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Short Tube 80 but better optics?

Beginner Equipment Refractor Mount
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#1 etnik

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Posted 27 November 2021 - 08:42 AM

Hello! I was wondering whether there was a telescope similar in shape, size, weight, to the Short Tube 80, but higher optical quality? Willing to spend $1500 on the whole setup, mount and OTA, plus like $100 of accessories, will this work?
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#2 AstroDog77

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Posted 27 November 2021 - 09:09 AM

The AT80EDT available from the sponsor site has better optics for sure at the same size. I have the AT72EDII, so less aperture but it's still a really nice portable scope. I use it with an iOptron Cube mount but I think the AT80EDT would be pushing the Cubes limits, but if a little less aperture with solid optics is acceptable I would consider that setup. The Cube A can be used in Alt/Az or equatorial modes and is easy to get going with the built in GPS. They would probably run about $900 combined giving you plenty of budget for decent accessories (diagonal, EPs, finder).


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#3 SeattleScott

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Posted 27 November 2021 - 10:05 AM

To get better optics than the ST-80 you have to get an 80mm Apo. There are quite a few options. They typically aren’t F5 though as they couldn’t correct for CA very well at that F ratio. A number could be reduced to F5 for imaging purposes at least. The shortest tend to be F6. The most expensive one without exceeding your budget is probably the Vixen SD81S, highly regarded.

Note these scopes will be considerably heavier than a ST80.

Scott

#4 Jon Isaacs

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Posted 27 November 2021 - 10:27 AM

To get better optics than the ST-80 you have to get an 80mm Apo. There are quite a few options. They typically aren’t F5 though as they couldn’t correct for CA very well at that F ratio. A number could be reduced to F5 for imaging purposes at least. The shortest tend to be F6. The most expensive one without exceeding your budget is probably the Vixen SD81S, highly regarded.

Note these scopes will be considerably heavier than a ST80.

Scott

 

The Vixen has a focal ratio of F/8, very different than the ST-80 at F/5 in terms of size and optics. 

 

This photo shows an ST-80 with a 2 inch focuser and an Astro-Tech AT-80 LE (F/6).

 

IMG_27112021_072340_(1024_x_700_pixel).jpg

 

The AT-80LE is slightly longer and in use will be longer still.  It's short length is because it has a sliding dew shield.  It's heavier than the ST-80 but optically much better, it has a FPL-53 Doublet objective.  They are no longer available but there are other 80mm F/6's with ED/apo objectives that would be similar in size. 

 

The Vixen is 23 inches in length, the AT-80LE is 15 inches.  

 

Jon


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#5 cookjaiii

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Posted 27 November 2021 - 11:10 AM

For small  lightweight refractors of high quality, check out the Borg line of telscopes.  I have an 89mm ED doublet (600mm focal length) that is very light compared to other refractors in this category. 

 

Not a refractor, but a 5" Schmidt Cassegrain is very lightweight.  The added aperture shows much fainter objects than a ST-80, but at a cost of the wide field of view.  The narrow field of view of the 5" SCT can be overcome somewhat with a 0.63 reducer lens.  This combination has replaced my Borg 89mm refractor as my preferred grab and go set-up.  


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#6 Jon Isaacs

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Posted 27 November 2021 - 11:15 AM

For small  lightweight refractors of high quality, check out the Borg line of telscopes.  I have an 89mm ED doublet (600mm focal length) that is very light compared to other refractors in this category. 

 

Not a refractor, but a 5" Schmidt Cassegrain is very lightweight.  The added aperture shows much fainter objects than a ST-80, but at a cost of the wide field of view.  The narrow field of view of the 5" SCT can be overcome somewhat with a 0.63 reducer lens.  This combination has replaced my Borg 89mm refractor as my preferred grab and go set-up.  

An ST-80 with a 1.25 inch focuser is capable of 3.9 degrees, with a 2 inch focuser, 6.5 degrees.

 

A 5 inch SCT with a 0.63 reducers struggles getting an honest 2 degrees.

 

Very different.

 

Jon


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#7 hcf

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Posted 27 November 2021 - 01:34 PM

If a 70mm F/6 would do the job

 

https://www.astronom...ractor-ota.html


Edited by hcf, 27 November 2021 - 08:39 PM.

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#8 SeattleScott

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Posted 27 November 2021 - 02:12 PM

The Vixen has a focal ratio of F/8, very different than the ST-80 at F/5 in terms of size and optics.

This photo shows an ST-80 with a 2 inch focuser and an Astro-Tech AT-80 LE (F/6).

IMG_27112021_072340_(1024_x_700_pixel).jpg

The AT-80LE is slightly longer and in use will be longer still. It's short length is because it has a sliding dew shield. It's heavier than the ST-80 but optically much better, it has a FPL-53 Doublet objective. They are no longer available but there are other 80mm F/6's with ED/apo objectives that would be similar in size.

The Vixen is 23 inches in length, the AT-80LE is 15 inches.

Jon

Yes the Vixen I mentioned because it matches the aperture, and the cost (plus suitable mount) would be around top of the budget. Certainly it is quite a bit longer and heavier than the ST-80. Hence I also suggested the F6 models. It isn’t clear to me if OP wants the best possible quality 80mm for $1,500 or if portability trumps quality and image contrast.

Scott
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#9 Echolight

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Posted 27 November 2021 - 02:38 PM

Maybe a Meopta TGA 75 could be reconfigured into an astronomical telescope? They can be bought new for about $900.

https://www.meoptasp...ukt/tga-75-729/

The objective lens focal length is 329mm. It weights 1250 grams without eyepiece.

F5079768-8768-440F-90D2-D6CA10E9B9FF.png

7A5CFCA6-8251-485D-94AB-95175EAE59FE.png

 

I’m trying to figure a way to attach a focuser to my old Pentax lanthanum ED 65mm spotting scope right now. Probably a helical. It’d be easy if I wasn’t trying to do it for next to nothing. It has around a 250mm focal length. It’d be an easy 6 degrees with 1.25 inch eyepiece.

I was testing it out for approximate focus point handholding the 26mm Plossl up to the opening.

9F02F03A-F0B8-41B5-BEB2-FF964C3405C3.jpeg


Edited by Echolight, 27 November 2021 - 02:54 PM.


#10 SteveG

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Posted 27 November 2021 - 03:06 PM

I've read good reviews on this:

 

https://www.amazon.c...y/dp/B085NTQL2C


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#11 sevenofnine

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Posted 27 November 2021 - 03:46 PM

Welcome to C/N! welcome.gif

The AT80ED on a SkyWatcher AZ-GTi could work really well for you. I really like mine. The scope is sold OTA only so it needs all accessories. OTA is $400, mount is $400, 1.25" diagonal is $70, ATFinder is $60, AT Duel ED eyepieces are $65 each (buy 3, low-med-high power). All from our sponsor too waytogo.gif

 

This would be a very nice set-up with go-to capabilities for $1125 with lots of room left in your budget. Best of luck to you!  borg.gif

 

p.s. To get the most out of this hobby you will need to add a scope with more aperture. Something like an 8-10" Dob or SC. Best of luck to you and your choices!


Edited by sevenofnine, 27 November 2021 - 08:02 PM.

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#12 AstroDog77

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Posted 27 November 2021 - 03:46 PM

I've read good reviews on this:

 

https://www.amazon.c...y/dp/B085NTQL2C

I use some Svbony EPs and have a backup diagonal from them as well. It looks like my AT72EDII and I'd bet it came out of the same factory. Svbony gets a bad rap but I've had good results from their products.



#13 Polyphemos

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Posted 27 November 2021 - 03:58 PM

The AT80EDT available from the sponsor site has better optics for sure at the same size. I have the AT72EDII, so less aperture but it's still a really nice portable scope. I use it with an iOptron Cube mount but I think the AT80EDT would be pushing the Cubes limits, but if a little less aperture with solid optics is acceptable I would consider that setup. The Cube A can be used in Alt/Az or equatorial modes and is easy to get going with the built in GPS. They would probably run about $900 combined giving you plenty of budget for decent accessories (diagonal, EPs, finder).

I think this is great advice, and I’ve taken a similar approach, but minus the electronics, so:

 

AstroTech AT72EDII @ $489

Manfrotto carbon fiber tripod MT055CXPRO3 @ $478

Desert Sky Astro mount DSV-M @ $200

 

Totals $1168, which leaves $432 for accessories.

 

The AT72EDII, by virtue of its 430 mm focal length vs 400 mm for the ST80, will give you 93% of the field of view of the ST80, while being 4” shorter when packed.  It will handily fit into a small and relatively inexpensive Apache 3800 case with room to spare for a diagonal, eyepieces, and filters, while an ST80 requires the basically twice as large Apache 4800 case.

 

I would expect the better corrected and slightly slower AT72EDII will allow for higher magnifications than an ST80, which may to some degree compensate for the 8 mm smaller aperture.

 

One other suggestion is to search for a Vixen made 80 mm f5 achromat, which are reported to be wonderful but are unfortunately somewhat uncommon.


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#14 gnowellsct

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Posted 27 November 2021 - 04:14 PM

ED81s or SD81s is actually f/7.7.  Not sure whether it matters but it rounds to f/7.5.   Whether it qualifies as a "wide field" with its 4.49 degrees at 15.5x is up to the user to decide.  I think 15.5x is pretty dang low for a telescope.  Jon likes to view through an f/5 and that certainly *is* shorter and hence wider field.  The SD81s offers an extremely well corrected field and sharp color free planet views at what for it is the "high power" range of 162 to 180x.    

 

Among f/5 and lower focal ratio scope users that I know, it is interesting that I only occasionally find someone who views "at the max field."   Almost everyone tightens it up from a 40mm XW or 41 Pan type view to a 30mm wide field view.  They might as well have gotten the f/6 or f/7.

 

If I were going to get in an f/5 80mm it would be the Skywatcher 80mm apo.  (Esprit) But I went through the astigmatism decision matrix and got the f/7.7 SD81s.  And the Vixen was on sale, I don't think it has ever been so low since. Something like $700, people here were going nuts with the news so I jumped on it.  I also opted against a fast 80mm because I have found that at 16x I am at my tolerance for my God-given astigmatism and there is nothing to be gained by going lower. 

 

So for visual use make sure you have a clear sense of your own astigmatism because if you start viewing at 12x in a wide field eyepiece built-in organic astigmatism is what you will surely get.  

 

According to a quick Google check 33% of U.S. population has astigmatism and among those who have gotten glasses 70% have astigmatism correction.

 

So I would recommend people who want to get a real fast scope who currently wear glasses take time to assess their own astigmatism before buying, or planning on using eyepieces with dioptrx corrector.  The XW 30 and XW 40, in addition to Televue eyepieces, are usable with a dioptrx.  

 

So I'll post a picture of the SW80 Esprit and the Vixen SD81s side by side.  Judging from the form factor you'd think they "handle" quite a bit differently but actually the Vixen 81 does quite well.  As one can see in the pic it looks long on a c8 but it does OK, I guess because the lenses are light and the focuser, diagonal, and eyepiece shift the weight to the rear, reducing the effect of the long moment arm.

 

Greg N

 

vixen and skywatcher- cn size.jpg

 

vixen 81mm on c8.jpg


Edited by gnowellsct, 27 November 2021 - 04:18 PM.

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#15 Polyphemos

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Posted 27 November 2021 - 05:28 PM

I've read good reviews on this:

 

https://www.amazon.c...y/dp/B085NTQL2C

I believe that is same telescope, minus badging, as the AstroTech AT80ED sold by the sponsor of this forum for $399.


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#16 Jon Isaacs

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Posted 27 November 2021 - 06:32 PM

ED81s or SD81s is actually f/7.7.  Not sure whether it matters but it rounds to f/7.5.   Whether it qualifies as a "wide field" with its 4.49 degrees at 15.5x is up to the user to decide.  I think 15.5x is pretty dang low for a telescope.  Jon likes to view through an f/5 and that certainly *is* shorter and hence wider field.  The SD81s offers an extremely well corrected field and sharp color free planet views at what for it is the "high power" range of 162 to 180x.

 

 

The maximum, TFoV with a 625 mm focal length is 4.22° based on a 46 mm field stop. At F7.7, the exit pupil with a 41 mm Panoptic is 5.3 mm.

 

I'm just trying to answer the ETNIK's questions, scopes similar in size and weight but with better optics than an ST-80.  

 

By the 7.7 rounds to 8.. to the nearest tenth it's 7.7..

 

There are lots of good choices.  A 4 inch like the AT-102EDL is about the same price as the 81 mm Vixen but more potent.. 

 

Lots of questions.. does the $1500 include the mount? Include the eyepieces? We're talk about eyepieces like the 41 mm Panoptic, that's nearly $600 all by itself. 

 

An ST-80 does 3.9° with a 32 mm Plossl..

 

An 80 mm F6 does 3.2° with 1.25 inch eyepieces, an 81 mm F/7.7 does 2.48°.

 

Jon



#17 SeattleScott

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Posted 27 November 2021 - 06:48 PM

It sounds like $1500 includes mount and then OP is willing to spend $100 on top for a few eyepieces.

Edited by SeattleScott, 28 November 2021 - 06:20 AM.


#18 Tony Flanders

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Posted 28 November 2021 - 06:06 AM

Hello! I was wondering whether there was a telescope similar in shape, size, weight, to the Short Tube 80, but higher optical quality? Willing to spend $1500 on the whole setup, mount and OTA, plus like $100 of accessories, will this work?

From the point of view of someone who often carries a telescope on foot, public transportation, or bicycle -- and therefore focusing more on the "similar in shape, size, and weight" rather than the "higher optical quality," I would say that the answer is no. Though as cookjaii says above, the first place to look would be Borg, the one line of high-quality scopes that truly emphasizes portability.

 

Let me explain that. First of all, there's nothing wrong with the optics of the ST80 except that it's an f/5 achromat, and therefore has considerable false color. As several other people have said, the only way to get significantly higher optical quality in comparable aperture and size is an apochromat. Most apochromats have 2-inch focusers and are built for serious astrophotography, neither of which is true of the ST80. That means that most 80-mm APOs weigh well over twice as much as an ST80, and are considerably bigger as well. And that, in turn, means that they need an entirely different class of mount. The ST80 works very well indeed on a medium-weight photo tripod. A typical 80-mm APO requires a much more robust, and therefore less portable, mount.

 

A 90-mm Mak is similar in size and weight to an ST80, but I would not call it much, if any, of any improvement in optical terms. They do have a bigger aperture, but that's compromised by the central obstruction. In net, my experience is that 90-mm Maks do slightly better on planets, just about the same on deep-sky objects that fit in the field of view, and of course are useless for the very large number of views that fit easily in the ST80 and don't even come close to fitting in a scope with 2.5 times the focal length.

 

Any Mak with more than 90 mm of aperture is, again, in a completely different portability class from an ST80.

 

In other words, the ST80 is a bit of a sweet spot in the portability/performance tradeoff curve. Very hard to beat.


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#19 SeattleScott

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Posted 28 November 2021 - 07:07 AM

So a lot of ideas have been thrown out there and now we really need some input from the OP. As stated there literally is nothing on the market that is an 80mm refractor that is as portable as the ST80 but higher quality. The Borg likely comes closest in terms of portability, but it is well above your stated budget, and probably any of the other Apo options mentioned here would provide sharper planetary views due to the blazing fast optics of the Borg.

Part of what makes the ST80 so light is the low quality. Plastic parts, just 1.25” focuser, compared to say the Vixen with 2.3” focuser. What makes the ST80 so short is the fast F5 focal ratio, which guarantees it will be a poor performer on planets or other high magnification targets. It makes little sense to build an expensive, high quality scope that doesn’t perform well. To get better performance, one can increase the focal ratio (Vixen A81M would be a much better performer than ST80 but MUCH longer), use ED glass, and/or use extra lenses. The ST80 only has two lenses. A two lens Apo can do well on planets down to around F7. To get down to F6 you really want three lenses. To get down to F5.4 or so you need four lenses to get great planetary views. So the shorter you go, the more glass it takes, and weight goes up. Borg is the one exception to the rule in that the emphasis is truly on portability more than performance, so they will sell very expensive, very portable Apos that don’t perform as well as people are accustomed to Apos performing (at least for visual observing).

So yeah as stated you really can’t get there. The things that make the ST80 so portable also make it poor for high power viewing. You can’t get a refractor that will give sharp high power views and still be as portable as the ST80, certainly not for $1500 system cost.

Now small Maks have been mentioned as an alternative. They do better than a ST80 for high power viewing but not as good for wide field viewing. No idea if that is of interest to you. We could provide more details if it is a suitable alternative for you.

Otherwise it is just determining the trade off of performance versus portability. Is length or weight more of a limiting factor? A triplet can be heavier but shorter. The Vixen SD81S is a top performer, in part due to the slower F7.7 focal ratio, but this makes it quite long compared to a ST80 or some of the other 80mm Apos. Does a sliding dew shield help? Makes it shorter for transport but not in actual use. So if the issue is transporting the scope in a small container the sliding dew shield is helpful. But if the small form factor is desired due to trying to mount the scope on a cheap camera tripod, a sliding dew shield doesn’t help. At this point we don’t have enough information to really narrow it down for you so we have just thrown out a bunch of options.

Scott
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#20 AstroDog77

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Posted 28 November 2021 - 08:47 AM

I'm confused, wouldn't the AT80EDT have better optics at the same length as the ST80?


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#21 Echolight

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Posted 28 November 2021 - 09:47 AM

From the point of view of someone who often carries a telescope on foot, public transportation, or bicycle -- and therefore focusing more on the "similar in shape, size, and weight" rather than the "higher optical quality," I would say that the answer is no. Though as cookjaii says above, the first place to look would be Borg, the one line of high-quality scopes that truly emphasizes portability.

 

Let me explain that. First of all, there's nothing wrong with the optics of the ST80 except that it's an f/5 achromat, and therefore has considerable false color. As several other people have said, the only way to get significantly higher optical quality in comparable aperture and size is an apochromat. Most apochromats have 2-inch focusers and are built for serious astrophotography, neither of which is true of the ST80. That means that most 80-mm APOs weigh well over twice as much as an ST80, and are considerably bigger as well. And that, in turn, means that they need an entirely different class of mount. The ST80 works very well indeed on a medium-weight photo tripod. A typical 80-mm APO requires a much more robust, and therefore less portable, mount.

 

A 90-mm Mak is similar in size and weight to an ST80, but I would not call it much, if any, of any improvement in optical terms. They do have a bigger aperture, but that's compromised by the central obstruction. In net, my experience is that 90-mm Maks do slightly better on planets, just about the same on deep-sky objects that fit in the field of view, and of course are useless for the very large number of views that fit easily in the ST80 and don't even come close to fitting in a scope with 2.5 times the focal length.

 

Any Mak with more than 90 mm of aperture is, again, in a completely different portability class from an ST80.

 

In other words, the ST80 is a bit of a sweet spot in the portability/performance tradeoff curve. Very hard to beat.

I agree with this almost entirely.

 

But.... I find that my deforked ETX90 is more similar to an ED80 on lunar and planets than it is to the ST80.

 

With the ST80 on Jupiter you’ll see a blurry band, or two if you’re lucky, at around 100x max. And if you observe very carefully, a blurry gray dot as a shadow transit.
The ETX 90 shows sharp contrast at 160x, and probably a little more if you have the eyepiece.

 

Of course the ST80 will have about triple the potential true field of view. Which, in my opinion, makes the ST80 more versatile. And easier to use on a simple medium duty photo tripod.


Edited by Echolight, 28 November 2021 - 09:49 AM.

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#22 CHASLX200

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Posted 28 November 2021 - 09:54 AM

I only use my ST80 for low power sweeping. For planets you need to step up to around F/6 or 7 and better optics.

Attached Thumbnails

  • IMG_0657.JPG


#23 Echolight

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Posted 28 November 2021 - 09:57 AM

I'm confused, wouldn't the AT80EDT have better optics at the same length as the ST80?

It is much heavier. And in use, much longer. Takes a different class of mount for best stability.

 

An ST80 does very well on a light mount. There’s no way I would put an 80ED on this. But I’d try an AT70ED.

C8B4577E-322B-451C-BF5D-011A815700B2.jpeg


Edited by Echolight, 28 November 2021 - 09:59 AM.

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#24 Echolight

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Posted 28 November 2021 - 10:02 AM

I only use my ST80 for low power sweeping. For planets you need to step up to around F/6 or 7 and better optics.

I look at planets and the Moon in mine. I just don’t expect to see as much. It is a bit of a challenge.

 

Using the aperture mask increases the contrast, the sharpness of image. But not necessarily the detail seen, unless you have an eagle eye maybe.


Edited by Echolight, 28 November 2021 - 10:04 AM.


#25 BradFran

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Posted 28 November 2021 - 10:10 AM

In addition to the already mentioned models, the older 80mm f/7 from William Optics are quite good and come up used: ZenithStar, Gran Turismo and Megrez 80 ED (2.5 kg). The current ZenithStar 81 can be had at the moment for $900, but due to being aimed at photographers is much heavier (3.5 kg, 1 kilo heaver than the Orion ShortTube). Both old and new models have far better optics and mechanics than the Orion ShortTube.

 

If weight and portability are the key considerations, the above mentioned AstroTech AT72EDII is the one to get. The slightly heavier and longer AT80ED is probably the best value available new at the moment. In a higher budget class, you can start to look at Takahashi or TV76. They can sometimes be had used in your price range.


Edited by BradFran, 28 November 2021 - 10:51 AM.

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