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Old 02-08-2019, 03:52 PM
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bigjoe (Joe)
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Bigjoes double star tips ammended

Made some small changes to these tips I did years back..
It's getting towards better seeing here in NSW so keep these in mind for when you what to look at some.
www.stelledoppie.it is a good site to use.

THIS WAS A LIST I COMPILED WITH THE HELP OF Steve (Tinderboxsky), bombardon and John Bambury(ausastronomer)..no 22.

Use these tips below when needed,.

1: SEEING - Must be very good for some tough unequal doubles.

2: ALTITUDE - Observe the Double well above the horizon if possible.


3: APERTURE -Depends on variables like Doubles separation, magnitudes , altitude, seeing and their delta etc.*

4: POWER - The use of it is necessary at times - Helps darken sky background, and with limiting magnitude ; 200x + may be needed.

5: USE A MASK - Hex , may be necessary.. Also be mindful of diffraction spikes, and thick diffraction rings on some scopes that can obscure the faint secondary.

6: ORIENTATION - Is your diagonal /scope combo displaying an UPRIGHT , EAST/WEST VIEW ? ; If not adjust accordingly ; this is critical to judge what direction the secondary will be...see 19.

7: PRACTISE: On some easy ones first.

8: DRIFTING - For a faint secondary, Is it preceding or following when your facing North say.

9: WARM CLOTHING , and stool if necessary.

10: PATIENCE - and lots of it - It could take many attempts!

11: LESS GLASS - Use of EPs with fewer elements, 4/5 max, even 3 LESS SCATTER to increase contrast and detection, may be of help.

12: AVERTED AND DIRECT VISION -
Go back and forth between direct and averted vision, until the companion is held in direct view.

13: ZOOM EP - Use of a good marked zoom EP, to find the optimum power for the seeing and filters if necessary, can be useful.

14: HIGHLY ACCURATE FOCUS with FLAT FIELD, FREE OF CURVATURE - this is a must also , as you may have to re-focus often to find that dim secondary near the edge of the field...keep stars as centered as possible as vignetting near edge will cause stars to appear fainter than they should be.

15: VERY STABLE MOUNT - Absolutely no wobbles!

16: VIEWING AT TWILIGHT - Can reduce the glare of a bright primary EG : Sirius A - and this goes for other bright primary doubles as well!

17:STANDARD EYEPIECE..Used to judge star separations in your scope..have one to use, medium 60 EPs like Dual EDs, Radians, Delites are good with FLAT FIELD..See 18.

18: KNOW YOUR FIELD-Know what say 10" arc looks like in your STANDARD* eyepiece for example as in Rigel.
Formula for working this is OCULAR FIELD IN MM X 57.3 DIVIDED BY FOCAL LENGTH OF SCOPE IN MM.
EG: EP Has field stop of 3 mm and scope 1719 mm focal length...

Then that is simply ( 3 x 57.3 ) 1719 = 1/10 degree true field of view, or 6 mins arc or 360" -So if a double has a separation of 36" it will be one tenth of the field width, so you'll get an idea were the secondary will be!

19: Position angle(PA) Is taken as I've said, from an IMAGINARY LINE on the Celestial Sphere due North , increasing North to East in a clockwise direction - East following (will be on the right if you face North)...
an example is in Sirius B being roughly around 90 degrees or more Position Angle East at this moment in time..
and simply let Sirius B drift into the field of view, by first letting SIRIUS A go past your left (West field) stop, so its GLARE IS MITIGATED .

20: HOOD or COWL; this WILL help if streetlights or other bright light sources are a nuisance -- I rarely observe without one in any case...increases contrast.

21: COLLIMATION.. Crucial that scope is Cooled and well Collimated esp SCTs , though not necessary to use more than 12" aperture, due to the affects of seeing on large obstructed scopes, most nights.*

22: USE OF AN OCCULTING BAR EYEPIECE.

PS: If anyone knows of more tips and suggestions that have not come to my attention please lets me know!

Cheers bigjoe.
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Old 02-08-2019, 08:49 PM
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Bobbyoutback
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Good post Joe

Well done Joe , it's always a great feeling to see the Pup with your own scope for the first time .

It's been over 40 years since I first observed it with a wonderful old 8 " F/7 newt on a pipe mount , that scope had an exceptional mirror & secondary .

So just to add ' you need very good optics as well .

For those who want to see it now :
https://www.youtube.com/watch?v=3GoaAc9oyx0

Bobby
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