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

RACI finder for widefield piggyback combo

Visual Refractor Equipment Accessories
  • Please log in to reply
7 replies to this topic

#1 nordude

nordude

    Lift Off

  • -----
  • topic starter
  • Posts: 8
  • Joined: 01 Sep 2021
  • Loc: SWE

Posted 26 November 2021 - 04:17 PM

I had a thought when looking for a new RACI finder to adress my lack of widefield telescopes, if it was possible and worth the cost to combine finder scope and widefield refractor into one glorious piggybacked telescope!

 

A. Is there a finder/guide scope good enough for enjoyable widefield visual?

B. Is it worth using a small quality refractor as a finder, lets say an ED60 or other?

C. Would you rather save your money on a budget finder and buy a second dedicated widefield telescope, lets say an ED80 or 100mm triplet?

 

Looking at A. using one of the 60mm ED guide scopes with helical or a VarioFinder cost run away quickly...

 

I'm probably not the first to go down this rabbit hole so would love to hear your thoughts, experiences and gear tips!



#2 havasman

havasman

    Hubble

  • *****
  • Posts: 13,486
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 26 November 2021 - 05:04 PM

I put a Stellarvue 50mm finderscope on my 12.5" Dob for just that purpose and it has been quite successful. Last time out to the dark site I observed NGC253 in the bigger scope and then checked it out in the "finder" to find it easily visible and quite enjoyable. While the supplied 23mm reticle eyepiece is just fine, I like an ES68 20mm even better for observing as the field is clear of x-hairs. Any of the SV finderscopes would work very well. The 50mm is lightest and a good choice for the small Dob.


  • Bean614 likes this

#3 nordude

nordude

    Lift Off

  • -----
  • topic starter
  • Posts: 8
  • Joined: 01 Sep 2021
  • Loc: SWE

Posted 26 November 2021 - 06:24 PM

That sounds sweet, thanks for sharing!

 

I've heard good things about the SV finders and reasonably priced although not exactly cheap. I'm a bit on the fence if I'd be content with achro though, but maybe I just have a bad body of reference.

I have not found Stellarvue available in Europe unfortunately, but they look very much alike some APM and TS finder scopes. Are they in fact the same?

Link for comparison: https://www.apm-tele...cle-eyepiece-55



#4 havasman

havasman

    Hubble

  • *****
  • Posts: 13,486
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 26 November 2021 - 07:50 PM

I don't know whether SV's finderscopes are the same as ones sold elsewhere. There are enough visible differences in those and the one you linked that I doubt they're the same. But that does not invalidate the APM or other scope. It might be worthwhile to contact SV directly to see if they will ship to Sweden. I expect they might. If not, my experience with APM makes me confident of the performance of their products. TS is likely also top rank but I have no experience with them.

 

I think your concept is sound and my bet would be that you'll find a good scope with which to implement it well.



#5 nordude

nordude

    Lift Off

  • -----
  • topic starter
  • Posts: 8
  • Joined: 01 Sep 2021
  • Loc: SWE

Posted 27 November 2021 - 02:02 AM

Thanks!
Import fees makes the SV 60mm cost twice the APM unfortunately.
At that point I could just as well buy an ED60 for a finder. Anyone tried this and can talk me into or out of that?

#6 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 97,322
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 27 November 2021 - 05:10 AM

My two cents:

 

I have a 50mm StellarVue finder.  It's F/4.  For what it is,with quality eyepieces, it's decent but it shows the difficulties of an F/4 finder, it's got a lot of field curvature as is expected so the stars are never all in sharp focus. 

 

I recently acquired a 50mm Astro-Tech finder scope.  It's similar but I roughly measured it at F/5.  It doesn't offer as wide a field as the SV finder but it is considerably sharper across the field with my standard finder eyepiece, a 20mm 68 degree Explore Scientific.  It's really quite an amazing view.  5.2 degrees or so at 12.5x with a 4mm exit pupil.

 

And at higher magnifications, not that this is super important, it is much better than the SV.  I routinely split Castor at 5 arc-seconds, something I haven't been able to do with the SV. And I have been able to split Porrima at 3 arc-seconds though that was very difficult.  

 

Here is a thread I started on the Astro-Tech finder.  I am using it with all my Dobs as will as with my 120mm ED refractor.  

 

https://www.cloudyni...45-50mm-f5-rft/

 

That color scheme is no longer available but others are:

 

https://www.astronom...ack-finish.html

 

Jon



#7 nordude

nordude

    Lift Off

  • -----
  • topic starter
  • Posts: 8
  • Joined: 01 Sep 2021
  • Loc: SWE

Posted 28 November 2021 - 07:05 PM

That is a great tip, thanks Jon! I sent them an email since most identifiable specs are missing in the link, if it's the same scope I'm trying it out!

 

I got on a bit of a deep dive into your thread and a hundred others regarding "super finders" and found so much great info. For example if I get the chance to buy this scope if it's restocked or second hand I'm pulling the trigger.

 

But I can't help feel a bit frustrated with the lack of options when it comes to good visual finder scopes. In contrast quality guide scopes that are just a bit too fast and with too little back focus are everywhere, what's up with that?

The Evoguide 50ED is a prime example that could have been a great super finder if they had shaved off a bit of the back and sold or shipped with spacers. Some more are doing modular tubes but keeping them too fast and adding anything between "semi apo coating" to quadruplets for good measure.

 

I found some interesting info over on stargazerslounge regarding how aperture and f-ratio affects CA that I wasn't aware of previously:

https://stargazerslo...comment=3382235

If I understand it correctly the CA is less with smaller aperture and longer f-ratio(also reducing field curvature issues), and extrapolating on the linked graph a 50mm scope should have almost no CA at f/6 or slower.

Does anyone have a good link to more solid information on this topic?

 

If this is correct maybe I should just find a small budget refractor and slap on a finder shoe on it :)



#8 Sky_LO

Sky_LO

    No Kick - Mount Marker Lights

  • *****
  • Vendors
  • Posts: 473
  • Joined: 22 Dec 2018
  • Loc: Oregon USA

Posted 03 December 2021 - 02:56 PM

I am working on a piggyback setup right now. 

 

I made an 80mm short tube refractor from a lens cell sold by surplusshed.com

And following the instructional article about it in S&T Magazine.  Basic cost of the piece is under $70 to make (cell + focuser).

 

With a 30mm plossel, it should give about a 3.9 degree FOV 

The goal is to have a wide FOV (without the crosshairs) at the same time as the DOB view.        

Now I just need some clear sky in our Oregon winter cloudfest to test it all.  

 

The 80mm is now officially a "gadget" with 3 mounts attached and available.    

a tripod quick-connect, an SE6 rail, and a telescope dovetail for the piggyback on my XT10

 

The 80M weighs about 2 pounds.  The cooling fan talent cell and a pound of welder weights was all that was needed for counter balance.  

 

 

-Lauren   

 

 

 

 

Attached Thumbnails

  • piggy_thumb.JPG
  • refr_thumb.JPG



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





Also tagged with one or more of these keywords: Visual, Refractor, Equipment, Accessories



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics