W. Ferris article in Sky and Telescope August 2003 article on ODM

(PrisNo6) wrote in message . com...

The purpose of all of this talk about ODM is to improve your
observing. Olof-Carlin summarizes Clark's optimum detection
magnification concept with following easily remembered rule-of-thumb:

"To detect a faint object, you can increase magnification till the sky
is so dark that you have difficulty seeing the field stop, or till the
object has an apparent size of 1 degree, whichever comes first."

and

"The thresholds here (using the ODM algorithm-program) are for
catching barely visible faint objects. If an object is brighter than
that, it may be possible to see detail by increasing the magnification
even further."

Certainly useful advice. Even better advice is from Jay Reynolds
Freeman, which I will paraphrase rather than quote.

Don't have preconceptions; experiment! If one magnification
doesn't work, try another. Often, different magnifications
will show different aspects of the same object. Small changes
in magnification can have surprisingly large effects on what
you see.

I have half a dozen rules of thumb w.r.t. magnification stashed in
my mind. For instance, in most cases, the greater the sky brightness,
the higher the optimal magnification for a given object. But every
rule has plenty of exceptions; there are cases where I have found
exactly the opposite to be true.

- Tony Flanders