I’ve been into photography for a long time, but it seems I am always learning something new.   What I learned today though, actually surpised me.   (How can it be that I never knew this?)  What I learned was that my DSLR can actually have its light metering system completely fooled by light entering through the eyepiece.

Let me give you this example:  Let’s say I place my camera on a tripod, and then set it to an automatic aperture preferred mode, and then I take a photo, while I look through the viewfinder.  Then I step back and immediately take a second photo without changing any settings on the camera.  What I discovered is that the two resulting images taken can be drastically different, simply based on whether I am looking through the camera when I take the photo!

 That’s because in one photo, your eye/head is covering the eyepiece so no light can leak inside the camera from the back side, and thus the meter is only reading light coming in through the lens.   In the other photo, with nothing covering the eyepiece, light can come streaming into the camera from behind and confuse the meter!

Here’s the shot where I discovered this.  It was taken in a normally lit room (a fitness center) and behind me about 30 feet were the front windows of the business.  Thus, light was coming in the room from behind the camera.  The camera is set on aperture preferred automatic mode at f/14 using evaluative metering with exposure compensation + 1/3 stop.  I am using a Canon EOS 40D with a Canon EF-S 10-22mm zoom lens.  In this first shot,  as I looked through the camera, this is the result:

Then, in this next shot, the only thing I did was step back from the camera and fire a 2nd shot.

At first, I was surprised by the difference in the two photos.  But after running a couple of tests, of simply putting my finger over the eyepiece and doing before and after shots, I discovered that light flowing into the eyepiece was the culprit.  

With the eyepiece covered, the camera was choosing a shutter speed of 5 seconds.  With the eyepiece uncovered, the camera was changing the shutter speed to 1 second!

I realize some of you might have already known about this phenomena.   But this was such a surprise to ME at least, I thought I’d share this little insight with you!

It’s funny I haven’t really noticed this before now.  But then a lot of times I am shooting in manual, or most of the time I am looking through the camera while taking the photo.

It turns out that Canon includes an eyepiece cover that is attached to the camera strap, which is designed specifically for this purpose (and it’s even documented in the camera’s manual).   Photographer Paul Timpa pointed that out to me. (Thanks Paul)   If you’re a Canon DSLR owner, take note of this little device on your camera strap!

 

 

 

 

 

 

Kevin Gourley
http://www.KevinGourley.com