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Splitting the Double Double...


F15Rules

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The Double Double in Lyra.(epsilon lyrae)..one of the most famous visual quadruple systems in the sky, and certainly one of my favourites. But what is the lowest power you have definitely split each pair with? And with which eyepiece(s) & scope did you make the split?

The pairs are separated by c2.3" and c2.6" respectively (e1 pair and e2 pair),.so a good test of optical quality.

I consider my eyesight to be at best average for my age (early 60's). I'd be interested to know how other SGLer's fare with this system for comparison?

To get us started, last night under very good conditions and good skies (I could see structure in the Milky Way overhead and down to just above my house roof), I got a definite split at c60x.

Equipment used was  my Tak FS128 (F8.1 with a focal length of 1040mm), with Baader T2 prism and Morpheus 17.5mm. Right at the limit for me to split at this power, but lovely vista with large 76deg FOV.

The most pleasing higher power view was with a Baader Genuine Ortho 6mm at x173 - two pairs of perfectly formed mini "headlights", each at right angles to the other, with clear, jet black sky between each component..

I look forward to hearing of your experiences?.

Dave

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I think I remember splitting the somewhere in the region of x55 a few years back. Will give it another go next time I get a chance with the Tak. I must admit I like them at around x100, still tight but nice clear splits, and the lovely bulleyes you get with a refractor :) 

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My TV Ranger 70mm splits Epsilon Lyrae at around 100x. I suspect the larger the aperture, the lower the magnification needed to get a clear split will be because the airy disk of the stars will reduce in size making the split clearer. But, I'd like to see if that theory holds good in practice :smiley:

There must also be, I guess, a lowest limit at which the split is clear even with really large aperture scopes.

Interesting to consider that Neptunes disk is currently 2.4 arc seconds in apparent diameter which would fit between the wider pair of Epsilon Lyrae stars.

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While in  Brussels a few years ago I used the Genesis (100mm f5) with a 10.5mm TV Plossl to split the double double - x48 mag.

With practise and good seeing anything is possible. Others have achieve splitting of the double double at even less magnification.....

 

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Interesting that some can see it at very low mags. Using the formula that the minimum mag to split a double (based on human eye acuity) is about 160/(split in arcsec) means that the minimum is normally about x70 for the 2.3 arcsec pair, although someone with extra-sharp vision might exceed this a bit. I find it easier to split at low mag with a small aperture scope as a larger scope gives a view that is just too bright, with the stars "run together".

Chris

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7 hours ago, chiltonstar said:

I find it easier to split at low mag with a small aperture scope as a larger scope gives a view that is just too bright, with the stars "run together".

I agree with this, a small scope seems to deal with these splits surprisingly well.

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Thanks for the replies guys:thumbsup:.

I am somewhat relieved, to be honest. I know my eyes (my right eye in particular) are not as good as they were even 5 years ago. My optician said it's just part of the ageing process (cold comfort!) and it "isn't anything serious"..well, it's serious to me when my main hobby needs decent eyes!

Although I did get a split at c60x, it wasn't a comfortable split, and I find that a 10mm at x100 is much more clear and pleasurable to view, using something like my Pentax 10.5XL or Parks Gold 10mm..

All in all Epsilon really is a beautiful system - at any magnification!

Dave

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I've just been playing around with my Tak FC-100DL and the 21.5mm - 7.2mm zoom on the "double double". Starting at 21.5mm (42x) and gradually increasing the power, the first point where I feel that a clear split in the 2 pairs (ie: a thin dark line between the stars rather than elogation of the pairs) is detectable with my eye is 13.5mm (67x).

The target is pretty much at the zenith tonight so pretty steady.

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From memory of a recent session with my Heritage 130P with good seeing, I didn't feel that 65x gave an obviously clear split so doubled the mag and it was clear as a bell. I didn't really try very hard at 65x though so will have another go next time out.

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16 hours ago, John said:

I've just been playing around with my Tak FC-100DL and the 21.5mm - 7.2mm zoom on the "double double". Starting at 21.5mm (42x) and gradually increasing the power, the first point where I feel that a clear split in the 2 pairs (ie: a thin dark line between the stars rather than elogation of the pairs) is detectable with my eye is 13.5mm (67x).

The target is pretty much at the zenith tonight so pretty steady.

That's interesting John, and it sounds as if our eyes are not too dissimilar- at least on this target☺. At c60x I could tell each pair was in fact a pair, but no clear black line between them: not just elongated, but more like twin tiny spheres touching each other. I think the slightly higher power (x67, or c+10% more magnification) that you used made that thin black line visible.

Do you feel that your eyesight has changed in the past say 5-10 years?

I wonder if different observers eyes perform differently on different targets, eg on nebulae versus planets for example?

Dave

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1 hour ago, F15Rules said:

Do you feel that your eyesight has changed in the past say 5-10 years?

I wonder if different observers eyes perform differently on different targets, eg on nebulae versus planets for example?

Dave

My eyes have changed over the past 5 years - I started to need reading glasses about 2 years ago.

I guess my observing skills are a bit better now though so perhaps that offsets this ?

I tend to think that the human eye is the least understood and least discussed element in the optical train !

 

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I got the pairs split at 65x tonight with my 130mm triplet refractor. 60-something magnfication seems to be the consistently lowest that I can get a definite split at with my fracs of 100mm and up. At the other end of the scale I got Lambda Cygni (sub-arc second split) at 370x as well :smiley:

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Just been out to try this with the Heritage 130P.  To cut a long story short, I could split the easier pair (EL 2) at a minimum of 65x and the harder pair (EL 1) at a minimum of 85x. In order to split I had to see a consistent clear gap to pass the test; I could make out elongation and fleeting gaps at lower mags than these. The test was done using my 10mm Hyperion with fine tuning rings, and my Seben zoom. I even tried  Bahtinov mask on Vega to get accurate focussing but bizzarely this made things slightly worse and I had to do a slight refocus on the double double. And oh for 10:1 Crayford focusser for such a job, the helical focusser was a pain! I hear a 130PDS calling me ......

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We split it with the Tak FS 60 a few years ago with quite a low magification.

 

The 60 is out on loan at the moment but I think it was about x50.

We started at a higher mag and worked down.

It might even be in a report on SGL somewhere - I will have a look back.

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On 22/08/2018 at 00:13, Saganite said:

I had slightly better results with the Tak FC100 DC.

59x with a UOVT 12.5mm just showing pairs, but a 24mm Celestron Ultima with a Celestron Ultima 2x barlow = 62X, a definite split.

That does surprise me Steve. Were the seeing conditions and eyepiece types used similar? (Obviously you'd get different magnifications with a 24mm Ultima in the D&G, but did you use a similar type of ep, such as a 30mm Ultima, which would give you 63.5 in the D&G)?

It's just that I'd expect the latter to beat the Tak 100 in equal conditions:icon_scratch:

Dave

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