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04-21-2014, 11:07 AM   #1
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Exposure problem

I have had my k-3 for about 6 months. Ususally using AV preferred.

Went to a photo seminar about manual exposure.

I seem to be consistentlyunder exposing

Today went out to shoot morning birds with the seminar group

We tested our cameras when the sun came up- We used the "sunny 16"

Iso 200 F8 1/800 0 compensation -

my shots were dark

The leader had an incident meter which confirmed that that was the correct exposure

We shot grey cards-

Two users with Nikons and a third with a Canon 'zeroed" the meter with the expected exposure (Iso 200 F8 1/800 0 compensation )-
My camera however indicated F8 iso 200 1/2000 (compensation =0) in the same light, same grey card

My meter appears to be a little over 1 stop off

None of us could figure out why it was that far off-

Does the camera need a trip back to Pentax??

Is there something I missed??



Any help appreciated

Steve

04-21-2014, 11:51 AM   #2
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QuoteOriginally posted by srock Quote
I have had my k-3 for about 6 months. Ususally using AV preferred.

Went to a photo seminar about manual exposure.

I seem to be consistentlyunder exposing

Today went out to shoot morning birds with the seminar group

We tested our cameras when the sun came up- We used the "sunny 16"

Iso 200 F8 1/800 0 compensation -

my shots were dark

The leader had an incident meter which confirmed that that was the correct exposure

We shot grey cards-

Two users with Nikons and a third with a Canon 'zeroed" the meter with the expected exposure (Iso 200 F8 1/800 0 compensation )-
My camera however indicated F8 iso 200 1/2000 (compensation =0) in the same light, same grey card

My meter appears to be a little over 1 stop off

None of us could figure out why it was that far off-

Does the camera need a trip back to Pentax??

Is there something I missed??



Any help appreciated

Steve
The K-3's meter is otherwise pretty accurate, but it does try to underexpose a bit when there are lots of highlights.

Did you have the meter set to spot or matrix? The former is more likely to give you consistent results across different cameras if you're using something in the center to test it.

Adam
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04-21-2014, 12:05 PM   #3
dms
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Verify the exposure bias is consistently low--if so I suggest simply setting an e.v. compensation, but the If not--then it needs repair. This may depend on the metering option chosen (one can never be sure what logic applies to matrix metering) and I probably would choose center weighted and/or spot as the first check.

There is no requirement that Pentax use the same metering values as others--in fact the use of a gray card is itself not strictly correct as the medium gray for metering is closer to 10% reflectance, but many instead use 18% (as in the gray card).
04-21-2014, 12:09 PM   #4
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Exposure problem

Spot metering

Dialing in 1 stop + compensation seems to correct exposure. That seems to me to indicate a problem with meter calibration- Am I wrong??

Steve

04-21-2014, 12:25 PM   #5
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what lens are you using?
04-21-2014, 12:36 PM   #6
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Exposure problem

Pentax 18-135 and sigma 150-500 today
04-21-2014, 01:40 PM   #7
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QuoteOriginally posted by srock Quote
Spot metering
Depends then, on the spot you were metering. If the area metered is brighter than average, your camera will underexpose.
04-21-2014, 01:57 PM   #8
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Others may disagree but I am old school when it comes to using manual exposure settings. Reciprocal exposure values haven't changed, In the situation you are expressing using manual settings there is no way I would have used that combination for early morning light with any camera.

As an example if you were dealing with an early light somewhere between an 11 or 12 EV or lower/higher depending on the sun's position in it's rise. If you were shooting, lets say the EV was closer to 11, and you were needing a faster shutter speed and wanting to keep your F8 depth of field then you would need to use an ISO of 1600 and 1/500 as a reciprocal exposure triangle initially prior to using any exposure compensation. Or if you needed a faster shutter in that same EV then you would need to drop to F5.6 and keeping the ISO 1600 and 1/1000 keeping your exposure triangle. Otherwise for faster shutter speeds you would need to step up your ISO to 3200 or higher and make changes from there unless your lighting was much brighter. If you wanted to keep the noise factor lower than you would need to use reciprocals for lower ISO's which would sacrifice shutter speed. It's all relative, Exposure Factor Relationships haven't changed and to me shooting with manual settings I feel it's still important to go back to using those reciprocals as a good place to start and work my exposures from there. The sunny 16 is fine when you have good light but not for early or late in the day times.

I will say in low contrasted light for birding using a flash with a Better Beamer can come in handy.


Last edited by Oldbayrunner; 04-21-2014 at 02:03 PM.
04-21-2014, 02:29 PM   #9
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Exposure problem

I'm sorry I wasn't clear- The testing was done with the sun high, nearly 11 am on a sunny cloudless day and sunny 16 would apply. I was most concerned that in the same light focused on an 18 % grey card in sunlight, that my camera registered a full stop different than the incident light meter and the meters of 2 nikons and a canon, all of whom agreed

Steve
04-21-2014, 02:45 PM   #10
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QuoteOriginally posted by srock Quote
The testing was done with the sun high, nearly 11 am on a sunny cloudless day and sunny 16 would apply. I was most concerned that in the same light focused on an 18 % grey card in sunlight, that my camera registered a full stop different than the incident light meter and the meters of 2 nikons and a canon, all of whom agreed
Ahh. Sounds like you need to have your camera repaired/recalibrated. Or, if the readings are *consistently* one stop off, you could just get in the habit of dialing in some exposure compensation.

Q: Is exposure compensation something that can be specified in a custom user mode?
04-21-2014, 03:21 PM   #11
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If anything, my Pentax DSLRs seem to underexpose a little bit when compared to Canons and Nikons (in a class situation like you described). It even looks this way when you review photos on the rear LCD screen.

But I'm OK with this, as the photos usually come out good that way, I think. Sometimes I end up turning up exposure in post (although I only PP certain sessions/events).


I am using matrix metering most of the time, so that may affect my results as well - as Adam already pointed out. I think Pentax matrix metering works pretty well - perhaps it actually betters much of the competition here (from what little I've read about it).


I haven't used gray cards much, but I'd expect it to underexpose the card in daylight if you were shooting in matrix mode (because the brighter background filling much of the frame would be compensated for in the camera's exposure decision).
04-21-2014, 05:15 PM   #12
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The comparison to the sunny 16 rule, and what another camera/light meter gives is really pointless--so long as your camera is consistent in it settings. If you halve the light falling on a surface is the exposure increased by 1 stop, and if it reduced by 1/4, is the exposure increased 2 stops, and so forth,

What you must do is decide what reading/exposure Is correct for you! The camera is ultimately a dumb machine and you need to give it guidance. And if you send it in (for warranty work) more than likely Pentax will say it is within acceptable bounds.

E.g., Using a K20d or a k-x, and using center weighted exposure mode, I find I need to (by observing the relative amount of light-to dark area) typically dial in anywhere between +1.5 e.v. to -1 e.v., for street shooting. But I use raw, and often want my exposure to be too high by 1/2 stop (for whites/grays) which I can recover in camera raw. On the other hand: if you aren't using camera raw, it is a narrower DR scene, low iso,, and/or a camera w/ wider DR (which you have), for good colors you may want to err on the underexposure side.
04-21-2014, 05:39 PM   #13
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I'm convinced that Pentax deliberately underexposes -- my JPEG previews look completely different than my RAW files when previewed in either ACR or DxO. In particular, I would say that on average, the JPEGs are almost exactly +1 stop "lighter" than the corresponding RAW images. Not that this is a problem per se -- the images clean up quite well, especially in DxO Optics Pro. But there is no question in my mind. You can see this most clearly when comparing Pentax RAWs to Nikon RAWs shot in the same conditions at the same exposures. As a side note, I won't use +1 to compensate because I use my JPEGs as "backup" and I want these to "properly" exposed in case of catastrophic failure of the RAW files or data storage.
04-21-2014, 08:50 PM   #14
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The Fstops are not necessarily the same; they do not indicate the amount of light that hits the sensor.

Spot metering on the K-3 is extremely sensitive. The spot is small and will pick up variations in light in a very sensitive way. If you want to get an accurate metering with spot I'd suggest putting the body on a tripod and fixing the grey card somehow. Movement across the card picking up the variation of reflection can easily give you a stop difference. Or use one of the other metering methods and fill the viewfinder with the card.

I have blown shots due to this, as well as gotten shots I would otherwise have missed.
04-22-2014, 02:58 AM   #15
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I read somewhere that the ISO are not the same on different brands, with the Pentax being more accurate.
It was suggested that the ISO difference was perhaps to mislead regarding noise levels.
This would also affect the exposure accordingly.
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