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04-09-2010, 05:08 PM   #1
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Problem with the Av mode on K10

Has anyone had this problem or know what settings I might accidentally set to cause this?

At a portrait shoot (a class) the instructor said to set our cameras to Av mode (aperture priority) with f 5.6 and ISO 100. With the lighting set up, the camera should set the camera shutter speed to 1/8. In Av mode my K10 camera needed to be at ISO 400 in order to get very dark and unacceptable pictures.

So I set the camera to manual with the above settings (f 5.6, ISO 100 and 1/8 shutter speed) and those pictures were only slightly dark but very workable in Photoshop.

Thanks for any help.

04-09-2010, 05:59 PM   #2
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F5.6 and 1/8 second for ISO 100 is rather dark. Is it possible you were beyond th e metering range of the camera, and it could not set the exposure that low?

Pentax does impose limits when lighting falls below the reliable metering point. Do you know what shutter speed the camera actually shot the very dark exposure to?

I still would have expected it to expose correctly however,

Can you post some images and exif data?
04-09-2010, 06:14 PM   #3
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I am not sure I understand the question. It sounds like you camera is set for Auto ISO. Perhaps, it bumped up the ISO to 400 (ie opened up 2 stops) and adjusted the shutter speed to 1/60 or faster speed as a minimum shutter speed. 1/60s is a reduction of 3 stops (1/8-->1/15-->1/30-->1/60) thus causing the exposure to be under exposed by a difference of a stop.
04-09-2010, 07:45 PM   #4
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sewwhat

Thanks for your replies.

To summarize the problem - in a studio lighting setting I set my K10 to Av mode, F 5.6, ISO to 100 the shutter speed should have been 1/8th under the studio lighting condition. But the pictures were dark.

When I set the camera to manual mode with F 5.6, ISO 100, shutter speed 1/8 under the same lighting conditions the pictures were lighter.

Could I have set something wrong while in Av mode? Why would the camera need more light in Av mode than Manual Mode?

I manually set the ISO to a specific number all the time.

Unfortunately I deleted most of the dark pictures. This first picture (3238) is a picture in Av mode and I had to change the ISO to 400. The second picture (3288) is in manual mode.

Also there were 11 other people there that did not have the same problem.

Thanks.

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04-10-2010, 02:23 AM   #5
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metering mode perhaps?

What metering mode was the camera set on? It looks like the dark picture was set at matrix mode when spot metering would have been the best mode to use, taking a reading off the subject's face.

The brighter picture could be matrix as well because now the camera was exposing mostly on the subject and not trying to find a balance between subject and background as in the dark picture.

Also, did you check that your camera was not accidently set on a minus EV adjustment? This would darken the picture.
04-10-2010, 04:06 AM   #6
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I'm also tipped to say that it's a metering issue - understanding which metering mode to use in which settings makes for a much more rewarding series of results.

Spot metering (as well as better focusing and framing) would be warranted here.
04-10-2010, 05:14 AM   #7
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the reason for the dark image is it was shot at 1/45th not 1/8.

the question now is why?

it goes back i think to hitting a limit of metering perhaps.

you should look at the shutter speed and also the metering mode, are you using spot, center weighted or matrix. Also look at the EV compensation, perhaps you have moved it off zero.
04-10-2010, 06:12 AM   #8
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I think the main issue is lack of light. For a portrait class that's just not enough. Unless it was something very advanced (like candle light) the instructor is complicating the issue.

He should have the lighting level at about 1/125, f/5.6, ISO 200. (ISO 100 if everyones camera can do it.)

The light levels you quoted are just too dark.

04-10-2010, 07:16 AM   #9
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I think jlaubza and Ash nailed the main issue - spot metering vs matrix. You can check your EXIF data to confirm

But Omega raises a good point - 1/8 of a second for a portrait? - too easy for the subject to move and blur the picture. It would be interesting to know if the instructor suggested you use a tripod for a shot at 1/8 second?
04-10-2010, 08:58 AM   #10
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sewwhat

Thanks everyone.

The metering was set to spot metering on all shots. The EV setting was at 0. And yes we did use a tripod and a remote shutter release.

Last night I made a couple of test shots with those same settings. And the only thing I changed was manual to Av mode. My camera produced the same results in both cases.

There are possible differences during the shoot that I cannot verify that might have caused my concern. I might have been closer and / or the when the model sat in a chair for the second half she might have moved in a little better light.

I feel much better that you all are saying that the lighting conditions are a low light setting and I will not invest in that specific lighting set up.

Thanks so much.
04-10-2010, 10:47 AM   #11
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What about back light enntering the viewfinder. Try a shade on the viewfinder
04-10-2010, 11:31 AM   #12
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sewwhat

I did not cover the viewfinder but sometimes I was focusing and standing behind the camera.

What difference would that make? If light comes in the viewfinder does it make it confuse the meter? If so in what way?
04-10-2010, 11:44 AM   #13
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Just a coupla comments, don't know if any apply:

a. If you have a split image screen installed on your K10, it will mess up your spot metering by up to two stops,

b. ISO levels are not consistent between different camera makes according to the some of the testers. Nikon's tend to be much lower than the number, don't remember where Canon's were. That would account for different settings between cameras.

c. When in Pentax's AV mode, i've found that its too easy for the camera to switch between manual iso settings and Auto ISO settings in that mode. I think what i'm doing is punching the green button and that enters the AV manual ISO mode into Auto ISO mode. to get it back one has to go into the Fn menu.
04-10-2010, 11:51 AM   #14
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Spot metering is indeed your basic problem here. By spot metering off the face, you asked the camera to render the face a little darker than 18%, and that's exactly what it did. Spot metering is more a special purpose metering mde, and not to be used unless you understand exactly how and when to be using it.

As for light entering the camera via the viewfinder - the camera sees this light and reduces exposure just as it would if you had more light coming in the front. So yes, that also causes darker pictures than you'd get if you were blocking the viefinder properly (eg, with your face pressed up to it, or using the cap your camera came with).
04-10-2010, 01:18 PM   #15
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QuoteOriginally posted by sewwhat Quote
I did not cover the viewfinder but sometimes I was focusing and standing behind the camera.

What difference would that make? If light comes in the viewfinder does it make it confuse the meter? If so in what way?
Your camera came with an eyepeice cover for this specific issue. Yes in any optical system light can travel both ways
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