Archived posting to the Leica Users Group, 2006/08/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Doug, that's a very comprehensive take on the finder differences. Up until now, I'd always thought that my MF Nikons (FE2 F2, F3 etc etc)were great finders vs all of the AF SLRs I've looked through. That is with proper pentaprisms and the split image (which is what I used the most). I guess that's still valid, however you've explained that the SL & SL2 are much better again. Why doesn't that surprise me? Now you've made me think about another new camera, thanks a bunch. This LUG is very bad for my bank balance. Cheers Hoppy -----Original Message----- From: lug-bounces+hoppyman=bigpond.net.au@leica-users.org [mailto:lug-bounces+hoppyman=bigpond.net.au@leica-users.org] On Behalf Of telyt@earthlink.net Sent: Thursday, 31 August 2006 03:50 To: lug@leica-users.org Subject: SLR viewfinders (was: Re: [Leica] M42x1-Canon EOS adapter ...) Scott McLoughlin <scott@adrenaline.com> wrote: > OK, so I give up. Why is it so hard to make a nice SLR VF? > A good SLR viewfinder delivers a bright contrasty image that can be seen clearly over the entire area. One of the supposed advantages of the SLR is being able to focus over the entire picture area, no? First you need to deliver a lot of light to the viewscreen, meaning you need a fully-reflective front-surface mirror, not the semi-silverd mirrors that AF systems require. The screen itself needs to transmit a lot of this light while providing enough of the 'ground glass' effect to focus the image. The 'ground glass' effect scatters light, so there's a trade-off between brightness and the 'tooth' of the ground glass (actually matte plastic). AF cameras compensate for the lower light delivered to the screen by giving the screen less 'tooth'. You can get a reasonably bright screen on an AF camera, at the cost of the 'tooth' required for efficient manual focus. Nikon makes (or, made) G- and H-series viewscreens for the F cameras that substituted either clear plastic (G) or microprisms (H) to make a very bright viewing image. The microprisms and fresnel rings on these screens were optimized for particular focal lengths and aperture ranges. The viewscreen also needs to include some way of delivering even illumination; this is generally done with fresnel rings etched into the screen in addition to a condensing lens on top of the screen. Next the good viewfinder needs to use a large glass pentaprism, not a skimpy prism or a pentamirror. Pentamirrors are light weight but they don't reflect light as efficiently as a pentaprism. I'll leave discussion of the viewfinder eyepiece to the optometrists among us, but here's what Leitz did with the SL and SL2: The mirror is fully-reflective except for the central region, where the meter reads the light. The standard screen in the SL has a coarse microprism in the central area and a very fine microprism over the balance of the screen. The fine microprism is small enough that you can't recognize it as microprisms, it focusses like ground glass yet transmits light like microprisms. The microprisms preclude the use of etched fresnel rings so instead the pentaprism has a condensing lens ground into the bottom. And of course the prism is big to provide good viewing out to the corners. The condenser lens in the prism is more expensive to make, the big prism is heavy, and the fully-silvered mirror means no AF. > So what about a a nice ~93% coverage , but otherwise spiffy > VF like in the Nikon FM series? Why aren't all SLR viewfinders > at least that good? in a word, Autofocus. Try and SL or SL2 and see if you still think the FM-series viewfinders are all that spiffy. They're quite good compared with what most people expect in an SLR viewfinder but compared with the SL or SL2 there's lot to be desired. Doug Herr Birdman of Sacramento http://www.wildlightphoto.com -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ . _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information