Rigel- Aperture experiment

[Lady Isabella]

Searching through books and online, I see lots of varying information

regarding the fainter companion to Rigel. Some say that you need a telescope

of at least 100mm to easily see the companion, while another says that a scope

of 150mm has to be used.

The companion to Rigel. should be visible in scopes much smaller than the above

sizes. Several sources I've seen knowledge this, but say that the glare from Rigel

will make spotting the secondary very difficult. Last night, I made the following aperture

masks, 80mm ,70mm, 60mm and 50mm, for use with a 102 f/8 refractor.

At full aperture (102mm) the companion star was easily seen, however due

to the atmosphere, the eyepiece view was a bit messy with alot of

glare and a quite rough looking Airy disk pattern. Working down in size with the aperture masks,

gave some interesting results. Instead of getting worse, the views got progressively better.

At just 50mm aperture the view was most interesting. The companion was very easy to see at magnification 65x.

Rigel produced a superb Airy disk pattern, with a near perfect faint first diffraction ring.

With direct vision there was no glare, only when using averted vision was any detectable.

Flicking back to 102mm, clearly showed the effects of low altitude and atmospherics.

It would be inteesting to see how well the skywatcher range of scopes work

with their 50mm aperture stops on this star.

[kniclander]

are you saying that seeing dim companions may be easier with smaller apertures because the primary "glows" less?

Dan

[MartinB]

It's that high F ratio thing again isn't it? Rigel's companion is mag 7 so shouldn't present a small scope with a problem. I've seen the same comments LI and was never quite sure why it needed a scope of 150mm or more so your observations are very interesting. I was looking at Rigel the other night with an ED120 at x90 and it wasn't a challenge once you've got used to how small the companion appears

[lunator]

I will have to check my records but I believe I have split Rigel in my old ETX70.

I have never found the split difficult in any scope.

It sounds like the seeing was poor if a 102mm scope was being affected.

Rgds

Ian

[GazOC]

Its a VERY easy split in a 100mm refractor, I don't think I've tried it with nay thing smaller.

[Lady Isabella]

Yes I agree with everyone, Rigel is not a hard double.

Even a 50mm scope will pick it up, as was shown last night.

I'm just curious why many books, magazines and now internet

sources still continue to regard this double as difficult?

Over 40 years ago Patrick Moore was telling us that the companion

can been seen in small aperture scopes (i.e. 70mm), and I don't think

it's got any harder to see over the last 4 decades.