Quote:
Originally Posted by usccharles
Bullis, Haris
thanks for your comments. this is very confusing for my head! haha
i'm still lost though. if i buy a film that reads 3200iso, shouldn't i be able to use it at 3200iso? if i'm only able to use it at 800 or 1000 or 1600, yet can process at 3200... i don't get the point in that when what i was looking for was a film speed of 3200 to increas my shutter speed...
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Thing is: Manufacturers put on box film speed they establish in strictly controlled laboratory testing conditions. They do not test film by making images in various real life situations. They put their emulsions into machines, machines give as result certain number, and that number they write on box as film speed (of course this is not completely like that, I just very much simplify things). Even further, manufacturers make calculations for emulsion formulaes, for example they calculate chemicals and procedures needed for 3200 film, they coate base (make film) with those emulsions, and they check if results are under those calculated parameters. They simply can not (don't have time and money) to test every amulsion in real life situations and that also has no point.
Imagine you once buy film where in box is written 118 ASA, next time 31,5 ASA, next time 1823 ASA... That is pointless. That's why nominated and standardized (laboratory established) film speeds are written on film box, and true film speed (real life photography situations) may be different more or less from that nominate speed.
With b/w film things are somewhere better because b/w film can tolerate few stops difference, it can be "repaired" during processing or print making. So, usually, people use film at theire nominate (written on box) speed without problems. But, now and then, some critical photographs and some difficult lightning situation when film is used appears, and in those situation "true" film speed become important.
Try to use slide film and then you will see how important true film speed and precise exposure mettering is
Me personally use films (Ilford FP4 and HP5) at their nominate film speeds (ok, I use FP4 as 100 ASA not 125 film), and I have no real problems most of the times, my photography tehnique is OK with that.
I use Ilford Delta 3200 film as 1600 speed film.
I develop my films in Ilford ID11 (stock solution) at nominate times for each film.
Regards