Question about Pentax SMC FA 2.8/100mm Macro

Hi folks,
Just received this lens of eBay in mint condition. One question about the clamp button though. The limit button is self explaining but what exactly does the clamp button do??
Thanks in advance,

Martin.
(A very happy macro lens owner)

PS, I found the answer already The clamp increases the friction of the focus ring so you get a very smooth manual focus feeling.

According to the manual, the clamp screw is to prevent the lens extending under its own weight when pointing down.

I can't say I've ever used it like that - like you, I use it to improve the feel of manual focussing

R

I had the pleasure of using a 50mm FA macro last year and had the impression that the clamp was supposed to stop the focus ring from moving at all, so you could lock a particular macro ratio and not worry about it drifting off

The clamp screw is a dial with an increasing effect from "Off" to On".

As I said, the manual says "the clamp screw is to prevent the lens extending under its own weight when pointing down".

R

definative answer:

my 100 mm macro will creep from the weight of my ringflash when pointed down. stays put with the clamp engaged.

Thanks everybody, for answering.
Martin.

The clamp button is not to stop it creeping it's so that you can simulate a manual focus feel.

As a lot of people like to use macro lenses in manual focus mode Pentax provided a little focus damping screw on both the FA50 and FA100 so that the user could set the "feel" of the focus.

If you use it on autofocus you should have it loose so that it doesn't put a strain on the auto focus mechanism.

Sorry John, but that is inaccurate mis-information. The clamp switch on the FA 100mm Macro lens is to stop the lens creeping when pointing vertical (up or down).

On the D-FA lenses it is to lock the point of focus and disengage AF.

FA series lens manual can be viewed here ( page 22 ).
D-FA series lens manual can be viewed here ( page 18 ).

Regards,

Apologies it looks like I was wrong.

I was right about one thing though, it should only be used in manual focus mode.