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Doubles in Hercules, Lyra, and Draco

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#1 nerich

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Posted 02 June 2020 - 06:53 PM

Hello Friends, 

Last night, after a hazy and uncertain day, I was treated to a mostly clear sky. This was my second session with my new Orion 150mm Maksutov, which I'm still evaluating. Some high-power observations revealed that I need to adjust the collimation a bit, but it wasn't off by enough to disrupt my observing. 

First up was a surprise pair: Gamma Herculis (3.8, 10.1, 43").  I had intended to use this star, which is not marked as double in my atlas, as a jumping-off point to get to my next target. Imagine my surprise upon seeing that pretty little speck of a secondary! I noted the PA as southwest, and the color of A as a creamy white. B gave me no color, but was a fine sight nonetheless. WDS lists an 8th magnitude D component at a separation of 8.3", which I didn't notice.

A short star hop away from Gamma was my intended target, STF 2052 (7.7/7.9, 2.5"). Even at 45x (3.3mm exit pupil), this object's duplicity was clear enough for me to estimate a PA along the NW/SE axis. At 72x (2.1mm exit pupil), they were split cleanly, although I still wasn't confident of which star was the primary. To the west was a silvery 8th magnitude star, and to the southeast a wide and dim double (I haven't so far found a designation for that pair in the WDS). Finally, at 120x (1.25mm exit pupil), I was confident that the western star was the primary. A was yellow, and B a darker orange. 

Also in Hercules was WEB 6 (6.4/7.3, 153"). This one was mentioned in the forum by someone recently, but I can't remember who. Aubrey? Rich? Whoever it was, thanks for the recommendation! This is a wide but very pleasing pair set in a trapezoidal asterism. I saw A as light yellow and B as white. 

Moving northeast into Lyra, I located STF 2362 (7.5/8.7, 4.4"). There are tons of doubles in this tight quadrant of the sky, so I was extra careful in my star hop, and double checked the data I had jotted down from WDS to make sure it matched what I saw in the eyepiece. And what a treat it is to look at: At 45x I saw A as a light greenish white, like a pale prasiolite gem, and B as blue-white, becoming grey-blue at 72x. I noted the PA as south. This is a beautifully tight and dainty pair at low and medium powers.

Nearby is STF 2362's twin, STF 2390 (7.4/8.6, 4.3"). This object is indeed very pretty, but just as remarkable as the double itself is its field: a stunning asterism of 6 brightish stars and several dimmer ones, forming a nearly straight line running southeast to northwest. It's almost like a miniature of Kemble's Cascade. Does anyone know if this asterism has a name? 

My last Lyra pair was STF 2349 (5.4/9.4, 7.2"). At 45x I saw bright white A, and the irregular cigar-shaped smattering of field stars along the north-south axis. I got one very brief glimpse of a tiny B before bumping the power up. At 72x I could hold B consistently, and A turned a more pearloid off-white. A very fine unequal pair. 

I ended the night with two spectacular Draco doubles, which I also sketched (if you feel so inclined, please visit the Sketching forum to see my work). First up was Omicron Draconis (4.8/8.3, 38"). The first time I observed this pair was in October of 2018, with my 80mm refractor. After revisiting it last night, I've come to the conclusion that this object isn't observed or talked about nearly enough! 

A is the most astonishing shade of electrum I can think of. The hue is impossibly rich and lustrous. B is a curious star that shifts maddeningly from green to blue to purple to orange; as I wrote in the Sketching forum, it seems to average out at lilac or pale pink most of the time. In 2018, I saw exactly the same effect with my 80mm, and wondered how much of the shifting color was a product of my achromat itself. Re-observing with the 150mm Maksutov has not settled the issue one bit: this is a baffling and beautiful star. 

Last, and least in magnitude if not beauty, was STF 2398 (9.1/10, 11"). This is another of the forum's recommendations, and despite its relative dimness is well worth a look. Both stars are M-type, and their color is quite noticeable, if somewhat subtle. A was very clearly orange, while B was just on the edge of colorless. With steady gazing at 72x, I could make out the auburn tinge in an otherwise dark grey speck. A thoroughly attractive pair. 

That's all for now! As always, comments, corrections, and complaints are most welcome. 
 


Edited by nerich, 02 June 2020 - 06:56 PM.

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#2 c2m2t

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Posted 02 June 2020 - 09:16 PM

Hi Nick!

What a great read!! Enjoyed every minute of it. John N. would be pleased that someone else is bringing such creative fervor to the art of observational recording. Makes you want to get out to the telescope...we have been asking for rain...now we are getting it in spades!!mad.gif grin.gif  Thank-you!!

 

Cheers, Chris.


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#3 nerich

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Posted 02 June 2020 - 11:37 PM

As always, Chris, I'm honored and humbled by your compliments. Happy to spread a little astronomical joy by sharing my observations! 

Sorry about your rain. We had a couple weeks of it with that last tropical storm. But I just got back in from another session. It was shorter than it would normally be because I spent an hour finely adjusting collimation. But boy, you should see the diffraction pattern on this scope now! Unfortunately, it seems like I won't get to enjoy it again for a while. bawling.gif


Edited by nerich, 02 June 2020 - 11:39 PM.

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#4 flt158

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Posted 03 June 2020 - 05:06 PM

Great report, Nick!

I am so pleased you are getting clear skies once again. 

And your new Orion 150 mm Maksutov is working a real treat.

I am also glad your collimation is good right now. 

 

I have observed successfully, Gamma Herculis, STF 2362, STF 2390 and STF 2349 in Lyra in the past. 

WEB 6 I have not observed. 

But Omicron Draconis I have; but years ago.  

 

Some time I will get stuck into the doubles in Hercules. 

But just not now. 

 

Best regards from your friend, Aubrey. 


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#5 John Fitzgerald

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Posted 03 June 2020 - 06:26 PM

First up was a surprise pair: Gamma Herculis (3.8, 10.1, 43").  I had intended to use this star, which is not marked as double in my atlas, as a jumping-off point to get to my next target. Imagine my surprise upon seeing that pretty little speck of a secondary! I noted the PA as southwest, and the color of A as a creamy white. B gave me no color, but was a fine sight nonetheless. WDS lists an 8th magnitude D component at a separation of 8.3", which I didn't notice.

 

The D component of Gamma Her is 8th mag in K band.  The visual magnitude is much fainter.



#6 Bigzmey

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Posted 05 June 2020 - 02:05 PM

Another excellent report Nick! Keep them coming. I am curious to hear more about 150mm Mak performance on doubles. From my brief experience with 127mm Mak and reports from a few friends it seems that Maks deliver resolution-wise, but star colors look washed out, at least compared to fracs.

 

Omi Dra was one of the first doubles I observed (with 90mm achro) and logged colors were yellow and green. But I know what you mean about shifting colors. I believe it is due to atmospheric fluctuations, because for a few doubles I have revisited I observed steady colors second time.   


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#7 nerich

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Posted 05 June 2020 - 02:42 PM

Another excellent report Nick! Keep them coming. I am curious to hear more about 150mm Mak performance on doubles. From my brief experience with 127mm Mak and reports from a few friends it seems that Maks deliver resolution-wise, but star colors look washed out, at least compared to fracs.

 

Omi Dra was one of the first doubles I observed (with 90mm achro) and logged colors were yellow and green. But I know what you mean about shifting colors. I believe it is due to atmospheric fluctuations, because for a few doubles I have revisited I observed steady colors second time.   


Thanks Andrey! Yeah, no doubt mirrors will always reduce color saturation and increase scatter more than lenses, all other things being equal. I'm sure that I'd get more of everything (contrast, resolution, color saturation) with a premium 6-inch apo. But that dream will have to wait for a bigger budget! 

I found that it helps to use a prism diagonal. I use a nice Baader prism on my Mak, which brings the total mirror count down from 3 to 2 across the optical chain. That had a noticeable effect on the scatter (although the 2" William Optics mirror diagonal I use on my Stellarvue is quite nice). Compared to a refractor with a mirror diagonal, I have just one extra mirror in the light path. A detriment, I'm sure; but a small one. 

Suffice it to say that on any given night, I worry much more about the sky conditions than about the telescope.


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#8 Bigzmey

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Posted 05 June 2020 - 02:51 PM

I am with you on prisms Nick. After testing quite few diagonals over the years I am using Baader prisms exclusively for doubles.


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#9 rugby

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Posted 05 June 2020 - 06:24 PM

Nerich    I bought a second hand sw 150 mak about three months ago and am very impressed so far. One little fly in the ointment however. I noted small miscollimation at high powers. I have watched every video possible to help me recollimate. I would be interested in hearing how you achieved it if you have the time


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#10 nerich

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Posted 05 June 2020 - 08:15 PM

Nerich    I bought a second hand sw 150 mak about three months ago and am very impressed so far. One little fly in the ointment however. I noted small miscollimation at high powers. I have watched every video possible to help me recollimate. I would be interested in hearing how you achieved it if you have the time


I feel your pain! The push-pull collimation screws are my biggest complaint about this scope. A total pain in the neck. 

I used the standard technique of de-focusing a bright star at fairly high power. I used 200x, but some folks say you should go even higher. Since I use an un-driven mount, it's easiest to collimate with Polaris. The star moves around the field as you adjust collimation, and I didn't want to have to deal with tracking an object on top of that (but if your mount tracks, you can of course use whatever bright star you want).

Defocus the star until it looks something like this: 


ringz.png


Sorry for my very rough MS Paint approximation! The important thing is that you should be able to see the concentric rings very clearly. 

At first glance the rings will probably look pretty good. But look very carefully to see if you can detect any radial asymmetry in the spacing. In my approximation, the thin inner rings are slightly more bunched up on the upper left, and slightly wider on the lower right. 

Now, start methodically testing your push-pull screws, just a little at a time (a quarter turn at most), and looking for what effect each has on the ring spacing. Loosen the small screw before tightening the big one, and vice versa. I don't know this for sure, but I worry that tightening the screws against each other will put pressure on the mirror, potentially compromising the image.

Re-center your target star after each adjustment. Eventually you'll get a feel for how each set of screws affects the ring spacing (i.e. how each screw moves the rings with respect to the center of the diffraction pattern). Adjust accordingly until the rings are as exactly even as you can get them.

When you're satisfied with collimation, go back and check your small screws. On this telescope, the small screws usually loosen very suddenly, giving you excess play. Again, just an unconfirmed suspicion, but I worry that extremely loose screws could allow the scope to become mis-collimated easily. Tighten them very gently, just enough that they stay put. 

Prepare for this to be a frustrating process that eats into your observing time. If you're a klutz like me, you will frequently drop your hex keys in the dark. When you bend down to find them, you will knock your tripod and shove your target star out of the field. You will utter profanities. But it will be worth it! The difference in the in-focus image and diffraction rings is huge, even if collimation was only slightly off. 

I hope that helps!

If anyone here has more experience with Mak-Cass collimation and would like to suggest improvements or clarifications to my method, please do! 

 


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#11 rugby

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Posted 05 June 2020 - 08:30 PM

Thanks , I will try tonite since it is partly cloudy


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