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

a good DSO refractor?

  • Please log in to reply
22 replies to this topic

#1 Cloudystars

Cloudystars

    Lift Off

  • -----
  • topic starter
  • Posts: 6
  • Joined: 07 Nov 2019

Posted 08 November 2019 - 07:38 AM

I was wondering about a good refractor for DSOs?   Visual only, low to medium power.

I was thinking a quality achromat might work but, not willing to do f/15.  I am thinking of 6" - 8" aperture. .. something to rival 8-10" newts in performance.

 

  I've enjoyed viewing through refractors with their excellent contrast and pinpoint stars.

 

I see Istar offers interesting optics.

Any other good suggestions?

 

Thanks

 



#2 junomike

junomike

    Hubble

  • *****
  • Moderators
  • Posts: 17227
  • Joined: 07 Sep 2009
  • Loc: Ontario

Posted 08 November 2019 - 08:00 AM

Celestron/SW 150 F5 is best for Wide Field DSO's but also suffers some CA on brighter Stars.

ES 152 F6.5 is also something to consider.

IME a 6" Refractor can "run" with an 8" newt but not meet it on DSO's. A 10" Newt will go far deeper and leave the 6" Frac behind.


  • Jon Isaacs, stevew, noisejammer and 6 others like this

#3 M11Mike

M11Mike

    Viking 1

  • *****
  • Posts: 870
  • Joined: 02 Apr 2016
  • Loc: Ballston Lake, NY

Posted 08 November 2019 - 08:45 AM

And a DARK OBSERVING location - really dark.  


  • JIMZ7, stevew, noisejammer and 2 others like this

#4 vkhastro1

vkhastro1

    Apollo

  • *****
  • Posts: 1227
  • Joined: 21 Aug 2005
  • Loc: Vankleek Hill, Ontario, Canada

Posted 08 November 2019 - 08:54 AM

A few other options:

Astrotelescopes/Canadian Telescopes 152mm f/5.9 with a 3" Crayford focuser

A Celestron/Skywatcher among others 150mm f/8 "yard cannon" 



#5 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • Posts: 6108
  • Joined: 30 Dec 2006

Posted 08 November 2019 - 09:15 AM

First, welcome to Cloudy Nights...Cloudystars.

 

Larger aperture achromats, I find, do indeed make for excellent deep sky scopes.  

 

There are several brands of well made 6" F6-ish achromats that will serve well.  And even more of the 6" F8 versions which have been out for decades, readily available on the used market, and bargains in the refractor world at ~$400 USD used.  They make excellent deep sky scopes and I consider them light weight for their apertures.  Eyepieces also "like" the slower focal ratio too. 

 

So you can hunt one down (won't take long) and try it out to see if that is the type of thing you want.  If you shop carefully, you can resell it for what you paid too.  AND...they can also be easily cut back for bino-viewer use if you have some simple hand tool skills. 

 

Yes, Istar does make some excellent lenses and if you, again, have some skill with hand tools, you can roll your own tube assembly around the lens.  I've done so many times as I just like it.  But, for the money the common 6" F8 is a great deal, especially used IMO.

 

Now stepping past the 6" aperture really ramps up the size and weight of the OTA quickly (roughly the cube of the aperture ratio), but also that of the mounting....and the cost too  But it can be done with careful design.  Attached is an 8" F9 scope I made that came in under 30 pounds for the bare OTA.  It had an OK lens that I dug up on the net but was indeed spectacular on DSO's art low to moderate magnifications and my Losmandy G11 could actually swing it around quite well, especially at low power.   

 

Jeff

Attached Thumbnails

  • Scope Bb.jpg
  • Stops B.jpg

Edited by Jeff B, 08 November 2019 - 09:17 AM.

  • ArizonaScott, vkhastro1, payner and 7 others like this

#6 j.gardavsky

j.gardavsky

    Mariner 2

  • -----
  • Posts: 247
  • Joined: 18 Sep 2019
  • Loc: Germany

Posted 08 November 2019 - 10:59 AM

Since many years I am using the 6" F/5 Sky-Watcher (Synta) achromatic refractor, and I am quite satisfied, not considering a replacement.

With the 2" zenith prism, the spherical aberration is fairly well corrected, allowing to magnify up to 300x on the Moon, globular clusters and doubles.

 

However, the fast achromatic refractors are very sensitive to the choice of the eyepieces, and the money you will save on the OTA is later spent on the EPs.

 

Best,

JG


  • tomwall, Bomber Bob, Tyson M and 2 others like this

#7 Eric H

Eric H

    Viking 1

  • *****
  • Posts: 533
  • Joined: 12 Feb 2010
  • Loc: Washougal, WA

Posted 08 November 2019 - 11:25 AM

APM 152ED F8 Doublet.

APM 140 F7 Fpl-53 Doublet



#8 Bomber Bob

Bomber Bob

    Hubble

  • *****
  • Posts: 15928
  • Joined: 09 Jul 2013
  • Loc: The Swamp, USA

Posted 08 November 2019 - 11:35 AM

Bresser Messier AR152S  -->  https://www.apm-tele...ier-ar-152s-ota

 

Explore Scientific AR152 (F6.5)  -->  https://explorescien...ublet-refractor


Edited by Bomber Bob, 08 November 2019 - 11:38 AM.

  • DeanD and j.gardavsky like this

#9 25585

25585

    Fly Me to the Moon

  • *****
  • Posts: 5989
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 08 November 2019 - 01:12 PM

Altair Starwave 152mm


  • j.gardavsky likes this

#10 j.gardavsky

j.gardavsky

    Mariner 2

  • -----
  • Posts: 247
  • Joined: 18 Sep 2019
  • Loc: Germany

Posted 08 November 2019 - 02:28 PM

Altair Starwave 152mm

This one may be the Kasai (red painted) with the zonal curves published in

https://www.teleskop...-Objective.html

 

Best,

JG


  • Tyson M, 25585 and DeanD like this

#11 MalVeauX

MalVeauX

    Fly Me to the Moon

  • *****
  • Posts: 5908
  • Joined: 25 Feb 2016
  • Loc: Florida

Posted 08 November 2019 - 04:07 PM

I was wondering about a good refractor for DSOs?   Visual only, low to medium power.

I was thinking a quality achromat might work but, not willing to do f/15.  I am thinking of 6" - 8" aperture. .. something to rival 8-10" newts in performance.

 

  I've enjoyed viewing through refractors with their excellent contrast and pinpoint stars.

 

I see Istar offers interesting optics.

Any other good suggestions?

 

Thanks

Get an i-Star Optical 8" lens and have Seibert Optics or Parallax Instruments make the OTA. You're set.

 

If that's too rich (expect $5k cost for the above), then look at the options from 150mm F5 (Celestron Omni XLT) to the 150mm F8 ED (Skywatcher) options, for cheap ($750 to $2k).

 

Very best,


Edited by MalVeauX, 08 November 2019 - 04:09 PM.


#12 Phillip Creed

Phillip Creed

    Idiot Seeking Village

  • *****
  • Posts: 3255
  • Joined: 25 Jul 2006
  • Loc: Canal Fulton, OH

Posted 08 November 2019 - 04:43 PM

For ~$1,000 used, you might want to consider a Vixen 140-NA.  It's no apo and I wouldn't want to go to 200X+ on planets with it.  But it's got *substantially* better color correction vs. any of the 150mm f/5 achros and should be able to handle 100X or so just fine.  You're not really giving up much aperture vs. a 6"-refractor and it's not as heavy as many of the 6"-refractors out there.

Clear Skies,

Phil


  • 25585 and DeanD like this

#13 Jeff B

Jeff B

    Fly Me to the Moon

  • *****
  • Posts: 6108
  • Joined: 30 Dec 2006

Posted 08 November 2019 - 05:51 PM

I can certainly vouch for the Istar 8" F6 doublet.  I wrapped an OTA around one for a friend.  It is a deep sky monster and not all that big...but I'm used to 8-11" achromats anyway.  You can also stop it down to 6" for nice high power views but it will still have unfocused color.  On the bench in DPAC test, this sample was very nice.  A couple of pictures.

 

 

BTW, how much are you willing to spend?   We can certainly spend it for you as the sky's the limit around here on CN's...pun intended.  grin.gif

 

Jeff

Attached Thumbnails

  • Complete OTA.jpg
  • Focuser and End Cap.jpg

  • plyscope, Colin exraaf, jjack's and 2 others like this

#14 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 5708
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 08 November 2019 - 06:26 PM

This one may be the Kasai (red painted) with the zonal curves published in

https://www.teleskop...-Objective.html

 

Best,

JG

This telescope has come up before here and its description continues to puzzle me.

 

First, I did not know Ohara made lenses. The oddness of the claim, even if correct, is heightened by the technical data, which lists the glasses as K9 and F4. Those are Schott designations, not Ohara. I also do not find K9 or F4 the current Scott catalog. 

 

The ad claims that the lens, at f/5.9, has better color correction than a standard 6-inch f/8. Using the catalog values from ATMOS for K9 and F4 to calculate the variation of focus from C to F shows essentially the same color correction as the traditional BK7/F2 doublet. (Actually, a tad worse, but not enough to worry about - just a bit under 1 part in 1800 for either combination.)

 

Either I'm missing something, or the ad does not convey the information needed to evaluate their claim of improved color correction.

 

Clear skies, Alan


  • Jon Isaacs likes this

#15 j.gardavsky

j.gardavsky

    Mariner 2

  • -----
  • Posts: 247
  • Joined: 18 Sep 2019
  • Loc: Germany

Posted 09 November 2019 - 04:03 AM

Hello Alan,

 

I can remember the discussion about the Kasai refractor here on the CN.

The published zonal curves, I have extra linked in my post, show no difference to  what one would expect from a conventional Fraunhofer. The glass material codes are suspect.

 

My only comments have been about the red paint differentiator,

JG

 

PS: Otherwise, I would likely have that Kasai as a replacement for my aged Synta.

But that's not the case.



#16 Cloudystars

Cloudystars

    Lift Off

  • -----
  • topic starter
  • Posts: 6
  • Joined: 07 Nov 2019

Posted 09 November 2019 - 07:22 AM

I would like to go > 6".  I would use it as a sky sweeper, keeping mags < 100X for sure.



#17 Alan French

Alan French

    Night Owl

  • *****
  • Posts: 5708
  • Joined: 28 Jan 2005
  • Loc: Upstate NY

Posted 09 November 2019 - 08:55 AM

Hello Alan,

 

I can remember the discussion about the Kasai refractor here on the CN.

The published zonal curves, I have extra linked in my post, show no difference to  what one would expect from a conventional Fraunhofer. The glass material codes are suspect.

 

My only comments have been about the red paint differentiator,

JG

 

PS: Otherwise, I would likely have that Kasai as a replacement for my aged Synta.

But that's not the case.

I saw the curves and noted they looked essentially like what you'd get from BK7/F2, but I didn't do a close comparison. Easy enough to calculate the focal variation based on the glasses claimed. 

 

Not good when ad claims and specifications have people scratching their head. 

 

Clear skies, Alan


  • j.gardavsky likes this

#18 j.gardavsky

j.gardavsky

    Mariner 2

  • -----
  • Posts: 247
  • Joined: 18 Sep 2019
  • Loc: Germany

Posted 09 November 2019 - 01:23 PM

I saw the curves and noted they looked essentially like what you'd get from BK7/F2, but I didn't do a close comparison. Easy enough to calculate the focal variation based on the glasses claimed. 

 

Not good when ad claims and specifications have people scratching their head. 

 

Clear skies, Alan

Hello Alan,

 

some people in Germany have already pointed the problem with the glass materials to TeleskopExpress, then the marketing has  removed K9 and F4, and now I can see it is back.

 

Another reason for the 6" F/5 Synta achro has been its comapartively low weight, I can mount the OTA on the Cullmann tripod, and fully accessorized, I can carry those 15kg in the backyard from one observing site to another just with one of my hands.

6inch 750mm Synta on Cullmann Titan CT200 tripod.jpg

 

Best,

JG



#19 garret

garret

    Apollo

  • ****-
  • Posts: 1477
  • Joined: 26 Jul 2009
  • Loc: Netherlands

Posted 09 November 2019 - 02:05 PM

 

good refractor for DSOs?   Visual only

Fits in any photo bag: the APM 25x100mm APO binocular, they excel in DSO, nebula and many other objects.

That is if you receive a good collimated sample...fits in the cabin baggage compartment of an aircraft.

 



#20 Paul Hyndman

Paul Hyndman

    Apollo

  • -----
  • Posts: 1184
  • Joined: 13 Jul 2004
  • Loc: Connecticut Shoreline USA

Posted 09 November 2019 - 02:30 PM

I was wondering about a good refractor for DSOs?   Visual only, low to medium power.

I was thinking a quality achromat might work but, not willing to do f/15.  I am thinking of 6" - 8" aperture. .. something to rival 8-10" newts in performance.

 

  I've enjoyed viewing through refractors with their excellent contrast and pinpoint stars.

 

I see Istar offers interesting optics.

Any other good suggestions?

 

Thanks

Just a thought, but, if you want high-level performance in a fast & more affordable format, you may want to consider a Mak-Newt. Most aficionados generally agree that MNs provide views very close to a slightly smaller apochromatic refractor.

 

FWIW, my 8" f/5.9 MN would give many 7" apos a run for the money (low power starfield sweeps OR highly detailed planetary/lunar views that are to die for) albeit in a somewhat more cumbersome design.

Attached Thumbnails

  • mn86.JPG
  • AP175AP160.jpg

Edited by Paul Hyndman, 09 November 2019 - 02:49 PM.

  • jjack's likes this

#21 Cloudystars

Cloudystars

    Lift Off

  • -----
  • topic starter
  • Posts: 6
  • Joined: 07 Nov 2019

Posted 13 November 2019 - 12:59 PM

Hi Paul
That looks nice but I hear they are heavy.
Maybe I settle for less aperture with the best optics, like Tak.
I can use a bigger dob for DSOs.
More aperture but, arguably less quality.
Just a thought.
  • Paul Hyndman and LDW47 like this

#22 TheFacelessMen

TheFacelessMen

    Viking 1

  • -----
  • Posts: 515
  • Joined: 15 Sep 2014
  • Loc: Canberra, ACT

Posted 13 November 2019 - 03:58 PM

I use my Tak TOA150 for DSO quite a lot.....main benefit being FoV over my other scopes.

 

But realistically my CN212 blows the TOA150 away for light gathering and detail on DSO's

 

Honestly your money is better spent on a high quality reflector....even going extreme high quality custom reflector you will be streets ahead on DSO visuals and save yourself a lot of money.

 

I tend to alternate my viewing between the TOA150 and the CN212 and Mewlon 300 which covers off all my needs......although I have been thinking of the addition of a nice Tak C400 lately wink.gif  



#23 Wildetelescope

Wildetelescope

    Surveyor 1

  • -----
  • Posts: 1522
  • Joined: 12 Feb 2015
  • Loc: Maryland

Posted 13 November 2019 - 04:43 PM

Just a thought, but, if you want high-level performance in a fast & more affordable format, you may want to consider a Mak-Newt. Most aficionados generally agree that MNs provide views very close to a slightly smaller apochromatic refractor.

 

FWIW, my 8" f/5.9 MN would give many 7" apos a run for the money (low power starfield sweeps OR highly detailed planetary/lunar views that are to die for) albeit in a somewhat more cumbersome design.

Sooo.... Now I am jealous:-)  That is certainly a nice collection of scopes!!!

 

JMD


  • Paul Hyndman likes 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