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12-31-2011, 07:17 PM   #1
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K-7 goes to ISO 100 by itself?

Happy New Year Pentaxians! Was playing with my new Sigma 10-20 today. Took a few shots to test Vibrant vs Portrait vs Landscape with super wide angle. When I looked at them on my computer, I noticed they were all shot at ISO 100. Checked the camera and it was set to Auto ISO. All my test shots were way too dark and I was about to blame the new lens.. Nope, it was me... But what did I do? Could it do this by itself?
Help!!

12-31-2011, 09:31 PM   #2
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Can't make a meaningful reply without samples, preferably with exif.

Could simply be an overcast sky fooling your meter.
12-31-2011, 10:35 PM   #3
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Hi, I managed to borrow , for this Holidays , a Sigma 10-20mm ( the older slower one, no HSM, F4-5.6 ) and I am amazed how it can record the blue sky and clouds.
uploaded some to:
Sigma EX 10-20mm F4-5.6 DC - a set on Flickr
will upload more today
All photos with K7 ( Vibrant ) and most in program P mode, I did have some underexposed but the majority are fine.
Possibly due to a glare from the sky, I was focusing on the object and then trying to recompose to catch as much sky/clouds as possible.
kind regards
jack
01-02-2012, 07:42 PM   #4
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I don't understand. If you set auto ISO, why are you surprised if the camera sometimes chooses 100? That's the whole point of auto ISO: the camera chooses the ISO. If the pictures are too dark, that has nothing to do with ISO - that's an exposure issue. Probably something as simple as a light source in the field of view. But changing the ISO has no effect on exposure except in M mode - in all other modes, the camera will automatically adjust shutter speed or aperture to yield the exact same exposure.

01-03-2012, 03:39 PM   #5
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QuoteOriginally posted by Marc Sabatella Quote
I don't understand. If you set auto ISO, why are you surprised if the camera sometimes chooses 100? That's the whole point of auto ISO: the camera chooses the ISO. If the pictures are too dark, that has nothing to do with ISO - that's an exposure issue. Probably something as simple as a light source in the field of view. But changing the ISO has no effect on exposure except in M mode - in all other modes, the camera will automatically adjust shutter speed or aperture to yield the exact same exposure.
Maybe, but it was strange that 6 shots, taken at different times, different angles, all were shot at ISO 100. My experience is that if I pick Aperture Priority, the camera will bump the ISO to make the exposure work. They were definitely underexposed. Will try again in Program mode.
01-08-2012, 02:06 AM   #6
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AutoISO selects ISOs in a range that can be reconfigured by the user - maybe you just configured your camera to not use more than ISO 100.

If that's not it, do make an effort and provide a sample image, scaled down, but with EXIF intact. It would speed up the investigation.
01-11-2012, 03:57 PM   #7
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I'll have to try again.. In a huff, I deleted them and can't seem to get them back....
01-11-2012, 04:23 PM   #8
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Found them. Not sure if the EXIF data is included. I tried...

Attached Images
View Picture EXIF
PENTAX K-7  Photo 
View Picture EXIF
PENTAX K-7  Photo 
01-11-2012, 07:36 PM - 1 Like   #9
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QuoteOriginally posted by GoldenRGuy Quote
Found them. Not sure if the EXIF data is included. I tried...
Yes, it is included.

That the camera didn't bump the ISO is not very surprising - the shutter speed is high enough to not require that.

What is surprising is that the images are underexposed even though you have applied positive exposure compensation. You used center-weighted metering, but I think that should have worked ok here.

The camera underexposes with this lens, but I am not sure why this would happen.
01-11-2012, 07:46 PM   #10
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QuoteOriginally posted by Laurentiu Cristofor Quote
Yes, it is included.

That the camera didn't bump the ISO is not very surprising - the shutter speed is high enough to not require that.

What is surprising is that the images are underexposed even though you have applied positive exposure compensation. You used center-weighted metering, but I think that should have worked ok here.

The camera underexposes with this lens, but I am not sure why this would happen.
Thanks Laurentiu! I can't figure it out either... The lens should have no effect on the exposure.. Hopefully others will chime in!
scott
01-11-2012, 10:36 PM   #11
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QuoteOriginally posted by GoldenRGuy Quote
Thanks Laurentiu! I can't figure it out either... The lens should have no effect on the exposure.. Hopefully others will chime in!
scott
I was in a hurry earlier and I couldn't write more. Here are some additional questions whose answers may help:

Are you seeing this issue with any lens or only with this one?
Does it underexpose in any scene or just in some?

The lens can have an effect on exposure. For example, maybe its aperture mechanism is broken and it stops down a bit more than it should - the camera meters okay, but the lens always uses a smaller aperture than called for. If the camera meters well with other lenses, then it's not the body that is at fault. On the other hand, if you see this behavior with any lens, you know the problem is probably with the body.

I don't think ISO is an issue because 1/50 and 1/80 are pretty good shutter speeds for 10mm.
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