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Accurate metering tip

A tip to ensure accurate metering with your Pentax SLR.

Posted: 10/06/2011 - 09:18

SLR cameras have through-the-lens (TTL) metering systems, that read the subject brightness and set the correct exposure accordingly. They can be easily fooled when used in any of the auto modes and most photographers just think it's the subject and light on the subject that cause meter errors, but there's another lesser known problem that I'm about to share.

This one essential tip will improve your photography for ever!

The meter inside your camera can be affected by the light passing through the viewfinder.  Normally you have your eye to the finder so it's not a problem, your head becomes a sheild for the viewfinder. When you are in manual mode and take your reading with your eye to the finder the result should be good. But when you have the camera on a tripod or other support in any auto mode and take your eye away to press the shutter, strange things can happen. The light going in through the viewfinder can reduce the exposure time, resulting in a dark photo.

So the tip is always to cover the viewfinder when taking a photo, especially when the viewfinder is facing a brighter light than the subject you are photographing.

Here's what happens. The photo below shows a Pentax K5 camera on an overcast day ready to be used to photograph a fossil on a metal background. The was pointing downwards. On the left the viewfinder was left exposed as the photo was taken on its self timer mode to avoid camera shake. On the right the viewfinder was covered by my hand (My hand wasn't touching the camera just positioned in front of the viewfinder.

Pentax SLR viewfinder uncovered Covering Pentax SLR viewfinder

The light entering the exposed viewfinder causes the meter to take an incorrect reading. 1/1000sec at f/3.2 and ISO200. This results in a dark (underexposed) photo. 

The viewfinder was shielded to ensure a correct reading. 1/400sec at f/3.2 and ISO200. This results in a natural looking (correctly exposed) photo.

 underexposed photo  correctly exposed

This is not a new problem - older cameras used to have a slip on viewfinder cover to save you using your hand. Some of the pro cameras have a built in viewfinder blind. 

To test your camera simply position it so the sun or a bright light is behind and shining on the eyepiece/viewfinder. Then switch the camera on, half press the shutter release to activate and display the exposure on the LCD. Now cover the viewfinder to see if the exposure values change. If they do you need to apply the technique described above.

Posted 11/06/2011 - 21:28 Link
This is not a new problem - older cameras used to have a slip on viewfinder cover to save you using your hand.

You also get them with new ones.

At least i got it them with the K10D and the K5
K10D, K5
DA* 16-50, DA* 50-135, D-FA 100 Macro, DA 40 Ltd, DA 18-55
Posted 12/06/2011 - 19:19 Link
Nothing is wrong but all above needs a premise. “If working in A,P,AV,TV,TAV mode it’s important to get right exposure values avoiding direct lights inside viewfinder. So it’s necessary to work using your tips...BUT if working in Manual mode it’s not necessary to protect viewfinder while shooting…the important is to keep your eye close to viewfinder while performing expo-readings, so that “backlight” doesn’t affect it. Then you can shoot using no devices to protect viewfinder because in Manual mode expo-values don’t change,anyway.”This is true for Digital and this was true for Analogic. Sorry for my comment. Giulio57
Peter Bargh
Posted 15/06/2011 - 10:06 Link
Good points. I've amended the article to include the manual and auto tips

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