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Splitting Delta Cygni with small scopes

double star observing observing report
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#1 db2005

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Posted 15 September 2019 - 02:17 PM

Hi all,

 

I had my ED100 out yesterday night, and managed to split Delta Cygni with relative ease at 150x. So I thought I'd have a go with my FC76 DCU-EX tonight, taking up the challenge with a significantly smaller aperture. It managed to split it clearly in moments of good seeing with my Vixen SLV 6 mm eyepiece (around 159x magnification). The faint companion star was located roughly in the first diffraction ring around the primary star. I was kind of excited because this is the smallest aperture I've successfully used to split this double star, and observing conditions weren't even ideal with fairly high winds and less-than-ideal seeing conditions.

 

What are your experiences splitting Delta Cygni (2.5" separation, magnitudes 2.9 and 6.3) using smallish apertures?

 

Clear Skies,

Daniel



#2 Rutilus

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Posted 15 September 2019 - 02:29 PM

I've used a 50mm aperture mask on my Sky-watcher 120mm f/8.3 Achromat refractor, and was able to see the secondary

star in the interspace between the primary and first diffraction ring.

With a 80mm scope I've seen the secondary in the first diffraction ring, much the same as your observation. 


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#3 fcathell

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Posted 15 September 2019 - 02:47 PM

I've managed it last year in a 102mm SW Mak. Was in the outer edge of the 1st diffraction ring. Need to check it out again now that our weather (summer monsoons) is starting to ease up.

 

Frank

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#4 Astrojensen

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Posted 15 September 2019 - 03:07 PM

It took me quite a few years of practice before I was able to split it with my 63mm Zeiss Telemator, but now I do it every summer. 

 

A few weeks ago, I had a night of superb seeing and I had my 4" f/11 ED on Delta Cygni at 714x and the view was just textbook perfect. 

 

 

Clear skies!
Thomas, Denmark


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#5 Astrojensen

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Posted 15 September 2019 - 03:10 PM

I've used a 50mm aperture mask on my Sky-watcher 120mm f/8.3 Achromat refractor, and was able to see the secondary

star in the interspace between the primary and first diffraction ring.

With a 80mm scope I've seen the secondary in the first diffraction ring, much the same as your observation. 

Wow! With a 50mm. That's quite something! I need to try that. 

 

 

Clear skies!
Thomas, Denmark


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#6 fcathell

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Posted 15 September 2019 - 03:43 PM

The really hard one is Sirius B due to the glare of the primary. After many tries I managed to do it with a C6 a couple of years ago. It was much easier in a C-8, but you better have totally steady seeing with either scope!

 

Frank


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#7 Pete W

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Posted 15 September 2019 - 11:07 PM

I’ve been able to split it with an old Sears model 6339a 76mm f/15 refractor using a 7.5mm Celestron Ultima giving 160x.  Not a routine split, only with above average seeing.  


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#8 Jon Isaacs

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Posted 16 September 2019 - 07:21 AM

l consider delta Cyngi a "routine" split under decent seeing in an 80mm ED/apo.  I doubt I could split in anything much smaller, my eyes are just not as sharp as they used to be.  I liken them to a poor quality optic, they focus but there are issues... 

 

About the best I have done is splitting it in an older Celestron 80mm F/5 fitted with a 2 inch focuser.

 

Jon


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#9 db2005

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Posted 16 September 2019 - 02:04 PM

The answers so far encouraged me to make a 2.5" (~63 mm) and a 2" (~50mm) aperture mask for my 3" (76mm) APO and seek out some classic double stars between the clouds tonight: Izar, Polaris, Epsilon Lyrae (the double-double), Gamma Andromedae, Iota Cassiopeia and of course Delta Cygni. With the exception of Izar, all these classic doubles were easy to split even with just 2" aperture. Delta Cygni was even fairly easy with 2.5" (63 mm), but I could only glimpse the companion vaguely as a slight brightening of the first diffraction ring around the primary star with 50 mm aperture. In brief moments I thought I saw a distinct star at the correct location, but if I hadn't already known where to look for it I probably wouldn't have found it.

 

All my observations were made with my FC76-DCU EX with a Vixen SLV 6mm eyepiece and Baader mirror diagonal.

 

I keep getting amazed at what can be accomplished by quality optics with so small aperture that many observers today regard them as toys. Of course, the limited light grasp means 50 mm isn't going to be much for for DSOs and faint clusters, but for splitting double stars an excellent 50 mm refractor is surprisingly powerful. And bad seeing isn't much of an issue with just 50 mm of aperture...


Edited by db2005, 17 September 2019 - 09:17 AM.

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#10 Bonco2

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Posted 16 September 2019 - 03:14 PM

Many clear views of Delta with my  Unitron model 128 60mm f/15. Refractor Same scope gives clear detection of Pi Aquilae  duplicity.

Bill


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#11 db2005

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Posted 16 September 2019 - 04:28 PM

Many clear views of Delta with my  Unitron model 128 60mm f/15. Refractor Same scope gives clear detection of Pi Aquilae  duplicity.

Bill

I definitely need to try that one as well. At around 1.4 arc seconds separation that should be a fine test of eyes, seeing and optics.



#12 Jon Isaacs

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Posted 16 September 2019 - 10:37 PM

I definitely need to try that one as well. At around 1.4 arc seconds separation that should be a fine test of eyes, seeing and optics.

 

At 1.4 arc-seconds it much closer than the Dawes limit of a 60 mm..what are you expecting to see?

 

Jon



#13 db2005

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Posted 17 September 2019 - 12:32 AM

At 1.4 arc-seconds it much closer than the Dawes limit of a 60 mm..what are you expecting to see?

 

Jon

I don't know smile.gif - Most likely just an elongation of the star. As a part of the hobby I just enjoy challenging my eyes, skills, optics and skies. But I'll of course start with the largest possible aperture, and mask it down until I can't see the split. But frankly I don't expect much. Eta Ori (around 1.7 arc seconds) is about the closest split I have managed with my 81 mm, so 1.4 arc seconds might be asking for too much with a 76 mm scope.


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#14 Jon Isaacs

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Posted 17 September 2019 - 06:27 AM

I don't know smile.gif - Most likely just an elongation of the star. As a part of the hobby I just enjoy challenging my eyes, skills, optics and skies. But I'll of course start with the largest possible aperture, and mask it down until I can't see the split. But frankly I don't expect much. Eta Ori (around 1.7 arc seconds) is about the closest split I have managed with my 81 mm, so 1.4 arc seconds might be asking for too much with a 76 mm scope.

 

I like the way you think.  

 

I was able to split Porrima with my WO 80mm F/7 FD back in 2010 when (according to Sky Tools 3) it widened from 1.43" in March to about 1.52" in August.  Towards the end of the summer, I was making the split with a 80mm F/11.3 Towa-Meade.  Of course maybe Sky Tools 3 was wrong.. 

 

You need an Iris on your scope.. :)

 

Jon


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#15 John Fitzgerald

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Posted 17 September 2019 - 07:37 AM

I followed Porrima as it closed and could not be split in my 150 mm achro, then as it opened again.  It is now what I consider wide and easy.


Edited by John Fitzgerald, 17 September 2019 - 07:37 AM.

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#16 David Gray

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Posted 17 September 2019 - 07:51 AM

 

You need an Iris on your scope.. smile.gif

 

Jon

Like this.......... a gov-surplus iris diaphragm; still being tweaked but the right-hand close-up shows it near finalized.

 

Mounted on the 76mm (3”) f/13 refractor (drops in dew cap) that is co-mounted on a 16.3” f/16-f/18 D-K.

 

Set here at 25mm it closes from 40mm (upper mark) to 10mm in 5mm steps – excepting I have inserted 12.5mm for ~½-inch aperture.

 

Delta Cyg was easy with the 76mm a couple of years back using an old ¼ -inch Ramsden EP (160x)...I’ll get back to it with the iris (and 50mm & 63mm stops) eventually.......!

 

Dave.

IrsDia Vws.jpg


Edited by David Gray, 17 September 2019 - 07:51 AM.

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#17 Bonco2

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Posted 17 September 2019 - 03:52 PM

At 1.4 arc-seconds it much closer than the Dawes limit of a 60 mm..what are you expecting to see?
 
Jon

Here's what I see with my 60mm F15 using a 7mm eyepiece @128X. Two peas touching. The secondary disc is smaller and you can see color differences of the two stars. Not a "split" but a very pleasing view none the less that reveals the duplicity.
Bill

Edited by Bonco2, 17 September 2019 - 03:54 PM.

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#18 John Fitzgerald

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Posted 17 September 2019 - 05:51 PM

Here are the WDS parameters of Delta Cyg in 2016:  PA=216, Sep=2.80", m1=2.89 m2=6.27.

 

Almost 3" of separation, Mag difference=3.38, the primary is about 22.5 times brighter than the secondary.


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#19 Sasa

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Posted 19 September 2019 - 02:56 AM

Routine pair for my 80mm refractors (AS80/1200, ATC82 and former SV80S), difficult but doable in 63mm Telementor and 60mm FOA60. In good nigths, it is in 60mm visible at 133x as a nice faint needle point attached from the inner side to the first diffraction ring.


Edited by Sasa, 19 September 2019 - 02:56 AM.

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#20 Bonco2

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Posted 19 September 2019 - 04:00 PM

Here's what I see with my 60mm F15 using a 7mm eyepiece @128X. Two peas touching. The secondary disc is smaller and you can see color differences of the two stars. Not a "split" but a very pleasing view none the less that reveals the duplicity.
Bill

For clarification my comment quoted above was concerning Pi Aquilae, not Delta Cyg.

Bill


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#21 azure1961p

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Posted 20 September 2019 - 10:09 AM

I was looking at a really old log, spring 1993 with the 8.  Said it was definitely split at 140x.  Jus saying.

 

Pete



#22 barbie

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Posted 20 September 2019 - 10:24 PM

I get good splits at 150x in both my 3" and 4" Takahashi's. Colors are well defined too.
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#23 azure1961p

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Posted 22 September 2019 - 02:45 PM

Colors??

 

They re both yellow.  

 

Pete



#24 barbie

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Posted 24 September 2019 - 10:00 PM

Beta Cygni has well defined colors, 
Both Delta Cygni components appear yellow in my scopes. Usually easily split in both 3" and 4" apertures.


Edited by barbie, 24 September 2019 - 10:19 PM.


#25 Astrojensen

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Posted 25 September 2019 - 01:30 AM

Delta Cygni does appear to have a color contrast to my eyes. The faint component appears faintly bluish. Likely a color contrast phenomena. 

 

It is stunningly beautiful in my 4" f/11 ED at 714x. The main star is pale yellow and the companion dim, grayish smoke-blue. HUGE airy disks and you could drive a truck between the stars. 

 

 

Clear skies!
Thomas, Denmark


Edited by Astrojensen, 25 September 2019 - 01:30 AM.

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