quick question

[Curtis Bouvier]

If the rotating shutter is about half an inch in front of the film, and you focus on something in the viewfinder.

 

wont that half inch distance cause the film to be slightly out of focus?

 

speaking with the K3 in mind.

 

what do you guys think?

[Tom Jensen]

I'm not familiar with that camera but usually the mirror just redirects the light into the viewing system and it's the image is focused on the ground glass which is the same distance from the film plane.

[Ian Cooper]

I'm not familiar with that camera but usually the mirror just redirects the light into the viewing system and it's the image is focused on the ground glass which is the same distance from the film plane.

 

 

Tom is quite correct, the mirror simply bends the light through 90 degrees. The critical part is to ensure the distance from the lens mount registration surface to the film plane is exactly the same as the distance to the ground-glass.

 

 

Without the mirror in place the light follows the green/yellow path and hits the film.

With the mirror/shutter in place the light follows the green/red path. The crital part is ensuring the ground-glass is accurately positioned to make both the red and yellow parts exactly the same length - the quick diagram above clearly shows the ground-glass is too close to the mirror in this example, so the focus will be off! :lol:

[Tim Carroll]

The middle section of this page shows what Ian is referring to, and explains it a little.

 

Motion Picture Camera Optics

 

Best,

-Tim