Archived posting to the Leica Users Group, 1998/01/18
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Pete Myers wrote: >..I have been going back through the different approaches that have been= used >for screens over the years - pre autofocus - and I was rather startled t= o find >such high praise of the Leicaflex SL (not the SL 2) focusing screen. The= >screen had coarse microprisms in the center and very fine microprisms on= the >rest of the screen. It supposidly was very bright and clear. If this is true;... Pete, did you reed in: In Viewfinder Volume 28 Nr 2 Second Quarter 1995 Page 19-23: <One of today's champion "users" The Leicaflex SL> by Dick Gilcreast Really one of the best article on the SL. If you want to buy it, the address is below. Some of its advantages: =2E.. The SL screen : central microprisms: =2E..When viewing a subject with the lens at full aperture the screen is uniformly very bright, the center no brighter or dimmer than the surrounding area. The central microprism circle of the SL screen is cut for the relatively large lens speed of F:2,8, giving the most precise focus of any micropris= m screen in the Leica R lineup. This is a legacy from the days before the widespread use of slow zoom lenses. In today's Leica R screens the central microprisms are cut for smaller aperture so the F:4 and 4.5 zooms won't black out. But focusing on a screen cut for these smaller apertures leaves room for = a little error when you're using much larger apertures. You may be focusing an F:2 lens using the rays of an effective aperture o= f F:4,5 or so, and then making the photograph with the lens wide open at F:2. Any little focusing error will be magnified by the shallower depth of field. The SL screen is cut for a full F:2,8, and therefore relatively more accurate shooting at F:2. The microprims are still usable at f:3,4 or 3,5, but by F:4 the central prism in the SL screen are starting to partially black out. The 250mm f:4 and 21mm f:4 lenses can be focused well enough, but the bes= t lens aperture is f:3,5 or larger to get the best breakup "go"/"no-go" effect from the central microprims.... Outer microprims: The tiny outer prisms of the screen are cut for about f:5,6, giving a goo= d visual idea of the picture showing the depth of field at that aperture while viewing with a lens of any speed up to f:1,4. It is just like having the stopdown button depressed for all but the central microprisms, but of course no screen darkening takes place. Just as in a rangefinder camera it is therefore easy to see a whole scene= with depth, or background interference behind a close subject. It is not like groundglass. The screen is very bright, the outer portion of the picture is seen with the apparent depth of f:5,6, yet the central prism focus accurately at f:2,8. This is a particularly nice feature of the SL (and SL-2) screen.... Ouf! = The rest of the article is also really interesting, but please buy it at:= LHSA Secretary-Treasurer (Stanley E. Hodges) 7611 Dornoch Lane Dallas, TX7548-2327 (214)386-4005 (phone/fax) Lucien BELGIUM