Many tolerances in the body and shutter are quite small, but tolerances in the viewfinder system to achieve accurate framing at 100% viewfinder coverage are very very tight. With a 92-96% framing coverage, you can have the focusing screen and image center off by a substantial amount, relatively speaking (up to around 1.5mm off center axis to first order approximation), and still not lose anything the user framed in the viewfinder. With a 100% coverage viewfinder, a tenth of a mm off and the framing is imperfect, with some loss and some unwanted area. That would be unacceptable. And the prism/mirror/focusing screen components are relatively large pieces that must be assembled together for this kind of precision.
If you ever used a Nikon F with a 4x Magnifying finder and reticle grid focusing screen for scientific data collection, you would know just how annoying having the framing off a by a millimeter might be. I found I was sensitive to framing errors in the range of about .25 mm... about six times the accuracy required for a 97% viewfinder coverage finder. That's a big step in manufacturing assembly processes and quality inspection: it costs a bundle. Every penny counts when you're making a few ten thousands of a product... Since the people who need such framing coverage are generally the same ones who demand reliable framing accuracy, the market is sensitive and the price goes up to ensure that the product delivered meets the needs of those buyers. Godfrey On Aug 21, 2007, at 10:57 AM, Tom C wrote: > I've heard that said before, but what kind of tolerances are we > talking > about? I would think that's it's not as expensive as it may seem, > but is > used as a value-added feature to raise the price on the high-end > bodies. > > Not arguing with you, but it just seems to me that everthing has to be > manufactured to pretty close tolerances already. A slop of 1 - 5% > in other > body parts would mean the thing wouldn't fit together. > > It just seems counter-intuitive to me. The reaosn for looking > throught the > viewfinder is to see the scene one will capture. In a perfect world > it would > be nothing more/nothing less. > > Tom C. > >> From: Godfrey DiGiorgi <[EMAIL PROTECTED]> >> Reply-To: Pentax-Discuss Mail List <[email protected]> >> To: Pentax-Discuss Mail List <[email protected]> >> Subject: Re: New 12MP APS-C CMOS sensor from Sony >> Date: Tue, 21 Aug 2007 10:42:56 -0700 >> >> The primary reason for less than 100% viewfinder coverage with SLR >> reflex optical systems is cost of manufacture and the resulting price >> to the users. Optical systems built to this standard require larger, >> heavier components with more rejects and more accuracy in assembly by >> a multiplicative factor to ensure accurate registration, high quality >> viewing, etc. Quality control alone is probably twice as expensive. >> >> Top of the line, pro SLRs have often had 100% viewfinder coverage >> (Nikon F series, Canon EOS 1 and F1 series, Contax RTS series, etc) >> but at a hefty premium price that the vast majority of users would >> not accept. I see from Boz' site that the Pentax LX had ~98% >> coverage. >> >> It's very easy and inexpensive to produce a 100% viewfinder coverage >> with a digital sensor and an LCD screen, presuming that the digital >> sensor is capable of real time capture. It doesn't cost any more than >> producing a viewfinder with less framing coverage. >> >> G >> >> On Aug 21, 2007, at 9:59 AM, Tom C wrote: >> >>> IMO, not having 100% coverage in a viewfinder is a far more serious >>> issue >>> than it being a little dim for one's tastes. Of course we've all >>> gotten >>> used to it, but I fail to see why, all things considered, that >>> viewfinders >>> don't approach a view that is within 1% of what is imaged on the >>> recording >>> medium. >> >> >> -- >> PDML Pentax-Discuss Mail List >> [email protected] >> http://pdml.net/mailman/listinfo/pdml_pdml.net > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
