John Petrush wrote:
> sorry, but I just can't help much on glass - I too would like to know more
> about that. All I know for sure is when the glass is special enough to get
> an acronym, the price of the lens in question goes **way** up.
Hey Olympians! We are two now, who wants to know more about ED and UD glasses.
Anyone got an interesting site to tell? Or any information at all?
> This one I think I know, but if I'm incorrect, I'm sure the right answer
> will come forthwith. A "normal" lens is focused by moving the elements
> closer or farther apart by some means, generally a helicoid thread
> mechanism. In this case, the physical distance between the rear-most
> element and the front-most element varies. With an internal focussing lens,
> an element, or group of elements, in between the front and rear move,
> shifting the place of focus but the physical distance from front to rear to
> not change.
Then Foxy wrote in another thread:
> I thought the normal lens just extended. Put a 300mm on a 25mm tube
> (focussed at infinity), or wind it out 25mm, same result.
>
> Internal focussing move elements and can focus closer (generally), but they
> reduce their focal length. This isn't a problem for most situations, but
> once you focus closer and on small things the focal length reduction becomes
> greater. Or so I'm told.
I guess internal focus is a newer design than "normal lens focusing", if so they
must have developed it to give lenses improvement. Now, how much better in
performance is an IF lens compared to a "normal"?Just curious.
Thanks, both!
--
Regards/
Ingemar Uvhagen
Gislaved, Sweden
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|