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cloudsweeper

In Hyades: A Very Easy Double, And A Diffraction Ring

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Having recently enjoyed full views of Orion's Belt and The Pleiades, I set up the ED80 Apo again (2nd Feb) in the cold, under very clear skies.  Mars appeared at 5.27pm, then Aldebaran, and that took me to The Hyades - the face of Taurus, a sisterhood of nymphs in Greek myth (said to bring rain, but no more about that!), also sisters to The Pleiades.  The Hyades open cluster (Caldwell 41) is over 5 degrees in scale.  Even this early, several of the stars were easily visible through the 'scope.  Before long, I had a marvellous view of the whole cluster in the EP - I was using a 42mm Revelation (x11; 5.7deg).  There was a little astigmatism at the very edges.  Next, the 36mm Aspheric (x13; 5.4deg), yet the field looked marginally wider - perhaps the AFOV for the Revelation is exaggerated?

At x80, more stars appeared since the large exit pupil was greatly reduced and the background was much blacker.  I concentrated on a nice set of six stars running EW, more or less in a line, taking in 80, 81, 85 Tau, and three fainter ones.  80 Tau is a triple (visual double), mismatched, with a separation of 1.5"/1.6".  Although the sky was darker by now, I could not split the two, even at x160, but that is about the limit for an 80mm 'scope, where the resolution is very close to the actual stellar separation.  What I did see however, was a diffraction ring around the bright primary.  It was expected from a small telescope, good optics, and highish mag, and came and went with the seeing,  The fine focus control helped to pin it down too.  So no secondary star, but a confirmation of the physics going on here!

On to Sigma 1, 2 Tau - a very close match (magnitude), with a very wide separation (7.2 minutes, 432").  This visual double is therefore one of the easiest to view.  (Sigma 1 is also a spectroscopic binary which can't be split visually.)

I then took a further look at the entire cluster - very pleasing, better contrast, with many very faint stars having joined the spectacle.  Finally, a comparative glance at the other sisters - smaller, denser, brighter - and in for a belated meal.  An interesting hour and a quarter!

Doug.

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A nice little session Doug, sounds like the scope is performing well. I'm surpised the ED80 is not used more widely used for visual, its got a focal length which is not so short that it is just rich field, and not too long to stop it being very portable. Hope you get to use it a lot more.

Edit: Just realised yours is the Explore Scientific triplet, not the Sw doublet which I had assumed. I am guessing it is still pretty portable though.

Edited by RobertI
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32 minutes ago, RobertI said:

A nice little session Doug, sounds like the scope is performing well. I'm surpised the ED80 is not used more widely used for visual, its got a focal length which is not so short that it is just rich field, and not too long to stop it being very portable. Hope you get to use it a lot more.

Edit: Just realised yours is the Explore Scientific triplet, not the Sw doublet which I had assumed. I am guessing it is still pretty portable though.

Thanks Rob.  Yes, it is very compact and portable.  At that aperture, the triplet is not heavy.  The main body is short, and two extension tubes are used, thus keeping the weight down.  I went for the ultra-wide field as well as the DS R&P focuser (no slippage), and the triplet is a bonus which gives zero CA.  Couldn't be more pleased with it!

Doug.

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