On Fri, 13 Aug 2004, Nenad Djurdjevic wrote: > Given that it has the same angle of view as a 21mm full frame lens why is it > so much bigger and heavier than the FA20/2.8? I thought that the idea > behind smaller image circle lenses was so that they could be lighter and > smaller?
APS-C sized sensors built into bodies with regular lens mounts (such as the Pentax-K) don't solve the hardest problem of building very wide angle lenses. The rear element of the lens can't get any closer to the sensor/film than it could with a full frame lens. Imagine the cone of light coming into the camera. With a 14mm lens it needs to have a focal point 14mm from the sensor/film. That is just about at the center of the mirror and well behind the last element in the lens. Now remember that the front element has to be large enough to prevent vingetting for this cone of light. With a 14mm lens you get a very wide angle of view, so that element needs to be very large. Put it all together and you end up with a large lens. Compare it to a full frame 14/2.8 lens and you'll see that it is small, light, and cheap. http://www.tamron.com/lenses/prod/14mm.asp shows the Tamron 14/2.8 as weighing 661g and being 89mm long and 87mm in length. The DA 14/2.8 is 420g (about 30% lighter) and only 69mm long and 83mm in diameter. On the other hand you can rejoice that a 50/1.4 (which has the angle of view of a 75/1.4 in 35mm) is so nice and light. alex
