From: chorley@vms.ocom.okstate.edu
Newsgroups: rec.photo
Subject: Re: moonlit landscapes / stars (4x5)
Date: 16 Oct 92 00:26:44 GMT
Organization: OSU College of Osteopathic Medicine

In article <1992Oct15.011901.9934@beaver.cs.washington.edu>, franz@cs.washington.edu (Franz G. Amador) writes:
> Does anyone know a good way to pick an exposure for a moonlit
> landscape?
Way #1  Bracket like crazy.
Way #2  Fake it by underexposing through a dark blue filter, bracket like 
crazy and superimpose a lunar image on the film by using a long lens to 
photo the moon, or photo-montage it.


  Seems like there ought to be a rule equivalent to "sunny
> f/16" for the full moon; the half moon ought to be one stop darker;
> etc.  I doubt my light meter will work; it reads only to EV 1 (ISO
> 100).

The sunny f/16 rule works for the surface of the moon because it is a 
sunlit surface ( read Ansel Adams on Moonrise over Durango)

The surface of the half moon receives the same amount of illumination and 
so obeys the same rule (Those of us who want to take pictures by available 
darkness please note.)
> 
> Also, does anyone have a good explanation for the effects of aperature
> upon star trails?  I've heard it said that the aperature affects the
> thickness of the trails, not their brightness, which depends strictly
> upon the "light gathering" ability of the lens.  Is this right?
Yes.
The thicknes of the trails depends on a concept known as "circle of 
confusion" ( By that I don't mean the newsgroup Alt.Scientology :-)
;-);-)
If you imagine the beams of light being focussed onto the film as being 
similar to a cone, then wider apertures would allow a thicker cone of light
. In day to day photography, the use is in depth of field, where narrower 
cones of light give acceptable sharpness in front of and behind the plane 
upon which you are primarily focussed. At night, with point objects at
infinity, (the stars) you will notice that their thicknesses on the image 
do vary according to your f-stop.
>  Does a single aperture/trail-thickness relation hold across all lenses?
> What is the light gathering ability of a lens,
The maximum aperture, f/stop, although purists will tell you it is the 
T-stop, which is basically the f-stop modified for light lost internally.

> and how can you determine it?
> 
> I ask all this because I have a photo idea involving shooting a snowy
> moonlit landscape with the stars turning above.  I'm shooting Velvia
> in a 4x5, though, so I don't want to blow a lot of film on
> experiments.  My lens is a Symmar-S 210/5.6, so my maximum aperature
> is limited.


My final advice is for you to practice shots on velvia 35mm and waste
relatively cheap film before you go investing in major silver.
Please be advised that with long time exposures, the reciprocity failure, 
which includes the fact that velvia, to my knowledge, isn't designed for long 
time exposure will mean that the colour rendition will vary from extremely 
unpredictable to ultimately SH*TTY.

More points: If you stop and think hard, what you will be photographing 
will be essentially a high-contrast monochromatic landscape. Why not try 
B&W THEN, you could use the Zone System and get really confused

Hope I helped...
		David N. Chorley, Osteopathic Physician in Training.
		....(or OPIT, for short)
		I took up medicine to support my photographic hobby