What is the texture visible on a Canon dSLR focusing screen when the lens is out of focus?

November 5, 2007 8:05 AM

What is the texture visible on a Canon dSLR focusing screen when the lens is out of focus?

On a Canon 40D, if I focus directly at a bright object (say, the edge of a lightbulb), the focusing screen appears completely clear and sharp. If I then bring the lens all the way out of focus, and focus my eye on the focusing screen itself, it seems to have a very fine texture that looks sort of like oil droplets (but the autofocus boxes are still sharp). At first I thought that my viewfinder was dirty, but cleaning it didn't help, and it disappears when the lens is focused. I never noticed anything like it on any previous body (D-Rebel line), but that may just be because of the dimmer, smaller viewfinder.

Is this normal for the x0D line? Is this a focusing aid? How does it work?

posted by Caviar to sports, hobbies, & recreation (4 comments total)

It's a focusing aid. The texture encourages your eye to focus on the ground glass rather than focusing "through" the lens.
posted by kindall at 8:17 AM on November 5, 2007

I tried it and noticed the same on my 10D.

This page mentions that focusing screens these days are plastic, and consist of "zillions of microscopic prismatic cuts." Hence the subtle texture you're noticing.
posted by fogster at 11:51 AM on November 5, 2007

Dpreview.com lists the 40D as having:

Focusing screen

• Interchangeable precision matte
• Two other screens available

So it's possible that if it bothers you, you can replace it fairly easily.
posted by quin at 3:35 PM on November 5, 2007

It doesn't bother me, I just wanted to know that it was correct.

This page mentions that focusing screens these days are plastic, and consist of "zillions of microscopic prismatic cuts."... It does? I don't see that text anywhere on the page you linked to.
posted by Caviar at 5:18 PM on November 5, 2007