Quality has a transverse affect between render time and how clean the image is. a lower quality setting will result in a grainy picture, but a shorter render. A High Quality setting will result in a smoother possibly brighter image but will elongate the rendering time. Prerenders of 5 to 100 are appropriate for getting an idea of what the image will look like, if you don't mind waiting some extra seconds or minute, prerenders of 100 to 1000 can give you a better idea of how smooth the image will become at even higher settings.

For high quality final renders I recomend between 5,000 and 100,000.

The image size will also have a drastic change on image quality and render time. if you want a smooth image to display on your screen then the image size should be at least the maximum resolution you keep your monitor at, such as 800x600 or 1280 by 1024 for standard vga monitors, and 1440 by 720 or 1920by 1080 for high def displays. (Keep in mind, doubling these numbers will multiple the total number of pixels by 4 not by 2, so the render times of larger resolutions will increase quite a bit)

Also, if your designing these for print, you'll want to operate at higher resolutions, standard screen displays work at 72 or 96 Pixels per inch or Ppi (I think) For printing, the bare minimum for a good print is 100 Dots per inch or Dpi, many printing companies used to require 300 dpi minimum for source files, but i think this has been reduced due to demand. Photographic companies will often scan negatives and slides at up to 3000dpi for good enlargement and printing. So keep in mind you'll want at least 800 pixels wide for a decent quality 8 inch wide print and for a higher quality print, 2400 pixels would be a proper width, for a 300 dpi 8 inch wide print.

Other settings include:
  • Filter Radius
Filter radius essentially gives your flame a gaussian blur, which will get rid of specks and pixellated looking parts but will also make it appear blurry. The default value of .4 will give you images that will probably have grainy looking parts where a value of say 1 will give you an image that isn't grainy but appears blurry. Filter radius is best used with oversampling or with a large render you intend to shrink down since that will get rid of the blurriness.

  • Oversampling
Oversampling renders the flame at a larger resolution then shrinks it down, so if you put in 1024x768 as the size and have oversampling at 2 it will render at 2048x1536 then shrink down to 1024x768. Higher oversampling will help reduce noise and jagged edges.

  • buffer depth
all I know about this is a higher number uses more ram, lower number uses less. I suspect higher numbers make it render faster, but I'm not sure about that.