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I have seen a battery grip listed in the K100 price list but the dealer could not get any from Pentax - maybe it was in the wrong section and should have belonged under the K10. I think the listed price list was about $285.00
If you want the grip mainly for a longer battery life there is another solution - using an voltage regulator you should be able to get a regulated 5.0 to 5.5 volt output that can be driven from a 4 D cell battery pack. I built one for a friend for his Canon 350 using ordinary Alkaline D cells and his battery life was two 1 GB compact flash cards with some power left over.
When i emaild Pentax here in Australia, the response was that the k10s didn't fit.. so either a 3rd party unit could be found (if any of our friends who create ipod or pda components are listening ... Hint!) then maybe the voltage regultor may be the go
thanks Chris, that sounds pretty cool. Although i've never heard of such a thing, i mainly wanted the grip for the comfort of taking portrait shots and longer battery life as a second priority. If i wanted to build this thing, where can i find instructions for doing so? I also asked someone at Henry's Toronto whether the DS battery grip fits the k100's and they said no.