K mount lens speed on *ist ds

I am looking at buying an *ist ds because I have an existing ME Super with a few K mount lenses. If the *ist DS has a focal length multiplier of x1.6 does this mean that my old lenses will have a max aperture divider of x1.6?
ie. an f4.5 max aperture lens becomes an f7.2 ??

No, it means the apparent focal length increases, because the sensor is smaller than a piece of 35mm film. So, if the multiplier were 1.5x then a 50mm lens would appear to act as a 75mm one would on a 35mm camera.
A 100mm lens would be equivalent to a 150mm, and so on.

This means that wide angle lenses have to be very wide indeed for digital SLRs.

The aperture relates to the amount of light that the lens lets in, and a f2 lens remains f2 because the aperture is focal length divided by the diamter of the front element. So, in our 50mm example, the focal length of the lens is still 50mm, divided by the 25mm diameter of the front glass gives us f2. The lens only behaves as though the filed of view id a 75mm because the small sensor only uses part of the field of view of the lens.

I shudder as I write this, because it is straightforward but horrible to explain!

Thanks.
I have been out of photography for such a long time I'm forgetting fundamentals.

I have been thinking of buying the istds too, ( i also have an me super) but some threads seem to suggest that the old PKa lenses will NOT fit. Does anybody know this for definite yet?

According to the previews I have seen so far, all Pentax lenses will fit, even screw thread ones with the appropriate adapter.

Hiya
I've been looking at the *ist DS as my step into the digital slr race. I've got a very reliable and still well used Pentax K1000 with quite a few of the K mount bayonet lenses. If i understand the posts so far these will fit the *istDS?
If so what differences will using them make over the newer lenses other than the older ones being manual focus?
Thanks
Kaylesh

K and M series lenses have no "A" setting on the aperture ring and will not enable shutter priority or program exposure modes. A series lenses and later should be more or less completely OK, but as you mention, obviously you need autofocus lenses to use autofocus!