In terms of making some kind of meaningful comparison test, i wonder whether this would work:
Set up a white background at a measured illumination (to allow you to re-shoot the same set up later). As my friends tell me they have more of a problem with noise at long exposure times... don't light it too bright (I do not shoot digi yet... i work from scans). Expose so the white background fills the frame and is at zone 5 (i.e. mid grey.. what the meter says). Note the aperture etc. Get the image into photoshop or like, and fiddle with levels so that darkest noise pixel is black, brightest is white, while keeping the grey where it is and note where the black/white points are on the scale (0 - 255). This will give you a figure for the amount of error that is the noise (min and max on scale of 0 - 255), and a levels histogram that is a distribution of the noise across this band. There are no figures, so you cannot work out the standard deviation, which would be really useful, but you will be able to see whether all the noise is nearly the same as the predominant grey mid tone (which would not really be a problem) or whether the noise is predominantly rather different from the mid tone (which would) and how much noise there is compared to the mid tone. This would manifest itself in radical variations of the 'bell shaped curve'. If this was done as an adjustment layer, the parameters would not reset (at least in PS 6 they don't), and you could do a screen grab to save and compare to other hardware or shutter speed/aperture combinations that you might be able to do later. You would also be able to compare the histograms for all colour channels (which might be very interesting). Though you might have to desaturate the image in order to make the setting of black and white work. I have no idea whether there would even be enough noise to show up... but i bet if you went dark enough with the subject there would be. I don't have a digicam or a studio, so I cannot try this out for myself without setting up lights in my house (annoying my wife and electrocuting the dog), shooting film, devving, scanning... but all this will change shortly and if this technique works it might be quite interesting. If anyone tries this, please let me know if it works. Giles Stokoe photographer/photojournalist. See some images at http://www.stokoe.co.uk =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
