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Re: [APML] Fuji Provia 400F and exposure time
>I always sticked to the rule of thumb of the square of the f/ratio for a
>400 ASA film, but I was wondering if, on a top of a mountain (1900 >meters
>a.s.l.) with clear sky it would be better to push the esposure a bit more
>of , let's say 1.5 times...especially with Provia 400F which I don't know
>if it's reciprocity failure is much higher than, for instance, E200.
Becouse I guide manually, I push both films two steps. Roughly, they increase their sensibility four times, without a very noticeable increase in the film's grain or loss in dinamic range (for astrophotos). From my dark site, I use to shot Provia 400F for 25min at f/4, and E200 for nearly 40 min.
>Unfortunately I go to this place only once a year and I don't want to >"waste"
>time in sky fog testing so I need a good estimate beforehand.
I thought the same about my dark site... but after four trips I did some sky fog testing, and I was surprised on how long I could reach. With a Minus Violet filter, I made exposures from 11 to 44 minutes (steps of 11 mins) with a 28mm, using E200+2, to the Milky Way. I found that the SFL is in the range 33-44 minutes from a site near La Silla Observatory (ESO). Just as a comparison, with Matt's setup, you could do a exposure 4 hours long! Anyway, if you push, try to make a series of pics from the same subject to stack.
> Any opinions?
Just a last suggestion. Use Michael Covington's Exposure Calculator for those estimations. For Fuji Provia 400F choose a speed of 400-800-1600 (normal, pushed 1, pushed 2), and reciprocity failure of 0.9. For E200 use speeds 200-320-640, with reciprocity failure of 0.95.
Regards,
Carlos Milovic F.
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