37 replies to this topic

[Gschnettler]

I was wondering what the best eyepieces are for splitting tight double stars.   Given all the light pollution in the city I am finding that splitting doubles is a fun way to enjoy astronomy - more satisfying to me than seeing faint gray patches of galaxies (or not seeing them). 

 

I already have Pentax 5mm and 7mm. With my 12” f5 dob that has a 1500mm focal length I tried both Pentax eyepieces last night and once again the 7mm was sharper.  I am guessing that the 5mm is pushing 300x and that might have been too much for the seeing.  I’m not really sure how to tell if the seeing is good or not.  This has happened a few times now.  Is the best test for seeing to simply try your high power eyepieces and see how far you can go before things start to look blurry?

 

If I can’t frequently use the 5mm due to seeing, then the most I can zoom in is with my 7mm which gives 214X magnification.  Should I consider getting a 6mm to get 250X?   There don’t see to be too many 6mm available but I could get a Delos 6mm.  Or would it be better to get something like the Baader Classic Orthoscopic 6mm? 

 

I do wear glasses but prefer to take them off when observing so eye relief doesn’t really matter much.  

[Jon Isaacs]

I spend a goodly amount of time splitting close doubles. 

 

It really is all about the seeing.  A 12 inch scope will split doubles under 0.5", that will require at least 600x and probably more.  

 

Thermal equilibrium is critical, the scope has to be rock solid steady..

 

As far as eyepieces, I use type 6 Naglers.  I track manually so the wide field is a help and they are parfocal so swapping eyepieces is easier.  

 

For those special nights when the seeing supports very close doubles, I recommend a 2X Barlow.  I like the TeleVue 1.25 inch since it's parfocal.  I use it with my 3.5mm and 5mm Naglers to get those high mags.

 

In more normal seeing, making sure the scope is cooled and collimated is about the best one can do.  In locations where the seeing is not generally super, refractors are popular because they are thermally stable and capable enough to match the seeing.

 

Jon

[Bigzmey]

300x for you DOB is not too much, you should be able to push beyond that on nights of good seeing. XW 7mm and 5mm are great EPs and on most doubles they will work just fine. I do notice that they have a bit more light scatter than good Orthos, so having a set of quality Orthos in your EP case is a good thing for those extra tight doubles. 

 

The only issue with Orthos is that it is sometimes tricky to track with manual mount, since like you I have to take my glasses off to use Orthos. Because of that I have tested a quite few EP lines on doubles and like Vixen SLVs the most. They have Ortho-like performance on Moon, planets and doubles but come with 20mm eye relief. They are now my default set for doubles. 

[John608]

I have bortle 5-6 skies here though they are often quite steady in the summer. I have done better with orthos, and also planetary type eyepieces like the tmb's have done well. In general for me, since I am not interested in wide fields, or perfect stars at the extreme edges of the field, I prefer an eyepiece that is sharp and contrasty with the minimum number of elements. I prefer the TMB Planetary type eps for extremely short focal lengths less than about 6mm, or a 9mm ortho plus a barlow and Orthos at 7mm and up. Just my experience. I have not had the opportunity to try any of the Televue or Pentax eps which I am sure are excellent.

[Mitrovarr]

There's a lot to be said for a high quality zoom, like the BHZ or a Nagler zoom. Being able to get the perfect magnification is worth a lot.

[Grounddweller]

My eyepiece universe is very small and I prefer it that way. The Radians I have suit my eyes well and perform excellently. Those have been discontinued for some time but comments almost universally state TV Delites perform equally, if not better, than my Radians. The 60° in the Radians give very wide views in the context of splitting doubles so the extra 2° would be ginormous

Edited by Grounddweller, 24 February 2021 - 09:34 PM.

[Mike W]

Find a used 6mm Radian

[Jon Isaacs]

My eyepiece universe is very small and I prefer it that way. The Radians I have suit my eyes well and perform excellently. Those have been discontinued for some time but comments almost universally state TV Delites perform equally, if not better, than my Radians. The 60° in the Radians give very wide views in the context of splitting doubles so the extra 2° would be ginormous

The nice thing about the Radians is that they were available in close step sizes, a big plus for working at double star magnifications.

 

Jon

[aeajr]

I am not a devoted double splitter but I do enjoy them from time to time.

 

My favorite eyepiece for splitting doubles is my Baader Hyperion 8-24 zoom.  Zoom eyepieces allow me to actually watch the double split as I zoom in and crank up the power.

 

I did this a lot with my XT8i.   Now I have an Apertura AD12 and the zoom is my eyepiece of choice for doubles. 

 

The zoom by itself, in the AD12, takes me from 63X to 190X.  If I need to go higher I attach a 1.5X Barlow which will take me up to 285X.  I typically don't go any higher than that on doubles as the seeing usually is not good enough.

 

Again, I am not a devoted double splitter and I don't delve deeply into the real challenging ones.  But I just love seeing the split happen as I crank up the power.

 

I use the Celestron zoom in my 5" Mak to split doubles.  Takes the scope to 237X which is enough to split doubles without needing a Barlow.

 

These are not specialized doubles eyepieces, they are just fun to use. 

Edited by aeajr, 24 February 2021 - 09:49 PM.

[havasman]

You have nice eyepieces. Apparently you may not have conditions capable of supporting the magnifications they will produce. More eyepieces will not really cure that. There are so many double/multiple stars that are valuable observations at your 214x magnification that you may want to pursue them at that magnification for a while as you learn how to recognize the effects of seeing. You should be able to gauge the effectiveness of your 5mm over time to learn what course is best for you. Whatever we may tell you is conjecture. What you see is more reliable.

[Jeff Morgan]

About 1/3 of my 2,000 or so logged observations are double stars.

 

I like using a zoom, and have had great success with the Nagler 3-6 and the Leica ASPH. Barlow as needed. Sometimes the "in between" magnification is the most important factor, even when your regular eyepieces are in 1mm increments. (Which makes sense when you realize at higher magnifications, a 1mm difference is a lot.)

 

For the very hardest ones (dissimilar magnitudes with the B component very close in), TMB Supermonos could often get a clean shot at what other eyepieces only hinted at. Or put another way, if they could not do it none of my other eyepieces could either.

 

I picked up Takahashi TOE's after a little over a year of use I am now comfortable saying they are in that same performance league as the SMC's.

[Sketcher]

How ambitious are you?  How deeply do you want to venture into the world of double stars?

 

A Celestron 12.5mm MicroGuide reticle eyepiece could be used, along with a suitable Barlow, to not only split doubles; but also measure separations and position angles.

[mtminnesota]

...I’m not really sure how to tell if the seeing is good or not.  This has happened a few times now.  Is the best test for seeing to simply try your high power eyepieces and see how far you can go before things start to look blurry? 
 

If the stars are twinkling, it's because the air is moving and you have poor seeing.  Steady dimmer stars (as seen with only your naked eyes) means get your best telescope out.  Even if the air is slightly hazy, you will see so much more when it's relatively still, it's really amazing.  Some of the best viewing I've had with a telescope in my suburban skies has been on those slightly hazy nights.

 

Of course, trial and error with your eyepieces is the best way to know exactly what your telescope will deliver on any given night.

Edited by mtminnesota, 24 February 2021 - 10:36 PM.

[jimandlaura26]

Good advice here... all around.

 

Tough issue to resolve, since there are many more factors than eyepiece focal length that determine upper magnification limit. Some that come immediately to mind are double star attributes, optics collimation, target altitude, mirror thermal stability, mirror quality and focal ratio, natural/artificial seeing impediments (mountain/upper atmosphere driven currents, radiating surfaces like roofs, roads, etc.), time of observation (late night/early morning being generally better) and eyepiece design/execution characteristics (the reality that none do everything optimally).

 

I had a good 10” f/5 reflector and still own a fairly solid Celestron C-8 Edge HD, which in theory would allow me to get to higher than 200x. But in practice, all the other factors along with seeing typically limited me to 200x. My 3 and 4” refractors deliver very tight stars, but are limited in aperture and my 150mm Mak-Cass delivers almost the same caliber of pinpoint stars as my apo and occasionally allows higher magnification (300x, via a 6mm Delos). But to your point/question, once you’ve mitigated all the other factors, backing off on magnification is generally the only recourse... along with trying other EPs in your arsenal; e.g., orthos versus wide field varieties (I have both).

 

With my outstanding 3” and 4” apos, I’m limited to  about 160 and 200x, respectively before I start running out of brightness for dimmer targets. With my 150mm Mak-Cass and 200mm C-8, I’m generally limited to 200x. I am roughly 25 mi north of San Diego with mountains about 2 miles to the east... along with a not-too-infrequent marine layer intrusion (fog) coming in from the west; so what the light pollution and fog does to me gets supplemented by winds transiting over mountains whose rocks are also radiating their daytime heat into the sky at night. Persistence is a worthy attribute in this hobby. As is the use of a comfortable adjustable observing chair, in what otherwise can prove to be uncomfortable circumstances which impede capturing subtle details like excruciatingly thin gaps between neighboring stars.

 

Aside - with my apo’s the challenge I place on myself is not how high in magnification I can go, but rather how low in magnification can I go to discern a distinct separation. And, I enjoy those with a discernible color difference - along with distinctly red individual Carbon stars... like Hind’s Crimson star or T Lyrae.

 

P.S. The 6mm Baader Classic Ortho is a solid eyepiece... I own one and see BillP’s reviews in this forum. 

Edited by jimandlaura26, 25 February 2021 - 12:28 AM.

[Jon Isaacs]

One more thought:

 

Excellent seeing happens. How often depends on your location and that can be very local. Jim lives 25 miles north east of me, I'm a few miles from the coast. The seeing here can be super.. In the high desert, it's dark but the seeing is typically so-so.

 

To double star observers, seeing is like sky brightness is the deep space observers.

 

But when it happens, you want to be prepared and ready to go.. that means having eyepieces and Barlows that provide any conceivable magnification.  Sidgwick in the Amateur Astronomers Handbook recommends up to about 80x/inch for double stars.  My experience agrees with that, on a very good night, I'll use about 320x in my 4 inch, 820x in my 10 inch.

 

It also means being setup and ready with the scope fully cooled. That that doesn't mean an hour with a fan running even in a mild climate.. 

 

Jon

[Ernest_SPB]

I was wondering what the best eyepieces are for splitting tight double stars...

Almost any with focal length which produces in your scope exit pupil 0.5-0.7 mm in diameter.

[Gschnettler]

This is all fantastic information! Thank you all!

I’m mostly surprised to see recommendations for magnifications over 300. I thought that 300 was about the upper limit. To achieve that I would need eyepieces smaller than 5mm.

What do you think of the Paradigm 3.2mm?

There is also the much more expensive Delos 3.5.

And a Vixen SLV 4mm

Or I could stick with Pentax and get a 3.5mm. That might be the most attractive option since it would match up well with my Pentax 5 and 7mm.

What do you think?

Also, are there any good apps or websites that give you “seeing” predictions? I live in the Ohio River Valley. I can see the Ohio River from my house. Seems like that might be bad for seeing. They always talk about how smog and humidity gets trapped and hovers around this region. But, I’m also just a half day’s drive from beautiful West Virginia where my friends and I rent cabins in the mountains a few times per year where maybe the seeing is a lot better(?). If so, I want to be prepared for that so I don’t miss a good opportunity by not having the right eyepiece.

[Jeff Morgan]

But when it happens, you want to be prepared and ready to go.. that means having eyepieces and Barlows that provide any conceivable magnification.  Sidgwick in the Amateur Astronomers Handbook recommends up to about 80x/inch for double stars.  My experience agrees with that, on a very good night, I'll use about 320x in my 4 inch, 820x in my 10 inch.

 

Double star astronomy is one time where the 50x/inch rule goes out the airlock.

 

 

Here is a website I have always liked, a strong section on double star observing:

 

http://handprint.com/ASTRO/

[aeajr]

I use Astrospheric as my primary astronomy weather app.  I have others but I trust this one the most.

 

https://www.astrospheric.com/

 

Seeing is very hard to predict, and very local, in my experience.   You have to go and look.   

 

If you are viewing over your neighbor's roof, that impacts seeing.   If you are on blacktop, that impacts seeing, and so forth. 

 

My seeing rarely allows double splitting beyond 300X and often tops me out around 250X. 

 

That is one of the reasons I like the zoom.  I have every focal length and every mag between 24 mm and 4 mm, depending on how I use the zoom.  If 16.3 mm gives me the best image, I have it.   If 7.7 mm is best, I have it.  And if 4.9 mm is best, I have it. 

[river-z]

This is all fantastic information! Thank you all!

I’m mostly surprised to see recommendations for magnifications over 300. I thought that 300 was about the upper limit. To achieve that I would need eyepieces smaller than 5mm.

What do you think of the Paradigm 3.2mm?

There is also the much more expensive Delos 3.5.

And a Vixen SLV 4mm

Or I could stick with Pentax and get a 3.5mm. That might be the most attractive option since it would match up well with my Pentax 5 and 7mm.

What do you think?

Also, are there any good apps or websites that give you “seeing” predictions? I live in the Ohio River Valley. I can see the Ohio River from my house. Seems like that might be bad for seeing. They always talk about how smog and humidity gets trapped and hovers around this region. But, I’m also just a half day’s drive from beautiful West Virginia where my friends and I rent cabins in the mountains a few times per year where maybe the seeing is a lot better(?). If so, I want to be prepared for that so I don’t miss a good opportunity by not having the right eyepiece.

I think you'd be better off getting a Barlow.  Your 7mm and 5mm eyepieces are good for what you want to do.  The Barlow will help you take advantage of good seeing, which is the most important condition for splitting tight doubles.  On nights when the seeing is excellent I use a Barlow + 5mm and 7mm Nagler to get 250x, 350x, 500x, and 700x and it works well in my 12" Dob.

 

When you go out to split doubles you'll find out pretty quickly what the seeing will allow you to spilt.  It's useful to have a "test double" to go to for different seasons.  And also useful to have a list of tight doubles ready to go for those good seeing nights.

 

When I split doubles I use 5 eyepieces: 27mm for star hopping, a zoom for centering the star, 7mm, 5mm for the actual observation, and a Barlow for high magnification on good seeing nights.

[jimandlaura26]

This is all fantastic information! Thank you all!

I’m mostly surprised to see recommendations for magnifications over 300. I thought that 300 was about the upper limit. To achieve that I would need eyepieces smaller than 5mm.

What do you think of the Paradigm 3.2mm?

There is also the much more expensive Delos 3.5.

And a Vixen SLV 4mm

Or I could stick with Pentax and get a 3.5mm. That might be the most attractive option since it would match up well with my Pentax 5 and 7mm.

What do you think?

Also, are there any good apps or websites that give you “seeing” predictions? I live in the Ohio River Valley. I can see the Ohio River from my house. Seems like that might be bad for seeing. They always talk about how smog and humidity gets trapped and hovers around this region. But, I’m also just a half day’s drive from beautiful West Virginia where my friends and I rent cabins in the mountains a few times per year where maybe the seeing is a lot better(?). If so, I want to be prepared for that so I don’t miss a good opportunity by not having the right eyepiece.

Some observations...

 

1. I stick by my comments for a small arsenal of EPs (and Barlows) when you want to go to high powers (or any power frankly), since the various choices all have puts and takes.

 

2. Don’t overlook modest price/design EPs, such as orthos; they can be spectacular.

 

3. The Pentax 3.5mm XW is a great eyepiece, but not necessarily a silver bullet for this intended use.

 

4. WV is a great state for observing. My former astro club, NOVAC, has viewing privileges at Spruce Knob (Mountain Institute) and has sponsored the Almost Heaven Star Party there for many years - outstanding spot. 

 

5. Seeing (and other) astronomical prediction - Astrospheric app.

Edited by jimandlaura26, 25 February 2021 - 01:02 PM.

[Jon Isaacs]

What do you think of the Paradigm 3.2mm?

 

 

I have the 3.2 mm Paradigm.  It's ok but not as sharp off-axis as the 5mm, 8mm and 12 mm Paradigms.

 

I recommend a 2x Barlow to use with your 5 mm and 7mm Pentaxes. I like the 2x TeleVue because it's parfocal, very little refocusing needed. I use it with the 3.5mm and 5 mm Type 6 Naglers, in my 10 inch, it provides 575x and 820x. 

 

Seeing like that probably does happen much in the Midwest but with a 2x Barlow, you will be ready when it does.

 

Jon

[BillP]

In addition to what Jon points out in post #2, if one of the components is very dim then exact focus can also make the difference between seeing it and not seeing it.  So a dual speed focuser can aid greatly for this circumstance.

Edited by BillP, 25 February 2021 - 01:15 PM.

[Gschnettler]

Once again, thanks for all the advice! I do have a 2 speed focuser. So that’s taken care of.

I also have a 2X Orion Shorty Barlow. I don’t use it much because I prefer just having the right eyepiece. I can’t think of any scenarios where it’s been particularly useful in the several years I’ve owned it. I’m not sure if the “shorty” part of it implies any sort of compromise in performance. Is there much difference between a Barlow like the one I have and something like the Tele Vue offering? Or should I be looking at the Tele Vue powermate?

I also like the ideas here about a zoom eyepiece. What do you think of the Baader 8-24 zoom with the unusual looking 2.25x Barlow as a good option for double star viewing? With the Barlow that could get down to 3.55mm of eyepiece focal length which would result in a magnification of 420x - which seems pretty good for most situations.

[Bigzmey]

This is all fantastic information! Thank you all!

I’m mostly surprised to see recommendations for magnifications over 300. I thought that 300 was about the upper limit. To achieve that I would need eyepieces smaller than 5mm.

What do you think of the Paradigm 3.2mm?

There is also the much more expensive Delos 3.5.

And a Vixen SLV 4mm

Or I could stick with Pentax and get a 3.5mm. That might be the most attractive option since it would match up well with my Pentax 5 and 7mm.

What do you think?

Also, are there any good apps or websites that give you “seeing” predictions? I live in the Ohio River Valley. I can see the Ohio River from my house. Seems like that might be bad for seeing. They always talk about how smog and humidity gets trapped and hovers around this region. But, I’m also just a half day’s drive from beautiful West Virginia where my friends and I rent cabins in the mountains a few times per year where maybe the seeing is a lot better(?). If so, I want to be prepared for that so I don’t miss a good opportunity by not having the right eyepiece.

In my experience Paradigm 3.2mm suffer from excessive light scatter, I would not recommend it for tight doubles. My vote is for SLV 4mm, or you can get a good quality barlow and use it with 6mm Ortho or your XW 7mm.