I've rendered some very large images. Most of the time when I finish an image, I render a 4,000-pixel version in UF, with one level of anti-aliasing (effectively, 12,000 pixels on the longest side). Since I print these at 200ppi, this is enough for a 20" print, and that's what I sell most often.

Occasionally, though, I will render larger. I have done a 48"x18" print at 400ppi (special request), which when you factor in the anti-aliasing works out to be 57,600 x 21,600 pixels. I once prepared a 7'x5' (yes, feet) image, but that was only 150ppi, so it was only 37,800 x 27,000. And for the ICM exhibition in Spain I did a couple at 12,000 pixels, so the effective size was 36,000 x 18,858.

The amount of time it takes to render any image is going to depend on how fast your computer is, how fast your software is, and how demanding your image is. The image I just uploaded took nine and a half hours to render at 4,000 (12,000 when you count the AA). That's using Ultra Fractal 4 and five computers, about 15GHz of power total. (I should add my wife's new laptop... wonder if she'd object...) But to do that render, I had to interrupt another render that's been going for... 590 hours, and has 919 hours to go. Rykk loaned me the use of his farm for a bit to help out with the long render, but it's still going to be a few weeks before it's done. This is the longest render for me so far, topping my previous 900-hour record (that I can now render in 100 hours due to upgraded computers).

That's another thing that I've noticed. My newer images almost always take longer to render than my old ones. I recently sold a print of a ten-year-old image; back when I made it, it took hours to render a 1,024 x 768 version, and I had to assemble the layers by hand afterwards. Now I can render the entire thing at 8,000 x 6,000 with full anti-aliasing (effectively 24,000 x 18,000) and the entire job is done in nine hours, automatically assembled. That's a 500-fold increase in speed, or roughly doubling in speed every year. Moore's Law was never so sweet.

For the most part, when I make an image I'm aiming for 10-20 hours to render the 20" print size. That means staying away from some formulas or settings on formulas that are too slow, unless I'm in a serious tinkering mood or the image absolutely doesn't work any other way. The most annoying thing is when I discover I've got a particular effect that requires heavy anti-aliasing to render properly; the 100-hour render I referred to above required two full levels of anti-aliasing to render properly, for an effective resolution of 36,000 x 27,000. And it was slow as mud to begin with.

Ten years from now we'll wonder at the simplicity of the fractals we're creating today.