Digital BW, The Print

Hi all,

I'm appealing to all you master printers here on this forum, specifically those of you who are lucky enough to own or have access to a printer capable of printing larger than 13x19, which is the largest output possible on my dastardly r1800.

I have read conflicting things about how many megapixels are needed to produce a "photo quality" print at a certain size, and I'm also a bit confused as to how interpolation works in this arena.

My Canon 1Ds (the flagship dinosaur) is an 11 megapixel camera that gives me 62 mb files. Pretty small at this juncture in the technology tornado. Everything i have read so far tells me 13x19 is optimal size, but I have an image I'd like to print larger.

How large can I print and still have decent detail? 

thanks!
Sarah