Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Wide Field Refractor

  • Please log in to reply
18 replies to this topic

#1 stoest

stoest

    Ranger 4

  • -----
  • topic starter
  • Posts: 325
  • Joined: 04 Jan 2016

Posted 23 February 2020 - 12:55 AM

Currently my main scope is an 18" dob and I'd like to find a wide field refractor to complement it.  My initial thought is something in the 102-110mm class with as short a focal length as possible to get the widest field possible in that aperture.  I'm looking to spend $1-1.5K for both the OTA and the mount.  I'm thinking about a used WO 110 Megrez, Orion EON or iOptron Versa if I can find one, as these are all around F6 but I'm looking for input.  I don't have a lot of experience with refractors so if there are other good or better options in my price range then I'm open.  I'm a little worried about CA in that fast a refractor doublet but since it will be a 100% visual scope I'm not sure I see the value in going to a triplet.  My main use will be looking at larger objects and just scanning the sky at low power.  I currently have 30 to 6.7mm ES 82 eyepieces and would like to be able to use them in the scope.

 

For the mount I would prefer a simple Alt-Az mount, just mentioning that since that has to come out of the budget as well.



#2 Taosmath

Taosmath

    Apollo

  • *****
  • Posts: 1,041
  • Joined: 21 May 2014

Posted 23 February 2020 - 01:27 AM

I have an Orion ST120 on a skywatcher Az-GTi (on a Meade Field tripod with 2" legs) to pair with my Dobs for exactly the reasons you describe.

 

 Yes it has some CA on bright objects but I only notice it on the moon and solar system objects (notably Venus) and since I mainly do DSO's and double stars, the CA doesn't worry me.  I bought some CA minimization filters, but I've never bothered with them.  The scopes you mention will probably be much better controlled than mine, but I do love the wide field view (F5) and large aperture (120mm).

 

I find when looking at double stars I sometimes want to go over 200x magnification and so I bought a nagler 3-6mm zoom, which combo would just about swallow your budget (Scope $300 new, Mount $300 new (get the mini pier extension- essential for a refractor), zoom $300 used, tripod $100 used).

 

I also have an 80mm ED refractor (F7) which has a very similar FOV to my ST120 with a given eyepiece.  The 80 mm image is a little sharper (but not a lot) but the ST120 is brighter, which I prefer.

 

So if you really want wide field low magnification sweeping, then I don't think CA will be a significant issue (except on venus) and hence  I would go for the largest diameter/mount pairing you can afford.

 

Just my 2c.


  • LDW47 and stoest like this

#3 russell23

russell23

    Voyager 1

  • *****
  • Posts: 10,284
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 23 February 2020 - 07:06 AM

I'd go with a 102mm f/7 ED doublet such as this:

 

https://agenaastro.c...lue/category/3/

 

For a mount a lot of people are using this one with 80-102mm class refractors:

 

https://agenaastro.c...-tall-plus.html

 

Whatever you choose I think there is a definite tipping point with the 102mm class refractor vs. the 80mm class.   I find the 102mm class to be enough light whereas the 80mm left me wanting more. 


  • stoest likes this

#4 Spikey131

Spikey131

    Apollo

  • *****
  • Posts: 1,238
  • Joined: 07 Feb 2017

Posted 23 February 2020 - 08:17 AM

Used Tele Vue 101.


  • Mike W, Terra Nova, areyoukiddingme and 1 other like this

#5 bobhen

bobhen

    Soyuz

  • *****
  • Posts: 3,749
  • Joined: 25 Jun 2005

Posted 23 February 2020 - 08:34 AM

The Sky Watcher 102 F5 and the Orion 120 F5 Achromats, both made by Synta, are popular as “low cost” choices for low power, wide field, deep sky observing.

 

Color error will not be an issue when used at low powers.

 

There will be some field curvature but well corrected eyepieces can midigate this and it is pretty mild and not obtrusive anyway.

 

Just about any reasonable alt/az mount will hold these scopes so pick one that works for your needs.

There are a few threads about how people love their Orion 120 F5 refractors. But if more portability is needed (like airline overhead bin portability) the 102 F5 will do the job.

 

You could also look for a used Televue Genesis. Those scopes will have a perfectly flat field but even used they will push your budget and those scopes are a couple of decades old by now.

 

I have owned a TV Genesis, Orion 120 F5 and a Synta 102 F5. I kept the 102 F5 because of its portability. I have owned that scope for 15 years, which I guess says something.

 

Bob

 

Photo below shows my 102 F5 mounted next to a Tak 120

 

Attached Thumbnails

  • IMG_0099.jpg

  • Bomber Bob and stoest like this

#6 SeattleScott

SeattleScott

    Fly Me to the Moon

  • *****
  • Posts: 7,113
  • Joined: 14 Oct 2011

Posted 23 February 2020 - 09:09 AM

I believe all three of those refractors are the same scope sold under different brands. Visually you will be able to see the difference between these scopes and a FPL53 on planets. Whether it is worth the cost to upgrade to FPL53 or a triplet is up to you. For DSO it shouldn’t matter.

My Skywatcher AZ4 Mount would support such a scope nicely. Unfortunately difficult to find anymore in the States.

I found my Vixen ED103S a joy to use on this mount. Used prices around $1,000 so you could come in on budget. Very well balanced scope, eliminating the need for a pier extension. Rather light for a higher end 4” Apo. And of course outstanding optically.

Scott

Edited by SeattleScott, 23 February 2020 - 09:15 AM.

  • Terra Nova, stoest and db2005 like this

#7 db2005

db2005

    Apollo

  • *****
  • Posts: 1,030
  • Joined: 23 Dec 2017
  • Loc: Living in Denmark, under Bortle 5 skies.

Posted 23 February 2020 - 09:10 AM

100 mm-class refractors are indeed extremely nice to look through. But I have found that affordable, light-weight and sturdy alt-az mounts that can hold a 4" APO satisfactorily are rare as hen's teeth. If you are willing to settle for a 3" class refractor there are many more options, including some decent low-cost options.


Edited by db2005, 23 February 2020 - 09:12 AM.

  • stoest likes this

#8 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 82,774
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 23 February 2020 - 09:18 AM

There are many approaches to the dark sky wide field refractor thing, Whenever I am out under dark skies, I set up at least one, sometimes two, short focal length fast refractors to go with the Dob I have chosen.  

 

Here's some thoughts and experiences.. 

 

- Achro versus ed/apo.  If the scope is only going to be used for deep sky, an achromat offers similar views to an ed/apo at a much more affordable cost.  If the scope is going to be a dual purpose scope that will see backyard use for the planets and doubles as well as deep sky from a dark site, then an ED/apo is worthwhile.  

 

- 80mm versus 102mm.  For me, these are two apertures I find to be the best companions for a Dob.  The 4 inch typically goes some deeper, the 80mm goes some wider.  Typically the 80 mm will be lighter and more manageable than the 4 inch.  In my mind, for this sort of observing, there is a noticeable difference between an 80mm and a 100mm but like an 8 inch Dob and a 10 inch Dob, they are much more the same than they are different.  

 

- Over the past 20 years I have owned a number of wide field refractors, currently I have 5, two achromats and 3 ED/apos, an ST-80 fitted with a 2 inch focuser, a Celestron 100mm F/5, an 80mm F/6 doublet, an 80mm F/7 doublet and the TeleVue NP-101.  Each one has it's place, has it's virtues.  Other scopes I have owned that are worthy of consideration are the ES AR-102 achromat, the AT-102ED, the Orion 100mm F/6 achromat.  

 

-  The 102mm F/5 achromat and the NP-101 are at opposite ends of the spectrum.  The 102mm F/5 achromat is just simple and crude, significant field curvature, chromatic aberration at higher powers, the NP-101 is as perfect as it gets for a wide field scope.  It's corrected for field curvature, the color correction is essentially perfect, whatever you want to look at, it's just about as perfect as perfect can be.

 

And yet, when observing deep sky, particularly at lower magnifications, one sees pretty much the same things in both scopes, 4 inches is 4 inches.  

 

The NP-101, even used, is not within the budget.  A used Genesis or SDF might be but I'd probably skip those. 

 

I see two approaches.  Something very capable and very affordable, the 102mm F/5 achromat.  Get your feet wet, with the 30mm ES 82 degree you're looking at a 4.8 degree TFoV at about 17x, that is going to be simply awesome.  Pop on an UHC or O-III filter and go to town.  

 

The other approach is the Astro-Tech 102ED.  It doesn't offer the widest field of views, about 3.4 degrees with the 30 mm ES 82 Degree, but they are plenty wide for most purposes and it's better at high magnifications on DSOs and it's a dual use scope, it is a grap and go doubles and planets scope, it's more versatile.  

 

Jon


  • Tropobob, stoest and db2005 like this

#9 MalVeauX

MalVeauX

    Fly Me to the Moon

  • *****
  • Posts: 6,586
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 23 February 2020 - 09:36 AM

Currently my main scope is an 18" dob and I'd like to find a wide field refractor to complement it.  My initial thought is something in the 102-110mm class with as short a focal length as possible to get the widest field possible in that aperture.  I'm looking to spend $1-1.5K for both the OTA and the mount.  I'm thinking about a used WO 110 Megrez, Orion EON or iOptron Versa if I can find one, as these are all around F6 but I'm looking for input.  I don't have a lot of experience with refractors so if there are other good or better options in my price range then I'm open.  I'm a little worried about CA in that fast a refractor doublet but since it will be a 100% visual scope I'm not sure I see the value in going to a triplet.  My main use will be looking at larger objects and just scanning the sky at low power.  I currently have 30 to 6.7mm ES 82 eyepieces and would like to be able to use them in the scope.

 

For the mount I would prefer a simple Alt-Az mount, just mentioning that since that has to come out of the budget as well.

Heya,

 

Maybe take a look at a robust alt-az mount like the SkyTee (can take two scopes) with two saddles and slow motion control.

 

Maybe consider a 110 F7 ED doublet for near 4 degree FOV and a bit more aperture. Or perhaps a 102mm F7 FPL53 ED doublet for near 4 degree FOV with better glass. Then a wee 70mm F6 ED doublet next to it for those ~6 degree FOV options.

 

Very best,


  • LDW47 and stoest like this

#10 LDW47

LDW47

    Gemini

  • *****
  • Posts: 3,182
  • Joined: 04 Mar 2012
  • Loc: North Bay,Ontario,Canada

Posted 23 February 2020 - 09:49 AM

Heya,

 

Maybe take a look at a robust alt-az mount like the SkyTee (can take two scopes) with two saddles and slow motion control.

 

Maybe consider a 110 F7 ED doublet for near 4 degree FOV and a bit more aperture. Or perhaps a 102mm F7 FPL53 ED doublet for near 4 degree FOV with better glass. Then a wee 70mm F6 ED doublet next to it for those ~6 degree FOV options.

 

Very best,

Now give them a price for all of that great stuff vs their budget, thats the key !  Clear Skies !


  • stoest likes this

#11 coopman

coopman

    Fly Me to the Moon

  • *****
  • Posts: 6,120
  • Joined: 23 Apr 2006
  • Loc: South Louisiana

Posted 23 February 2020 - 09:53 AM

I'd rather have a 6" f/5 Newt with a 2" focuser.
  • SteveG and stoest like this

#12 MalVeauX

MalVeauX

    Fly Me to the Moon

  • *****
  • Posts: 6,586
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 23 February 2020 - 11:36 AM

Now give them a price for all of that great stuff vs their budget, thats the key !  Clear Skies !

The links are to the items with their prices. Various combinations of the above links fit into the specified $1.5k budget.

 

Very best,


  • Jon Isaacs likes this

#13 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 82,774
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 23 February 2020 - 11:41 AM

The links are to the items with their prices. Various combinations of the above links fit into the specified $1.5k budget.

 

Very best,

 

I have a StellarVue MG-2 mount, it seems to be the Sky-Tee mount set up for a single scope. It's solid with my 120 mm Eon but overkill for most 4 inch refractors.

 

Jon


  • MalVeauX likes this

#14 LDW47

LDW47

    Gemini

  • *****
  • Posts: 3,182
  • Joined: 04 Mar 2012
  • Loc: North Bay,Ontario,Canada

Posted 23 February 2020 - 12:03 PM

The links are to the items with their prices. Various combinations of the above links fit into the specified $1.5k budget.

 

Very best,

 

The links are to the items with their prices. Various combinations of the above links fit into the specified $1.5k budget.

 

Very best,

Sounds great, with tax, shipping and what have you, probably several hundred over the high end of the budget. But thats OK its close !  Clear Skies !



#15 stoest

stoest

    Ranger 4

  • -----
  • topic starter
  • Posts: 325
  • Joined: 04 Jan 2016

Posted 23 February 2020 - 04:33 PM

Appreciate all the great information, it's given me a lot to think about and I'll start watching the classifieds here and on Astromart and keep doing my research.  Seems like there are a lot of great options.



#16 MalVeauX

MalVeauX

    Fly Me to the Moon

  • *****
  • Posts: 6,586
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 23 February 2020 - 05:13 PM

Appreciate all the great information, it's given me a lot to think about and I'll start watching the classifieds here and on Astromart and keep doing my research.  Seems like there are a lot of great options.

Used is a great way to go!

 

I'm a bit of a wide field junky, and really, achromatic doublets are where the speed is at.... hard to find F5 in the ED/APO world. And really, when you're at low power and wide FOV, the CA is not the problem, you rarely will see it other than ultra bright stuff, like Venus or Sirius. The thing to consider with really fast scopes is the coma/SA.

 

Two very inexpensive but excellent fast achromatic doublets are the ST120 (120mm F5) and ST80 (80mm F5) with 2" focusers and 2" diagonals. Plop in a long wide eyepiece and you have a near 5" aperture with 4 degree FOV and a 3.5" aperture with a 6" degree FOV that can be side by side. Inexpensive, light weight, easy to mount, you could put them on a dual-saddle mount and cruise the sky.

 

Very best,


  • stoest likes this

#17 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 5,811
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 23 February 2020 - 05:36 PM

This graph might be helpful. It shows the true field for focal lengths from 400 to 1000mm, both for 1.25-inch (blue line) and 2-inch eyepieces (red line). The maximum field stop was considered to be 27mm in diameter for 1.25-inch eyepieces and 46mm for 2-inch eyepieces. 

 

I'm am sure most folks shopping for a true wide field telescope are going with 2-inch eyepieces, but felt the comparison was useful.

 

True Field.jpg

 

Clear skies, Alan

 

 


  • eros312, desertlens, stoest and 1 other like this

#18 Mike W

Mike W

    Surveyor 1

  • *****
  • Posts: 1,603
  • Joined: 30 Apr 2006
  • Loc: Upstate NY

Posted 23 February 2020 - 07:13 PM

Definitely get a used TV101 or Genesis SDF. Here's my old TV102, a couple decades old but none the worst for wear!

 

5.jpg

 

Here's a TV101

https://www.cloudyni...-1580884452.jpg


Edited by Mike W, 23 February 2020 - 07:18 PM.

  • areyoukiddingme and stoest like this

#19 areyoukiddingme

areyoukiddingme

    Aurora

  • *****
  • Posts: 4,692
  • Joined: 18 Nov 2012

Posted 23 February 2020 - 07:18 PM

Another vote for a used Televue 101.

 

You get performance very close to the latest NP, and they go for less than $1500. They are built to last more than a lifetime, they go wide, have a flat field, and can take magnification without any false color too.


  • Mike W and stoest like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics