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Refractor For Purely Visual Astronomy?


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Most definitely! Refractors are renowned for their exquisitely sharp, tight star images, and that makes them virtually unbeatable for viewing wide, rich star fields. Depending on the aperture you're considering, they can be excellent for brighter deep sky and comet seeking. When considering a refractor for such tasks their being achromatic isn't such a big issue, as chromatic abberation isn't nearly as noticeable on such targets as it is on the Moon & planets. I would consider a 4" to 6"  F5 to F8 achromat to be a serious visual instrument.

For lunar & planetary I'd prefer an Apochromatic or ED doublet refractor, again between 4" to 6", but the costs increase because of the exotic glasses used in manufacture. For many seasoned lunar & planetary enthusiasts a good 4" refractor may well be prefered to a 6" or even an 8" reflector due to their sharp imagery and ability to often be relatively unaffected by poor seeing conditions. The beauty of the ED or apo doublet is that it can often take higher magnification on such things as the Moon, and double stars due to no or virtually no chromatic abberation. They make excellent all round instruments, but as with all telescopes, as well as having wonderful attributes, they have their limitations.

 

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Well, I'm guessing from your avatar that you already have an 8" Dob.  A 3" to 4" ED or APO refractor can nicely complement such an instrument for wide star field views, splitting tight, uneven double stars, etc. thanks to their tight star images.

I would suggest starting with an ED doublet because triplets are very slow to acclimate.  Cheap, short tube achromats often have loads of spherical aberration and purple fringing.  I was put off by my ST80 because of both.  My 72ED changed all that.  I then moved up to a 90mm FPL-53 triplet for more general use.  However, I have to think ahead and set it out the equilibrate, or I'll have spiky stars for 30 minutes or more.  The 72ED does not have this issue being a smaller doublet.

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Modern doublets can be so good that for visual use you might not see any difference compared to a triplet. They also cool down faster, weigh less, and tend to be a bit easier to mount and balance due to being less lens-heavy which also makes them a better fit for a grab-and-go scope.

If your budget can stretch to a 4" apo then I think you'd really enjoy it and it would make a great companion to your dob.

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8 hours ago, Ian McCallum said:

Just wondering if there much use in getting either an Acromat, Apocromat or Triplet for purely visual observering? 


if the 8” Dob in your avatar is yours then you will have to spend a lot of money on a refractor to beat it’s visual performance on both deep sky objects and the planets.

Edited by dweller25
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40 minutes ago, dweller25 said:


if the 8” Dob in your avatar is yours then you will have to spend a lot of money on a refractor to beat it’s visual performance on both deep sky objects and the planets.


 

There’s no doubt that a good 4” refractor gives lovely views with stars as tight points of light.  But if you want to see globular clusters looking like a ball of stars rather than a fuzzy patch then a larger reflector gets the job done at a fraction of the price.

The old “horses for courses” applies.

Ed.

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Just now, NGC 1502 said:


 

There’s no doubt that a good 4” refractor gives lovely views with stars as tight points of light.  But if you want to see globular clusters looking like a ball of stars rather than a fuzzy patch then a larger reflector gets the job done at a fraction of the price.

The old “horses for courses” applies.

Ed.

That’s the point though, isn’t it Ed. If the OP has an 8” dob then that aspect is covered. A refractor can give superb complementary views such as widefield views of nebulae, open clusters and objects like M31. They are also very capable as a lunar and planetary scopes, cutting through poor seeing better than larger ones. Double stars are  often much nicer to observe in refractors. In addition, I love which light solar viewing in my frac with a Herschel Wedge.

So, to the OP I say ‘yes’ to a 4” ED doublet, with the right expectations.

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I think there is a lot to be said for a small 3" APO that can be "thrown outside" at short notice when unforseen clear skies arise. In my limited time peering upwards some of my most enjoyable nights have been impromptu visual sessions like that. IMHO a light weight easy to move set up is worth it's weight in gold to maximise viewing opportunities. 

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I am very pleased with my APM 80 mm F/6 triplet, which complements my 8" SCT nicely on wide-field views (about 5.3 degrees at 15.5x with the Nagler 31T5 "Panzerfaust"). I did have imaging in mind when I bought it, and the price at that time was great (699 euro), but a fast 80 mm to 100 mm ED  doublet or triplet is an outstanding wide-field visual instrument, and excellent travel scope. For the latter purpose, I would go for 80 mm, given the weight.

 

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Perhaps one of the 102mm f7 fpl-53 refractors would be worth a look, although if your budget needs to include a mount and accessories then one of the fpl-51 Ascent models at £499 would leave plenty to spare.

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These created a bit of a buzz on the forum, when they appeared at Auntie @FLO's.  

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-stl80a-l-80mm-f125-classical-refractor.html

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-stl-80a-maxi-80mm-f15-classical-refractor.html

Can I ask what would they be suitable for visual observing, or just for astrophotography?

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25 minutes ago, Ian McCallum said:

These created a bit of a buzz on the forum, when they appeared at Auntie @FLO's.  

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-stl80a-l-80mm-f125-classical-refractor.html

https://www.firstlightoptics.com/scopetech-telescopes/scopetech-stl-80a-maxi-80mm-f15-classical-refractor.html

Can I ask what would they be suitable for visual observing, or just for astrophotography?

I actually have both of these on trial from FLO at the moment. They are actually exactly the opposite of what you said ie they are dedicated visual instruments, not really suited to astrophotography at all.

They have a long focal length and slow focal ratio, with well figured optics so are good planetary and lunar and double star scopes, but don’t have the widefield capability you would get with a 100mm f7 for instance. They also only have 1.25” focusers so the maximum field of view in the f15 would be about 1.3 degrees, vs around 3.8 degrees with a 40mm 2” eyepiece in the f7. Personally I wouldn’t recommend one as your first/only refractor as they are quite specialised although I have had some lovely lunar and double star views with both scopes.

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52 minutes ago, Ian McCallum said:

Up to £1,000.

Does that include the mount or do you have one ?

And what kind of visual astronomy do you do - deep sky, lunar, solar, planetary or all of them ?

 

Edited by dweller25
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11 minutes ago, dweller25 said:

Does that include the mount or do you have one ?

I've got an old Meade 114-900 reflector with a EQ1B mount and tripod.  I was going to use that mount and tripod, but just manually track. I can put up with the vibration...

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2 hours ago, Gogleddgazer said:

I think there is a lot to be said for a small 3" APO that can be "thrown outside" at short notice when unforseen clear skies arise. In my limited time peering upwards some of my most enjoyable nights have been impromptu visual sessions like that. IMHO a light weight easy to move set up is worth it's weight in gold to maximise viewing opportunities. 

Yes that's the real beauty of a small refractor. You can do reactionary astronomy. See an unexpected weather window, grab the scope and go. With the 200P and 250P I would talk myself out of it. Too much hassle to setup. 

Definitely worth owning both. Aperture always wins, and nothing beats a dob for value. But for low power sweeps of star fields, nothing beats a small frac. 

 

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When I had a 200P dobsonian I had a 102mm F/6.5 ED doublet to compliment it and the pair covered a very wide range of observing interests.

Currently my "fleet" of refractors has grown to 4 scopes from 100m to 130mm in aperture. I still have just the one dobsonian which is a 12 inch.

I do a lot of visual observing with my refractors :smiley:

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I am a visual only observer and like many others have a mixed fleet,
as per my signature, but I adore my Vixen ED103, it hits the magic spot for me and my conditions.

Edited by Alan White
typos of course
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