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ATX vs ATS with astro eyepiece, for occasional astronomy

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Old Sunday 8th March 2020, 18:30   #1
mbb
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ATX vs ATS with astro eyepiece, for occasional astronomy

The current bad weather during the weekends, and some outdoor working to the house getting priority during dry/sunny moments, is resulting in my spotting scope getting little use these weeks, sadly enough. However, during clear nights, I'm amazed at what I can see of the moon with my ATX65. There really some magic to it.
It triggers some curiosity for some occasional 'astronomy' or just night sky contemplation and I'm wondering: what is the big advantage of astro-eyepieces in spotting scopes?
Is it (just) an increased magnification? (They are labelled based on 'mm', what makes me wonder how to compare them to the 25-60x of the ATX.)

I realize I cannot put an astro-eyepiece on my ATX. I didn't think about that when buying it, when I came across a great second hand offer for it.
(I also realize that the 65mm diameter of my ATX is not a lot, but that is a choice considering its size/weight advantage.)

What extra would an ATS (or other spotting scope) + astro-eyepiece offer more for astronomy?
Would it be comparable to adding the Swarovski 1.7x extender in an ATX setup?
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Old Sunday 8th March 2020, 19:00   #2
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Astronomy is just so very different from earth observations, which shifts the priorities.
The moon is big and bright, so it still falls within the scope of earth observation, but the planets transition to astronomy, small, need tracking and really hard to see clearly unless the atmosphere is very kind.
After that, it is stars and nebulae, the former just points of varied colors, the latter gray on black images if you have good seeing. That generates aperture fever, because more light makes a more visible image.
Aperture is not the key for the ATX-65 and frankly it is not for the ATX-95 either. An astronomy telescope that more or less is a counterpart to the ATX would be an 8"or 11" Meade or Celestron. But if you stick to the moon and the planets, the ATXs are wonderful tools. They allow a glimpse at the splendors of the skies while remaining thoroughly practical tools for birding here on earth.
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Old Sunday 8th March 2020, 19:19   #3
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I am not familiar with spotting scopes used for birding, so I do now know the details of which eyepieces can be put on what spotting scope (which depends mostly on the mechanical construction), but the overall principle is simple: the magnification is the ratio of focal lengths of the telescope and the eyepiece - that's why you see eyepieces marked in mm, it's so that people can determine the magnification for their particular telescope. In common amateur astronomical equipment, the mechanical interfaces are standardized, so you can put basically any eyepiece to any telescope if needed.

Your ATX65 seems to be a 65-mm telescope, which is on the small side for astronomy when it comes to diameter. The diameter determines both maximum practical magnification, which tends to be around 2x the diameter in mm IF the optics is limited mainly by diffraction (can be less if color, spherical or other aberrations are less compensated for), and the amount of light collected, which tells you the faintest objects you can look for.

The magnifications available to you are reasonable also for astronomy. Maybe a shorter eyepiece (with higher magnification) would allow you to get a better look at the Moon and the planets but I have no idea whether the telescope's optics would support that well. You can also opt for even less magnification - for brighter views of extended objects - the lower limit being the size of you eye pupil, which varies between 7 mm for young people and 3 mm for the old - and you don't want the exit pupil to be larger and that's given by the diameter of the telescope divided by magnification. So for a 65mm telescope, a young person would benefit from a 10x magnification, while for older folks, the 25x available is broad enough already. But for a 65mm telescope, there is not that much to target here.

The idea expressed in the previous reply that you "need" tracking for planets is misinformed - especially at magnifications attainable with these small telescopes, the Earth rotation is not a problem for visual observations. More important is to have a tripod or astronomical mount with movement smooth enough to be able to track the planet by hand without much vibration.

What is very correct in that reply though is that if you really get into astronomy, you are gonna long for a larger telescope. To put things in perspective, mine has a diameter of 500 mm :)
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Old Sunday 8th March 2020, 19:24   #4
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Quote:
Originally Posted by mbb View Post
...
I realize I cannot put an astro-eyepiece on my ATX.
...
You can use astro-eyepieces on the Swaro X - http://www.pt-ducks.com/cr-telescope..._X_derivations - for birding, I found a compact straight version erector but still didn't update the page since I'm waiting for some special adapters at almost 1 year... One of the good things of it is that I can use my Ethos 17 without vignetting...

With astro-eyepieces you can choose the magnifications and AFOVs you want.
For estimating the magnification you divide de focal length of the scope by that of the eyepiece - see some birding experience at http://www.pt-ducks.com/cr-telescopes.htm

Although I'm not a astro guy, for occasional astro observation the 1.7x extender is very nice and, compared to astro-eyepieces on spotting scopes, you only are "limited" to the AFOVs of the eyepiece module and 1.7x magnification increase jumps of the extender, but you gain in compactness and easy to use.
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Old Monday 9th March 2020, 16:47   #5
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mbb,

For astronomy, the darkness of the sky is more important than the scope, except for the Moon and Jupiter, Saturn and Mars.

On Jupiter with a good 65mm scope two equatorial bands should be easy and possibly 4 belts seen.
4 moons easily seen.

With a very good, dark sky 5 Saturn moons might be seen, but really one needs, say, a 95mm good spotter for this.
Saturn's rings and maybe the Cassini division.
Vague disc detail.

Mars will only show detail when close.

Venus shows a phase, as maybe Mercury also.
Uranus might just show a small disc.
Neptune probably needs something bigger.

The Pleiades, Orion nebula, some globular clusters, double stars etc. will be seen with 65mm aperture.

I sold my 520mm aperture scope as I cannot use it nowadays. Too big.

A 200mm Dobsonian is probably the best and cheapest introduction to astronomy.

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Old Monday 9th March 2020, 19:17   #6
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A 200mm Dobsonian is probably the best and cheapest introduction to astronomy.
Hi,

this is very good advice. A chinese 8" dobsonian is not much more than a 1.6x extender for the ATX and will show so much more than a spotter.
Plus you can expect diffraction limited optics at least...

Or learn to star-test with an artificial star (100ft or 30m distance should be plenty for a 8" f6) and buy a used example in person for even less...

Joachim
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Old Saturday 14th March 2020, 23:05   #7
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Post

Thank you all for all the replies and info! There seems to be a lot(!) more for me to read about

If I understand correctly, and please correct me if I’m wrongly over simplifying things(!?):
  • even a (relatively) ‘cheap’ but way bigger ‘dobsonian’ would allow me to see a lot more and be better investment than the Swarovski magnifier. However, I would indeed probably stay with a 200mm. I’ve looked up their sizes and I think it would require some negotiations bringing that home :) Still, it is something I might consider in the future if I’d want to ‘dive further into space’, but I’ll probably start with the spotting scope in the meantime and maybe see if I could find someone with such a Dobsonian, to see how much what I could see through it ‘triggers’ me or makes me ‘dream’ at the stars
  • if I want to use a more ‘portable’ spotting scope, there is ‘relatively’ little added value in moving to a bigger spotting scope (e.g.85mm, as 95mm scopes are too heavy and expensive for me) or using astro eyepieces on such spotting scopes. I have the impression I must be missing something considering the number of posts referring to putting astro eyepieces on spotting scopes. Or is that mainly because astro eyepieces used to be better while current alpha eyepieces like the ATX are now great enough?


@David: thank you for the links! I still have to go through the impressive amount of information on your webpages. It looks like you have tested many more options that I even knew existed. I have to admit, based on the pictures of the setups, the only setup I might consider would be the one with the 90degree angled prism, resulting in a short enough, and angled setup. The ease of use you refer to is important to me. Apart from that ease of use, do you notice a considerable advantage for the astro eyepieces (image quality, brightness or FOV) compared to the ATX eyepiece, with or without 1,7 magnifier?
You also say “With astro-eyepieces you can choose the magnifications and AFOVs you want.” while with the ATX eyepiece and Swarovski magnifier you are only “ "limited" to the AFOVs of the eyepiece module and 1.7x magnification increase jumps”. Do you reach a much better FOV with those astro eyepieces than with the ATX eyepiece at the same magnifications, with or without magnifier? Or do you mainly see an advantage of being able to have lower magnifications (<25x) or higher ones (>60x)?

I have to admit that a larger FOV would seem helpful to orient myself at the night sky
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Old Sunday 15th March 2020, 17:16   #8
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Hi,

I would strongly recommend to find a stargazing club and join them for an observation night or go to a telescope meeting (well, ok, the latter maybe next year, those this spring have all been cancelled lately due to the plague).

And yes, certain astro EPs show quite a bit more field of view than your spotter. If a spotter has a wide field EP, that usually means 70 degrees of apparent field of view or thereabouts.

For astro EPs there's many which offer 82 degrees - which happens to the field where the field stop becomes invisible for most people without moving their eyes - thus creating that window into space effect.

But there is also models with 90, 100 or even 120 degrees of afov - to use the full field of those you have to move your eye around quite a bit - I personally am fine with 82 degrees.

Also a spotting scope can only take 1.25" astro EPs at best and will often vignette with some of the wides EPs available in 1.25" like the 24mm Panoptic and clones. And for such a small instrument one would also like to use long widefield eyepieces with a 2" barrel for really wide field views - because that's what a small instrument is good at. For higher magnifications, a larger instrument will always be better.

Joachim

Last edited by jring : Sunday 15th March 2020 at 17:23.
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Old Sunday 15th March 2020, 17:18   #9
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Mbb,

With a high power eyepiece on a spotting scope, say 100x, astro eyepieces like Naglers or clones give 82 or 84 degrees apparent field and some give 90, 100 or 110 degrees. This is way bigger than spotting scope eyepieces.
But the size of the prisms and field stops limit these large fields to short focal length high power eyepieces.

A 200mm Dobsonian will show way more than a spotting scope just because it is bigger aperture.
It will show detail on Jupiter, some detail on Saturn and plenty of detail on Mars when close.
6 moons of Saturn. However, Saturn and Jupiter are currently low in the sky, so not well placed.
It will show Neptune's disc, numerous planetary nebula, globular clusters, galaxies etc. so long as you have a dark sky.

And the price is low compared to top spotting scopes and eyepieces.

But it takes dedication to be out at night.

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Old Sunday 15th March 2020, 17:24   #10
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mbb,

Though not an amateur astronomer, I do take an occasional look at the night sky with my binoculars and birding scopes and think I should straighten out a few optical misconceptions.
If you want wide angle views, use binoculars. Spotting scopes are unsuitable for use at lower magnifications than the minimum offered by the manufacturers' eyepieces.
I have experimented with a variety of astro eyepieces in my birding scopes (ATM 65HD & Kowa 883) and the longest focal length I have is a 28 mm Edmund RKE, which gives about 16,5x and 18x respectively but with only about 50° AFOV. The field stop is about as large as the plane glass sealing windows in the scope bodies, so even a 32 mm Plössl (for lower magnification) or a 24 mm Panoptic for wider AFOV would vignette.
The 4 mm and 5 mm exit pupils are quite pleasant but would only be of use under the very darkest of skies.
It's possible that the simpler optical constructions of Plössls or RKEs would show less flare than the spotting scope eyepieces but the latter (in my case, Swarovski 30x W and Kowa 25-60x zoom) are designed specifically for the scopes' field curvature and show much better edge correction than any astro eyepiece.
Trying to adapt an ATX/STX objective for higher magnifications (except for David's specific application) is IMO not a good idea. The glass path in the prisms is part of the optical construction and eliminating or altering this will result in increased spherical and chromatic aberration.
Enjoy your ATX 65 as it is. What it can do, it does pretty well.

John
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Old Thursday 26th March 2020, 14:24   #11
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65mm is limited aperture for astronomy but that doesn't mean you can't enjoy the night sky or the moon using a small scope. The 25-60x eyepiece already gives you a pretty decent magnification range but at the upper end your already getting to a small exit pupil. I would enjoy your scope for what it is, with this aperture there really is little point in trying to push the magnification much higher except for maybe viewing the moon or planets but with only 65mm of aperture its just not worth it.

I used an 85mm Televue scope for many many years. I had eyepieces covering - 15x-200x. It really excelled at wide field deep sky views and for lunar observing. For planets i.e Jupiter/Saturn/Mars/Mercury my experience is rarely would seeing support going much above 120-140x. With 120-140x magnification for sure you see some details but its pretty challenging and the size of Jupiter/saturn is still pretty small and so it takes careful observation to really see the details. If planets or deep sky are what you want to look at then your money would be much better spent on a telescope with much greater aperture. For sure the optics of spotting scopes can support higher magnification but quite simply with this small aperture you just run out of light and lose contrast/detail etc. An additional factor is the more you push the magification the more critical it becomes that the scope is on a really solid mount. At higher magifications trying to see the finest details is quite challenging if your not using a driven mount to keep the object in a fixed location to allow detailed study.

The 1.7x is an option and I would go down that route rather than trying to use astro eyepiece but I would bet you find it has limited value except for lunar observing. Pushing the magificiation high for deep sky is of limited value with only 65mm of aperture. As I pointed out above even adding the 1.7x is really going to test the stability of your mount and you may find you get frustrated with working at higher magnifications.

My advice, take your small spotting scope and a pair of binoculars to really really dark sky and just enjoy the views, you will be surprised what it can do. 65mm scope is a gem, great for occasional nightsky and fantastically portable for daytime viewing. If a telescope is what you want, get the biggest dobsonian/aperture you can afford and are prepared to handle as this will give you the best views and value for money.

Last edited by dmcharg : Thursday 26th March 2020 at 14:48.
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Old Yesterday, 11:28   #12
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Thank you a lot for the great and helpful input and advice!

I do really like my spotting scope for its impressive image and build quality and size and will continue enjoying as such as much as possible! (I have to admit sometimes I wonder if I shouldn't have gone for a 80-85mm and/or for a cheaper model/series, notwithstanding the very good deal I got for it second hand.)
It's just a pity that, now that the weather is better, we're in a pseudo/kind of-lockdown, resulting in not using him again. But that is really only a very minor and temporary problem considering the current situation and the challenges many are facing now.

I won't buy the 1.7x extender, at least unless I'd stumble across a véry good second hand deal and as long as I stay with the 65mm objective. For birdwatching, I've (almost) never been wanting for more than the 60x extreme of the zoom, even in bright daylight. And if it is only for night-use, I'd apparently better invest that money in a 200mm Dobsonian or so if I were to get more serious about it.

Quote:
Originally Posted by Tringa45 View Post
mbb,
I have experimented with a variety of astro eyepieces in my birding scopes (ATM 65HD & Kowa 883)
...
The 4 mm and 5 mm exit pupils are quite pleasant but would only be of use under the very darkest of skies.
John
Quote:
Originally Posted by dmcharg View Post
65mm is limited aperture for astronomy but that doesn't mean you can't enjoy the night sky or the moon using a small scope. ...
I used an 85mm Televue scope for many many years. I had eyepieces covering - 15x-200x.
Would you say that a 80-85mm would already give a meaningful advantage for night-sky watching compared to a 65mm (with a 25-60x magnification range), or only negligibly little difference, for that purpose?
(Just to know if I should consider the option to switch to a 80-85mm solely based on my daytime/birdwatching use and, for night-use, just don't bother about it and only consider a larger e.g. 200mm Dobsionian if I'd get more serious about is.)
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Old Yesterday, 14:14   #13
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Any larger aperture gives incremental advantages assuming similar quality.

Astro telescopes don't need erectors or prisms, so the quality can be better than spotting scopes.

Even a 150mm Dobsonian will outperform an 85m spotting scope.

B.
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Old Yesterday, 16:46   #14
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Would you say that a 80-85mm would already give a meaningful advantage for night-sky watching compared to a 65mm (with a 25-60x magnification range), or only negligibly little difference, for that purpose?
(Just to know if I should consider the option to switch to a 80-85mm solely based on my daytime/birdwatching use and, for night-use, just don't bother about it and only consider a larger e.g. 200mm Dobsionian if I'd get more serious about is.)
I have used various small refactors/scopes ranging from 60 up to 100 and much larger telescopes. As you already have one scope in this aperture range I wouldn't switch to an 80-85mm scope, its just not worth it for the small incremental upgrade for daytime or night time. Your money is better spent elsewhere.

Your ATX65 excels at daytime viewing, if you want to get serious about the night sky then buy 200mm+ telescope. Then you have the best of both worlds and an instrument best suited to its applications. In my experience the differences between scopes in the 60-85 range is often over stated and this especially so under the night sky. I think many people would struggle to tell the difference in the view thru a 65 vs 85 scope under the night sky. For wide field deep sky the incremental increase in aperture will give you a little more little gathering but its a tiny difference and you will see no difference with open clusters, globular clusters or galaxies. For the moon you have plenty of light so again you will see little difference. For the planets even with 85 you are still limited by aperture and available light.

Last edited by dmcharg : Yesterday at 21:11.
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Old Yesterday, 21:04   #15
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Just to add to above depending on your night sky interests i would also give some serious consideration to a good pair of 70-80mm binoculars as these would be a nice complement to your 65mm scope. I have used various telescopes over the years and many of my most memorable nights are those with binoculars under nice dark skies. Whilst the binoculars don't give you high magnification or large aperture of a big telescope they more than make up for it with 2 eyed viewing. I would encourage everyone interested in astronomy to get a 70-80mm binocular before buying a telescope as its a great way to find your way around the night sky. Another benefit of binoculars rather than a telescope is you are more likely to use them and they are much easier to transport to darks skies. Panning around a really dark night sky with two eyes/binoculars is really an experience everyone should have. I was down under many years ago and the experience of panning the southern milky way with a pair of 70mm binoculars is still by far the best night sky experience i have ever had.

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Old Today, 08:29   #16
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Regarding a Dobsonian telescope a few things to bare in mind.

For sure a 200mm+ dobsonian is the best value for money and will easily out perform any small scope. But a telescope is no where near as portable and this is why many prefer the instant/portability of a small spotting scope, refractor or binoculars. In addition a dobsonian telescope is a mirror configuration and as such these mirrors need to be correctly aligned/collimated to really get the best performance and this is especially true if you want to get the best planetary views. So its worth investing the time to learn how to collimate the telescope.

Don't forget to factor in buying a few good eyepieces as this can make the world of difference as the eyepieces that come with many dobsonians are pretty poor. You don't have to spend a fortune but with many dobsonian telescopes you will find the quality of the mirror is pretty decent and with correct collimation and a decent eyepiece(s) it will make a big difference.

A further point to consider is that these mirrors need time to reach thermal equilibrium with the surroundings. A 200mm+ mirror/chunk of glass is quite considerable. In order to provide the best possible views generally speaking you need to put the scope out a little in advance of observing to allow this and the greater the temperature difference or the bigger the scope the more time is required.

So its all about what works for you - binoculars, spotting scope, refractor telescope, large aperture dobsonian each has its pros/cons. I think a lot depends on your local weather as well, if you are lucky enough to live somewhere with plenty of clear skies then you will get much more use out of what you buy. Here in scotland we have so few clear skies that binoculars are my preferred instrument these days simply because i can setup and use them in 5 minutes and hence i can take advantage of clear skies when the clouds clear which isn't very often :-(.

Last edited by dmcharg : Today at 10:05.
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