If you compare the two most recent 600mm constructions in the K-mount to their siblings of same max. aperture in 645 and 67 respectively, you get diverging results. The 67 600/4 is actually lighter than the corresponding FA*, while the 645-A* 600/5.6 is considerably heavier than its K-mount sibling (measures below).
But speaking of circle arguments, there's no reason to assume that the current choice of materials is final. I'll grant you that there was a major change from A series to the FA, going from metal to plastic "before the digital era". Since the introduction of digital, however, there has already _been_ another major change in choice of materials, effectuated by EU legislation only a couple of years ago. Jostein Here are the hard facts about the 600 lenses: K-mount vs. 645: Pentax 645-A* 600/5.6: Weight: 4800g Dimensions: 325.5mm x 155.5mm Source: http://www.photodo.com/product_558.html Pentax K-mount A* 600/5.6: Weight: 3280 g Dimensions: 386 mm x 133 mm Source: http://www.bdimitrov.de/kmp/lenses/primes/extreme-tele/A600f5.6.html K-mount vs. 6x7: Pentax 67 600/4: Weight: 6000 g Dimensions: 370mm x 170mm Source: http://web.mit.edu/dennis/www/pentax67/lens-info.html Pentax K-mount FA* 600/4: Weight: 6800 g dimensions: 457 mm x 176 mm source: http://www.bdimitrov.de/kmp/lenses/primes/extreme-tele/FA600f4.html 2007/6/13, John Francis <[EMAIL PROTECTED]>: > On Wed, Jun 13, 2007 at 12:05:46AM -0400, Doug Franklin wrote: > > John Francis wrote: > > > > > But there's no reason for the lens design to be any different. A design > > > that works for 16x24mm sensors will work for 24x36 sensors (or film). > > > There's more than enough image circle to spare, so there's no need for > > > (or benefit to be gained from) a different optical design. And if the > > > lens mount is the same (which it is, for a K-mount camera) then there's > > > nothing to make two different mechanical designs necessary, either. > > > > Sure there is. Savings in weight and the materials that compose that > > weight. Reduced structural design and strength requirements because the > > entire assembly is lighter. Gimme a minute, I'm sure I can come up with > > more. > > You're arguing in circles. You're assuming that there will be a saving > in weight, and then using that to say that therefore there's a reason > for a new design. I'm saying that your initial assumption is incorrect. > Any lens design that is suitable for use with a 16x24mm sensor would also > work with a 24x36mm sensor, so there's no reason for Pentax not to have > taken any weight and cost savings years ago, long before the digital era. > > > By the logic you're using above, it seems to me there'd be no reason for > > them to have replaced the FA series withe DA series. I can't imagine > > how a 50-200/4.5-5.6 for full frame could be as small and light as the > > DA version. That could simply be a failing of imagination on my part, > > though. ;-) > > There is no reason to replace any FA lenses with a focal length greater > than somewhere around 100mm with DA equivalents. It's only worthwhile > when you get down to focal lengths where the size of the desired image > circle is a significant factor in the optical design of the lens. > I don't know how badly the 50-200 would vignette if used with an old > film body. It may work just fine at all focal lengths, or it may not. > Somebody on the list has probably tried it. > > The big weight saving with a small-sensor camera comes because I don't > need to carry my 300mm/f2.8 - for the same field of view I can instead > get away with using my 200/f2.8, and that weighs a great deal less. > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > -- http://www.alunfoto.no/galleri/ http://alunfoto.blogspot.com -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
