46 replies to this topic

[Jon Isaacs]

Well, I did in fact get one last clear moonless night before the late winter Milky Way becomes unobservable. This time instead of using my 8-24 zoom for closeups, I used my Pentax XL's: 14, 10.5, 7, and 5.2 mm for 34X, 46X, 69X, and 92X, respectively. I didn't want to bother with a Barlow, and my 4-mm eyepiece is at my other home. In any case I don't think it would have helped much with any of my targets.

 

 

 

Tony:  A nice report. With a short focal length refractor, I normally use a full gamut of eyepieces, ranging from the 41mm Panoptic or an eyepiece like the 31mm Nagler to a 3.5mm wide field plus a 2x Barlow.  I always mix in some binary stars and the planets so the high magnifications are useful.  But they can help with DSOs as well.  The Blinking Nebula, the Eskimo Nebula show more at higher magnifications.  Bright globulars like M13 are better resolved at maybe 140x in an 80mm.

 

Jon 

[Terra Nova]

Just about a year ago I bought my first APO as a 70th birthday present to myself. I did it for a variety of reasons, including simply scratching an itch. I knew I'd always be dreaming of buying an APO if I didn't actually do so.

 

My choice was an AT80EDT on the grounds that I wanted the scope to be clearly superior to my very first -- the Tele Vue Ranger -- in every way except price and portability. Actually, in inflation-adjusted dollars, the AT80EDT is considerably cheaper than the Ranger was when I bought it 28 years ago -- which makes its far superior optical and mechanical quality all the more impressive. As a cute plus, the AT80EDT has exactly the same focal length as the Ranger (480 mm), meaning that with any given eyepiece it delivers the same magnification, but with a bit more aperture to back it up, and much less false color on bright objects.

 

On the other hand, the AT80EDT is nowhere close to the Ranger in terms of portability. It's small enough, but weighs more than twice as much, and requires a much beefier mount. Which may be a good thing, because I finally splurged for a Bogen 3046 tripod, which works far better than lighter tripods do for the Ranger. Eventually I think I will want a Go To mount for the AT80EDT -- or more likely two, a lightweight alt-az Go To for visual observing, and a serious EQ mount for imaging. But the Bogen 3046 is just about ideal for wide-field browsing, and still perfectly adequate at high power.

 

All this raises the question: what's an APO good for? Part of the answer is that APOs are ideal for attaching cameras and other instruments -- but I haven't gotten around to doing that yet. For the moment, I'm thinking strictly in terms of visual observing.

 

From one point of view, APOs are good for everything. From a more cynical point of view, they're good for nothing, due to their ridiculously small apertures. (I'm basically a Dob kinda guy.) With the hindsight of a year of (admittedly rather limited) experience, I'd say that they excel at two things: providing truly expansive low-power, wide-field views, and providing great views of bright stars and multiple-star systems -- within the limits of their apertures. Oh yes, and they're also great for viewing Venus. Not so great on the other planets, due to their tiny apertures, but since there's hardly any detail to see on Venus, small aperture isn't much of a limitation. Likewise for stars -- they show precisely zero detail in any telescope, no matter how big. But if you want to see diffraction rings, you can't do better than a small APO.

 

I spent a very enjoyable few hours a couple of nights ago on my first serious deep-sky session with the AT80EDT -- the kind where I actually record my observations, and look for objects other than the two or three hundred that I more or less know by heart. I tried all three of my two-inch eyepieces with the telescope, the 27-mm Panoptic, 30-mm UFF, and 40-mm Orion Optiluxe. I specially bought the 30-mm UFF as a companion for the scope, and indeed it proved to be the best of the lot for my purposes. The Optiluxe is a great finder eyepiece, but 12X is ridiculously low magnification for an 80-mm scope, especially given that my pupils now open only to 4.5 mm. The 27-mm Panoptic shows significantly fainter star and finer details than the 30-mm UFF, but at the cost of a much smaller true field of view. The difference in TFOV is much bigger than the numbers suggest, because I can see very nearly the entire field of the UFF in a glance, even while wearing glasses, whereas I have to crane my neck at weird angles to see the Panoptic's field stop.

 

I also viewed (or attempted) all the same targets with my Oberwerk 15x70 Deluxe binoculars. It was quite an instructive comparison, because those binos theoretically have almost exactly the same true field of view as the scope with the 30-mm eyepiece, slightly over 4 degrees. But again, I absolutely cannot see the whole field of view of the binoculars wearing glasses, and my astigmatism is really obtrusive at wide-open exit pupils when I don't wear my glasses. Also, it's much easier to fit the scope with filters, which mattered for some of my targets, notably the Rosette Nebula.

 

As is my custom, I was using the binoculars hand-held, so it's not surprising that I could see much finer detail with the scope. On the flip side, large, none-too-bright objects like M46 definitely had more presence in the binoculars. That's not surprising given that the binoculars two 70-mm objectives gather far more light than the scope's 80-mm objectives. And as we all know, two eyes really are better than one.

 

Overall, though, I'd have to say that I enjoyed wide-field observing a lot more in the scope than in the binoculars, due primarily to the 90-degree viewing angle. Oh, by the way, I was using an Amici prism. I have no desire to return to a conventional star diagonal, except maybe for splitting close double stars. I despise mirror-imaged views, especially at low power where the correlation between the naked-eye view and the view through the scope is so obvious.

 

For close-up views I used my Baader Hyperion 8-24 zoom, which I find complements the scope beautifully. I was observing the tail end of the winter Milky Way, in Monoceros, Canis Major, Puppis, and Hydra, which contains many bright clusters and nebulae that are well suited to small apertures. Even so, I kept thinking "gosh, I sure wish I had just a little more aperture." Any way you slice it, 80 mm isn't much. Nor is 100 mm, for that matter.

 

I ended the session just before the Moon rose by observing NGC 2903, the first of the great spring galaxies. It was nice enough, and perhaps even exhibited a hint of its bar structure. But I think I will put away the little refractor for galaxy season, and return to my 7-inch and 12.5-inch Dobs. Which, when all is said and done, are much more versatile instruments as far as visual observing is concerned. And certainly far superior for galaxies.

Your reasoning was identical to mine in late December of 2023 when I decided to basically trade-in my TV Pronto for a new AT80EDT. As lovely and charming as the little Pronto was, I have enjoyed my AT80EDT so much over the past year.

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[Terra Nova]

Well, I did in fact get one last clear moonless night before the late winter Milky Way becomes unobservable. This time instead of using my 8-24 zoom for closeups, I used my Pentax XL's: 14, 10.5, 7, and 5.2 mm for 34X, 46X, 69X, and 92X, respectively. I didn't want to bother with a Barlow, and my 4-mm eyepiece is at my other home. In any case I don't think it would have helped much with any of my targets.

And indeed, 60X is lower than optimal for most of those DSOs in an 80-mm APO. For instance, I got significantly better resolution of M46 and M93 at 92X than at 69X -- though M46 barely fit in the field of view at the higher magnification. NGC 2261, Hubble's Variable Nebula, was a more interesting case. I had seen barely any detail at 60X with the 8-24 zoom, but the 7-mm Pentax at 69X showed the comet-like structure clearly while still leaving the nebulosity quite bright. The nebulosity became surprisingly dim at 92X, but arguably showed more structure, especially when using averted vision.

 

I was using my 7-inch Dob side by side. It happens to have exactly the twice the AT80EDT's 480-mm focal length, allowing me to use identical magnifications in both scopes. I confirmed that for the brightest and coarsest of the clusters that I observed, such as M41 or M47, magnification makes much more difference than aperture. But when it came to M46, the bigger scope allowed me to see more stars at lower magnification, yielding a far more pleasing view. Moreover, NGC 2438, the superposed planetary nebula, was just sitting there in plain view through the 7-inch, whereas I couldn't make it out at all in the 80-mm scope. (Granted, I didn't really try all that hard.)

 

The difference in aperture is most obvious by far on nebulosity rather than star clusters. Hubble's Variable Nebula is gloriously bright in a 7-inch scope, and the aperture allows me to use all the magnification this object deserves without fading below visibility. Nonetheless, it has an ethereal beauty of its own in the smaller scope.

I’m a big fan of 5mm to 0.5mm exit pupils. I’m also a big fan of maximizing light throughput by minimizing layers of glass and not introducing an intermediate stage of refraction; and for those reasons, I’m not a big fan of barlows. I have several good ones but I seldom use them. The the AT80EDT, with it’s native 480mm f.l. gives me 160X with a 3.2mm eyepiece like the Paradigm Dual ED, and also 15X with a 32mm Plossl, a perfect 0.5 to 5mm exit pupil range. It’s also fun to use a 2” 42mm eyepiece and open it up to 11.4X and 7mm of exit pupil when sky and ground conditions are dark enough to allow it.

[Mike W]

Your reasoning was identical to mine in late December of 2023 when I decided to basically trade-in my TV Pronto for a new AT80EDT. As lovely and charming as the little Pronto was, I have enjoyed my AT80EDT so much over the past year.

I like your surveyors tripods too, so much that I just ordered a CST/Berger fiberglass (20lbs) for my new 102 f7 ED. I miss my TV102 but at my age don't want to buy another. I rarely use high powers anyway. With the 102 (714mm F/L) my 10mm Radian is all I need, maybe a six or 7mm? 24 pan will be my low power 29X. Not a fan of barlows either!

Edited by Mike W, 30 March 2025 - 11:56 AM.

[skyops]

 But the Bogen 3046 is just about ideal for wide-field browsing, and still perfectly adequate at high power.

 

 

*

 

What head did you mate with the 3046?

[Jon Isaacs]

I’m a big fan of 5mm to 0.5mm exit pupils. I’m also a big fan of maximizing light throughput by minimizing layers of glass and not introducing an intermediate stage of refraction; and for those reasons, I’m not a big fan of barlows. I have several good ones but I seldom use them. The the AT80EDT, with it’s native 480mm f.l. gives me 160X with a 3.2mm eyepiece like the Paradigm Dual ED, and also 15X with a 32mm Plossl, a perfect 0.5 to 5mm exit pupil range. It’s also fun to use a 2” 42mm eyepiece and open it up to 11.4X and 7mm of exit pupil when sky and ground conditions are dark enough to allow it.

 

We all seem to observe differently, have different strategies.

 

In my experience, eyepieces like Plossls do not have enough glass to get all the light going where it is supposed to go at F/6.  In the center of the field it's ok but out towards the edge, not so hot.

 

I frequently use Barlow's, often 160x is not enough magnification.. 

 

An 80 mm F/6 with a 32 mm Plossl provides a 3.3° TFoV.  The reason I own an 80 mm F/6 is to get the really wide views it offers. 5.0° with the 31 mm Nagler, 5.5° with the 41 mm Panoptic. These are 6 element eyepieces with matched coatings.

 

Jon

[Tony Flanders]

Oh, here are a couple of equipment questions asked in this thread that I neglected to answer. Not intentional, but I tend not to remember model numbers, and by the time I looked them up I had gotten distracted.

 

I'm using the Baader 2-inch Amici prism -- the regular one, not the T2 nor the Deluxe. And the Bogen 3046 tripod with the 3047 head, scope mounted sidewise. Works beautifully.

[Jon Isaacs]

Oh, here are a couple of equipment questions asked in this thread that I neglected to answer. Not intentional, but I tend not to remember model numbers, and by the time I looked them up I had gotten distracted.

 

I'm using the Baader 2-inch Amici prism -- the regular one, not the T2 nor the Deluxe. And the Bogen 3046 tripod with the 3047 head, scope mounted sidewise. Works beautifully.

 

 

A couple of photos of an AT-72ED on a Bogen 3046-3047. 

 

 

 

I use star diagonals for everything including terrestrial. The left-right reversal never bothered me. 

 

Jon

[Oldfracguy]

Oh, here are a couple of equipment questions asked in this thread that I neglected to answer. Not intentional, but I tend not to remember model numbers, and by the time I looked them up I had gotten distracted.

 

I'm using the Baader 2-inch Amici prism -- the regular one, not the T2 nor the Deluxe. And the Bogen 3046 tripod with the 3047 head, scope mounted sidewise. Works beautifully.

Thanks, Tony.  We always appreciate your insight after having been an observer for so long.

[areyoukiddingme]

I also prefer to use my reflectors, but I can think of a few things where my small refractors 80, 92, 101mm excel.

 

First would be Andromeda galaxy under dark, transparent skies. Being able to see dust lanes and the satellite galaxies in the wide field is something that can't be replicated in a bigger reflector.

 

Second, when an interesting comet shows up, and you don't know exactly where to look so you pan about until it shows up. My 80mm has been very handy for that on a couple of occasions, and I hope for a few more.

 

Third, as others have brought up, it's easy to just pick one up and head out the door for a quick look. I use mine also for checking out what's going on on the local mountain, birds, paragliders . . . 

 

It's also good for a quick assessment of the seeing and determining whether I'll bother to grab a bigger reflector.

[Terra Nova]

I’m a big fan of 5mm to 0.5mm exit pupils. I’m also a big fan of maximizing light throughput by minimizing layers of glass and not introducing an intermediate stage of refraction; and for those reasons, I’m not a big fan of barlows. I have several good ones but I seldom use them. The the AT80EDT, with it’s native 480mm f.l. gives me 160X with a 3.2mm eyepiece like the Paradigm Dual ED, and also 15X with a 32mm Plossl, a perfect 0.5 to 5mm exit pupil range. It’s also fun to use a 2” 42mm eyepiece and open it up to 11.4X and 7mm of exit pupil when sky and ground conditions are dark enough to allow it.

Correction, 150X with the 3.2mm Paradigm Dual ED eyepiece, 160X with the 3mm Delite to get a 0.5mm exit pupil.

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While the 3.2mm Paradigm Dual ED eyepiece is a nice ocular, 3mm Delite is my perfect high power eyepiece for my AT80EDT and also with the AT90CFT, also F6, where it yields 180X and the same 0.5mm exit pupil. The beauty of 0.5mm is that there is still plenty of light so it's a nice bright image, and still easily within Dawes resolution limits so it's all useful magnification with no hint of image breakdown. In minimizing eyepiece weight for easy tube balancing, I find that my 1.25" 30mm Ultima provides a nice low magnification alternative (16X and 18X in the AT80EDT and AT90CFT respectively, with  5mm exit pupil in each. The 35mm Ultima is another nice low magnification/ widefield option in the 1.25" eyepiece caliber. Both are long out of production but can be found on the used market and are valued members of my eyepiece collection.

Edited by Terra Nova, 01 April 2025 - 03:40 PM.

[ABQJeff]

Great discussion on small apo’s.  After much deliberating in purchasing, and two years of use, I am very happy with my 80mm F/6.  It is a great small travel scope (the do everything camp) and a great little wide field scope.  One thing not mentioned is it provides full disc solar H-a with a Quark and binoviewers.

Edited by ABQJeff, 03 April 2025 - 01:33 AM.

[Tony Flanders]

Great discussion on small apo’s.  After much deliberating in purchasing, and two years of use, I am very happy with my 80mm F/6.  It is a great small travel scope (the do everything camp) and a great little wide field scope.  One thing not mentioned is it provides full disc solar H-a with a Quark and binoviewers.

You don't need an APO to do H-alpha viewing. In fact you don't even need an achromat -- a singlet lens will do nicely.

[Tony Flanders]

I use star diagonals for everything including terrestrial. The left-right reversal never bothered me.

Parity reversal doesn't bother me for viewing birds and animals. They likely do have dominant limbs just like us, but I sure can't tell which is which by looking at them.

However, parity reversal bothers me hugely for viewing the sky at 16X, where there's a direct and obvious correlation between what I see with my unaided eyes and what I see through the eyepiece. And even at higher magnifications, I'm quite familiar with the appearance of most of the major deep-sky objects, and I find it disconcerting to see them mirror-reversed.

Finally, even after decades of experience, I constantly find myself going in the wrong direction while attempting to star-hop with a parity-reversed image.

I suspect that people's ability to handle parity-reversal varies widely, and is largely innate. Yes, I have learned to deal with it better than I used to, but it will never be effortless as the 180-degree rotation of a Newt is (for me).

[Terra Nova]

Parity reversal doesn't bother me for viewing birds and animals. They likely do have dominant limbs just like us, but I sure can't tell which is which by looking at them.

However, parity reversal bothers me hugely for viewing the sky at 16X, where there's a direct and obvious correlation between what I see with my unaided eyes and what I see through the eyepiece. And even at higher magnifications, I'm quite familiar with the appearance of most of the major deep-sky objects, and I find it disconcerting to see them mirror-reversed.

Finally, even after decades of experience, I constantly find myself going in the wrong direction while attempting to star-hop with a parity-reversed image.

I suspect that people's ability to handle parity-reversal varies widely, and is largely innate. Yes, I have learned to deal with it better than I used to, but it will never be effortless as the 180-degree rotation of a Newt is (for me).

That’s why my Baader T-2 90° Deluxe Astro-Grade Amici Prism Diagonal with a 2” nosepiece and Baader Click-Lock eyepiece holder has a semi-permanent home on my AT80EDT. 

[kmparsons]

I use a TV Barlow with my 18.4mm and 15mm DeLites, and the results are fine. However, an excellent alternative to Barlows is the TV 3-6mm zoom. For short FL refractors, it is practically a necessity. 

[Jon Isaacs]

Parity reversal doesn't bother me for viewing birds and animals. They likely do have dominant limbs just like us, but I sure can't tell which is which by looking at them.

However, parity reversal bothers me hugely for viewing the sky at 16X, where there's a direct and obvious correlation between what I see with my unaided eyes and what I see through the eyepiece. And even at higher magnifications, I'm quite familiar with the appearance of most of the major deep-sky objects, and I find it disconcerting to see them mirror-reversed.

Finally, even after decades of experience, I constantly find myself going in the wrong direction while attempting to star-hop with a parity-reversed image.

I suspect that people's ability to handle parity-reversal varies widely, and is largely innate. Yes, I have learned to deal with it better than I used to, but it will never be effortless as the 180-degree rotation of a Newt is (for me).

 

I suspect that it's a learned response. There is nothing innate about which direction to push the rear of a telescope to move the image in a given direction.

 

With a RACI finder in a Dob, I always go in the correct direction. That's because I don't the natural thing, pushing the telescope towards the object of interest.

 

With a RACI diagonal, I do poorly but am fine with star diagonal. I think it's just a learned response.

 

As far as star hopping, flipping the chart right to left in my mind it pretty easy and star hopping in a short focal length refractor is not like trying to put a faint galaxy near the center of the field at 280x.

 

Jon

[Tony Flanders]

I use a TV Barlow with my 18.4mm and 15mm DeLites, and the results are fine. However, an excellent alternative to Barlows is the TV 3-6mm zoom. For short FL refractors, it is practically a necessity. 

I borrowed a friend's TV 3-6 zoom for a while. The image quality is excellent, and the small size is delightful, but I find it exceedingly unpleasant to use due to the short eye relief. I find a Barlow together with an 8-24 zoom to be much more practical.

[Tony Flanders]

I suspect that it's a learned response. There is nothing innate about which direction to push the rear of a telescope to move the image in a given direction.
 
With a RACI finder in a Dob, I always go in the correct direction. That's because I don't the natural thing, pushing the telescope towards the object of interest.
 
With a RACI diagonal, I do poorly but am fine with star diagonal. I think it's just a learned response.
 
As far as star hopping, flipping the chart right to left in my mind it pretty easy and star hopping in a short focal length refractor is not like trying to put a faint galaxy near the center of the field at 280x.

I think your post proves my point. For you, mirror reversal is a learned response. For me, it will always be a struggle.
 
It's flipping the chart that's hard for me, not physically pushing the telescope. I can track objects quite easily in a refractor with a conventional star diagonal. It's star-hopping that's the problem.

[Jon Isaacs]

I think your post proves my point. For you, mirror reversal is a learned response. For me, it will always be a struggle.
 
It's flipping the chart that's hard for me, not physically pushing the telescope. I can track objects quite easily in a refractor with a conventional star diagonal. It's star-hopping that's the problem.

 

What I find a problem:  A star diagonal that is not mounted vertically.. Flipping a chart right-left is straightforward.  But if the diagonal is at some other angle, then flipping the chart is not easy, the sky is flipped at some arbitrary angle.  

 

It occurs to me that a significant difference may exist between us.  I always use electronic charts, the sky is always correctly oriented for the time and location.  So all I have to do is flip the image left-right.  If one is using paper charts, you first have to orient the chart and the orientation is not so obvious. I know you use SkySafari at times but I believe you prefer paper charts.

 

Jon

[azure1961p]

I also prefer to use my reflectors, but I can think of a few things where my small refractors 80, 92, 101mm excel.

 

First would be Andromeda galaxy under dark, transparent skies. Being able to see dust lanes and the satellite galaxies in the wide field is something that can't be replicated in a bigger reflector.

 

Second, when an interesting comet shows up, and you don't know exactly where to look so you pan about until it shows up. My 80mm has been very handy for that on a couple of occasions, and I hope for a few more.

 

Third, as others have brought up, it's easy to just pick one up and head out the door for a quick look. I use mine also for checking out what's going on on the local mountain, birds, paragliders . . . 

 

It's also good for a quick assessment of the seeing and determining whether I'll bother to grab a bigger reflector.

 

 

So true,

 

When I got my Ranger back for Hale Bopp, I used it to test seeing rather then dragging out the long 8 for Pickering 5 again. 

 

As much too, at the end of a long days or nights work, it sooooo much easier to set up the small refractor, quick cool down and pristine views rather than setting up a 35lb. 7 foot long ota . 

 

And the refractor just has its own observer vibe.  The reflector beats it on everything ultimately but there's something sweet and less hassle on those nights you set up the refractor.

 

Pete

[Tony Flanders]

I've had three clear evenings since I last posted -- two short ones when the Moon was up, and a longer one last night without the Moon.

 

I spent the two moonlit sessions at high power, viewing single stars, double stars, and the Moon itself. I also did my first star tests; I don't know why it never occurred to me to do that when I first used the scope. All this high-power work was revealing.

 

First of all, it's a little pig-headed to use an Amici prism for high-power work. It didn't degrade the view of the Moon much, but it did cause some strange and undesirable artifacts on double stars, above and beyond the obvious line. And it causes some extremely strange star tests.

 

Second, I never got a clean star test. The rings inside focus were as tidy as could be, but it was a sloppy mess outside focus, even after I switched back to the conventional star diagonal. The star test got better as time went on, which leads me to suspect the poor results were due to inadequate cooldown. But it was still very far from perfect an hour after I brought the scope out. That suggests that the 80-mm triplet actually has worse thermal characteristics than my 7-inch Dob, which is disappointing.

 

For the moonless session I continued my Messier survey, trying to take Jon's advice and experiment with more magnifications. Instead of relying on the 8-24 zoom as my workhorse I used the same set I use with my 12.5-inch Dob: 27 mm Panoptic, plus Pentax XL in 14, 10.5, 7, and 5.2 mm focal lengths. That yields 18X, 34X, 46X, 69X, and 92X.

 

I viewed all the Messier galaxies (and one planetary) in UMa and Leo, plus the northern Virgo Cluster. And a few non-Messiers thrown in, most notably NGC 3384 and 3628. Unsurprisingly, 18X was useful only for the big view -- and it was a bit low even for that. Once I'd found all the galaxies at higher magnifications, I could also see then when I backed down to 18X, but the fainter ones certainly weren't obvious at such low magnification. So I ended up doing most of my star-hopping at 34X, which revealed all the Messier objects effortlessly.

 

It's very interesting progressing from 34X to 92X on any given galaxy. In the case of M82, the results were straightforward; the higher the magnification, the more detailed the view in every way. The two main concentrations were obvious at 92X, but I could see only one at lower magnifications, and that with difficulty. But M82's surface brightness is off the charts as far as galaxies are concerned.

 

In most cases, it was a tradeoff between seeing a relatively bright but feature-poor view at 34X and 46X versus scanning a much dimmer view with averted vision at 69X and 92X. If I had to pick just one of those magnifications for the entire bunch, it would be 69X with the 7-mm eyepiece for sure.

 

To some extent my take-home for galaxy observing with this scope is that it's hardly worth messing with individual eyepieces when the Baader 8-24 zoom comes so close to doing the best possible job -- usually at 8 mm, but not infrequently at 12 mm or even lower.

 

I also ended up feeling a bit frustrated that there was obviously more detail to be seen. But there's a lot of Messier objects and not many clear nights, so I cannot dawdle forever if I want to complete the Messier survey in one year. Also, it seems a tad silly to be beating my head against faint galaxies with an 80-mm scope when I could easily pull out my 7-inch Dob and see far more detail with no effort at all. But I knew that beforehand; it's part of the rules for this particular game.