Hi Rob, On Wed, 10 Mar 2004 12:43:12 +1000, Rob Studdert wrote:
>Has anyone here proven that DA lenses are designed to be sharper than their FF >35mm equivalents? My take on the DA lens revolution was that they are designed >to only cover an APS sensor (and secondarily designed to extract more cash from >your wallet) and are more controlled in their CA given that image sensors seem >more prone to magnify such errors. And as a consequence of the limited image >circle the lenses can be designed to be physically much smaller. I guess my >theory will be put to test when Pentax releases a DA 600/4 lens. I would guess that the 'size & weight' advantage may work out that way for wide-angles and zooms with a complex optical construction where the lens-parts are way bigger than the theoretical smallest possible aperture. (focal-length divided by f-stop) For a 600mm f/4 you are going to need a 150mm diameter front-element to get that aperture ... No reason to make DA lenses for that reason. I also have a feeling that the image circle on those longer lenses is way bigger than needed anyway. The only thing they could do is save on optical design cost since only the very center of the image-circle will be used ... Regards, JvW ------------------------------------------------------------------ Jan van Wijk; http://www.dfsee.com/gallery
