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Pushing my limits with AS80

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#1 Sasa



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Posted 18 August 2013 - 04:29 PM


yesterday there was a strong haze and quite bright Moon so I decided to test my skills on tight doubles with 80mm refractor. I had out my old uncoated Zeiss AS80/1200 from about 1930ties. I was also using Baader Zeiss prism.

I started with pi Aql (6.3+6.9, 1.4") which I already knew that I can split with 80mm lens. This evening it was also very good and clean split at 170x and 190x. I could see two nice touching discs at PA~120deg. There was a hint of some darkening between. The view was very encouraging.

Next stop was tougher mu Cygni (4.7+6.2, 1.9"). I could see small star in the 1. difractive ring at PA~315deg. It required some concentration.

Next on the list was STF2780 in Cepheus. I just vaguely remembered that it was difficult one. Indeed it was (6.1+6.8, 1.0"). All I could see at 170x and 200x was small bump at PA~210-240deg. It was even difficult to judge its position but it roughly agrees with correct one.

The last one was even tougher pi Cephei (4.6+6.8, 1.1"). The main component was very nice orange star. There was almost no sign of its companion. But from time to time I could glimpse with averted vision something strange going on at PA~0deg. Oddly enough, I found out later at home that this is about the correct position.

#2 Asbytec


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Posted 18 August 2013 - 09:45 PM

Sasa, sounds like fun. Thanks for your report. I wish you good luck (and skill, of course.) I am waiting for the skies to clear so I can enjoy a few tight splits, too.

#3 azure1961p


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Posted 19 August 2013 - 07:52 AM

I swear I think there's three people on all the boards.

I'm saving this to add to my own list - very well done and told.

Those last two sound like very difficult doubles to make out but you did it. I tried some elongated doubles the other time out but the seeing was elongating it in its own way so my attempts were dashed. Again very impressive results here Alex. I don't think Ive pushed my 70mm much beyond 2.5" and not because it can't - its a beauty - but I've been a little relaxed with its doubles *diet* .

I truly enjoy your cutting edge observations!

Post edit: Sky Safari doesn't recognize STF2780 - it merely skips over it. In putting the SAO number merely gives me an 0.1" double at 5.9v. They omit every once in a great while. See pic attached. Going to the Stella Doppe site however clarified all. Nothing's perfect!

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Posted 19 August 2013 - 02:14 PM

While Pi Aql and Mu Cyg are well within the reach of 80mm (Mu Cyg not necessarily more difficult - larger delta_m but also larger separation) STF2780 and Pi Cep would require 130mm for a comfortable resolution.

#5 Sasa



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Posted 27 August 2013 - 02:33 PM

Hi Wilfried, you are definitely right that pi Aql and mu Cygni are not that difficult for 80mm lens (but still I can remember that it took me quite a few sessions with my former 150/750mm Newtonian before I actually splitted pi Aql, this was of course due to lack of my experience). They were meant mostly as a warm-up for the other two. I knew that I could see the secondary of mu Cygni in my 63mm refractor. Couple of days ago I was observing pi Aql in 63mm refractor as well and I could clearly see it elongated at PA~110deg at magnifications of 130x and 140x. From time to time I had even a feeling that I could see two overlapping airy discs.

BTW, in May I noticed in 63mm refractor that pi Cep is elongated at PA~0deg without prior knowledge about the secondary star position. That is why I wanted to check this tight unequal double in 80mm. Paradoxically, I was observing pi Cep last year in larger 110mm and 130mm refractors. I could not see even a hint of the secodary.

#6 fred1871


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Posted 27 August 2013 - 10:28 PM

Pi Cephei is a tough one - it's that brightness difference again, along with a fairly tight separation. Some years ago I had 6 months of northern hemisphere observing and this was one of the doubles I have notes for. I had a C8 at the time, so there are no small telescope notes. My note from that time included the description: "...at 200x the companion was nestled against the primary to the North, quite a bit less bright...." The stars appeared just about touching at that power; with some dark sky between at 335x.

Seeing elongation on this double with 80mm is very good. If the 63mm Telementor hinted at it being double that would be pretty much a "limit" observation (~0.5R) for an even double, and this one isn't. I'd expect the seeing to be very good for that to be possible.

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