The experience has been to actually work at a canvas size that is about 50% larger than what you actually want your final scene to be, then resize down in Photoshop when you’re done. This results in very nice antialiasing.
Of course, working on a 6000x6000 canvas, you’d better have one heck of a computer!
In terms of brush size, those numbers are in pixols as a radius from the center point (a 100 pixol brush paints a swath that’s 200 pixols wide). Which does mean that a 100 width brush on a 600x600 canvas will paint a swath covering 1/3 of the canvas while the same width on that 6000x6000 would paint only 1/30th. However, in the Preferences palette near the top there is a setting for Max Brush Size. You can raise the slider to as high as 512, which then lets you paint with a brush twice the size of what is normally available. That brush size is actually larger than the whole default canvas!
Most people set up the 3D elements of the scene using a small canvas size (with dimensions that are scaled from the final planned size) and placing markers. This requires a fairly small amount of processing power. When the scene is laid out just right, then they finally clear the layers to leave only the markers and scale the scene up. You then activate each of the markers to put the pieces back in place exactly as you had them laid out. The markers will scale up with the document, so everything gets instantly drawn into place with the proper size and without any distortions caused by sizing up the canvas. It’s a very nice feature! Also, if you use the Markers palette you can activate various other pieces of info that the marker stores, allowing you to actually recall such things as material and color with the marker – this allows you to plan all of that stuff at the smaller size, which again requires less processor heft.
A final note is that ZBrush exports at 72dpi. I have found that when I use Photoshop I can do a little cheat: I first increase the dpi to 300 and at the same time size the image down by 25%-50% for antialiasing. I can then turn around and resize the image back up a surprising amount without losing image quality appreciably. I’ve actually gone as large as 25% larger without any noticeable loss, and 50% with only marginal loss. It’s pretty amazing, because when I first started with ZBrush I was continually challenged by how to get clarity without having enormous filesizes. Using this technique I can make a scene at 1200 width, resize to 800 for antialiasing, and then increase it again to 1200 before making my jpg. Since Photoshop allows much higher in dpi, I imagine you could apply it to go way beyond print resolution and then scale the dpi back down again when you’re done with your image dimensions.
Hope that helps you out!
