On 15 Nov 2003, at 12:31, Patrick Baldwin wrote:
You said that 1250 was a misnomer and was really just messing with curves. I know what curves is/do but can you clarify. Sorry to be so longwinded.
Hi Patrick .
On the Sinar we seemingly have the choice of 25 , 50 or 100 'ASA '....... except that we don't really. The CCD chip has one sensitivity , and records accordingly. All that we do when we 'change ASA ' is move the film curve up and down the histogram of recorded information. So if all the info falls into the bottom third of the histogram , I can set my white point at the first point at which information registers , reset the mid tone and black point , and thus increase my apparent ASA. On the Sinar software , I can achieve the same effect by hitting command B and step up the exposure by third stop increments , but once again , I'm only shifting the curve.
Put more simply , all I have to do is place the film curve neatly over the recorded information, whatever that may be. If this is a tiny peak at the lower end of the histogram , so be it. And 'voila' , 'hey presto' or 'bobs your uncle' , I suddenly have an image with a black , a white and a mid tone. And seemingly with very little light being used at all , hence the apparent gain in 'ASA' .As mentioned above , this fix can be built into the software , giving an apparent choice of ASA .
With a high end back that has true 16 bit capture and a cooled chip , you can abuse the curves like this dramatically making huge gains in apparent ASA and still get reasonable quality, but at the end of the day , there are always going to be compromises with noise and dynamic range , in much the same way as pushing development on film. The smaller and hotter the chip , the more the relative noise . The smaller the amount of recorded information to work with , the smaller the dynamic range.
Hope this helps,
Regards,
Bob Marchant.
=============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
