which pentax digital camera..

My first thought is that you don't need massive files like that for a website....

Only you can decide what you need, but the pentax DSLRs are capable of producing stunning A3 prints. Do you print bigger than this?

If you do need more resolution, then moving to the high end Nikon or canon DSLRs is of course an (expensive) option. You need all the new lenses as well, and don't forget the necessary computing power and hard drive capacity to cope with the very large image files.

You will know if this is what you need for your particular applications.

I learned that 35mm is capable to print max 18x24.

I know the D645 is coming next year, but i am afraid of the price it will cost...
I already have the 35mm, 75,120 macro and 200 lens for the 645 and love this system.

After thinking over and reading a lot of problems from guys with a canon 350, saying it stopped focussing. O no problem, send it back and pay 200 euro and it will be solved. Yeah! that's what i want....

I think to stay with pentax, but now comes the determining of which camera.
The Ist-D is already some years old withou the lack of usb2.0, smaller lcd screen etc... But has maybe nicer functionality what i use now on my mz-s. the istd-ds2 is very well priced, but not available in europe???

18x24 what? Inches, feet? However, I know this is rather misleading anyway. 35mm in the right hands can produce wall sized murals. In the wrong hands it can struggle to produce a decent postcard sized print! There really is no particular maximum size - it depends on the technique, the film, the processing, the printing, the viewing distance.

What I can tell you is that a good lens will produce a 16" x 12" print that will exceed the resolution of the human eye when viewed at arm's length.

cm of course..

The max enlargement is 8 times the size of the neg so is= 19x28 cm. for 35mm film. Above that you loose quality if you want it or not. changing development can decrease grain structure, but you will loose sharpness....

It could have been mm.......

There are some extraordinary 35mm films available that will defy the limitations you mention, and, of course, the 8x "limit" is an arbitary one. Quality will be lost at any magnification, even 2x, and it will continue to slide ever downwards as you magnify more. At some point we decide it is unacceptable, but even this will vary between viewers.

We already know the effects of viewing distance, and a 300ppi print is needed for viewing close up, but a 150ppi one may look just as sharp from a distance, so it can be bigger.

The very best negatives can yield even better results, and on the New York Subway there have been wall sized pictures from 35mm; when films were not as good as they are today.

However, unless we use a sturdy tripod, all this could well be irrelevant anyway!