On: Sun, 05 Dec 2004 Robin Scagell wrote:- > * The IR filter of digital cameras almost completely blocks the light of > hydrogen alpha at 656 nm, which gives the lovely red colour to photos of > nebulae. Film, however, is quite sensitive to this, and a shot on film > of, say, Orion shows the Orion Nebula glowing red. On the 10D, however, > it is an insignificant grey blob -- much less extensive and attractive. > No amount of fiddling with the red channel seems to be able to bring up > the red. You can even now buy a doctored 10D with the IR filter removed > just for astro work.
I am completely familiar with what you are talking about in terms of luminance mapping via IR. > * Star colours are much less strong on digital. The array of four colour > pixels gives lower colour resolution than film, as we discussed on > Prodig a year or so ago. This is really obvious when comparing faint > stars -- on film, even the faintest stars usually have colour, whereas > on digital they all appear white. (A star's colour depends on its > temperature, so stars cooler than the Sun appear yellow or orange, and > hotter stars appear blue. Sunlike stars are white.) This is where greyscale LRGB recording comes into its own. I know this stuff inside out - big time. Enough for now. > * Major drawbacks of film for astro work are of course reciprocity > failure and the low contrast at the toe of the characteristic curve. But > these can be an advantage as well, which I didn't appreciate until > attempting constellation photos with the 10D. Any light pollution around > in even a comparatively dark site (in the UK) will rapidly build up into > an unattractive brown background, whereas film, particularly slow film > such as K64, is relatively insensitive to it and will give a darker > background to the stars. Hey, Antartica is THE place to be right now... > Of course there are numerous benefits of digital in astro work, but I > wouldn't like to see the end of the yellow box just yet. Me neither, I was talking to a good photo-pal of mine recently, someone who builds top quality large-format cameras for a living, and he reckons that there are about 10,000 serious hard-core large-format photographers worldwide who are determined to carry on using film - to the point where if the mainstream manufacturers do stop making the stuff, you can be absolutely certain that a sizeable minority will start coating their own glass plates. And before everybody here falls about laughing at the prospect, I ain't talking rocket science here, anybody with a halfway decent darkroom can do this kind of thing (albeit with the proper knowledge) - no problem at all. William Curwen =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
