I have a question regarding reciprocity, not sure how it works in case of star trails.
1. Star (projection) is moving across the film and each second (or a bit more) it is exposing new part of film, which wasnt exposed before (dark sky was in this area). So as I understand that tiny part of film has only +/-1 sec of exposure and reciprocity failure of most films will not affect anything?
2. However if we have foreground lit by by some light, film with "worst" reciprocity failure can give us longer exposure and longer star trails (in case 1st point is true)?
Not sure if it is correct.
Also I heard that Provia has less color shift in case of long exposure. Not sure how true it is, and how important it is in case of star trails.
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