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11-12-2010, 06:10 AM   #1
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Metering Question

In extremely low light conditions the metering info in my K7 viewfinder flashes like a Christmas tree. Auto ISO is at my high set limit and flashing, aperature is at the lens maximum of 2.8 and flashing, shutter speed is also flashing even though there is still room for the camera to adjust (program or Av mode). Its like the meter gives up and throws up its hands in low light. Funny thing is that if I raise the flash the meter info stops flashing and the camera takes a nice picture. Also, in M mode in very low light the shutter speed, aperature, and ISO also flash but if I follow the ev number on the lower right of the viewfinder and adjust the shutter speed to zero it (it took a shutter speed of 5 seconds with a 3.5 aperature and ISO 2000), even though the numbers are still flashing the camera will take an image that is indicative of the very dark scene.

I hope I've given a good description. I guess the question is why won't the camera automatically go to max aperature and ISO and then just choose the right shutter speed even if it's 5 or 8 or more seconds? Is there some minimum shutter speed that the camera will automatically choose even though you can manually set it for up to 30 sec. ? I guess a lot of the automatic camera operations frustrate me a little because I don't know how or why the camera is making its choices; it seems the descriptions of the mode settings are just a hint.

This post is not a criticism of the camera, just my desire to better understand and therefore take better pictures.

11-12-2010, 06:17 AM   #2
Ira
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QuoteOriginally posted by Workingdog Quote
In extremely low light conditions the metering info in my K7 viewfinder flashes like a Christmas tree. Auto ISO is at my high set limit and flashing, aperature is at the lens maximum of 2.8 and flashing, shutter speed is also flashing even though there is still room for the camera to adjust (program or Av mode). Its like the meter gives up and throws up its hands in low light. Funny thing is that if I raise the flash the meter info stops flashing and the camera takes a nice picture. Also, in M mode in very low light the shutter speed, aperature, and ISO also flash but if I follow the ev number on the lower right of the viewfinder and adjust the shutter speed to zero it (it took a shutter speed of 5 seconds with a 3.5 aperature and ISO 2000), even though the numbers are still flashing the camera will take an image that is indicative of the very dark scene.

I hope I've given a good description. I guess the question is why won't the camera automatically go to max aperature and ISO and then just choose the right shutter speed even if it's 5 or 8 or more seconds? Is there some minimum shutter speed that the camera will automatically choose even though you can manually set it for up to 30 sec. ? I guess a lot of the automatic camera operations frustrate me a little because I don't know how or why the camera is making its choices; it seems the descriptions of the mode settings are just a hint.

This post is not a criticism of the camera, just my desire to better understand and therefore take better pictures.
What lens?

And I guess we'll work on the first problem first.
11-12-2010, 08:07 AM   #3
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Note that regardless of camera model, all of the pentax cameras function ( with respect to metering) in a similar manner. When the light level falls below the metering limit of the camera they will flash and not set the exposure any lower.

the K10 for example has a metering range from 0 to 21 EV, the *istD is 1 to 21.5 EV and the K7 is 0 to 22EV

If you fall below the lower limit of metering the exposure will flash. Pressing the green button will set the exposure to the lower limit, based upon what ever ISO and native Fstop you have
11-12-2010, 08:44 AM   #4
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QuoteOriginally posted by Lowell Goudge Quote
When the light level falls below the metering limit of the camera they will flash and not set the exposure any lower.
Can I put this is dummy terms, Lowell? And tell me if I'm correctly explaining this?

Yeah, you can take the picture, even if it means hand-holding it for 10 seconds, but there's not enough light for the meter to operate and either do it for you in an auto mode or allow you to meter it manually.

In other words, your camera in a pitch-black closet can indeed take a picture of that old Nehru jacket--that requires lets say a 20-minute exposure--but the darkness is outside of the meter's sensitivity range to TELL you that you need 20 minutes.

11-12-2010, 09:54 AM - 1 Like   #5
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metering for dummies

QuoteOriginally posted by Ira Quote
Can I put this is dummy terms, Lowell? And tell me if I'm correctly explaining this?

Yeah, you can take the picture, even if it means hand-holding it for 10 seconds, but there's not enough light for the meter to operate and either do it for you in an auto mode or allow you to meter it manually.

In other words, your camera in a pitch-black closet can indeed take a picture of that old Nehru jacket--that requires lets say a 20-minute exposure--but the darkness is outside of the meter's sensitivity range to TELL you that you need 20 minutes.
Ira, the light meter reads a level of light coming through the lens. Let's imagine this level has a range EV0 through EV22.

EV 0 corresponds probably to something like a cloudy moonlit night.. This is the bottom limit of the metering range, and as a result, any light level below EV0 will be interpreted by the meter as < EV0.

The camera will only give you the equivelent aperture and shutter speeds possible (for the ISO you have selected) to match EV0, and the indications flash because the level is too low to accurately predict your exposure.

Depending on how you program your green button, this will change shutter, aperture or both, but will always tru to set it for EV0. If your setup restricts reaching EV0 the indication will flash. For example, let's assume you have a shutter speed set, and the green button function is to set aperture. If you (based on light conditions) need an F1.4 lens, but you have an F2 lens, the indications will flash because it is not possible to set the exposure within the range desired,

You may be able to also do this within the exposure range above EV0 if the combination of ISO, lens and shutter you have available make it impossible to set the exposure within the range the camera can control.
11-12-2010, 12:24 PM   #6
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Thank you Lowell and Ira for the explanation in both technical (I'm ok with that, I'm an engineer) and everyday terms. I suspected that there was some low light point where the meter would say, in effect, I can't read that low. But..... what aboput this part; "Also, in M mode in very low light the shutter speed, aperature, and ISO also flash but if I follow the ev number on the lower right of the viewfinder and adjust the shutter speed to zero it (it took a shutter speed of 5 seconds with a 3.5 aperature and ISO 2000), even though the numbers are still flashing the camera will take an image that is indicative of the very dark scene." The image matched about what I was seeing with my naked eye. FYI, using the Tamron 18-250 at 18mm, f3.5


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