[BlueSky]

I was in a chain-store the other day and got a rare chance to talk to a prospective new user teetering on a purchase based on the advice from the salesman.

One thing I find that salesmen never seem to point out about competing systems with kit lenses is that the front of a Pentax kit-lens (DA 18-55) doesn't rotate. This makes it a lot easier to use a polarizer, gradated filter, etc.

Although the other camera this person was considering was just as fine, I pointed out this "feature" of the Pentax kit lens and guess what? It was the final point needed to persuade them to go with Pentax *st/DL (on sale) since he already had some filters from years past.

When you lay these similar systems out on the counter, I am always amazed that this isn't pointed out.

[Snoopy]

The reason the front element doesn't move while focusing is because it is an internal focus lens (IF), that is, the elements move within the barrel rather then moving the external front element. Many lenses have this feature and it is handy when using a Polarizer that must be turned to acheive maximum results. That's why one can use a "Petal" type hood... if you notice the bottom petal of the Pentax kit lens comes off to allow easier rotation of a polarizing filter.

[Edvinas]

Hmm, I always thought that internal focus is when lens front element does not move at all, not just rotate. DA 18-55 front element doesn't rotate, however it moves forward-backward during focussing. It's not internal focus.

[Matjazz]

Yep, internal focus means that nothing but focusing ring moves on the outside of the lens when focusing.