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02-23-2009, 07:35 PM   #1
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*ist D underexposure problems

Hey gang,

This Christmas I bought myself a used *ist D for a very nice price. It's a realy nice camera and is practically new (aside from the almost 13,000 shutter actuations).

Only problem is, it seems to consistently underexpose by at least 1 stop, with every lens and under every light source.

How can I fix this (aside from the obvious exposure compensation)?

02-23-2009, 07:40 PM   #2
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QuoteOriginally posted by Stevopedia Quote
Hey gang,

This Christmas I bought myself a used *ist D for a very nice price. It's a realy nice camera and is practically new (aside from the almost 13,000 shutter actuations).

Only problem is, it seems to consistently underexpose by at least 1 stop, with every lens and under every light source.

How can I fix this (aside from the obvious exposure compensation)?
define under exposure?

what is the greyscale value if you shoot a block wall uniformly lit? if it is 110-120 it is right on the money.

my *istD meters like this and it is perfect. Also which metering mode are you using?, it may be that your camera is getting fooled by the scene.
02-24-2009, 02:17 PM   #3
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By block wall, you mean a brick wall, correct?

I'll have to go out and shoot one and see what happens.
02-24-2009, 02:27 PM   #4
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QuoteOriginally posted by Stevopedia Quote
By block wall, you mean a brick wall, correct?

I'll have to go out and shoot one and see what happens.
I mean concrete block wall.

sidewalks and paved roads also work well.

with a uniform lit uniform surface, the histogram should be in the 110-120 range, and relitively narrow.

I prefer to use concrete and pavement to eliminate as much color as possible.

02-24-2009, 07:17 PM   #5
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QuoteOriginally posted by Stevopedia Quote
Hey gang,

This Christmas I bought myself a used *ist D for a very nice price. It's a realy nice camera and is practically new (aside from the almost 13,000 shutter actuations).

Only problem is, it seems to consistently underexpose by at least 1 stop, with every lens and under every light source.

How can I fix this (aside from the obvious exposure compensation)?
Lowells correct opinion aside (110ish) you may find that the D is more in the 90 range... 1/2 stop off the more common 110, and a full stop off the Canon (on some models) 126.....
this (90ish) is just how Pentax had the D calibrated and boy did THAT cause a stir..
Anyways see this:
Headroom in Highlights : Where is Zone V in The Digital World? | LibRaw
According to this the "real" value is 101... ANSI standards pretty much left a fudge factor of 1/2 stop so all (except Canon ) are correct
So, in the perfect world of a spot-meter calibrated to ISO standard and pure gamma = 2.2 transform of perfectly linear data coming from the sensor, the neutral surface should render 101 RGB if exposed according to the spot-meter; next stop is 138 RGB, then comes 189 RGB, and finally we are getting clipping increasing exposure full 3 stops instead of 2.97 stops which are the theoretical limit as it was shown above.
ONLY major problem w/ the D is that you only have +/- 2 EV compensation which is sometimes not enough and you just have to work around it BUT the 6MP really work in your favor. you can really push/pull the files quite a bit without creating too much noise...
After having spent some time w/ a K200 I find I miss this. The D was a very forgiving camera, unfortunately later models, though more socially acceptable, have lost that edge it seems. At least based on my limited experience....and my opinion

Last edited by jeffkrol; 02-24-2009 at 07:42 PM.
02-24-2009, 07:59 PM   #6
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It just behaves like that.

QuoteOriginally posted by Stevopedia Quote
Hey gang,
Only problem is, it seems to consistently underexpose by at least 1 stop, with every lens and under every light source.

How can I fix this (aside from the obvious exposure compensation)?
There is no way to fix the issue. As you have already suggested, exposure compensation is the only way to go. For the whole issue and my case study on the issue as well as the possible exposure compensation values for different lenses, see my homepage:

RiceHigh's (Pentax) DSLR and Lens Measurbation Page on Exposure Accuracy and More..

The particularly flat tone curve of the *ist D deteriorate the problem further and the underexposed pictures look even darker.
02-24-2009, 08:37 PM   #7
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QuoteOriginally posted by RiceHigh Quote
There is no way to fix the issue. As you have already suggested, exposure compensation is the only way to go. For the whole issue and my case study on the issue as well as the possible exposure compensation values for different lenses, see my homepage:



The particularly flat tone curve of the *ist D deteriorate the problem further and the underexposed pictures look even darker.
May I congratulate you on your tone and a partial acknowledgment of what I have tried to show you for (is it 4 years now?) a while.
Please read carefully the article I linked to. I believe that was done by Illyah Borg (though I am not 100% certain). If you remember Julia (his daughter) was the first to inform me (and I later told you) of the 110ish value as the correct value for a meter.....
Incidently on incident meters: Pentax SLR Talk Forum: Digital Photography Review
Maybe time to read and reflect,,,,,,,,, AND edit all your lens exposure data to 110, as it should be.
Re: HEARSAY! ( Still NO URLs are provided?? ): Pentax SLR Talk Forum: Digital Photography Review
Re: Why capture only portion of a different part of my homepage?: Pentax SLR Talk Forum: Digital Photography Review
Re: There should be no other industrial standard!: Pentax SLR Talk Forum: Digital Photography Review
Julia's wonderful spread sheet.....
http://www.pochtar.com/gamut_view/gamma.xls

Last edited by jeffkrol; 02-24-2009 at 08:59 PM.
02-26-2009, 01:06 PM   #8
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Good info, I feel better now about the results I have been getting with my *istD! I thought something was wrong, I also have to nearly always compensate by one stop.

Now, I guess they were known for poor white balance metering also!?

02-26-2009, 06:59 PM   #9
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QuoteOriginally posted by skid2964 Quote
Good info, I feel better now about the results I have been getting with my *istD! I thought something was wrong, I also have to nearly always compensate by one stop.
You could do that, but better would be to learn to meter better. The situations that cause "underexposure" (correct exposure, actually, but darker less than msot would subjectively want) include backlit scenes, scenes that are lighter than 18% gray on average, and scenes with bright highlights. In all these cases, the camera is doing exactly what it was designed to do - trying to make the exposure resemble 18% gray on average, unless that would blow out highlights - in which case it will expose darker. Armed with that knowledge, you can learn to meter off subjects that don't have those properties. For example, point at the ground and hit AE-L before composing your shot.
02-26-2009, 07:22 PM   #10
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QuoteOriginally posted by skid2964 Quote

Now, I guess they were known for poor white balance metering also!?
Hmmm... not really and not any morew than other brands if you look closely at the "other" forums. Only constant nag is w/ tungsten. And that is also a bit by design apparently. Tungsten light is very low in color temp. Sometimes as low as 3000K or less. AWB pretty much cuts out at 4-5000ish as do most DSLR's. Using the pre-set tungsten setting gets you a lot closer but it was(is) generally believed to be set to "studio tungsten" lamps which can reach 3500 plus (no concrete evidence of this but some scuttlebutt).
Sunrise /sunsets can hit 3500 so if AWB went to or below that figure you would get funny looking sunsets. As in anything "automatic" any variables, seen or unseen (the human eye/brain is really a poor judge of color due to our built in compensation), can throw it off. There are just too many situations from candlelight/sunsets/high tungsten/low tungsten to be handled and the D and all Pentax DSLR's seem to do the best they can.
Flourescent and some mixed lighting seems to work well w/ AWB.
I'm pretty much in agreement w/ this review but would argue the AWB and tungsten knock based on what I presented above:
Pentax *ist-D Digital Camera Review: Test Results & Conclusion
Color: Generally good color, with accurate hue and saturation. A slight tendency to under saturate flesh tones though. Indoors, good handling of incandescent lighting with the right WB settings. The *ist D produced pretty accurate color in most cases, though I often noticed a slight warm or cool cast, depending on the white balance setting. I typically chose the Auto white balance, though the Manual setting did a good job as well. Outdoors, the always-difficult blue flowers came out a little darker than in real life, and with a bit more purple in them, common problems with that subject. I also felt that Marti's skin tones there were a bit more pale than they should have been. Indoors, the camera's Manual and Incandescent white balance settings produced good results under incandescent lighting, but it's Auto setting failed miserably. Overall, I found the *ist D's color very pleasing.
http://www.imaging-resource.com/PRODS/ISTD/ISTDPICS.HTM
While we are on the subject, the D has quite a strong AA filter rendering initial images soft. Pentax was knocked about quite a bit on resolution tests but some well applied unsharp mask REALLY punches it up.

Last edited by jeffkrol; 02-26-2009 at 07:32 PM.
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