[canajuneh]

My K5 came with a little plastic cover that looks like it is for the viewfinder. Other than protecting the viewfinder (I've never done that) does it have a purpose? Am I supposed to protect the viewfinder?

I'm wondering if it could be used when taking night shots with unwanted, unavoidable light behind the camera. This was the case once when I stopped to take some aurora shots - big light in a nearby farmyard.

[riff]

I'm wondering if it could be used when taking night shots with unwanted, unavoidable light behind the camera.

Indeed you can, that's is what it is forr. It scares me though, very easy to em misplace this little piece.

[claimed4all]

When you are taking shots without looking through the viewfinder (tripod/remote) it prevents unwanted light coming in though the view finder and affecting your metering.

[Adam]

If you don't need yours there was someone on the forum recently looking for one...perhaps a search will bring up the thread.

Adam
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[blackcloudbrew]

I've never been really convinced that these make much of a difference. I'm willing to change my mind but does anyone have a good example where using this cover made a difference?

[smigol]

I use this device every time I do long bulb exposures with Astrophotos. There is a small amount of light that can leak through the viewfinder. Generally at night this is not a problem but it can be an issue if there is an light source near the camera. I see more light leaking around the k mount than around the viewfinder.
I've also noticed a metering difference without my eye near the viewfinder, so it does make a difference if you are going to use the camera in an automatic mode - trap in focus is one example.

[philbaum]

I've never been really convinced that these make much of a difference. I'm willing to change my mind but does anyone have a good example where using this cover made a difference?

I've been trying to think how one would test this. My reaction is pretty much the same as yours - no ready proof.

I suppose one could place the camera on a tripod and take a picture while looking thru it. Then stand back and let light enter the VF, take a picture by pressing the shutter at arms length, and look at the difference in settings. would require that the camera be in some auto mode like AV.

One could just place a ball cap over the VF to cutout light while taking a picture. Is this more of an issue with LiveView?

[smigol]

Easy enough to test:
Put the camera someplace where there is a decent amount of ambient light -- so that some is falling on the back of the camera and could make its way in through the viewfinder.
Put the camera into AV mode. Put your finger over the viewfinder so it's blocking light source. Press the green button. Note the settings.
Take your finger away, press the green button, note the settings.

You should see a difference, depending on how much light is shining in through the back of the camera.

[toooldtocare]

As others said, it keeps the light coming in the back of the camera from messing up the light meter reading. They only time it would make a difference is when it is brighter behind the camera than the scene you are shooting. Normally, as others said, your eye blocks this light.

An example of where it would be useful is putting a camera on a tripod in the sun and using a remote control to take a photo of a group of people in the shade, such as under a tree. In that case the extra light entering the viewfinder would cause the camera to stop down further than needed.

Night shots it would have no effect, unless the camera was inside with the lights on and the lens pointed outside. If both were outside and it is dark, I would not expect to see any difference.

[blackcloudbrew]

Interesting...I would have thought that the difference would be greater at night. Thanks for the insight. It's one of those things that was always gently gnawing at me to look into.

[callmeraymon]

I remember having that cover on my K1000 so when you weren't using it, the button battery wouldn't deplete. It would try to meter the light at all times.

[sussexphoto]

Here is an example of light leaking in through the viewfinder. Not only does it affect exposure, it can affect the image. This is done with a ND110 filter, so it is a 30 second exposure with the sun behind me and to the right. You can see the effect on exposure by putting the camera on a tripod and watching the meter reading change as you place your finger over the viewfinder.

[demp10]

The exposure sensor is somewhere within the focusing screen, pentaprism and viewfinder assembly. As such, it receives light from both from the mirror and through the viewfinder. If the lights entering from the viewfinder is brighter, it will fool the meeter and you'll under expose.

[TomB_tx]

As a long-term eyeglasses wearer I've seen underexposure with bright light behind me since the days of the Spotmatic. When the cameras have metering cells at the prism reading the screen I've seen 1-1/2 stops difference just taking off my glasses and putting my eye close.
I haven't noticed this yet with the K-5, but since they included the blind, it probably can be a problem; or they just included it due to company history with other models.

[smigol]

Here is an example of light leaking in through the viewfinder. Not only does it affect exposure, it can affect the image. This is done with a ND110 filter, so it is a 30 second exposure with the sun behind me and to the right. You can see the effect on exposure by putting the camera on a tripod and watching the meter reading change as you place your finger over the viewfinder.

I've seen bands like that appearing and assumed they were mostly from light leaks around the lensmount. Some of the patterns I've seen that are on the right hand side of the image are identical. The pattern that is on the left is something I've not seen before. I've been meaning to cover the mount with gaffer tape but haven't seen much of this issue since I've covered my bright LEDs.