Pentax film SLR lenses on Pentax Digital camras

There is a lot on the site about compatability of varoius lense functions but what i would like to know is the focal length equivalent on both types of camera, ie do you get the same field of view using the same lense on a film and digital camera without adjusting the zoom.

No, the digital sensor is smaller than the 35mm frame, so effectively you only use the central part of any lens' field of view. If you multiply the actual focal length by 1.5x then you will get an idea of the "equivalent" focal length.

The most recent DA lenses only cover the CCD and if you use them on film cameras you will get some vignetting. I haven't explored this yet, but it is possible that there may be some creative mileage in this effect.

The main effects of the smaller sensor are:

1 Every lens effectively has it's angle of view reduced, so a 200mm becomes a 300mm, etc. This is great if you always wanted a longer lens, but couldn't afford it, but it's less good news at the other end. Your nice wide 28mm lens becomes a 42mm. Manufacturers are busy designing new super-wide lenses.

2 Lens sharpness becomes more important, because you are having to "enlarge" the captured image more than you would have to if the sensor was the same size as 35mm film.

3 Light fall-off and poor resolution at the edges/corners don't matter so much because you are no longer capturing this part of the image.

4 Some lenses are said to work less well with digital sensors than they do on film. Apparently, sensors respond badly when light hits them at an angle. As a result, many lenses are being re-designed, and the new versions are described as "optimised for digital". Some people think this is being over-hyped in order to sell new lenses.

George

Taking up one of George's points, I understand the theory regarding optimising a lens for digital capture - that is, the CCD prefers light arriving perpendicular to the surface rather than at an angle. But as we are using only the central part of the frame, surely that is less of a problem anyway?

It will also mean that we are using the part of the field of view with the highest resolution and best control of abberations (which fall off towards the edges) so the APS sized CCD should give conventional lenses more than an equal break :

Thanks to every one for there replys, the matter is now clear to me. Best to buy a 'Standard' lens with a digital camera but retain older long focus types and take advantage of the apparent longer focal length.

I think that the hype about the new generation of lenses is just about selling us more pieces of glass.
I have just upgraded to a DS2 and i have gone through the whole of my lens collection and found them all to be functioning well and producing good images,
The filters also seem to be operating well and the polarizing filters are giving good results at intensifying sky tones.
Early days as I have only owned the camera for three days but I am pleased with the results so far.

One other difference with the so-called 'digital only' lenses that hasn't been mentioned so far is the lens coatings. Digital lenses have, amongst others, an anti-ghosting coating to prevent the problems of internal reflections. This is not such an issue with film, but it is, or can be, a problem with digital bodies and their shiny glass sensor covers.