[APML]: measuring reciprocity failure

[bortech@OntheNet.com.au (Mark Bolton)]

Hi All

Our society is going bush this weekend to our dark sky location and i've 
been thinking about testing the resiprocity failure of the Kodak Royal Gold 
film that i've just started using. This film seems to be doing some strange 
stuff (in a nice way ) with regard to exposure times but  i've only tested 
it on bright objects so far. This post is probably in a round about way 
related to Michael Covington's post regarding 'Does all film need hypering ?'.

I don't have access to any technical gear (densometers etc)  but i'm 
thinking about comparing this film with the Fuji i usually use for colour 
work. I just have to compare timed exposures visually but i was just 
thinking about doing stepped slightly defocused star trails, defocusing 
every minute say, to pick a figure, and comparing the results. The contrast 
on the film suffering higher reciprocity failure should decrease (am i right 
here ?) for the same step in relation to the other film. I know this wont 
give me a quantative value (Schwarzschild Exp. ?) but as far as i can see it 
will let me compare a film i know against a new films properties.

Does anyone have any suggestions re this methodology or any suggestions on 
other methods. I like this idea because i done have to do a lot of exposures 
of the same object when i could be photographing seriously (not that this 
isn't serious).

Any suggestions on measuring reciprocity are welcome.

Mark Bolton

Border-Tech
Geotechnical Engineering Services
(Just a front for an astrophotography hobby)