Do different focus screens have better or worse focus accuracy?

Do different focus screens have better or worse focus accuracy? I

changed the FS on my F4 to the "P" model, and now it appears to hunt

more than before. I had the "B" (standard?) one in before. I know

the F4 is no speed demon, but it was tested within the same room and

view. Is the AF detected within the View Finder DP-20?

Interesting question, never seen the F4 AF system documented on the web. I just did a simple test: AF with a DP-20 finder, AF without a DP-20 finder, AF without a DP-20 finder or a focus screen. I didn't time any of them, just judged whether or not the camera was finding a valid 'focus solution' each time. It did, with no noticable difference in response time. From this simple observation, I assume the AF sensors for an F4 are below the mirror in the bottom of the mirror box somewheres. The focus screen should matter not a whit to the AF.

That is true!

 

Alex

Todd's right. The F4's AM200 AF module sensor (with incorporated spot-meter SPD) is located below the mirror. There is a small sub-mirror attached to the underside of the F4's main mirror that deflects some of the incoming light down to the sensors at the bottom of the mirror box.

 

Only the matrix and CW meter sensors are located in the DP-20 Multi-Meter Finder. That is the reason why, when the DP-20 is removed, you lose matrix and CW metering but retain spot metering and AF functions.

There must have been another variable I haven't thought of that could have affected the performance, or maybe I created it? I only changed to a split focus screen to accomodate my manual lenses.