment.

At least, that's my two cents on the subject!

Curt
01-18-2008, 08:30 PM   #15
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QuoteOriginally posted by mc5 Quote
(snip) btw.: light metering has nothing to do with sensor noise, nor with noise reduction. (snip)

I realize that. I've tried to respond to two issues you brought up previously - metering in message one and pictures in message five. For example, in my last message (message 10), paragraph one referred to the metering issue while paragraph two referred to the image.

Again, I think you're wasting your time worrying about something that just doesn't matter. The only useful test is metering with normal images in the real world. However, it is very much your time to waste. Take care.

stewart
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