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

EAA and refractors

EAA Refractor
  • Please log in to reply
57 replies to this topic

#1 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 14 June 2022 - 11:05 AM

Although this could be considered a general equipment question, it's the EAA perspective I really want discussed.

 

Many EAAers have an SCT and many have a refractor and quite a few have both.  Some came to EAA from other places and brought the kit they had.  I'm not sure that Errol bought his 130mm triplet for primarily EAA use.

 

Assuming a desire for 'hardcore' EAA, but only casual Visual or casual AP, is there any good reason for doing EAA with a refractor OTA better than an ED doublet?  A triplet WILL be better is some ways, but at significant cost, so is it 'worth' it for EAA only?  Is there a specific EAA practice that would benefit from something better than an ED doublet, in a meaningful way?  Heck, narrowband can be done well with an achromat.

 

I'm interested in both opinion and experience.  I realize that factors such as focuser quality, speed, focal length, and the availability or necessity of reducers and flatteners matters too.


  • vtornado likes this

#2 MarMax

MarMax

    Mercury-Atlas

  • *****
  • Posts: 2,708
  • Joined: 27 May 2020
  • Loc: SoCal

Posted 14 June 2022 - 11:33 AM

I can only speak about my opinion as I have minimal experience. I'll relate it more to eyepiece selection than doublet vs. triplet. I quickly learned that I did not like the views through the low cost EP's where the center 60% is in-focus and the outer 40% is not. After buying a TeleVue 22T4 it was game over on the cheap EP's.

 

Even though I have nice triplet refractors I could not tell you how much better they are than a doublet, but I know they are "best corrected" to the edge of field and this IMO very important for my happiness. Would it matter for EAA, I can't say. I did notice some egg shaped stars at the edge of field with the Stowaway and the QHY183C (no flattener). So even with a nice triplet you will need the flattener if you plan to use a larger sensor camera.

 

M20edgecrop_92mm_533c_YV_96F_960S_NoEdit_05312022s.jpg



#3 vtornado

vtornado

    Fly Me to the Moon

  • *****
  • Posts: 5,543
  • Joined: 22 Jan 2016
  • Loc: NE Illinois

Posted 14 June 2022 - 12:12 PM

I just started imaging.  

 

I have a small chip camera 1/3 inch.

So far I am happy with a 130 f/5 reflector.  (Cheap,Light,Fast, No CA)

I assume ... if I moved to a larger chip I would have to start dealing with coma,

but at 1/3 inch I don't see it.  Focusing is really tough.   

 

I have yet to try my ED fpl53 f/7.5 refractor.  That will be next on the list of things to

try to see how the CA is presented.  I am in no mood to do post processing to remove it.  I asumme as the FL is reduced, I will have to deal with field curvature

if I were to move up to a larger chipped camera.

 

from a newb, but very observant, and not biased  (pragmatic)


Edited by vtornado, 14 June 2022 - 12:15 PM.


#4 barbarosa

barbarosa

    Soyuz

  • *****
  • Posts: 3,722
  • Joined: 11 Apr 2010
  • Loc: E of San Francisco Bay and W of the Awahnee

Posted 14 June 2022 - 12:34 PM

Are you asking because you are seriously contemplating the purchase of a better refractor, a triplet or an ED doublet semi-apo? Is there something about your images that you think might be improved if you purchase  an ED doublet or a triplet?  Is there something about the mechanicals of your current scope that you would like to improve?

 

I wonder as well if the opinions of those who do not or have not used an apo or semi- apo for EAA imaging or any imaging, can be of much practical value to someone contemplating the purchase of an apo or semi-apo? 

 

But let me vote anyway by saying that an SCT was my weapon of choice for EAA. Then I sold my SCTs and the standing rig is now a RASA and an Esprit 120, on an EQ mount on a pier.

 

I am a "hardcore" EAA guy. Last night it was mostly 30s frames, with a few targets getting 60s. But that is just my opinion. As for what my vote is worth remember that Bud Light, Coors Light, and Miller Lite are the best selling beers in America, and Bud is said to be the best selling beer in the worldshocked.gif


Edited by barbarosa, 14 June 2022 - 04:01 PM.

  • steveincolo likes this

#5 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 14 June 2022 - 12:38 PM

Are you asking because you are seriously contemplating the purchase of a better refractor, a triplet or an ED doublet semi-apo? Is there something about your images that you think might be improved if you purchase  an ED doublet or a triplet?  Is there something about the mechanicals of your current scope that you would like to improve?

 

I wonder as well if the opinions of those who do not or have not used an apo or semi- apo for EAA imaging or any imaging, can be of much practical value to someone contemplating the purchase of an apo or semi-apo? 

 

But let me vote anyway by saying that an SCT was my weapon of choice for EAA. Then I sold my SCTs and the standing rig is now a RASA and an Esprit 120, on an EQ mount on a pier.

 

I am a "hardcore" EAA guy. Last night it was mostly 30s frames, with a few targets getting 60s. But that is just my opinion. As for what my vote is worth remember that Bud Light, Coors Light, and Miller Lite are the best selling beers in America, and Bud is said to be the best selling beer in the worldshocked.gif

 

 

 

 

 

 

 

f/7 ED doublet and the f/7 triplet that I currently own and use for EAA are superior to the lower cost doublets that initially used for EAA. The f/7 semi-apo was so good 

I am always considering possibilities.  I have both 70mm and 80mm ED inexpensive doublets and in my ignorance, I am satisfied.  I'm actually trying to rule out the siren call of better kit without having to go through the exercise of actually buying it and trying it.  The experiences of others will inform my future plans.


Edited by SchoolMaster, 14 June 2022 - 12:39 PM.

  • barbarosa likes this

#6 Alien Observatory

Alien Observatory

    Vanguard

  • *****
  • Posts: 2,063
  • Joined: 13 Nov 2015

Posted 14 June 2022 - 12:45 PM

I believe any FPL-53 and Lanthanum air-spaced doublet will have excellent color correction and minimal CA.  These types of telescopes scopes have been available for decades and are very reasonable priced.  With the proper reducer installed they are even better for EAA and about 1/2 the cost of a triplet.   Pat Utah :)


  • barbarosa, steveincolo and Far_Southern_Skies like this

#7 azcubs76

azcubs76

    Mariner 2

  • -----
  • Posts: 202
  • Joined: 06 Apr 2020
  • Loc: Chandler, AZ

Posted 14 June 2022 - 01:25 PM

I used an old Celestron C80ED F7.5 reduced to F6 for quite awhile and was quite happy with it. I ended up grabbing at AT80EDT F6 reduced to F4.8 off the classifieds here and have not looked back. The extra field of view and significant reduction in image acquisition time was worth it to me. So for me it's all about focal ratio as both scopes are semi/full ED and produce quality results. All refractors will need a flattener for perfect stars on the edges.

 

I've always been interested in what you could get out of an Orion 120st F5 or equivalent. Not interested enough to actually acquire one so far though.



#8 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 14 June 2022 - 03:46 PM

I used an old Celestron C80ED F7.5 reduced to F6 for quite awhile and was quite happy with it. I ended up grabbing at AT80EDT F6 reduced to F4.8 off the classifieds here and have not looked back. The extra field of view and significant reduction in image acquisition time was worth it to me. So for me it's all about focal ratio as both scopes are semi/full ED and produce quality results. All refractors will need a flattener for perfect stars on the edges.

 

I've always been interested in what you could get out of an Orion 120st F5 or equivalent. Not interested enough to actually acquire one so far though.

The f/5.5 and reduction further of the $900 SharpStar EDPH 76 is intriguing compared to my simple 80ED at f/7 reduced to f/5.6


Edited by SchoolMaster, 14 June 2022 - 03:48 PM.


#9 alphatripleplus

alphatripleplus

    World Controller

  • *****
  • Moderators
  • Posts: 130,608
  • Joined: 09 Mar 2012
  • Loc: Georgia

Posted 14 June 2022 - 04:12 PM

 

 

Many EAAers have an SCT and many have a refractor and quite a few have both.  Some came to EAA from other places and brought the kit they had.  I'm not sure that Errol bought his 130mm triplet for primarily EAA use.

 

 

In my case, I also wanted a nice planetary scope that was reasonably fast for EAA. I think an ED doublet would be fine for those goals as well. 

 

If my sole intended use was EAA, I doubt I would have gone with the 130EDT.


  • Tfer likes this

#10 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 15 June 2022 - 07:45 AM

Have an AT70ED an SVBONY80ED which are FPL-51 doublets.  I have 80ST and a StarTravel 102mm which are achromats.

 

 

So, in general and realizing that there are always exceptions, and for f/5 to f/7.5 ratio, faster being better for collecting photos, but worse for CA, other things being equal, and FPL-51 and FPL-53 include 'similar' or equivalent glasses.

 

Aperture is less important for EAA because Exposure can always be increased.  FOV does matter.  Since I also have a C8, anything I might get is unlikely to be heavier, or much longer than the StarTravel 102mm, which is f/4.9, although the weight distribution will be different.

 

Here is my current understanding.

 

I expect that this is the hierarchy

 

0. Achromat

1. FPL-51 doublet

2. FPL-53 doublet (FPL-51 triplets)

3. FPL-53 triplet

4. Even better, more, and exotic.  Likely more expensive than I want to afford.

 

For EAA, focal ratio affects total exposure, and glass quality affects size of stars and general 'crispness'

 

Quantitative improvement.

 

0.   1

1.   3

2.   6

3.   8

4.   No clue, don't care.

 

I'll edit this to correct misunderstandings.



#11 Alien Observatory

Alien Observatory

    Vanguard

  • *****
  • Posts: 2,063
  • Joined: 13 Nov 2015

Posted 15 June 2022 - 10:23 AM

An interesting link on Glass Types from a high end telescope manufacturer.....  Pat Utah :)

 

https://www.stellarv...al-glass-types/


  • steveincolo likes this

#12 steveincolo

steveincolo

    Apollo

  • *****
  • Posts: 1,371
  • Joined: 26 Sep 2017
  • Loc: Boulder, Colorado, US

Posted 15 June 2022 - 10:56 AM

I believe any FPL-53 and Lanthanum air-spaced doublet will have excellent color correction and minimal CA.  These types of telescopes scopes have been available for decades and are very reasonable priced.  With the proper reducer installed they are even better for EAA and about 1/2 the cost of a triplet.   Pat Utah smile.gif

Is this what Stellina has? 


  • Alien Observatory likes this

#13 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 15 June 2022 - 11:26 AM

An interesting link on Glass Types from a high end telescope manufacturer.....  Pat Utah smile.gif

 

https://www.stellarv...al-glass-types/

Yes Pat, That's what I meant about 'similar' or equivalent.  There's more to filet mignon than just Prime beef. Everything I've read agrees with the 'good' doublet approach, except that there is so little written when talking about EAA.  The vast amount is written by Visual or AP experts.

 

EAA does not operate at 'high magnification' on bright targets, most of the time, and that's where a lot of visual observers talk about the benefits of 'the good stuff'.

Similarly, most of us in EAA are not concerned in 'gnats whisker' deviations from perfection it the way that really serious AP practitioners do.

 

It would seem to me that for most of us and most of what we do in EAA, a good doublet made from a premium glass, should be good enough, if executed properly.  OTA like AT80ED, AT72EDII, Orion 80ED and similar would seem to be good enough.  But that's only theory.  What about practice?  The purpose of this post.

 

For those of us the do serious Visual or AP as well, then the calculus is different.


Edited by SchoolMaster, 15 June 2022 - 12:25 PM.

  • steveincolo likes this

#14 Alien Observatory

Alien Observatory

    Vanguard

  • *****
  • Posts: 2,063
  • Joined: 13 Nov 2015

Posted 15 June 2022 - 11:26 AM

Is this what Stellina has? 

Yes.  I have posted many images and the color balance and CA are quite good.  Pat Utah :)


Edited by Alien Observatory, 15 June 2022 - 11:29 AM.

  • steveincolo likes this

#15 jimhoward999

jimhoward999

    Viking 1

  • -----
  • Posts: 683
  • Joined: 01 Aug 2020
  • Loc: Brentwood, Tennessee

Posted 15 June 2022 - 12:01 PM

For me a good flourocrown/lanthanum objective wins over a triplet for EAA.   The reason is weight for a given aperture.  An 80mm F/7 doublet (with 0.8 reducer) goes on an AZ-GTI mount or similar and makes a 25lbs set up plus/minus with camera, computer and all equipment.  Very highly portable.  An 80mm APO triplet is heavier and takes a bigger mount.  First thing you know you are on an AVX or similar and your set up weights 50+ pounds and can't be picked up moved as an assembly in one piece.   At that point you are better off with a C6 or C8.

 

I think however, the new harmonic drive mounts may change the calculus.  You will be able to get a bit more payload weight in a portable set up, so a faster APO triplet starts looking attractive.

 

I also think the image quality argument is not true at least at slow speeds.   At F/7 or slower, with a field flattener/reducer and over the smallish formats typically used in EAA (like a 178 or even a 533 for example), there is no reason a good doublet should not more or less equal the triplet.  At least that is what ray tracing says.    If the triplet shows markedly better, it is not inherent in the design, it is just manufacturing quality differences between particular scopes.


  • steveincolo likes this

#16 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 15 June 2022 - 12:13 PM

For me a good flourocrown/lanthanum objective wins over a triplet for EAA.   The reason is weight for a given aperture.  An 80mm F/7 doublet (with 0.8 reducer) goes on an AZ-GTI mount or similar and makes a 25lbs set up plus/minus with camera, computer and all equipment.  Very highly portable.  An 80mm APO triplet is heavier and takes a bigger mount.  First thing you know you are on an AVX or similar and your set up weights 50+ pounds and can't be picked up moved as an assembly in one piece.   At that point you are better off with a C6 or C8.

 

I think however, the new harmonic drive mounts may change the calculus.  You will be able to get a bit more payload weight in a portable set up, so a faster APO triplet starts looking attractive.

 

I also think the image quality argument is not true at least at slow speeds.   At F/7 or slower, with a field flattener/reducer and over the smallish formats typically used in EAA (like a 178 or even a 533 for example), there is no reason a good doublet should not more or less equal the triplet.  At least that is what ray tracing says.    If the triplet shows markedly better, it is not inherent in the design, it is just manufacturing quality differences between particular scopes.

You make a good point about slowness which is why I mentioned the f/5 to f/7.5 faster if reduced.  Slowness 'cures' a lot of CA.


  • MarkCosmos likes this

#17 jkw119

jkw119

    Vostok 1

  • -----
  • Posts: 113
  • Joined: 13 Aug 2019
  • Loc: Pittsburgh, PA

Posted 15 June 2022 - 01:00 PM

I am really into EAA at moment and can share my experience.  I seem to be of the same thought process as you... 

 

I am always considering possibilities.  I have both 70mm and 80mm ED inexpensive doublets and in my ignorance, I am satisfied.  I'm actually trying to rule out the siren call of better kit without having to go through the exercise of actually buying it and trying it.  The experiences of others will inform my future plans.

 

I started with a Celestron NexStar 102mm refractor, but I didn't notice problems with it until getting into EAA with my ASI camera.  

 

Here is a sample showing a lot of chromatic aberration...

https://www.cloudyni...he-leo-triplet/

https://www.cloudyni...irlpool-galaxy/

 

I then bought ASTRO-TECH AT72EDII REFRACTOR OTA FPL-53 AND LANTHANUM F/6 DOUBLET trying to improve and am satisfied.

https://www.cloudyni...nd-a-full-moon/

https://www.cloudyni...umbbell-nebula/

 

My equipment plans are as follows with my EAA setup...

Planets and Moon: Celestron C6 SCT, covers these bright objects great with ASI studio ASICAP

DSO: ASTRO-TECH AT72EDII REFRACTOR OTA FPL-53 AND LANTHANUM F/6 DOUBLET and ASTRO-TECH AT102EDL REFRACTOR OTA FCD-100 AND LANTHANUM F/7 DOUBLE covers all the faint fuzzies and nebulas using ASI LIVE.

 

with that, I will be completely satisfied combined with my ASI 482 to cover all the main objects easily.  And these scopes are modest and fit nicely on an ALT-AZ mount for further simplicity. 


Edited by jkw119, 15 June 2022 - 04:39 PM.


#18 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 15 June 2022 - 01:10 PM

I am really into EAA at moment and can share my experience.  I seem to be of the same thought process as you... 

 

 

I started with a Celestron NexStar 102mm refractor, but I didn't notice problems with it until getting into EAA with my ASI camera.  

 

Here is a sample showing a lot of chromatic aberration...

https://www.cloudyni...he-leo-triplet/

https://www.cloudyni...irlpool-galaxy/

 

I then bought ASTRO-TECH AT72EDII REFRACTOR OTA FPL-53 AND LANTHANUM F/6 DOUBLET trying to improve and am satisfied.

https://www.cloudyni...nd-a-full-moon/

https://www.cloudyni...umbbell-nebula/

 

My equipment plans are as follows with my EAA setup...

Planets and Moon: Celestron C6 SCT, covers these bright objects great with ASI studio ASICAP

DSO: ASTRO-TECH AT72EDII REFRACTOR OTA FPL-53 AND LANTHANUM F/6 DOUBLET and ASTRO-TECH AT102EDL REFRACTOR OTA FCD-100 AND LANTHANUM F/7 DOUBLE covers all the faint fuzzies and nebulas using ASI LIVE.

 

with that, I will be completed satisfied combined with my ASI 482 to cover all the main objects easily.  And these scopes are modest and fit nicely on an ALT-AZ mount for further simplicity. 

That's the sort of experience I wanted to hear.  Thanks for the pictures too.  We are getting about the same sorts of results.


Edited by SchoolMaster, 15 June 2022 - 01:13 PM.


#19 robodan

robodan

    Apollo

  • -----
  • Posts: 1,149
  • Joined: 04 Feb 2011

Posted 21 June 2022 - 05:55 PM

For EAA, the type of scope does not really matter, unlike astrophotography your not looking for perfection, but just viewing the objects, so any acromatic lens will do. Don't need a triplet.

The only time you need the best or worry about CA is doing astrophotography which is far less forgiving as your after the best colour free images, not so important for EAA

Edited by robodan, 21 June 2022 - 05:55 PM.

  • AhBok likes this

#20 Tfer

Tfer

    Surveyor 1

  • -----
  • Posts: 1,504
  • Joined: 05 Sep 2019
  • Loc: Northern Alberta, Canada

Posted 21 June 2022 - 06:05 PM

I’m following this thread closely.

 

This Christmas, my wife has offered to replace my F4L with a short tube refractor.

 

My problem in researching my options, is that every scope I’m looking at REQUIRES a corrector lens…



#21 steveincolo

steveincolo

    Apollo

  • *****
  • Posts: 1,371
  • Joined: 26 Sep 2017
  • Loc: Boulder, Colorado, US

Posted 21 June 2022 - 06:44 PM

I’m following this thread closely.

 

This Christmas, my wife has offered to replace my F4L with a short tube refractor.

 

My problem in researching my options, is that every scope I’m looking at REQUIRES a corrector lens…

What about the WO Redcats? 



#22 Tfer

Tfer

    Surveyor 1

  • -----
  • Posts: 1,504
  • Joined: 05 Sep 2019
  • Loc: Northern Alberta, Canada

Posted 21 June 2022 - 09:21 PM

What about the WO Redcats? 

Pricey. Trying to keep it around $650CAN. 
 

I’m looking closely at this one:

 

https://all-startele...i-apo-refractor


Edited by Tfer, 21 June 2022 - 09:23 PM.

  • steveincolo and SchoolMaster like this

#23 SchoolMaster

SchoolMaster

    Gemini

  • *****
  • topic starter
  • Posts: 3,301
  • Joined: 05 Sep 2018
  • Loc: Florida

Posted 22 June 2022 - 04:20 AM

I have looked at that scope too, and the forthcoming Askar FRA300.

 

Many refractor users catch the dreaded Aperture Fever and wake up with an emptier bank account and a 140mm triplet APO (and a burning need for an even better mount to carry it).  I feel very lucky that I'm only suffering from a case of FOV Fever.  The path to greater FOV leads to smaller, fast, decent refractors, with add-on or built-in focal reducers.   I started my Journey with a 'C6', which turned out to be a C8.  It was free.  My first purchase was an 80ED, my next purchase was a 70ED.  (I see a pattern here)  The largest OTA I've looked at is the Askar FRA400, which has a little more FOV than the AT70ED with 0.8 focal reducer.

 

To treat my FOV Fever, I stare at this:

 

astronomy_tools_fov (57).png

 

It shows the FOV for the 294MC (I have no plans for a larger camera, and spending a lot of money there has modest returns) with Reduced C8, Reduced 80ED, HyperStar C8, and reduced AT70ED.  All of this I can do already.  Where to from here?

 

Same diagram with seven possibilities with increasing FOV:

 

astronomy_tools_fov (59).png

 

a. Askar FRA 300 native (60mm) ($950) - too expensive for moderate improvement

b. AT60ED + 0.8 reducer ($550) - go-to if I want this FOV

c. Askar FRA400 with 0.7 reducer (72mm) ($1450) expensive alternative if I also want aperture.  The AT72EDII is off the list because of it's f/6 o.8 reducer combination being inadequately large.

d. SharpStar 61EFPH11 with 0.8 reducer ($700)  OK for a modest improvement over the AT60.

e. Williams Optics RedCat 51 ($850) good quality, but small aperture

f.  Askar FRA 300 with hypothetical 0.7 reducer (60mm) ($1200)  worth considering if a reducer actually exists for this OTA.

g. Askar FMA 180 including reducer (40mm) ($400)  need to wrap my mind around a 40mm aperture, but great guide, spotting scope, hugest FOV.

 

The optical and physical quality of all of the above is at least GOOD, for EAA, with a bit of CA in some circumstances with some OTA/Reducer combinations.

 

I've seen images of what the FMA 180 can do.  FOV is over 6 x 4 degrees with the 294 camera, and I'm also planning to get a cooled mono version.  At that price, I'm planning to get one, mostly to stop, or at least delay for a long time, other temptation.


Edited by SchoolMaster, 22 June 2022 - 04:31 AM.

  • Tfer likes this

#24 Tfer

Tfer

    Surveyor 1

  • -----
  • Posts: 1,504
  • Joined: 05 Sep 2019
  • Loc: Northern Alberta, Canada

Posted 22 June 2022 - 07:59 AM

Aperture fever isn’t an issue here. That has been cured with my C11.

 

I also need to keep the size down, because it will be riding piggyback on it, and I still want the widest FOV possible.  My maximum is in the 60mm range. 



#25 steveincolo

steveincolo

    Apollo

  • *****
  • Posts: 1,371
  • Joined: 26 Sep 2017
  • Loc: Boulder, Colorado, US

Posted 22 June 2022 - 08:36 AM

Pricey. Trying to keep it around $650CAN. 
 

I’m looking closely at this one:

 

https://all-startele...i-apo-refractor

In other words, EAA prices not AP prices? 


  • SchoolMaster and Tfer 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





Also tagged with one or more of these keywords: EAA, Refractor



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics