Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Izar very difficult to split

  • Please log in to reply
78 replies to this topic

#26 StarAlert

StarAlert

    Apollo

  • *****
  • Posts: 1,274
  • Joined: 11 Aug 2019

Posted 06 May 2021 - 08:49 AM

Do you know what magnification you used, Star Alert?

 

Clear skies from Aubrey. 

Hmmm, good question. I can’t remember exactly, but I was using an 8.5mm XF most of the night. So 365x. If it wasn’t the XF, it was the 3.4mm HR. 


  • flt158 likes this

#27 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 9,808
  • Joined: 04 Jan 2004
  • Loc: near Elkins and Pettigrew, Arkansas

Posted 08 May 2021 - 10:18 AM

Seeing was so poor Thursday night, that I couldn't split Izar with a good 12 inch reflector. 


  • flt158 likes this

#28 flt158

flt158

    Vanguard

  • *****
  • Posts: 2,422
  • Joined: 11 Aug 2014
  • Loc: Dublin, Republic of Ireland

Posted 08 May 2021 - 12:43 PM

Gosh! shocked.gif

That is very surprising, John. 

 

Maybe next time you will have success with Izar. 

 

Clear skies from Aubrey. 



#29 John Fitzgerald

John Fitzgerald

    In Focus

  • *****
  • Posts: 9,808
  • Joined: 04 Jan 2004
  • Loc: near Elkins and Pettigrew, Arkansas

Posted 08 May 2021 - 09:22 PM

Aubrey,

Frequently, seeing is so poor here that no airy disk is even remotely visible.  Star images may appear to be 3 or 4 seconds across, like little boiling blobs.  The terrain is very rugged, and cut by hills and valleys, which may contribute to turbulent conditions.  Thursday night, we had a north wind, which is unusual this time of year.


Edited by John Fitzgerald, 08 May 2021 - 09:24 PM.

  • flt158 and rugby like this

#30 chemisted

chemisted

    Viking 1

  • -----
  • Posts: 556
  • Joined: 24 Feb 2012

Posted 11 May 2021 - 07:01 AM

This thread got me out last night to have a good look at Izar.  I gave up double star work when I lived on the eastern slope of the Rockies for ten years as the seeing was just consistently bad.  I am now better located and went back to this old friend.  I used my Sky 90 with Extender Q (800 mm fl) and slowly ramped up the power.  Seeing was good enough to see partial diffraction rings come and go.  When I got to my 5mm LE eyepiece (160X) the split was excellent and the colors golden for the primary and greenish-blue for the secondary.  Interestingly my 6mm LV (133X) also gave a split but the colors were muted and not nearly as enjoyable.  My conclusion is that everything matters when attempting these tight but wonderful targets.


Edited by chemisted, 11 May 2021 - 07:02 AM.

  • chrysalis, flt158 and rugby like this

#31 Rutilus

Rutilus

    Mercury-Atlas

  • *****
  • Posts: 2,932
  • Joined: 17 Dec 2010

Posted 12 May 2021 - 12:44 PM

Hi all! This question may have been asked many times, sorry if thats the case. Anyway, I was looking at Izar yesterday and honestly couldn't make out that it was a double. I found it odd, because everywhere online it says it is a very brilliant visual binary. So I look to see if the scope was the limiting factor here, I have a 4 inch, 660mm achro. However I saw some comments of people saying they could split it even with 70mm scopes. I tried 33x, 66x and 132x. The only time I can say I saw something resembeling a second companion was in the 66x. But I think that was just my imagination working with the chromatic aberration, because the "companion" I saw wasn't where it's supposed to be. Seeing was also good as far as I could tell, I could easily split Mizar for example. Wondering if its the achro, the light pollution (I live in bortle 6ish maybe 7 skies) or the potential poor seing (although this last one seems unlikely). Thanks in advance! If I simply can't split it with my current setup, could you recommend some nice, easy doubles I can see? I've already seen Almach, Mizar, Achird, Cor Caroli etc... I've heard Albiero is very nice, any others? Thanks in advance and sorry for the long post.

If your dewshield lens cap has a centre aperture  (usually 50 - 52mm) then give this a try. It will increase your scopes 

focal ratio to around f/12.6 - f/13.2. If it does not, then a 50mm aperture mask is easy to make from a piece 

of old card. At 50mm, the companion star sits in the dark interspace  between the primary and first diffraction ring.

I 've found that the companion is easier to see at 50mm than with a 70mm scope. 

I made a 50mm aperture mask for my 120mm f/8.3 achromat scope and here is a drawing of how Izar appears to me.

The companion appears to be just touching the inner edge of the diffraction ring with some light spread into the ring itself.

There is also dark space visible between companion and primary. Magnifications used were 100x  up to 200x. 

Attached Thumbnails

  • Izar-cn-50mm.jpg

  • payner, Bonco2, flt158 and 5 others like this

#32 dhkaiser

dhkaiser

    Apollo

  • *****
  • Posts: 1,143
  • Joined: 23 Dec 2019

Posted 12 May 2021 - 08:59 PM

Just came in after locating Izar 45 minutes after sunset.  Using my 102mm ED f/7 refractor I had an occasional split with the 7mm/102x eyepiece and a nice split with the 5mm/143x. Pale yellow primary and blueish secondary.  Thanks for the nudge to get out under the stars.


  • payner, flt158 and Rich5567 like this

#33 barbie

barbie

    Surveyor 1

  • *****
  • Posts: 1,729
  • Joined: 28 Jan 2013
  • Loc: Northeast Ohio

Posted 12 May 2021 - 09:57 PM

I split Izar very easily at 114x in my 76mm F7.5 fluorite apo refractor for the first time this year!!  It's a very pretty double star that I make a point to look at whenever it's favorably placed in my suburban sky!! Tonight's split was made under average seeing and transparency conditions.


Edited by barbie, 12 May 2021 - 10:06 PM.

  • payner, flt158 and sunrag like this

#34 JimOfOakCreek

JimOfOakCreek

    Viking 1

  • *****
  • Posts: 536
  • Joined: 07 Jul 2010
  • Loc: Wisconsin

Posted 13 May 2021 - 10:24 PM

I found Izar quite a challenge tonight with my 8”SCT. I did split it with a Pentax XW 10mm. That’s about 200X! That’s what it took. Sky conditions were not great, a bit turbulent. 


  • payner, ewave and flt158 like this

#35 barbie

barbie

    Surveyor 1

  • *****
  • Posts: 1,729
  • Joined: 28 Jan 2013
  • Loc: Northeast Ohio

Posted 14 May 2021 - 06:03 AM

Thursday night, I again split Izar, this time with my 60mm fluorite apochromat at 151x under much better sky conditions than I had while observing it with my 76mm fluorite apo on Wednesday evening. 


  • payner, Astrojensen, Bonco2 and 1 other like this

#36 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • Posts: 14,125
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 14 May 2021 - 12:50 PM

I found Izar quite a challenge tonight with my 8”SCT. I did split it with a Pentax XW 10mm. That’s about 200X! That’s what it took. Sky conditions were not great, a bit turbulent. 

The large central obstruction and poor thermal behavior of most Cassegrains can make such bright, unequal doubles a LOT harder than you'd expect, considering the aperture. On many nights, the stars are just large, fuzzy balls. This is because the first (and sometimes second) diffraction ring around the Airy disk becomes so bright, that it/they become easily visible, and the turbulence merges it all into a big, boiling glow, completely negating any resolution advantage the larger aperture should have had.   

 

My own Vixen VMC 260L is no different, but I've found that wrapping the tube in insulating material helps quite a lot, on the condition that the tube and optics have cooled first. If the seeing is good, it can then split Izar wide open at 273x (11mm ES82), in a way none of my smaller scopes can. The stars are TINY in such a large aperture! 

 

 

Clear skies!

Thomas, Denmark


  • JimOfOakCreek, Rutilus, Bonco2 and 4 others like this

#37 JimOfOakCreek

JimOfOakCreek

    Viking 1

  • *****
  • Posts: 536
  • Joined: 07 Jul 2010
  • Loc: Wisconsin

Posted 14 May 2021 - 05:30 PM

The large central obstruction and poor thermal behavior of most Cassegrains can make such bright, unequal doubles a LOT harder than you'd expect, considering the aperture. On many nights, the stars are just large, fuzzy balls. This is because the first (and sometimes second) diffraction ring around the Airy disk becomes so bright, that it/they become easily visible, and the turbulence merges it all into a big, boiling glow, completely negating any resolution advantage the larger aperture should have had.   

 

My own Vixen VMC 260L is no different, but I've found that wrapping the tube in insulating material helps quite a lot, on the condition that the tube and optics have cooled first. If the seeing is good, it can then split Izar wide open at 273x (11mm ES82), in a way none of my smaller scopes can. The stars are TINY in such a large aperture! 

 

 

Clear skies!

Thomas, Denmark

I’ll try my 4” APO when I get the chance.


  • Astrojensen likes this

#38 fred1871

fred1871

    Surveyor 1

  • -----
  • Posts: 1,867
  • Joined: 22 Mar 2009
  • Loc: Australia

Posted 14 May 2021 - 10:00 PM

A cassegrain is not guaranteed to be a problem scope on unequal doubles when they have separation that's not especially close. At 2.8" Epsilon Bootis (Izar) is well beyond the first diffraction ring of an 8-inch SCT. Even though the stars differ a good deal in brightness, at mags 2.6 and 4.8, it's not as if that will much effect separating them that far apart. For an 8-inch, the first diffraction ring (by far the brightest one) will centre at about 0.9" - that's one-third the separation of the pair. Certainly for that delta-m a separation near 1" or just below could be seriously difficult, especially in poor seeing, but given the much greater separation this seems unlikely. More to be expected is the report above in #34, of needing 200x for a split with turbulent conditions added.

 

It'd be different with, say, a 60mm refractor, where the first diffraction ring (though less bright than with a central obstruction) is centred at 3.0", just wider than the double. A companion sitting on the inner edge of the ring might be expected.

 

The fairly large central obstructions of SCTs and other Cassegrains do have a deleterious effect on splitting doubles of larger magnitude difference, when those doubles are close for the aperture, typically with diffraction ring interference. I've found that for not-too-faint pairs of delta-m around 2 to 3 magnitudes, my C9.25 is similar to my 140mm refractor for showing these as doubles. That's quite a difference in aperture. But for outright splits of similar brightness stars the C9.25 wins easily - a Dawes split at 0.5" (Zeta Bootis some years back - the 140 refractor showed, as expected, some elongation and no notching).

 

Cassegrains that are not thermally settled will give the "puffball" images that Thomas refers to, especially if the atmosphere on the night is tending to that all by itself. I had a Vixen VMC 260L for about 5 years, and found it more difficult to get thermally settled than the various Celestron SCTs I was long familiar with; it's an open tube, they're closed tubes (corrector plate). Different approaches needed. Mine rarely even matched the C9.25XLT (an average sample, non-EdgeHD) that I had bought it to replace; not an outright bad scope, just disappointing most of the time. Certainly not dreadful optically like some examples of SCT I've used from Meade and Celestron.

 

Regarding Epsilon Bootis (Izar, Struve's "Pulcherrima"), my only notes from observing it are with my 140mm refractor, which showed it nicely at 105x (didn't try lower), perhaps best at 160x, a lovely pair of contrasting brightness and colour. I'll now have to try it with the C9.25 for comparison.


Edited by fred1871, 14 May 2021 - 10:35 PM.

  • payner, Astrojensen, JimOfOakCreek and 5 others like this

#39 Bonco2

Bonco2

    Viking 1

  • *****
  • Posts: 660
  • Joined: 01 Jun 2013

Posted 15 May 2021 - 03:53 PM

Fred,

Great post. Your description of Izar in a 60mm is exactly what I see. 

Bill


  • flt158 likes this

#40 JimP

JimP

    Mercury-Atlas

  • *****
  • Posts: 2,560
  • Joined: 22 Apr 2003
  • Loc: USA

Posted 15 May 2021 - 04:18 PM

I was at my Farm last week. Skies were finally clear but the seeing was awful. I went out anyway because I was testing out my Ski-Fi and iPad with Sky Safari Pro to see if I could get things working properly.  Using a very fine quality AP 130 F/8.35 I was not able to “split” Izar. Actually I could not even  tell it was a double! The good news is the Sky-Fi  and Sky Safari pro worked perfectly with my AP Mach1 mount.

 

JimP


  • flt158 likes this

#41 Rutilus

Rutilus

    Mercury-Atlas

  • *****
  • Posts: 2,932
  • Joined: 17 Dec 2010

Posted 16 May 2021 - 07:02 AM

I’ll try my 4” APO when I get the chance.

I have a C9.25 SCT, and when it comes to close un-equal doubles all of my refractors win everytime.

For example, last year I had excellent views of the double Eta Geminorum with my 80mm refractor.

While the split should be easier with the larger SCT, I struggled to see it and when I did the view was

very messy.  


  • JimOfOakCreek, Bonco2, flt158 and 1 other like this

#42 fred1871

fred1871

    Surveyor 1

  • -----
  • Posts: 1,867
  • Joined: 22 Mar 2009
  • Loc: Australia

Posted 16 May 2021 - 10:21 PM

I have a C9.25 SCT, and when it comes to close un-equal doubles all of my refractors win everytime.

For example, last year I had excellent views of the double Eta Geminorum with my 80mm refractor.

While the split should be easier with the larger SCT, I struggled to see it and when I did the view was

very messy.  

 

Interesting. What size refractors? - as they're not in your signature line....

 

I looked up my notes on Eta Gem, and I have notes for it, but the C9.25 notes were on a night I described as having poor seeing; companion was seen anyway, but it wouldn't be a useful comparison with the better night I observed it with the 140mm refractor. Gone from my sky at present, so not immediately able to be checked.

 

I'll look through my notes on other doubles, where both scopes have been used, so I can give examples for comparison. Mostly after I got the refractor I took to using the refractor for unequal close pairs (not too faint), and near equal and fainter ones with the SCT. Because I had the SCT for five years before I got the refractor I have a lot of notes on unequal pairs with the SCT, mostly pre-refractor, and some later for deliberate comparison with the refractor. Watch this space.... grin.gif


  • flt158 likes this

#43 JimOfOakCreek

JimOfOakCreek

    Viking 1

  • *****
  • Posts: 536
  • Joined: 07 Jul 2010
  • Loc: Wisconsin

Posted 17 May 2021 - 10:01 PM

Amazingly, I split Izar with my 4” APO and a 7mm X-Cel LX (100X). I tried a 10mm UFF (70X) but couldn’t do it. The best view was a ES 52* 4.5mm (158X). 
 

The other night I needed a Pentax XW 10mm (200X) with my 8” SCT.

 

The view was much cleaner in my refractor vs the SCT.


Edited by JimOfOakCreek, 17 May 2021 - 10:03 PM.

  • payner, ewave, Rutilus and 3 others like this

#44 flt158

flt158

    Vanguard

  • *****
  • Posts: 2,422
  • Joined: 11 Aug 2014
  • Loc: Dublin, Republic of Ireland

Posted 18 May 2021 - 07:49 AM

Great job, Jim, and everyone else who is splitting Izar.

 

I would say 100X is about the bare minimum to get some black space in between the 2 stars. 

It is an interesting call stating that refractors can be better than Schmidt Cassegrain Telescopes on separating some difficult doubles.

 

Clear skies from Aubrey. 


  • JimOfOakCreek and Rich5567 like this

#45 Spikey131

Spikey131

    Vanguard

  • *****
  • Posts: 2,197
  • Joined: 07 Feb 2017

Posted 18 May 2021 - 06:14 PM

My wee little Questar 3.5 Mak gave me a nice look at Izar last night, splitting it nicely at 160x.

 

So with good seeing conditions, catadioptric scopes can do a good job with uneven doubles. 


  • flt158 likes this

#46 dhkaiser

dhkaiser

    Apollo

  • *****
  • Posts: 1,143
  • Joined: 23 Dec 2019

Posted 18 May 2021 - 07:55 PM

My wee little Questar 3.5 Mak gave me a nice look at Izar last night, splitting it nicely at 160x.

 

So with good seeing conditions, catadioptric scopes can do a good job with uneven doubles. 

Now I will have to try it with my C90.  Next clear night.


  • flt158 likes this

#47 Rutilus

Rutilus

    Mercury-Atlas

  • *****
  • Posts: 2,932
  • Joined: 17 Dec 2010

Posted 19 May 2021 - 04:22 AM

Interesting. What size refractors? - as they're not in your signature line....

 

I looked up my notes on Eta Gem, and I have notes for it, but the C9.25 notes were on a night I described as having poor seeing; companion was seen anyway, but it wouldn't be a useful comparison with the better night I observed it with the 140mm refractor. Gone from my sky at present, so not immediately able to be checked.

 

I'll look through my notes on other doubles, where both scopes have been used, so I can give examples for comparison. Mostly after I got the refractor I took to using the refractor for unequal close pairs (not too faint), and near equal and fainter ones with the SCT. Because I had the SCT for five years before I got the refractor I have a lot of notes on unequal pairs with the SCT, mostly pre-refractor, and some later for deliberate comparison with the refractor. Watch this space.... grin.gif

Refractors of the following 80mm f/7 triplet, 100mm f/13, 120mm f/8.3, 150mm f/8 and 150mm f/15 all used with

various aperture masks. Going back to Izar, I observed it a couple of nights ago with the SCT. The companion

was easy to see, but the views are not as clean and crisp as with the refractors. Scope cooled and collimated.

The effect of the central obstruction is easy to see with a brighter diffraction ring that appears to get scattered more

by atmospheric conditions. 


  • Astrojensen, Bonco2, flt158 and 1 other like this

#48 Mr.Furley

Mr.Furley

    Lift Off

  • -----
  • Posts: 17
  • Joined: 19 May 2021

Posted 19 May 2021 - 07:20 PM

Refractors of the following 80mm f/7 triplet, 100mm f/13, 120mm f/8.3, 150mm f/8 and 150mm f/15 all used with
various aperture masks. Going back to Izar, I observed it a couple of nights ago with the SCT. The companion
was easy to see, but the views are not as clean and crisp as with the refractors. Scope cooled and collimated.
The effect of the central obstruction is easy to see with a brighter diffraction ring that appears to get scattered more
by atmospheric conditions.


Your description if the view in your SCT is close to my observations with a 10in GSO in my average seeing conditions. Nice split at 156x with a constant gap. Excellent sketch you posted above.

Edited by Mr.Furley, 19 May 2021 - 07:26 PM.

  • flt158 likes this

#49 barbie

barbie

    Surveyor 1

  • *****
  • Posts: 1,729
  • Joined: 28 Jan 2013
  • Loc: Northeast Ohio

Posted 19 May 2021 - 09:27 PM

The lowest power I've used to get a clean split of Izar was 114x in my 3" F7.5 fluorite apochromat.
  • flt158 likes this

#50 JimP

JimP

    Mercury-Atlas

  • *****
  • Posts: 2,560
  • Joined: 22 Apr 2003
  • Loc: USA

Posted 20 May 2021 - 09:57 AM

I went back out last night with good seeing conditions using my AP 155 F/7

and Takahashi TOE 4.0, 3.3 and 2.5 mm eyepieces. The view was spectacular! A light yellow primary and beautiful blue secondary. The blue secondary almost seemed to glow at times!!

 

JimP


Edited by JimP, 21 May 2021 - 07:57 AM.

  • Astrojensen, Stellarfire and flt158 like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics