Re: [photo-3d] aurora warning

[Brian Reynolds <reynolds@xxxxxxxxx>]

Bill Costa wrote:
>      What kind of stereo base would you need to actually shoot
>      an aurora in 3D?  Unless you are capturing foreground 
>      objects in the image, I'd think it would have to be *miles*
>      to see any depth in just the aurora itself.
> 
>      Also, anybody have exposure recommendations?
> 

The book I'm currently reading ("Wide-Field Astrophotography" by
Robert Reeves) just happens to have a mention of stereoscopic
astrophotographs in one of the picture captions.  The book suggests
taking two separate pictures four minutes apart with an object in the
foreground (tree, buildings, etc.).  The change in sky position will
create depth in viewing.  The book even explains how to detect
pseudo-stereo (although it doesn't call it that).  I haven't yet tried
to view the pair reproduced in the book.

I would think that the aurora would appear to be a foreground object
compared to the background stars.  If a ground based object is in the
field of view the aurora should appear between the foreground object
and the stars.

Exposure depends mostly on tracking and sky conditions.  If you are
not tracking the sky (i.e., camera on a fixed tripod) you can expose
from 15 seconds (near the celestial equator) to 40 seconds (near the
celestial pole) with a 50mm lens before getting star trails.  Shorter
lenses can stand longer exposures and longer lenses need shorter
exposures to avoid trailing.  You should close the aperture one or two
stops from fully open in order to minimize various lens aberrations.
If you are tracking exposure times are generally limited by local
light pollution and your guiding ability.

A long duration stereoscopic exposure of circum-polar star trails with
an interesting foreground would be pretty neat.  There are all sorts
of examples of star trails around the North celestial pole with
various rock formations in the western US.  Perhaps someone will try
this at the NSA meeting in Mesa.  A hyper spacing on a twin camera
setup would be ideal.

Robert Reeves' web page is
<URL:http://www.connecti.com/~rreeves/index.html> and you can get a
sample chapter (Chapter 1: Introduction to Wide-Field
Astrophotography) from his publisher's web site
<URL:http://www.willbell.com/> (look for the book in the "CCD's &
Astrophotography" section).

-- 
Brian Reynolds                  | "Dee Dee!  Don't touch that button!"
reynolds@xxxxxxxxx              | "Oooh!"
http://www.panix.com/~reynolds  |    -- Dexter and Dee Dee
NAR# 54438                      |       "Dexter's Laboratory"

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