ISO and Print Size

Is there a chart or rule of thumb that equates ISO speed to final print size? For instance, use ISO of at least 100 for poster prints. Or you should use ISO 400 or higher for 8 x10s.

Hi Scott,
As I see it ISO shouldn't relate to print size. ISO selection should be made in relation to light conditions and although a higher ISO does increase file size, this doesn't mean a higher ISO should be used for a larger print.

Make ISO decisions for what you shoot, not for what you'll do with the image afterwards.

tkd

Not sure about the ISO angle, but most online labs have charts relating print size to file size. Lots of variability from camera to camera and subject to subject in the effects of ISO, not to mention additional function of "denoise" programs like Noise Ninja, plus lots of personal taste and sensibilities. Interesting question, though.

'Graininess' as a function of ISO selection may be good or bad, depending upon how you want the final print to look.

Basically, this goes back to the visualization process: One must know what they want the final print to look like, before tripping the shutter.

-PB

ISO is always a compromise, and shouldn't be chosen based on print size. Simply put, always choose the lowest ISO the particular image you are taking will allow given the other exposure settings that you feel are neccessary. Also, with modern Dslr's, many of our older notions of ISO are changing to some extent. Oftentimes, the ISO can be bumped up a bit with very little quality loss. This is especially true if it's carefully used in conjunction with noise reduction software for smooth gradients and shadows.

Also different sensor technology respond differently to changes in ISO. Some cameras are cleaner at a given rating than other. Ultimately it also depends on the subject matter. I don't see a way to come up with a generic rule here.

Guy

I'm still trying to stop calling it ASA. Pete D.

Higher ISO settings have larger file sizes because the files contain additional color info pertaining to the noise. Whereas lower ISO's have little or no noise and the files have to record less or no additional color information as a result of noise. This has no bearing on allowing larger prints to be made from higher ISOs. In fact, just like high speed film has more grain, high ISO digital files make prints with less detail. You can "wash" a high ISO file through a noise reduction program but this almost always reduces fine detail. Generally speaking ISO 400 or less will make large prints just fine without noise reduction software. Higher ISOs are not so good, IMO. Again, this is just a general "rule".

I have read somewhere that the printing process (and I mean real printing, not pc printers) deletes the noise of digital photos in great extent. Could that be true?