Simple: the lens elements in a 50/2.8 are very small in relation to the 35mm lens mount. Making it fit a much smaller lens mount produces a much smaller lens. The diameter of the glass is about the same though. That is what they did with the M300/4 which is why it has that distictive potato masher shape (while the could reduce the diameter of the barrel they could not reduce the diameter of the head). However, the D series cameras have the same mount as the 35mm cameras so they can not reduce the barrel by much. Note that what is happening here is just the opposite of the situation with long lenses.
-- graywolf http://www.graywolfphoto.com http://webpages.charter.net/graywolf "Idiot Proof" <==> "Expert Proof" ----------------------------------- John Forbes wrote: > So how do you explain the fact that a Pentax 110 1:2.8 50mm is about 1/4 > the size of a Pentax 1:2.8 50mm in K-mount? > > John > > > On Fri, 18 Aug 2006 10:35:13 +0100, DagT <[EMAIL PROTECTED]> wrote: > >> They will be smaller of you compare field of view (as a 135 2.8 is much >> smaller than a 200mm 2.8), but if you compare with the same focal length >> with the same maximum aperture the front element will be the same no >> matter how small the sensor is. >> >> DagT >> >>> Fra: "John Forbes" <[EMAIL PROTECTED]> >>> >>> If the image circle is designed for APS-C, then the lenses will be >>> smaller >>> and lighter than those designed for 35mm. So they WILL be small and >>> light, relatively speaking. >>> >>> But, like you, I hope they have USM. We shall know in good time. >>> >>> John >>> >>> On Fri, 18 Aug 2006 09:41:15 +0100, DagT <[EMAIL PROTECTED]> wrote: >>> >>>>> Fra: "John Forbes" <[EMAIL PROTECTED]> >>>>> >>>>> On Fri, 18 Aug 2006 10:03:00 +0100, DagT <[EMAIL PROTECTED]> wrote: >>>>> >>>>>> I'd give it a few months more to decide. If they are going to >>>>> introduce >>>>>> USM lenses it will be a logical explanation for why they have >>> stopped >>>>>> producing a lot of long lenses. They may be planning to revive >>> them >>>>>> with USM. >>>>> I'm sure they will introduce more long lenses - they can't afford not >>>>> to. >>>>> At the moment, the lens line-up is unbalanced; there is lots of stuff >>>>> below 50mm, and very little above 100mm. >>>>> >>>>> Whether the new long lenses will be USM or just small, light, DA >>>>> versions >>>>> remains to be seen, but if they are USM it certainly makes sense not >>> to >>>>> announce them until after there is a camera body that they can work >>>>> with. >>>>> >>>>> I would be most surprised if there are not new 200mm, 300mm, 400mm >>> and >>>>> 600mm primes within two years. And, of course, the fast zooms have >>>>> already been announced. >>>> Long lenses with larger apertures will never be small DA or D-FA wil >>> be >>>> about the same. Because of this they will also have heavy focusing >>>> mechanisms (even if the gain some by using IF), and that is were they >>>> really need USM. All of the lenses they have introduced recently have >>>> light focussing mechanisms that can be drivenby the motor in the >>> camera >>>> without any problems. This, together with the fact that som many long >>>> lenses have disappeared, make me believe that they are up to >>> something. >>>> DagT >>>> >>>> >>> >>> >>> -- >>> Using Opera's revolutionary e-mail client: http://www.opera.com/m2/ >>> >>> >>> -- >>> 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
