FreeLists / az-observing / [AZ-Observing] Re: Mag sequence was:(Saturn's Rings)

[Russell Chmela~ <rchmela@xxxxxxxxxxxxxxxxxxx>]

  I may have to track down that September S and T and look at that 
article. Yes... GUILTY... I no longer subscribe to Sky and Tel. 
   
  This subject of magnitude capability is a very complicated one. 
I recently got into a similar discussion on a chat area run by a 
club I used to be a member of back east.
  If I could be allowed a 2 cents into this, my first impression
is that the second explanation for the difference between scopes
One observers' eyes different than another's can be answered somewhat by 
Tom trying the magnitude sequence in the 10" Spooner optics telescope
and Frank doing same with Tom's Dobsonian 20".
  This month, I will celebrate 17 years of visual observing as a
amateur astronomer. I have noted a change in my ability to see faint
objects, and not in the desired direction. If I take my drawings
as a guide, I now get about 10x more out of every view than I did in
1984. There are trade-offs.
   
  I tend to take these instrument tests a bit more lightly than 
some folks will. There are a lot more items in the equation than
visual acuity and OTA's. I suspect most on this list know these
things too, that such things as the atmospherics (variable on 
short time scales) the equally variable stamina of the observers
and the average adjustment of the optical telescope. For grins, try 
this at the next evening out under the stars, put your adjustment
collimation tool of choice, be it laser, Cheshire, whatever- into
the telescope just before you take it down at the end, see what 
the drift was. You may be surprised.
  I might like to try that magnitude sequence in my instrument at
varying altitudes of an object to see what the horizon extinction
really is at some of the sites we use. I have found that to be 
more variable than I first thought from looking at it so far. The air
here in the Valley this week looks like it could stop a Kilowatt
laser beam. :-(
 
 RC    
 
*****************************************************************
Mike is referring to the magnitude sequence that appeared in Brian Skiff's
article in the September issue of S&T.  I spent a half hour or so with my
20-inch Dobsonian on a tracking platform (a necessity for this kind of
observation).  I was disappointed to only reach magnitude 17.1.  If I
remember correctly, there was a magnitude 16.8 star, and I was able to see
it all of the time.  I put 17.1 as the limit, as I could only see it about
one-fourth of the time.  I think the next one down in the sequence was
17.4 or 17.6, and I had no luck with it.

Frank Kraljic did the same thing for a similar length of time with his
10-inch Spooner Newtonian, also on a tracking platform.  He was able to
see the magnitude 16.1 star.  If you simply take the square of the ratio
of our two apertures, my mirror should gather 4 times as much light as
Frank's.  he should see 1.5 magnitudes fainter [(2.512)^1.5 ~ 4].  So
Frank should be able to see a magnitude 17.7 star in my scope.  I
attribute my disappointing result to:

1 - Poor optics in the 20-inch, which were demonstrated later that night
by a lousy view of Saturn.  At 400x, the star discs are larger than they
could be with good optics, so you can't see as faint.

2 - Frank's eyes are 17 years younger than mine.


I want the answer to be #1, of course.

Tom
*************************************************************************

-- 


---
This message is from the AZ-Observing mailing list.  If you wish to be
removed from this list, send E-mail to: AZ-Observing-request@xxxxxxxxxxxxx,
with the subject: unsubscribe.

The list's archive is at:  http://www.freelists.org/archives/az-observing

This is a discussion list.  Please send personal inquiries directly to
the message author.  In other words, do not use "reply" for personal
messages.  Thanks.