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11-24-2007, 02:26 PM   #1
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K10D Green/P underexposes, sometimes by 2+ stops?

My brother just pointed this behavior out to me, and I'm not sure if we're doing something wrong, there's something wrong with my camera, or if this is just "normal" behavior.

I'm seeing that when using the camera's choice of exposure though green mode or pressing the green button, the image is always underexposed, but the camera "knows" it's underexposed. In a bright room the amount is minimal but in the dark with flash it can be 2+ stops underexposed.

This is on a K10D, firmware 1.30. Using DA 18-55. (Also happens with DA 50-200.)

For example (all in a dim room)

Program mode, no flash:
  • Pressing green button selects 1/8s f/4, flashing "flash" indicator.
  • Dialing the shutter to 1/6 through 0.5 the arrow flashes on the top LCD for shutter speed. Once I dial to a slower shutter the camera does not let me change back to a faster one (turning the dial back doesn't affect shutter speed.)
  • Once I'm down to the acceptable range it does let me go up or down to choose between speeds (30 - 0.7).
  • If I press the green button again it selects 1/8s f/4 with flashing "flash". I don't understand why it's choosing values that it thinks (through restricting my range of adjustments) are wrong.
Program mode, on-board flash up:
  • Green selects 1/45 f/4.5.
  • Dial lets me to down to 1/8 while shutter arrow (underline in viewfinder) flashes, can't adjust back to faster shutters.
  • Once I'm down past that I can choose 8" through 1/6.
  • Pressing the green button again chooses 1/45 f/4.5, a setting I can't even get to with the dial.
Manual, flash up:
  • Pressing green button sets camera to 1/45 f/4.0 and EV bar shows 2- flashing.
  • Dialing up to 1s, f/4 is at zero on EV bar.

This occurs in all metering modes.

So, if 1.5" f/4.0 is correct according to the EV bar, why is the camera choosing 1/45 when I press the green button?

I've read the manual and searched this forums to no avail. I've also reset the camera settings (just using Reset function) to make sure I didn't change something buried deep somewhere.

Is this normal behavior that I just don't understand or is something wrong? TIA

11-25-2007, 01:11 AM   #2
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Consistent underexposure with Pentax DSLRs, especially even much more in low light conditions, is not a new news. Just read my homepage for the whole case.

Also, I think you should read about this:- RiceHigh's Pentax Blog: K10D Hyper Program Defeats Auto ISO

When you use Hyper Program, the "Auto" ISO can be brought back to the lowest 100. And if you force a higher shutter value by turning the Tv dial, underexposure will result.
11-25-2007, 02:13 AM   #3
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QuoteOriginally posted by chrisjs Quote
For example (all in a dim room)[*]Pressing green button selects 1/8s f/4, flashing "flash" indicator.
What you have observed was the result of light level below the metering range.

K10D can meter down to EV 0 (this is as low or better than most other DSLRs) with f/1.4 lens. With your kit lens being a slower lens, the lower limit would be around 3 stops higher (depending on the focal length); so the effective lower metering range is roughly EV 3.

Assuming you are using Auto ISO, it will self adjust to ISO 1600 in very dim room. Guess what's EV 3 at ISO 1600? 1/8s f/4!

So what K10D is telling you with its flashing lines is that it has reached the bottom of its metering range - and it would just stay at the lowest metering range limit at 1/8s f/4 even if you are in complete darkness; as the exposure meter can no longer give valid readings.

You should not observe this "underexposure" reading in lighting within the metering range.
11-25-2007, 02:13 AM   #4
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Use M mode!
set appropriate ISO.
Press green button.
Dial in the speed/aperture you want.

Flash in the Auto modes is not very practical because the camera overrides your settings constantly.

Use M!

One nice thing:
If you set the flash mode (via Fn button) to '2nd curtain' and press the green button (with flash open!) you will get the exposure values, as if you are using NO flash at all. This way you can estimate the light and can choose e.g. two stops lower with flash.

11-25-2007, 02:32 AM   #5
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Or just set it to + 1-1.5 ev compensation and leave it there for lenses with a max aperture of F3.5 - F4. Works for me.
11-25-2007, 09:31 AM   #6
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Thanks for all the replies! I should have mentioned that I'm new to SLRs (though that's probably obvious based on my question).

My confusion wasn't simply that it appeared to be underexposing, that by itself isn't a big deal. I didn't understand why the camera was automatically suggesting (with green button) shutter and aperture values that it otherwise knew were incorrect. (Since it wouldn't let me choose those values in P).

But it makes sense now with regard to Auto ISO. I was using the default Auto ISO range of 100-400, if I change that upper limit to 1600 the green button's suggested values are within the allowable range.

That is a strange and annoying "bug".

Thanks
11-25-2007, 12:00 PM   #7
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QuoteOriginally posted by Kaimarx Quote
Or just set it to + 1-1.5 ev compensation and leave it there for lenses with a max aperture of F3.5 - F4. Works for me.
Actually, this I too have found to be my best friend..
11-25-2007, 12:01 PM   #8
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QuoteOriginally posted by blende8 Quote
Use M mode!
set appropriate ISO.
Press green button.
Dial in the speed/aperture you want.

Flash in the Auto modes is not very practical because the camera overrides your settings constantly.

Use M!

One nice thing:
If you set the flash mode (via Fn button) to '2nd curtain' and press the green button (with flash open!) you will get the exposure values, as if you are using NO flash at all. This way you can estimate the light and can choose e.g. two stops lower with flash.
This is good advice and worth exploring...Thank you..

11-25-2007, 01:41 PM   #9
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What nosnoop explained is also -most- educational! Reading this Ultimate Exposure Computer , and commiting it to memory helped me immensely a few months back; only because of it do I unstand what mosnoop is talking about here.

Chris, when I 1st got the camera a few months ago, I experienced similar in 'green mode'. After about a 1/2 dozen shots, I went to Av mode, then soon after that to TAv mode, and never went back! (and I always use EV compensation as needed based on looking @ the histogram after a test shot) Now just 4 months later, I'm evern comfortable in M mode (usually only with a manual focus lens), but TAv mode unique to Pentax is still my fav..

Ya, I don't know why green mode is so 'off' even at EV6 w/all that technology built into the camera, where cheap point & shoots can get it right ... but after all I didn't buy this camera w/a all the manual controls & capable of incredible detail, to be just pointing & shooting at something & expecting reasonable results.... I want fantastic results, when shooting available light (no flash), so I read a lot and learned of the ways to adjust the setting to give as good as i can (which admitedly isn't all too great still compared to many others on the board here )
11-25-2007, 05:31 PM   #10
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QuoteOriginally posted by m8o Quote

Ya, I don't know why green mode is so 'off' even at EV6 w/all that technology built into the camera, where cheap point & shoots can get it right ... but after all I didn't buy this camera w/a all the manual controls & capable of incredible detail, to be just pointing & shooting at something & expecting reasonable results.... I want fantastic results, when shooting available light (no flash), so I read a lot and learned of the ways to adjust the setting to give as good as i can (which admitedly isn't all too great still compared to many others on the board here )
Yep, this is exactly where I am at...I ask allot of questions and read allot and experiment allot, but some day I hope to be able to give back in the way of help...
11-25-2007, 08:27 PM   #11
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M80
Thanks for that web site link Ultimate Exposure Computer
I have already figured out a bunch off stuff...,makes sense now..
Thanks javier
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