Doubles - what magnification do you use?

[Mr Spock]

I was having a think about this last night. I was looking at Rigel through the 102mm at x119. At 9.4" it looked quite wide.

I've not tried any tight ones so far. What if, for example, it was 2" instead of 9.4"?

I'll find out in due course but just wondered what everybody else used.

[John]

I often use 250x-300x on double stars sometimes as much as 400x. I tend to be drawn towards the closer pairings.

I seem to prefer the "sledgehammer to crack a nut" approach even with the wider ones

 

[Space Hopper]

As much as i can get away with !! 

I often use Rigel as a guide, if it splits well and seems stable than its a go for hunting others.

Plenty of times though that it looks a bit mushy and the seeing is simply not up to it.

I still have had no success with Sirius pup yet. And its not for the want of trying.

More likely to be consistently poor seeing and my deteriorating 54 yr old eyes ! 🧐

 

[JeremyS]

Indeed, for close doubles I rack up the mag as much as seeing allows. 

[Ian McCallum]

I did try 320x magnification on Almach, last night. That was using the Sky-Watcher Evostar 120 and BST StarGuider ED 3.2mm eyepiece. To be honest, it was too much for the seeing conditions and scope. 

Edited November 21, 2021 by Ian McCallum

[Stu]

I like close pairs, so would prefer to view some of the wider ones at lower power so the separation is not too huge. The tighter ones need more, though something like the double double clearly splits at x80 even in small apos if the seeing is good. Nice at x120 or more too of course. Even tighter stuff calls for higher power still, so x250 to x300 or even more when conditions allow and the target demands it.

[MylesGibson]

I tend to just use the highest I can get away with on the night. With some wider doubles, I do like a lower magnification to get in some of the surrounding star field too

[mikeDnight]

The highest power I've ever used on a double was 1000X when I first bought my FC100DZ. It was a silly magnification to try, as at 1000X you need to keep everything critically centralized. Things move fast at that power, and I only used that high power to see if I could break my Tak. The view was really quite lovely, and although the atmosphere was steady, it did begin to push things a little. The view however was still so good that I had to repeatedly keep checking I wasn't mistaken with the magnification. I was using a 1.6mm Vixen high resolution eyepiece and a 2X barlow in my 100mm F8. Removing the barlow to give 500X  improved the sharpness of the star image, which was technically perfect. Having a driven equatorial on a solid pier was an advantage. I don't often use 500X but its nice to push the power on double stars at times.

[Mr Spock]

Splitting close doubles is what my 2.5mm is for. It gives x286 in the 102mm and x480 in the 250mm. Only for use in the best seeing conditions though.

[John]

I used 400x with my 130mm refractor on Iota Cassiopeia earlier this year:

[mikemarotta]

On 21/11/2021 at 04:46, Mr Spock said:

I was having a think about this last night. I was looking at Rigel through the 102mm at x119. At 9.4" it looked quite wide.  ... I'll find out in due course but just wondered what everybody else used.

I have an Explore Scientific 102mm achromatic F=660 and first view of Rigel was last week 8 December at 165X with an StellarVue 4mm and then at 94X with a 7mm Nagler Type-1.  When I tried the 14-mm Meade Series 5000, I knew that it was there, but, truly, I could have not reported it on that basis alone. (My other hobby is numismatics, where optimistic grading is common.)  Last night (this morning 0005 Hours), I got very good separation with an Explore 5X focal extender and the 14mm Meade for 235X. 

On 21/11/2021 at 10:02, Stu said:

I like close pairs ...  though something like the double double clearly splits at x80 even in small apos if the seeing is good. Nice at x120 or more too of course.

That is not my experience at all. Skies and eyes are all individualized.  I have been able to split the famous double-double epsilon Lyrae with 70mm entry-level telescopes (Meade and Celestron). Here from my notebook for 05 November 2021. However, I was unable to do this with the National Geographic 70mm and for that, I had two of them, one older (2015) and the other new from the box. 

The Meade F=700mm. So 233 X to do this. The Celestron is a longer f/13 F=900. So 225X. For myself, the one pair is always harder to split and here even with the longer focus, the Celestron had trouble.

Because the Naitonal Geographic could not do this, I bought the other two to test the limits. Otherwise, I use (as above) my 102-mm with F=660. My first view was on 20 November 2020 with an 8mm Ploessl and a 2X Barlow (both Celestron) for 165X.  

1 hour ago, mikeDnight said:

The highest power I've ever used on a double was 1000X when I first bought my FC100DZ. It was a silly magnification to try, as at 1000X  ...  

Silly? Let me tell you about silly: "Jupiter at 1100X" here on my blog. However, there, I do cite Ronald Stoyan "The Visual Astronomer" blog at http://visualastronomer.com/ (Note that it is not secure socket https.) He says that magnification is never wasted.   But, as much as I agree that more power can serve a purpose, I still view casually mostly at 40X to 100X.  (47X with the Meade 14mm now. Previously, I tended to the Celestron 32mm + 2X Barlow.) 

 

 

[Stu]

5 hours ago, mikemarotta said:

That is not my experience at all

I’m not sure which but doesn’t match your experience Mike? I was referring to small apo refractors (such as a TS 72mm f6 follow-53 for example). You were using some entry level achro refractors which might be expected to need more power to split the Double Double.

I have done it at x151 with an old 60mm f15 Prinz Optics scope which cost me a fiver off eBay so ultimately it’s not that difficult a target, skies probably make most difference if the scope is reasonably ok.

 

[Mr Spock]

My 1970’s Prinz 550 60mm could split it too. 

[Stu]

6 minutes ago, Mr Spock said:

My 1970’s Prinz 550 60mm could split it too. 

Like this?

 

[Mr Spock]

Yes, but on an EQ mount with slo-mo controls. I still have a few of the eyepieces. 12mm and 6mm Kellner, and a 4mm Ortho. I also had a 20mm Huyghenian and 40mm Achromatic Hughenian - don't know where they went.

The scope cost £39.95 from Dixons - my dad paid for it on weekly  It was a Birthday present, my 16th probably (1974). Things were expensive back then. The ortho cost a month's money 

[cloudsweeper]

I cracked the 1.0" barrier (0.94" and 0.97" for O-Sigma 418 Cyg; O-Sigma  95 Tau) using x318.  

But it's never clear-cut, and depends on the difference in magnitudes of the stars as well as the seeing.

For the examples given, I was using a 10" and an 8".  Aperture is key here, since with smaller apertures, seeing  prevents splitting before the theoretical magnification limit.

Doubles are not only pleasing, they are very challenging, which is their appeal!

Doug.

[Zermelo]

I've got down to 1.2" so far with both a 150mm Newt and a 127mm Mak.

For example, 36 Andromedae was (barely) split with the Mak at 300x. The seeing was exceptional that night, and I managed over 400x on the moon (breaking the "two times aperture" rule by some distance).

 

[cloudsweeper]

1 hour ago, Zermelo said:

I've got down to 1.2" so far with both a 150mm Newt and a 127mm Mak.

For example, 36 Andromedae was (barely) split with the Mak at 300x. The seeing was exceptional that night, and I managed over 400x on the moon (breaking the "two times aperture" rule by some distance).

 

The 2x aperture thing is a scientific convention rather than a hard law, and works on an exit pupil of 0.5mm.  You can go lower, and get to about 2.5x aperture, seeing permitting!

Doug.

[Sunshine]

I find that even though I may be able to go higher on a particular double there’s always that sweet spot where they look just right. Take the double double in Lyra for example, I can just make them out as doubles at around 90x. Even though I can pile on the power we’ll past 200 I find they just look sweet at around 180, I tend to stop and enjoy doubles when they wow me rather than just pushing it for the sake of it.

Edited December 14, 2021 by Sunshine

[Stu]

3 minutes ago, Sunshine said:

I find that even though I may be able to go higher on a particular double there’s always that sweet spot where they look just right. Take the double double in Lyra for example, I can just make them out at doubles at around 90x. Even though I can pile on the power we’ll past 200 I find they just look sweet at around 180, I tend to stop and enjoy doubles when they wow me rather than just pushing it for the sake of it.

I do agree actually. There is a lot of talk about how low you can split the Double Double, somewhere around x50 seems to be the limit. I think I’ve managed x55 or x60, can’t quite recall, but like you I enjoy viewing it far more at higher power with a nice clean and clear split.

[John]

1 hour ago, Sunshine said:

I find that even though I may be able to go higher on a particular double there’s always that sweet spot where they look just right. Take the double double in Lyra for example, I can just make them out as doubles at around 90x. Even though I can pile on the power we’ll past 200 I find they just look sweet at around 180, I tend to stop and enjoy doubles when they wow me rather than just pushing it for the sake of it.

That's the nice thing about using a decent quality zoom eyepiece for double star observing - instant variability of magnification to find the most pleasing view 

 

 

[Nik271]

I tend to use about 100x for wide doubles (Albireo, Almach) and 200x-300x for tight doubles, seeing dependent.

For equal close doubles even with 1'' separataion  a magnification of 200x is actually sufficient (provided  the scope has the needed resolution) The pair will look 3.3 arcminutes apart in the EP wich is wide enough to resolve for most people. Unequal doubles is another matter, I would say at least 50% extra magnification is needed and sometimes even more.

[Ags]

I'm not a big fan of swapping eyepieces, so I normally use a general-purpose 60x to 100x on most nights. This may change when I get a zoom 😀

[Mr Spock]

I can see where a zoom might be handy for doubles. I’d still prefer fixed focal lengths for planetary though. 

[Ags]

I hear the hyperflex 7-2-21.5 is quite good on doubles, particularly with the Baader Q barlow.