zoom lens on DSLR and compact

[mikeeeey]

Hope I dont get flamed for asking such questions, again.

Was wondering.

Why is it that in DSLR, when using zoom lens, it extends out. Then when using compact cam like my LX3, zooming in will make the lens retract back.


thanks in advance

 

[daredevil123]

Hope I dont get flamed for asking such questions, again.

Was wondering.

Why is it that in DSLR, when using zoom lens, it extends out. Then when using compact cam like my LX3, zooming in will make the lens retract back.


thanks in advance

It has everything to do with lens design. For prosumers and compacts, when adding converters or filters they usually attach fixed length barrel tubes. So, with these tubes, to make sure the lens do not actually hit the attached filter or convertrors, the lens should not extend more. And there is an advantage in retraction during zooming in, is vignette control, especially with that barrel there.

 

[chiangkxv]

not necessary.. haha.. my Minolta extends when zooming out, retract when zooming in.

 

[Blur Shadow]

The optical design of the lens will dictate if it will protrude or otherwise. Nothing to do with dSLR/compact.

 

[miaoteh]

yea all because of lens design, one of my lens, when i zoom in from wide to tele, actually retract and then protrude out again, i.e. shortest at focal length somewhere in the middle.

 

[mikeeeey]

It has everything to do with lens design. For prosumers and compacts, when adding converters or filters they usually attach fixed length barrel tubes. So, with these tubes, to make sure the lens do not actually hit the attached filter or convertrors, the lens should not extend more. And there is an advantage in retraction during zooming in, is vignette control, especially with that barrel there.

Ahhh.. this make sense. Now I know.. Thanks!!!

But what do you mean by

"And there is an advantage in retraction during zooming in, is vignette control, especially with that barrel there."

I thought with a fixed barrel, lens retracting in will have higher chance of vignetting? why is that an advantage though?