Re: [APML] What's the Longest Exposure for an ASA 800 Film

[Ray Butler <ray.butler@nuigalway.ie>]

Hi Thomas,

NPZ Fujicolor 800 has _bad_ reciprocity failure ... which actually 
should make it a very good choice for catching fleeting meteors! The 
spec sheet shows a +2 stop correction required after only 64 seconds; so 
for targets which require a 1 minute exposure, it's effectively ISO 200. 
For sky fog, which requires still longer exposure, it's effective ISO is 
even smaller.

On a film with good reciprocity like E200, you can probably get 15 
minutes at f2.8 for a moderately high target at a dark site, before sky 
fog gets too serious. With its bad reciprocity, my guess is that you 
could run NPZ 800 for an hour in these conditions. The low ISO 
sensitivity to sky fog, coupled with the raw ISO 800 speed for bright 
bursts of meteor light, should make for a good combination. This is also 
explained (for Kodak Tri-X) in Robert Reeves' "Wide Field 
Astrophotography" book.

Ray "who's just been through the 2nd wettest September on record in 
Galway" Butler


Thomas W. Earle wrote:

> In preparing for the Geminids, I'm trying to figure out what is the
> ideal/maximum exposure at F/2.8 using NPZ Fujicolor 800.  I'll be
> using a Pentax 67 camera so there's not too many film choices left
> in the medium format arena, especially color negative films.  I have
> a very dark sky with an elevation of 4000 feet.  Here's a link to a
> light pollution map of my observing location:
> 
> http://cleardarksky.com/lp/RttBttORlp.html
> 
> I used some old Fuji NGHII 800 during the Perseids which I exposed
> for 10 minutes, but a few shots seem a little muted; however, the
> film is a little over a year past its expiration so I'm not sure if
> I exposed too long or not.  I'll primarily be shooting around Orion
> area which should be about at an altitude of 40-45 degrees at its
> highest.  I plan on doing some testing over the next few months;
> however, it's all dependant on mother nature.
> 
> Any comments or advice would be greatly appreciated.
> 
> Wade
> 
> 
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-- 
Dr. Ray Butler (ray.butler@nuigalway.ie || ray@physics.nuigalway.ie)
Lecturer, Dept. of Physics || Computational Astrophysics Laboratory
National University of Ireland, Galway, University Road, Galway, Ireland.
Tel: +353-91-524411 ext. 3788   FAX: +353-91-525700

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