Depth of Field with Digital SLRs

[Glen]

Does having a sensor which is smaller than a full 35mm frame have an effect 
on the perceived depth of field?

It seems that I have to stop down the lens on *istDS farther than I would 
have expected to get the depth of field I would like to have. I'm using the 
Pentax 18-55mm "kit" lens. Maybe it's just the lens being somewhat less 
sharp than what I'm used to, and stopping down the lens is more of a 
requirement in general? (I was mostly accustomed to using Nikkor prime 
lenses in the past, but I have also used a few 3rd-party zooms on occasion.)

So am I imagining things, or do you really have to stop down farther with 
the *istDS to attain a particular depth of field? (Maybe I'm just not 
familiar enough with this lens yet?)


thanks,
Glen