Was that what Coulter(or was it Odyssey) was thinking? Makes sense.

Best regards,
Bill

"Jan Owen" wrote in message
news:lR5fb.45341$vj2.16502@fed1read06...
Yikes! I guess that would put the next half magnitude at 16", then...
and NOT 17.5"

I guess the 17.5" size must have been created to target 15.0 Magnitude...,
rather than extend the previous convention...

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"Jan Owen" wrote in message
news:wH5fb.45321$vj2.22890@fed1read06...


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"JBortle" wrote in message
...
The reasoning for 12.5 inches was that in theory it gave you a full
half
magnitude gain over a 10 inch mirror (14.0 vs. 14.5 using the old
magnitude
parameters from about 1960, when 12.5 inch mirrors surplanted those of
12
inches aperture), just as going from an 8 inch mirror to a 10 produced
a
half
magnitude jump. I guess you might consider it as a selling point.

John Bortle

Sounds like following that pattern, the 17.5" (as opposed to 18")
probably
came about based on the NEXT half-magnitude mark...

Thanks, John!

Like I said, a higher authority!