[bigjoe (JOSEPH)]

THIS WAS A LIST I COMPILED WITH THE HELP OF Steve (Tinderboxsky), bombardon(Eugene)and John Bambury(ausastronomer).

Use these tips below when needed, and for cracking my future Monthly Constellation double star lists..or even this months.

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 near the East, or following near the* West when your facing North?

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, 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.

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..read JOHN BAMBURYS excellent take on this quoted from his post No. 9 above.

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

Cheers bigjoe.