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A trial without the error


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Hi all,

It's been a while since I've been here and also looking up at the night sky. Recently, I read an article on using an aperture mask on a reflector to get rid of diffraction spikes when viewing double stars. 

This was all I needed to get my blue peter head on and make my own mask as well  as dusting off the heritage 130p.  

I quickly realised the aperture wasn't going to be very big at all. The best I could do without encroaching onto either the single vain or the edge of the telescope was 50mm, but also making it f13. This may have put a few people off but I already had a cardboard cereal box and a pair of scissors in front of me. The main reason I wanted to try this experiment however was to see why people prefer refractors over reflectors for double stars.

I didn't have long under the stars last night due to the constant flow of clouds passing by.

I chose my targets wisely, knowing 50mm wasn't going to be enough to start splitting any double I landed on. 

The targets I chose were Mizar a+b, Achird, Albireo and 61 cyg.

I used the scope at 130mm first and then stopped it down to 50mm. Eyepieces used were 25mm (26x) and 8mm (81x). Combined with a x2 Barlow I also had a 12.5mm (52x) and a 4mm (162x).

At 50mm I could split each star except Achird, this required the 12.5mm. After running through all the eyepieces the best views were through the 8mm. It just seemed about the right kind of magnification to resolve the stars without dimming them too much, or it could be that my 25mm is a standard eyepiece and my 8mm is a BST. 

The result of the refractor vs reflector I think was obvious. The refractor won hands down. Due to the 50mm size the background was darker and the stars were dimmer compared to the 130mm, but without the single vain, the stars were pin sharp! I had never seen stars so crisp! Obviously, a bigger refractor would have been even better, but for now it was great just getting back out there again.


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1 hour ago, happy-kat said:

Interesting idea. I wonder whether a large lozenge shape would fit within the area and also yield those pin points.

I thought exactly the same thing whilst I was making it, but then I thought the stars being elongated. As the intention was splitting double stars I thought this would pose a problem if the stars are close together. Obviously, this is just my opinion, so it should definitely be tried! There's a weekend project for you @happy-kat 

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