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Opinions on smaller APO scopes?

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#1 Matty S

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Posted 03 February 2020 - 07:07 PM

Ok folks, I'd like to pick your brains about small aperture APO scopes.
As my b-day is coming up this May I have been given the go-ahead to purchase a small, travel-sized APO.
I've checked out higher-end spotters from Zeiss, Swarovski, Leica, etc, but can't justify the high cost for a day scope with limited use for astro.
I'd like a scope that will do double-duty in both daytime spotting and astro use.
I am excited to finally be able to add some really nice glass to the stable.
Ya, it's apples to oranges here, but I know you folks have opinions on some of these, both good and bad. Not looking for any particular brand name or anything like that; looking for a real "keeper".

 

My candidates (so far):
Takahashi FC-76DS
William Optics APO’s (several)
Tele Vue TV76
Sky-Watcher Esprit 80 mm Triplet
Orion 80 mm ED F/6 CF Triplet
Meade 80 mm Series 6000 f/6
Astro Tech 72 ED ll

 

In a nutshell:
True APO optics
Small physical size
Mostly visual use, no AP.
70mm to 80mm
Up to $2500

Prefer larger, 2.5" dual-speed focusers
Also interested in classic scopes that may meet these requirements.


Edited by Matty S, 04 February 2020 - 09:38 AM.


#2 csrlice12

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Posted 03 February 2020 - 07:22 PM

The Vixen ED81S/SD81S has quite a following in these forums.  Bit more expensive than some, but top notch optical quality.


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#3 scadvice

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Posted 03 February 2020 - 07:53 PM

The Stellarvue SVX 70T is not in production right now so you might look at the Stellarvue SVX080T-25SV.

 

Sky-Watcher Esprit 80 mm ED APO Triplet Refractor or the Esprit 100 mm seem popular but I know nothing about them other than what I read.

 

Since your not looking to do AP you might look at some of the higher end Doublets like Takahashi or Tele Vue.


Edited by scadvice, 03 February 2020 - 08:08 PM.


#4 ButterFly

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Posted 03 February 2020 - 07:55 PM

Although it may seem a triplet is not needed for visual use, I have found balancing to be an issue with the heavy mega-eyepieces.  I love widefield during the day.  I am glad it's a triplet.  Also, with that much more light, the cromatic abberation can be more apparent.  I use an ES80CF with FCD01 glass.  At very high powers, the colors are apparent.

 

Don't discount the high end spotters for astro use.  I am sure you have heard of the Leica zoom and will save room in your budget for it, whichever way you go.


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#5 ButterFly

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Posted 03 February 2020 - 07:59 PM

 

Mostly visual use, no AP.
...

Prefer larger, 2.5" dual-speed focusers
 

Why the preference for 2.5" for only visual?


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#6 mrsjeff

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Posted 03 February 2020 - 08:43 PM

I would suggest the Astro-tech AT92.
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#7 sojourneyer

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Posted 03 February 2020 - 08:44 PM

Is the $2500 your all up budget or is it just for the OTA?

Also look at the Stellarvue certified pre-owned scopes if

they have any for sale on the Stellarvue website.



#8 Matty S

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Posted 03 February 2020 - 09:12 PM

Why the preference for 2.5" for only visual?

Well, since focusers tend to be of 1.25" or larger, I assume the light cone would improve with a larger focuser. I recently bought a SV102 with a 2.5" focuser and the views are very nice with 2" ep's.  Would they be the same with a 2" focuser or even a 1.25" focuser? I don't know yet.

I do know I would like to use my 2" ep's without an adapter. I'm not sure if the light path suffers from smaller diameter focusers but all my best ep's are of 2" barrel diameter right now so I'd like to make the best use of them. No other preference than that.


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#9 Matty S

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Posted 03 February 2020 - 09:14 PM

I would suggest the Astro-tech AT92.

I've read up on that one too, nice bit of kit but a bit too big and I don't know what it can offer since i already have a sv102 ed in the stable.



#10 Matty S

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Posted 03 February 2020 - 09:25 PM

Is the $2500 your all up budget or is it just for the OTA?

Also look at the Stellarvue certified pre-owned scopes if

they have any for sale on the Stellarvue website.

$2500 for the ota and focuser. I will build up my own kit from there.

And yes, I will check SV for pre-owned, Thank you!


Edited by Matty S, 03 February 2020 - 09:26 PM.

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#11 Matty S

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Posted 03 February 2020 - 09:58 PM

Although it may seem a triplet is not needed for visual use, I have found balancing to be an issue with the heavy mega-eyepieces.  I love widefield during the day.  I am glad it's a triplet.  Also, with that much more light, the cromatic abberation can be more apparent.  I use an ES80CF with FCD01 glass.  At very high powers, the colors are apparent.

 

Don't discount the high end spotters for astro use.  I am sure you have heard of the Leica zoom and will save room in your budget for it, whichever way you go.

Ah. there's the rub... I've heard that. Is a triplet superior for "visual" or is a doublet of the same quality sufficient? Heavier, sure, but optically?



#12 Paul Hooper

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Posted 03 February 2020 - 10:26 PM

If you are looking for a scope that will double as a spotter, I’m not sure a triplet is the best idea.  The advantages of the doublet are a lighter weight and a fast cool-down time.  I am no birder, but it seems to me those qualities would greatly assist with most terrestrial uses.  I also wonder how much difference there is in CA between a doublet and triplet when used visually.


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#13 Jon Isaacs

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Posted 03 February 2020 - 10:39 PM

My two cents:

 

As a dual purpose birding Astro scope, my choice would be the TeleVue 76. It's a short, compact scope with a build that sets it apart from the rest, it's rugged and robust but not massive.

 

I owned the Pronto, the 70 mm achromatic version off the 76. When the affordable apos arrived on the scene, I sold the Pronto and have owned a number of 66mm to 80 mm ED/apos. They're all been good optically and mechanically but none have combined the optics with the well thought out ergonomic package that the Pronto/ TV 76 represents.

 

I do a fair amount of birding and I think this is where the 76 excels. 

 

Jon


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#14 scooke

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Posted 03 February 2020 - 10:39 PM

I've read up on that one too, nice bit of kit but a bit too big and I don't know what it can offer since i already have a sv102 ed in the stable.

I had an 80 and a SV102.  After I got the AT92, I found I didn't neither either of the other scopes.  It has the size of the 80F6 (in fact it's a little shorter) with the ability to use high resolution and high magnification of the 102.  From 5.5 degree field of view all the way up to over 300x on the moon.


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#15 Spikey131

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Posted 03 February 2020 - 10:59 PM

I just went through this decision.  I wanted a scope that I could travel with, so it needed to be small.  But it needed to have enough aperture and good enough optics for planetary observation (if I am going to fly to the tropics, I want to see the planets high in the sky).  The focuser needed to be robust enough for 2” EPs for wide field views in dark Canada skies, and to carry my Quark and binoviewer for eclipse chasing.

 

My choice?  The TV 76.  
 

14.5” long, 3” diameter, 5 pound chunk of optical wizardry.

 

Here it is in a backpack that fits under an airline seat with all accessories and room for a snack:

 

 

 

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#16 Matty S

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Posted 03 February 2020 - 10:59 PM

I wonder how much difference there is in CA between a doublet and triplet when used visually.

Ya, I agree. Anyone actually in the know about this?

I am intrigued with the 76mm Tak doublets and TV's are nice too, I'm sure, but pricey for what they offer. The Tak costs less than the TV... apples and oranges again.



#17 Matty S

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Posted 03 February 2020 - 11:03 PM

I just went through this decision.  I wanted a scope that I could travel with, so it needed to be small.  But it needed to have enough aperture and good enough optics for planetary observation (if I am going to fly to the tropics, I want to see the planets high in the sky).  The focuser needed to be robust enough for 2” EPs for wide field views in dark Canada skies, and to carry my Quark and binoviewer for eclipse chasing.

 

My choice?  The TV 76.  
 

14.5” long, 3” diameter, 5 pound chunk of optical wizardry.

 

Here it is in a backpack that fits under an airline seat with all accessories and room for a snack:

You guys are seriously making me lean towards the TV 76. I have time, b-day isn't til May.cool.gif



#18 SeattleScott

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Posted 03 February 2020 - 11:07 PM

A focuser larger than 2” will help avoid vignetting on max FOV 2” eyepieces. F ratio is a factor too. My Orion 100ED only had a 2” focuser, but it is F9 so the light cone doesn’t shrink very fast, and it played well with 2” eyepieces. Vixen uses a 2.3” focuser for their F7.7 Apos.

A high quality doublet can be great for visual, practically color free. However a triplet allows you to go faster. So while a Vixen or Tak are very well corrected, they are also F7.4 or F7.7. Which may be perfectly fine. But if you really want F6 or lower then a triplet might be in order.

Scott
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#19 Spikey131

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Posted 03 February 2020 - 11:09 PM

You guys are seriously making me lean towards the TV 76. I have time, b-day isn't til May.cool.gif

Then you have time to find a nice used one.

 

You won’t see any color in focus in a quality doublet.


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#20 Matty S

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Posted 03 February 2020 - 11:23 PM

A focuser larger than 2” will help avoid vignetting on max FOV 2” eyepieces. F ratio is a factor too. My Orion 100ED only had a 2” focuser, but it is F9 so the light cone doesn’t shrink very fast, and it played well with 2” eyepieces. Vixen uses a 2.3” focuser for their F7.7 Apos.

A high quality doublet can be great for visual, practically color free. However a triplet allows you to go faster. So while a Vixen or Tak are very well corrected, they are also F7.4 or F7.7. Which may be perfectly fine. But if you really want F6 or lower then a triplet might be in order.

Scott

Thank you! I knew there was some good science behind this somewhere out there.

I see the conundrum now too, don't know why I didn't clue into it before; optical physics. "ya can no break the laws of physics"

I think I need the tube lengths of the Tak and TV 76's. Those are what I'm leaning towards at this point. Anyone got specs?



#21 Jon Isaacs

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Posted 03 February 2020 - 11:31 PM

A focuser larger than 2” will help avoid vignetting on max FOV 2” eyepieces. F ratio is a factor too. My Orion 100ED only had a 2” focuser, but it is F9 so the light cone doesn’t shrink very fast, and it played well with 2” eyepieces. Vixen uses a 2.3” focuser for their F7.7 Apos.

A high quality doublet can be great for visual, practically color free. However a triplet allows you to go faster. So while a Vixen or Tak are very well corrected, they are also F7.4 or F7.7. Which may be perfectly fine. But if you really want F6 or lower then a triplet might be in order.

Scott

 

Visually, you won't see the vignetting with a 2 inch focuser even with eyepieces like 41 mm Panoptic. 

 

Color correction depends on both aperture and focal ratio. Bigger needs slower ratios.

 

In my mind, the important thing here is the dual use, birding and astronomy. Sliding dew shields and a compact, robust build are more important birding than they are for astronomy. This scope will get banged around and maybe even carried in a backpack.

 

This is why the TV 76 is popular with birders.

 

Jon


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#22 Spikey131

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Posted 03 February 2020 - 11:47 PM

I really like the Takahashi 76 refractor and gave it serious thought.  They make 2 models:

 

The DS has a retractable dew shield and is over 22 inches long.  Won’t go under an airline seat.

 

The DCU has a non-retractable dew shield but screws into 2 pieces, 13” and 8”.  But it comes with a 1.25” focuser.  Starlight apparently makes (or made) a 2” focuser for this but it is expensive and has limited travel and back focus, so not all eyepieces work and it just all sounded too complicated to me.

 

Hence, the TV 76.  It just works.


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#23 ButterFly

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Posted 04 February 2020 - 12:30 AM

Ya, I agree. Anyone actually in the know about this?

I am intrigued with the 76mm Tak doublets and TV's are nice too, I'm sure, but pricey for what they offer. The Tak costs less than the TV... apples and oranges again.

My doublet SW120 at f/7.5 is better corrected for color than the ES80 at f/6.  The difference is very noticable visually.  Triplet alone doesn't mean much without the glass and spacing of the elements.

 

You won't be disappointed with a TV76.

 

The length of a refractor drawtube is more relevant in practice for vignetting than its width, particularly in the daytime when focus is further from the objective.  Extension tubes may be necessary for closer distances than the drawtube allows.  See here for an explanation: Field of Full Illumination.



#24 Redbetter

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Posted 04 February 2020 - 12:58 AM

"Travel-sized" to me would mean retractable dew shield. 

 

I don't see the point of a 2.5" focuser for visual.  I don't see vignetting with my AT60ED and a 41 Pan.  No color either, visually it is an apo. 

 

For less than $500 an AT72EDII would seem a good fit with very similar color performance as the 60ED.  You could try it, and if it doesn't suit your needs resell it, losing very little...while potentially saving yourself ~$1,000.  Seems a no-brainer to me.  (I will probably talk myself into one of these some day...as an Orion 80ED is a considerably larger scope, while the AT60ED is my widest field scope.)



#25 SeattleScott

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Posted 04 February 2020 - 01:02 AM

Visually, you won't see the vignetting with a 2 inch focuser even with eyepieces like 41 mm Panoptic.

Color correction depends on both aperture and focal ratio. Bigger needs slower ratios.

In my mind, the important thing here is the dual use, birding and astronomy. Sliding dew shields and a compact, robust build are more important birding than they are for astronomy. This scope will get banged around and maybe even carried in a backpack.

This is why the TV 76 is popular with birders.

Jon

Good to know a 2” focuser won’t cause noticeable vignetting.

The TV76 could be an excellent option as well. I just don’t have the specs for it memorized like the Vixen and Tak.

Scott


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