Archived posting to the Leica Users Group, 2005/09/26
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I came acrossed this at http://www.imaging-resource.com/PRODS/R1/R1A3.HTM seemed to be relevant to the whole M8 digital hope .... "While a live LCD viewfinder display is a nice feature, it's actually not the biggest benefit of the Sony DSC-R1's design. It turns out that eliminating the large mirror box required in digital SLRs conveys huge optical benefits to the lens system. What's involved is reducing the "back-focus distance" of the lens, which makes it much easier to reduce chromatic aberration and other optical defects. The illustration at right shows a cutaway view of a typical digital SLR. The green arrow highlights the distance between the rear lens element and the sensor surface. (Image courtesy Sony corporation.) As noted, back-focus is basically the distance between the rear element of the lens and the surface of the imager, and has much to do with how difficult it is to engineer the lens system for low chromatic aberration and other distortions. One way to understand this is to consider that the lens has to "project" the image across the gap between the back of the lens and the sensor itself. It makes sense that the smaller this distance, the more accurate the "projection" would be. In a conventional SLR, the minimum back-focus distance is set by the space required for the rotating mirror assembly. SLRs built on conventional 35mm bodies typically have back-focus distances of 30mm or more, while special digital-specific lenses (like Canon's EF-S series) have back-focuses of about 20mm. By contrast, the R1's optical system has a back-focus distance of only 2.1mm. This should translate into noticeably lower chromatic aberration at wide angle focal lengths, and in fact, we saw very little chromatic aberration with the R1 our test shots. (There was a small amount of chromatic aberration present, but it was quite a bit less than we'd normally expect on a high-end "prosumer" digital camera.) The DSC-R1's lens also showed considerably better corner sharpness than we're accustomed to seeing from cameras in this price range." __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com