In article <41kbc9$t51@crocus.csv.warwick.ac.uk>, phsap@csv.warwick.ac.uk says..
>(....) I am curious as to what the difference between
>individual film speeds are. For example does an ISO (or ASA) 100 need
>double the amount of light that an ISO 200 film to produce the same
>results. And so does say an ISO 800 need an exposure time of 1/8th of
>that for an ISO 100. Also on these films there are words like 21 >degrees and 31 degrees, what are they?
---- You correctly stated the relationship between ASA and exposure.
---- I think 21, 31, etc. refers to DIN speed ratings (every increase
---- of 3 requires 1/2 the exposure, if I remember correctly). BTW,
---- each increase of ASA (50>64>80>100,etc.) or DIN (21>22>23>24,etc.) ---- represents 1/3 stop increase in sensitivity.
>Is there any way to check the granularity of a film or do you just guess
>that an ISO 1000 will be worse than an ISO 100?
---- Correct, again, though manufacturers do put out ratings on their
---- films - which have the believability of car horsepower ratings
---- in the 1950's
>And lastly am I correct in assuming that there is only one way to >develop a particular colour film. The reason I am asking this is can I >get my films developed and printed at any old lab (eg Boots in the UK) >and then if I want decent prints I would have to get them printed >properly from the negatives (that are hopefully OK) from the lab?
---- Gosh, correct again! (The world of color film processing has
---- mysteriously shrunk to C41 equivalents for negatives, and
---- E6 for slides [plus Kodachrome processing for Kodachrome] - all
---- Kodak processes.) (Though pushing and pulling is still an option
---- with some films.) Hope this helps.