Mundane Carl Zeizz Planar 80mm F2.8 CF question

Hi

Just purchased a Hasselblad 503 CW and thanks to the help from this forum, I've now been able to load the camera with film correctly and I have a better understanding on how it works.

But, the camera also came with a Carl Seiss 80mm F2.8 CF Planar T* (I believe)

Looks like this:



Question:

Next to the flash sync port on the lens, there is a sliding knob.

I cannot find any information on this knob's function (I don't have the manual and googling it is a nightmare).

What is the function of this knob?

Also, there is a input port on the left side of my camera, what's this for?
Sorry for still newbie questions, will post some photos later to make good

You may find info and manuals here http://www.hasselbladhistorical.eu/

The manuals you need: 503CW ; CF lenses

The sliding knob on the lens should be the Depth of Field preview, The input port in the camera is the dedicated flash connector for SCA module

I have older "C" lenses but if I recall correctly:
The larger tab is a depth of field preview.
Slide it one way and it stops the lens down to the preset aperture.
Slide it back and it give full aperture for focussing.

Ok, thanks, was wondering if it had something to do with curtain sync settings or something like that, thanks for the link as well =)

Regards