DA560/5,6

Hi,

I'd like to deal with a different matter from the preceding discussions.  The 560mm lens is long.  Does anyone know why Pentax have elected to go for the particular optical design they've chosen for this lens? It's not the approach they've taken in the past.  I don't know enough about super teles to answer this question.

Russell gave the length spec as 20.5 inches.  That's 520.7mm.  Add 46.45mm for the FFD of the K mount (and allow a few mm off for the distance between the front element and the filter rim) and you've got a measurement of roughly 560mm from the front element to the film plane.  I think that makes it technically a long focus lens, not a telephoto - it has a telephoto ratio of 1:1.  That's a very far cry from say the A*300 which was only 135mm long for a 300mm or the DA* 300 which is 184mm long for a 300mm.  Why have Pentax elected to use a long focus lens (at cost to size and perhaps weight) rather than a telephoto design?  How does this affect IQ, and what does it offer photographers?

Thx, Rod