All, Let me clarify the statements below just a bit. It's not just light losses, but more importantly lens element positions that make a big difference. Consider a lens with numerous thick elements. If you do a simple ray-tracing from a subject to the film, you see that the elements farthest away from the film plane have to be big in order to "intercept" and bend the light rays that eventually end up at the edges of the film. So it's not just the amount of light absorbed or reflected away, but also the element positions that are key.
With small field-of-view lenses like telephotos, the rays entering the lens are nearly parallel. Hence, the elements at long end of the lens don't have to be much bigger than you might expect. With large field-of-view lenses (e.g., 28-XX zooms), the rays entering the lens may span a wide angle. Hence, the front element must be large to avoid severe vignetting. Most of these lenses vignette quite a lot when wide-open anyway. --Mark Len wrote: Yep, that's the case. They could give you smaller filter sizes but, if they did, you'd end up with a 70-210mm f/3.5-10.3, kinda like some of the point-and-shoot cameras have, or you'd have drop in filters at the rear of the lens. Len --- Brenden wrote: Due to the fact that it is a zoom, you have more groups and elements, there needing more light to enter to get the same F stop, needing bigger front elements needing bigger filters. Price you pay for getting zooms - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
