[APML] What's the Best Way to "Combine" Two Images of DifferingTimes?

["Thomas W. Earle" <twade@bmi.net>]

For bright objects, such as M42, it is a known fact that combining
several images at various times helps in getting the full dynamic
range of this nebula; however, I'm not quite sure what's the best
way to go about this.  I have Registar, but none of the Functions to
apply seem like the "perfect" choice.  I feel using them will either
destroy the shadows or the highlights.  I see that many recommend
using Ray Gralak's Sigma function; unfortunately, he recommends one
should have ten or more images to combine for "best" results.
There's no way I can get 10 shots since each film shot ranges from
30 minutes to 3 1/2 hours.  Anybody have a proven technique to get
the most out two or more images exposed differently?  For example,
let's say I take three images of M42 at F/5.0: one 30 minute, one 90
minute, and one 180 minute.  What's the best way to get the full
dynamic range of these images (i.e. visible structure from the
center of M42 to its faintest extensions?  Any suggestions or
comments would be greatly appreciated.

Thanks in advance,

Wade


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