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Re: (IAAC) Obj: Alpha sco/ M4 - Inst: 4" Off Axis Dobsonian f10
Shane:
Some thought on splitting Antares:
You list your scope as a 4" off axis. I assume you are using an
off-axis mask to eliminate the diffraction spikes. But you are losing
resolution if you do. Try a hex-mask. Cut a piece of cardboard or the
like to a circle big enough to cover the open end of your tube, and cut
out the largest practical hexagon within. What this does is
re-distribute the light from the diffraction rings into six spikes. I
have found that the companion lies on the first ring and tends to be
hidden by it. Rotating the mask will move the position of the spikes,
hopefully until the companion lies between two of the spikes.
Another technique some people have found useful is using filters to cut
down on the glare of the primary. Some people have reported luck using
an OIII filter; I personally have used an Orion UltraBlock filter with
some success. Apparently, the sceptroscopic differences of the two
stars help here, as the companion apparently has more in the bandpass
of the filter and thus is less affected by it.
Also, some people report better luck splitting this during twilight,
when the brighter ambient light reduces the primary's glare.
William Schart
On Monday, May 26, 2003, at 04:07 AM, Apache User wrote:
> ----
>
> Observation Poster: Shane Sweeney <shane_sweeney@hotmail.com>
>
> Observer: Shane Sweeney
> Your skills: Intermediate (some years)
> Date/time of observation: 05/25/2003 0600UT
> Location of site: Tahlequah, OK, USA (Lat 35 9', Elev 250M)
> Site classification: Rural
> Sky darkness: 8 <1-10 Scale (10 best)>
> Seeing: 7 <1-10 Seeing Scale (10 best)>
> Moon presence: None - moon not in sky
> Instrument: 4" Off Axis Dobsonian f10
> Magnification: 79,125,255
> Filter(s): None
> Object(s): Alpha sco/ M4
> Category: Multiple star.
> Class:
> Constellation: Sco
> Data: mag size
> Position: RA : DEC :
> Description:
> I have yet to split Antares!! I thought I had something but couldn't
> tell at 255x a little dot now and agian. I have a little bit of dust
> on my primary and at 255x I get little arcs around the airy disc out
> to about 3" on really bright stars. M4 looked agreat at 29x and was
> very mottled at 79x, many stars resolved all across ellipse at 129x
> with averted vision. 255x was very dark and started to look like a
> very very tight open cluster with a bit of background haze.
> --
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