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Orion ShortTube 80-A

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#1 penguinx64

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Posted 06 July 2014 - 01:18 PM

I'm considering this scope for visual use up to 150x. Any comments?

http://www.telescope...r-Optical-Tu...

#2 seasparky89

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Posted 06 July 2014 - 01:28 PM

I can get nearly 100x with mine on the moon and Saturn using quality eyepieces (that cost up to 4x the scope), but IMHO, the ShortTube 80 is best for low power/wide field. One can use the stopped-down feature to get even more power on a very bright object (i.e., the moon).

Stan

#3 Patrik Iver

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Posted 06 July 2014 - 01:31 PM

If high magnification is your goal, that is the wrong telescope.

I have a somewhat similar Vixen 80 mm f/5 Achromat, and I like it a lot up to a magnification about 40 - 50, but above that the false colour in an achromat that fast makes it a bit fuzzy. At a magnification of 80, the Vixen is clearly not sharp compared to my f/7.5 80 mm ED doublet (Celestron ED 80), which can easily take magnifications up to 120 and above while remaining sharp.

#4 Jon Isaacs

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Posted 06 July 2014 - 02:35 PM

I have owned a number of ST-80s and currently have two of them. For low powers and widefields they do the job. They can be pushed to higher magnifications but their performance quickly falls off in comparison to telescopes with less chromatic aberration, with sharper optics. If I were looking for an 80mm achromat that performed at 150x, I would be looking at a 80mm x 900mm (F/11). There is still some CA but it is very minimal.

Jon

#5 penguinx64

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Posted 06 July 2014 - 03:33 PM

Interesting about the magnification. The specs say 160x is the highest useful magnification, but 200x is the maximum theoretical magnification. On the other hand, you guys say 80-100x max is more realistic, which is about half what the manufacturer suggests. It sounds like any short tube refractor will be limited to less than 100x. Thanks!

#6 Jon Isaacs

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Posted 06 July 2014 - 08:36 PM

Interesting about the magnification. The specs say 160x is the highest useful magnification, but 200x is the maximum theoretical magnification. On the other hand, you guys say 80-100x max is more realistic, which is about half what the manufacturer suggests. It sounds like any short tube refractor will be limited to less than 100x. Thanks!


Manufacturers generally use the 50X/inch = 2x/mm guideline when stating the maximum magnification, this is irregardless of the optics or the optical quality. This is an 80mm scope, 2x 80 = 160... If this were the Celestron C80ED, then 160x and more would be reasonable.

It is often stated that 50/inch is a "theoretical" maximum but when one looks a little closer, it's really no more than a relatively vague guideline obtained by matching some measure of the resolving power of the human eye to the size of the Airy disk of a telescope, that is the resolving power of a telescope. However, the resolving power of the human eye depends on the conditions, there is no single number that can be used..

The bottom line.. out under the stars, looking through the telescope, let your eye tell you what works best.

Jon

#7 csrlice12

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Posted 06 July 2014 - 08:37 PM

You can get a short tube and use high mags with no CA, but it won't be cheap. Maybe a 80mm f7ish APO. But if high mag planetary viewing is your primary use, I'd get a longer f/l scope as these shorter f/l scopes, especially achros, are designed for low power wide field viewing.

#8 Don Taylor

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Posted 06 July 2014 - 08:59 PM

I'll second what Jon Isaacs said in his posts -

I have an ST80 equipped with a 2" focuser and use if for both wide field viewing and as a finder for my 16" Dob. It's great for those purposes.

I also have an 80mm f11 refractor similar to the vixen A80Mf available today. That scope has received good reviews here but I understand an upgrade of the diagonal prism is desirable.

Mine gives stunning lunar views and I often use it with 5 and 6 mm eyepieces giving about 180x and 150x respectively.

You might find the vixen will do what you want without costing a fortune. At the other end of the magnification spectrum a 32mm Plossl or 24mm ES 68 or Panoptic will yield almost a 2 degree fov or nearly 4 times the full moon.

#9 georgegeo

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Posted 13 July 2014 - 04:06 PM

I have an 80/400mm achro, which is great for those wide field views, the plossol 32mm 1.25" being my most used
eyepiece.

But straight out of the box there was an issue with the lenses not sitting properly in their retaining cell, as the stars were showing obvious comatic trails, across the visual field of the eyepiece. I

I spent a couple of hours fiddling about with bits of sticking tape, to correct the optical centering, the stars becoming pin-point across most of the viewing field.

When i pointed the scope to Jupiter, after the colimation, all i could see was a featureless, bright yellow object, even in the higher magnifications. Saturn's rings were barely noticeable, as two little blurred lines, either side of the planet's disc .

So my attempt at planetary viewing, with my short refractor, was somewhat frustrated, perhaps because of issues i had with the lens centering, or simply i was expecting too much out of my little scope.

George.

#10 Jon Isaacs

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Posted 13 July 2014 - 08:15 PM

When i pointed the scope to Jupiter, after the colimation, all i could see was a featureless, bright yellow object, even in the higher magnifications. Saturn's rings were barely noticeable, as two little blurred lines, either side of the planet's disc .

So my attempt at planetary viewing, with my short refractor, was somewhat frustrated, perhaps because of issues i had with the lens cell, or simply i was expecting too much out of my little scope.



Goerge:

How long ago was it that you looked at Jupiter. If Jupiter were well above the horizon (>40 degrees) and the seeing reasonably steady, I would expect to see the two cloud belts as a minimum.

Jon

#11 Sarkikos

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Posted 14 July 2014 - 06:24 AM

I'm considering this scope for visual use up to 150x. Any comments?

http://www.telescope...r-Optical-Tu...


I have an ST80. It is good for deep sky, especially low-power wide-field views. I upgraded mine with a 2" Crayford focuser to take advantage of the wider fields offered by 2" eyepieces.

But don't expect great views of planets or the Moon. IME there is too much chromatic aberration on these f/5 80mm scopes for planet/lunar. If you want to observe planets and the Moon, an 80mm f/11 achromat, or a Newt or Mak would be a better choice.

Mike

#12 astroneil

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Posted 14 July 2014 - 06:44 AM

Hello,

I've been using essentially the same 'scope over the last several months and have found it to be quite a versatile performer. Beautiful low and moderate power images of larger deep sky objects. Decent on Jupiter and the moon at powers up to ~100x. You can make out many details in the Jovian cloud belts with a bit of effort and training.
I have been pleasantly surprised by its ability to resolve fairly tricky double stars;

Rigel
Epsilon 1&2 Lyrae
Iota Cassiopeiae
Delta Cygni
Izar (Epsilon Bootis)

I have successfully pushed it to 213x with barlows on these doubles.

A Baader Fringe Killer (or a light yellow #8 Wratten) helps tidy up the star, lunar & planetary images but at a small additional cost and a slight colour shift.

All in all, a very sweet 'scope.

Cheers,

Neil. ;)

#13 Sarkikos

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Posted 14 July 2014 - 07:02 AM

I've used my ST80 for planet/lunar, after careful collimation and using various filters. IME these short little achros just don't cut it for planets and the Moon compared to longer achromats or Newts and Maks. Even my C102 f/9.8 wasn't quite there for me. I guess I've been spoiled by mostly observing these objects with reflectors over the years.

Mike

#14 astroneil

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Posted 14 July 2014 - 07:16 AM

Hi Mike,

I agree; it ain't a planetary 'scope. No 80mm 'scope makes the cut. But what if it were your only 'scope? Would you not be able to see that Jupiter is a great big world of its own with four large moons that change their positions with the minutes and hours?
The ST-80 will show you something; and a determined observer will get the goods out of any situation.

Regards,

Neil. ;)

#15 georgegeo

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Posted 14 July 2014 - 09:35 AM

jupiter/saturn was positioned favourably in the Athenian light polluted sky, but my standard for judging the 80/400, my 60/700mm homemade refractor, could make out planetary details, whereas the 80 achro failed into a blurry, yellowish dissapointment, for me.

Under terrestial night viewing, the 60mm could clearly make out the words of lighted road signs, in the distance, but i could not resolve the words with my 80/400mm.

I am guessing that the deep curves of the 80mm are incompatibly mated with the simple retaining cell of my skywatcher tube, my initial attempts at improving the centering of the lenses within the cell, only having so much effect, optically.

I believe that the 60/700mm lens set, with it's lighter curves, is much more forgiving of lens decentering, even in my rudimentary constrcuted homemade cell, of plumbing parts, whereas the short 80mm, even if only an achro, is still susceptible to lens decentering. ED scopes are usually provided with some means to center the elements within their cell, to within fine tolerance.

Initially i wanted a short 80mm achro to be capable of planetary veiwing, but my long focus 60mm proved far superior in this respect, at least under my subjective optical tests.


George G.

#16 Sarkikos

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Posted 14 July 2014 - 10:04 AM

yes jupiter/saturn was positioned favourably in the Athenian light polluted sky, but my standard for judging the 80/400, my 60/700mm homemade refractor, could make out planetary details, whereas the 80 achro failed into a blurry, yellowish dissapointment, for me.


Yia sou, George.

Yes, I agree. IME & IMO, an 80mm f/5 achromat has too much chroma for acceptable planet viewing. No sense using a hammer to turn a screw.

Mike

#17 Jon Isaacs

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Posted 14 July 2014 - 10:08 AM

Jon,

yes jupiter/saturn was positioned favourably in the Athenian light polluted sky, but my standard for judging the 80/400, my 60/700mm homemade refractor, could make out planetary details, whereas the 80 achro failed into a blurry, yellowish dissapointment, for me.



George:

I have owned a number of ST-80s and yours does not seem typical to me, something seems wrong. They are not the best planetary scopes, I certainly do not recommend buying one for double star and planetary observing. But as Neil said, if you have one, they can provide enjoyable views of the moon and larger planets.

The CA I see is purple rather than yellow, I wonder if your respacing messed up the color correction.

Jon

#18 Sarkikos

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Posted 14 July 2014 - 10:20 AM

I hope George did not make a mediocre planet/lunar scope even worse. :(

I did not respace the optics in my ST80 or do anything other than replace the 1.25" focuser with a 2" Crayford. But even after close alignment with a refractor collimator, the views of Jupiter and other bright planets were smeared by CA and unimpressive. My little C90 Mak is much better for planet/lunar. Even better is my C80 ED.

This is a wide-field, low-power scope good for deep sky. Is that such a bad thing? :shrug:

Mike

#19 astroneil

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Posted 14 July 2014 - 10:45 AM

I found studying Jupiter images with the ST-80 to be a lot of fun. The sharpest images I got from my sample was from either a Baader Contrast Booster (CB) by itself or a combination of Fringe Killer/ Light blue 82A Wratten, with the latter providing the most detail.
In the end though, it's the spherical aberration at f/5 in such a scope that takes the shine off the high power images. They are always 'soft' irrespective of whether you remove all the unfocused light or not.

A 90mm Mak has no CA and much more punch, but you cannae get wide field out of that 'scope.

Cheers,

Neil. ;)

#20 Sarkikos

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Posted 14 July 2014 - 10:52 AM

In the end though, it's the spherical aberration at f/5 in such a scope that takes the shine off the high power images. They are always 'soft' irrespective of whether you remove all the unfocused light or not.


I'm pretty sure it's the CA not the SA that's the planet killer - in a bad way - for the ST80. Maybe some optics experts can weigh in on this question.

A 90mm Mak has no CA and much more punch, but you cannae get wide field out of that 'scope.


Agreed. But I never think of Maks or SCTs as wide-field scopes, because they aren't. That's where fast little 'fractors shine. :grin:

Mike

#21 astroneil

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Posted 14 July 2014 - 10:55 AM

CA and SA are inter-related. It's called spherochromatism.

Neil. ;)

#22 georgegeo

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Posted 14 July 2014 - 10:57 AM

At low magnification the stars looked pin-point across most of the viewable field of my 80/400 scope. But originally the scope showed comatic flaring of the stars, which i reduced to some degree after centering the lenses within their cell.

I think the chromatic error of the 80mm is within the tolerances of my 60/700mm reference. I think the yellowish tint on the planet is less the effect of the CA, but perhaps combination of other optical errors, which the short focal ratio of the f/5 might be more suspeptible than an f/11 scope.

The 60mm showed the main banding features clearly, Jupiter's moons very sharply. I could not resolve banding with the 80mm f/5, the moons looked faint with respect to the 60mm.

The 80/400mm makes a nice terrestrial day scope for lightness, CA being within reasonable limits.

I am happy for its wide field views, but i expected better planetary performance than it delivered.

George G.

#23 Sarkikos

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Posted 14 July 2014 - 01:07 PM

CA and SA are inter-related. It's called spherochromatism.

Neil. ;)


Then we're both correct!

:grin:
Mike

#24 astroneil

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Posted 14 July 2014 - 01:38 PM

CA and SA are inter-related. It's called spherochromatism.

Neil. ;)


Then we're both correct!

:grin:
Mike


I suppose so Mike :)

I'm really fond of mine. I learn more from these kind of 'scopes than from any other. Not much else floats my boat these days.

Regards,

Neil. ;)

#25 astroneil

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Posted 28 July 2014 - 11:51 AM

I have enjoyed nights during the winter where my eye has been able to see the two main equatorial bands (SEB and NEB) on Jupiter as well as a few of the fainter belts at higher and lower latitudes with Gaius, my trusty 80mm f/5 achromatic. The Great Red Spot can also be seen with appropriate scrutiny. Doubles are not appreciably affected by the telescope’s secondary spectrum; indeed, it may actually help stabilise the images. I would wager that the instrument could split any binary system within the remit of its aperture. All you need is good seeing and the will to investigate thoroughly enough.

You see, you must put everything to the test and take nothing for granted!

Neil. ;)

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