Question about Pentax *ist DS Digital Camera

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DS Exposure Question

After my first 1000 pictures I'm beginning to adjust to how my DS "thinks". By now I've decided to use centered spot focus only for more control, occasionally like & use the comfort of the Auto ISO feature, and I'm pretty comfortable with both auto and manual focusing. What still puzzles me is the way the DS exposes. I've read a lot of threads here in this group and have seen that "underexposure" of the D/DS has been subject of several heated debates. I don't want to start this off again, but by now and after checking out several lenses - among them my very newly acquired Pentax DA 16-45 - I think that I have a very often a very pronounced underexposure with the DS; the histogramm pretty consistently doesn't reach into the right quarter of the scale, and importing the images into Photoshop CS (I only shoot in RAW) I have to adjust exposure also very often for one full EV. That doesn't help image quality. And this is not only happening in high contrast situations. As I said I don't want to do another round of "underexposure discussion". My question simply is: Do I have a faulty DS at hand which I should have checked for readjustment of its exposure measurement system? Or is this behaviour - especially this routinely "exposing to the left" leaving the right quarter of the histogramm empty - not a bug but a feature of the DS? I'd hate to send the camera in and to get it back four weeks later with nothing changed ... I could live with an permanent exposure compensation setting (and have the occasionally overexposed pic then), but surely would miss the Auto ISO feature which is locked if one uses the compensation. So it boils down to: Send it in - or live with it?

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Re: DS Exposure Question

I believe I see the problem: "0 exposure compensation". Based on the scene I would have compensated to +1 EV (diffuse light/thin clouds) or even +1.5 (sunny/clear sky). And I would have used M mode and center-weighted metering or gray card and spot metering. Now the logic behind the scenes and the procedure: 1) Camera sets Av/Tv to produce MID-GRAY exposure (is it 18% or something else is irrelevant here, one will need to "feel" what camera assumes to be mid-gray). 2) Parameters established should be used just as a *starting point*. It is up to a photographer to compensate exposure and "brighten" scene if it is brighter than mid-gray, or "darken" the scene if it is darker than mid-gray. That's why we have exposure compensation. Examples with approximate values based on my experience (assuming Av mode is used so camera sets Tv only): A) Winter scene, snow, around noon, clear sky - camera sets 1/1000 - I compensate to 1/250 B) Beach scene, light-gray sand, bright sunny day: - camera sets 1/500 - compensate to 1/250 C) City streets, clear sky or light clouds (hint: lots of concrete and asphalt, already gray!) - camera sets 1/125 - no correction D) Cloudy day, murky weather: - camera sets 1/30 - compensate to 1/60 E) Night scene (bar or a street) with no bright lighting: - camera sets 1/8 - compensate to 1/30 Without compensation examples A and B would produce boring "cloudy looking" winter scene pictures and D and E in brighter than normal with all bright surfaces or well lit areas totally overexposed (especially E). We can practice this at home: we have everything from bright lamps, white walls to "gray" floors to dark corners and black sofas and recliners. Switch to center weighted, point, think, compensate then press shutter release. It was not easy but I got it eventually got it. (With K1000 was actually easier since you have analog light meter, MX was quite a shock to me with LEDs, now DS is showing only numbers... believe it or not I would pay $$$ for K1000-style reading in DS

Posted on Sep 08, 2005

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Re: DS Exposure Question

I suggest you get your camera checked. You are seeing the same problem I've observed with two different DS bodies. My son and I call it the "sunglasses effect" -- it makes me feel like I am looking at my computer monitor while wearing sunglasses. The easiest way I found to test was to compare side-by-side with another Pentax DS. I took it back to the store (the dealer has been VERY helpful) and we compared how my DS, the store's demo DS, and a Rebel XT metered the same scenes. My DS was consistently a stop or more below the other two cameras, while the demo DS and the XT were basically in agreement. The symptoms I saw were as you describe: noticeably underexposed pictures for no apparent reason. I would often get photos with virtually no data on the right half of the histogram (even when looking at individual color channels), which is just not right. (Just as an aside, my results were *not* the type of underexposure that RiceHigh seems to be reporting, with lens variations and 1/3 stop stuff -- it was really bad and consistent across all lenses.) I ended up using the faulty bodies with +1.0 EV permanently dialed in, except that didn't work well when I used my old Pentax flash. Anyway, after the dealer tried it, he insisted I exchange it. I did, and it was like night and day (yes, pun intended :-) ). The replacement body metered much better (it had other problems, so had to go back as well, but that's another story...). I am sensing a repeated theme here, but I don't know what to make of it. Faulty calibration equipment in the factory for one of the assembly lines? I dunno....

Posted on Sep 08, 2005

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Re: DS Exposure Question

I haven't found any underexposure problems with my DS. The only "underexposure-thing" I found is that when it's sun reflections within the image (from water, cars with metallic paint and other highly reflective surfaces) the camera will underexpose to avoid blowing out the highlights. In complex lighting situations with many dark and bright areas, it will expose to retain texture in the shadows but still without burning out the highlights. The only image-processingt that I sometimes needs to do, is to lift up the midtones. The darker tones and the bright tones are in most caes exposed just the way I would do it myself if I was a camera, but the midtones can be off. Now, this is not a fault in the camera - it's an effect of the limited dynamic range that digital has in comparision with film. Lighten up the midtones without affecting exposure of dark and bright areas, is image processing and has nothing to do with exposure settings.

Posted on Sep 08, 2005

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2 Answers

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1 Answer

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