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EVAC Double Star Observation Program
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This is always a question which draws many different answers. Actually, there are many factors to
consider. Among the things to consider are: The double that you are looking for; The separation of the
stars; The brightness of the stars; The relative size of the stars in the double; The telescope that you
are using; The light situation of your viewing area; The aperture of the telescope being used; just to
name of few.
A review of the EVAC Double Star Observation List, shows that out of 100 targets, there are 18 that
are over 50 Arc Second (") separations. These should be relatively "easy" viewing with just about any
piece of telescope equipment, or a good pair of 7x50 binoculars (with exception of course to the
triplets with close in values).
Thus far, in my observations, I find that the "main" viewing configuration of my 8" Meade LX200R
(2000mm Focal Length), with a 26mm eyepiece, has provided excellent observations from 5 Arc
Second views, out to the 100 + Arc Second (") separations. This is a magnification of 77x (2000/26).
Below 5 Arc Seconds, I use a variable eye piece (8mm to 24mm), and adjust to the 8mm setting for
clear observation. At 8mm, the magnification is (2000/8) 250x. Thus far, I have viewed all the way
down to a 1.7 Arc Seconds, split very clearly, which is our closest target on the list.
The Meade 80mm ED APO (480mm focal length) produces excellent "views" down to the 10 Arc
Second range with a 26mm eyepiece. This is a magnification of 18x (480/26).
From an imaging standpoint, I use the DSI-2(c) camera, which is used as an eyepiece replacement for
the telescope. I find that I can use either telescope all the way down to a 7 Arc Second separation,
with the use of 2x and 3x barlows. However, as the images show, there is a BIG difference in the
presentation. Thus far, the Meade 8" LX200R, along with 2x and 3x barlows, has worked well down to
and including a 4 Arc Second separation. Below 4 Arc Seconds, I am doing observation only with the
variable eyepiece, as described above.
There was an interesting dialogue on the Cloudy Nights web forum recently about this subject. Ed
Zarenski, one of the two moderators for the Double Star Observing section of the forum, made the
following post. The actual discussion was centered around the question "What is tight to you",
meaning, the double stars are "really close" in the observation. Again, depending on what "view" you
are looking for, more magnification would probably be better.
By the way, note that Ed views doubles, a lot, using binoculars! Now I tip my hat to that kind of
expertise.
EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12218
Loc: Cumberland, R I
, USA42N71.4W
Re: What is tight to you?
#2573234 - 08/10/08 06:55 PM (Post From Cloudy Nights Forum)
I observe doubles in at least 10 different sizes of instruments. just a few listed here.
in an 80mm scope tight is 2.5-3". Extremely tight is under 2".
In my 5" tight is 1.5-2". Extremely tight is 1.3-1.5"
In my binoculars tight is entirely dependant on the power of the binocular, not the aperture.
In 25x100, limit is 6", very tight is 8"
in a 20x80, limit is 7.8", tight is 9-10"
in a 16x70, limit is 9.8", tight is less than 12"
in a 10x50, limit is 14.2", tight is under 20"
in a 8x40, limit is 18"-20", tight is under 30"
Mag 8 pairs and mag 9 pairs need to be much wider and still appear tight.
edz
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