Focusing Methods

[polarcow]

I was reading through Gunter Osterloh's Leica M: Advanced Photo School book the other day and he mentioned briefly how split prisms and micro prisms work in slr cameras and how they relate to range finding mechanisms as far as focusing accuracy is concerned. I was wondering if anyone knows where I can find a more technical description of how these focusing aides (prisms) work in principle, their limitations and considerations when designing/choosing them etc. Sorry if this is off-topic from typical m-series threads.

-polarcow

 

[Pherdinand]

Try to find a book of Sydney F. Ray called Optics applied in photography or stg like that, from about 2000-2001. Preferably in a library because it's rather expensive.
It has an extensive description with figures, about focusing aids, focusing screens, as well as autofocus techniques, lens design, photometrics, and many more.
I borrowed it from our university library and went through it; it is rather easy to read if you are interested in such details.

 

[x-ray]

My experience has been that focusing accuracy with a SLR is more related to the photographers own eye sight and focusing screen combination. I use a variety of SLR's from the mid 60's up to present. My personal preferences and combinations differ from other photographers that i know. Each of us have our particular favorite focusing screens / camera combo and differ widely from person to person. In past years focusing screens were rather dim and coarse and generally had a split image or micro prism center with a mat field. Some screens had a combination of split image and micro prism ( my personal favorite) with a mat field. I even had a Nikon screen that had a total microprism field across the entire screen. Some screens were fine ground glass for tele lenses. There were screens for particular focal lengths to keep the split image from blacking out and different a pitch of the prism or micro prisms for different lenses. Nikon did a great deal of different screens. Now the trend is very bright fine texture screens that i find very hard to manually focus. For my Canon 1DsII equipment I use a combo mat, microprism collar split image in the center. Still I dislike the new screens. I seems AF is the trend with a sacrifice in manual focus ability in favor of a bright screen. I still like my old Nikon screens even though they are dim compared to the new screens.

The answer to focusing accuracy depends on your eyes in combination with the screen. The best thing would be to try different screens with the particular lenses that you normally shoot. There's no real formula for this.

 

[polarcow]

Thanks for the replies. You weren't kidding pherdinand, that book is very expensive. Worth it i'm sure but out of my range for now due to new leica purchase. No local libraries have it (not even local university) but I will be moving before christmas so maybe then.

-polarcow