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

Question for Achromat Owners

  • Please log in to reply
22 replies to this topic

#1 sojourneyer

sojourneyer

    Apollo

  • *****
  • topic starter
  • Posts: 1,114
  • Joined: 07 Sep 2019

Posted 13 October 2020 - 02:19 PM

This question applies to standard Meade, Orion, Celestron, etc 4 inch achromats (focal length between f/ 6.5 to  f/7.5) found on the market and not to APOs.

 

Will a better eyepiece make a considerably better viewing experience with a standard achromat scope or will a better scope make a considerably better viewing experience with a standard eyepiece?  Or both.

 

By standard eyepieces I am alluding to those such as Orion Sirius Plossls, Celestron Omni, etc. 

 

Viewing would be associated with the moon and planets.

 

Obviously a better eyepiece and better scope is the way to go.


Edited by sojourneyer, 13 October 2020 - 04:52 PM.

  • Rollo likes this

#2 junomike

junomike

    Hubble

  • *****
  • Moderators
  • Posts: 19,872
  • Joined: 07 Sep 2009
  • Loc: Ontario

Posted 13 October 2020 - 02:27 PM

Depends on the Target.  IME a better telescope (ED) is far better with a genric Plossl for Planetary/Lunar than a premium eyepiece is with an Achro.

For DSO's It's a little difference as I'd probably prefer the wider eyepiece with an Achro over a Plossl + ED.


  • doctordub, Astrojensen, ShaulaB and 3 others like this

#3 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • Posts: 13,371
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 13 October 2020 - 02:32 PM

Junomike is spot on. For targets, where image quality really matters, like lunar-planetary observing, the quality of the objective is overwhelmingly more important than minor eyepiece improvements. For DSO, it's usually more subtle, depending on the object in question, of course. 

 

 

Clear skies!

Thomas, Denmark


  • Jon Isaacs, Alan French, doctordub and 5 others like this

#4 MellonLake

MellonLake

    Viking 1

  • *****
  • Posts: 810
  • Joined: 16 Dec 2018
  • Loc: Toronto, Canada

Posted 13 October 2020 - 02:54 PM

It is also somewhat dependent on the focal ratio of the telescope. Long focal lengths are very forgiving for eyepieces. Short focal lengths (f/6 or less) require better corrected eyepieces especially at longer eyepiece focal lengths (20mm and above). If you have an f/5 or f/6 short tube (ST) achromatic refractor or a fast (less than f/6) apochromatic refractor, high quality eyepieces will perform much better on wide field views. However, in general views are better with APO telescopes and other designs that don't have as much chromatic aberration. Bigger apertures also provide better planetary resolution and more light gathering power for DSOs.

Edited by MellonLake, 13 October 2020 - 03:56 PM.

  • AndresEsteban and eblanken like this

#5 sg6

sg6

    Cosmos

  • *****
  • Posts: 9,073
  • Joined: 14 Feb 2010
  • Loc: Norfolk, UK.

Posted 13 October 2020 - 03:50 PM

Will make a small difference with better eyepieces. Think of it this way - if a perfect image is 100 and the achro objective only delivers say 90, then no eyepiece will get you above 90.

 

If a poor eyepiece is delivering say 80, then a better eyepiece might deliver 90.

 

If you say the result is the product of the 2 - objective and eyepiece - then poor eyepiece and achro is 72 whereas better eyepiece and achro is 81.

 

So yes something to be gained but it is a interdependant. Especially as the eyepiece works on the image formed so as others say a better objective give a better image to the eyepiece for it to work with.

 

Somewhat oddly it seems that often a "better" eyepiece is one that is more comfortable to look through and use. And often one of the clearest is still the TV plossl.


  • eblanken likes this

#6 VNA

VNA

    Ranger 4

  • -----
  • Posts: 366
  • Joined: 13 Nov 2009
  • Loc: Northern California

Posted 13 October 2020 - 04:06 PM

Hello: with a better eyepiece one will get a better quality image, but at the same time you will notice more the shortcomings of an achromat? 


  • eblanken likes this

#7 bobhen

bobhen

    Aurora

  • *****
  • Posts: 4,540
  • Joined: 25 Jun 2005

Posted 13 October 2020 - 04:17 PM

A better quality objective will always make the biggest improvement because it grabs the most light and has the most impact on the light path.

 

The impact of aberrations on a specific object and with a specific magnification used might be more or less noticeable but that is true with any objective. For example: a 6” F5 achromat has plenty of CA but it is hardly noticeable when used on some deep sky objects at very low power. The objective is still producing the same level of CA aberration but you can’t see it (like you can’t see many other aberrations) when used at low power. Eyepieces alone can’t undo the CA aberration to the light path caused by the objective. Start adding magnification and aberrations become more apparent.

 

Most good/decent quality eyepieces are good in the center of the field. What you are paying for with many (not all but many) higher priced eyepieces are more ER, wide and ultra-wide fields and better edge correction.

 

Bottom line: want the biggest improvement then get a better objective –of equal size of course.

 

Bob


  • Jon Isaacs, daquad, sojourneyer and 1 other like this

#8 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 87,440
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 October 2020 - 03:02 PM

Will make a small difference with better eyepieces. Think of it this way - if a perfect image is 100 and the achro objective only delivers say 90, then no eyepiece will get you above 90.

 

If a poor eyepiece is delivering say 80, then a better eyepiece might deliver 90.

 

 

The thing to keep in mind is that on axis, any decent eyepiece is very close to 100% whereas objectives vary anywhere from essentially perfect to not good at all.

 

Jean Texereau wrote the following in his classic How to Make a Telescope:

 

"It is not usually made clear, that these elements, objective and eyepiece, are by no means comparable in importance. The astronomer's hopes are almost wholly tied to the size and quality of the objectve. The objective of even the smallest telescope, because of its larger dimensions, the severe optical requirements it must meet, and the difficulty of its construction, completely overshadows the eyepiece."

 

- "How to Make a Telescope," by Jean Texereau, Page 1, Paragraph 2. "

 

Jon


  • doctordub, daquad, Astrojensen and 4 others like this

#9 eblanken

eblanken

    Vostok 1

  • *****
  • Posts: 153
  • Joined: 21 Mar 2020
  • Loc: Portland Oregon Area NW USA

Posted 16 October 2020 - 01:20 AM

Hi All,

 

I agree with most all of what has been replied. I have quoted sg6 below because I like the numbers and the "interdependent" message it sends:

 

Will make a small difference with better eyepieces. Think of it this way - if a perfect image is 100 and the achro objective only delivers say 90, then no eyepiece will get you above 90.

 

If a poor eyepiece is delivering say 80, then a better eyepiece might deliver 90.

 

If you say the result is the product of the 2 - objective and eyepiece - then poor eyepiece and achro is 72 whereas better eyepiece and achro is 81.

 

So yes something to be gained but it is a interdependant. Especially as the eyepiece works on the image formed so as others say a better objective give a better image to the eyepiece for it to work with.

 

Somewhat oddly it seems that often a "better" eyepiece is one that is more comfortable to look through and use. And often one of the clearest is still the TV plossl.

I have never owned a "really good" APO (YET). I have compared my Achro refractors against SCTs and MCTs. The color differences are clear and obvious, but I still appreciate the achro refractors. I have now added ED refractors in addition to my achro scopes, so that is another point of comparison. Even the SCTs and MCTs show ATMOSPHERIC DISPERSION, so be aware of that reality.

 

In my yard this summer, the DOMINANT FACTOR was the atmospheric conditions: 100 power was about all that many nights would support on Jupiter and Saturn (at my 46 Deg North Latitude). I can use higher powers near the zenith: Vega, Double-Double in Lyra, M-57, etc. so I know that some of the achros and both the SW100ED & SW80ED and the SCTs & MCTs are working, just not so low in the sky as the gas giants this summer. Oh, and the smoke from the wildfires "shut down" my plans for "half-a-month" or so as well.

 

When I thought of your question, I thought of days of long ago when I used an open-reel tape recorder: I could use REALLY GOOD=EXPENSIVE tape or I could use inexpensive tape. I could hear the difference, but it was my choice. Before I bought the EXPENSIVE, SEMI-PRO recording machine, what I heard was not as much difference BECAUSE the machine (like the refractor's front glass) was the GATING, LIMITING factor. After I invested BIG MONEY (I was a junior in high school, when I bought the BIG, 15 IPS, 10.5 inch reel size, SEMI-PRO machine), the game changed in a fundamental way. Now the choice was mine, cheap tape or good tape as the situation called for on a case-by-case basis.

 

Having learned that "interdependent" lesson early in life, I applied it to the Compact Cassette uses: (A) Good machine vs (B) cheap machine and (1) THE BEST TAPE vs (2) the-cheap-tapes give four options: A1, A2, B1, B2. So, to be clear, A1 cost the most and gave the best, A2 and B1 were intermediate and B2 was cheap-and-poor, but sometimes that was just fine, depending on what I was doing. B2 was just fine for taping men talking on the AM radio, maybe B1 or A2 for music off the AM radio, for live recording of music that I wanted to really enjoy, the extra cost of A1 was the way to go.

 

With all my observations this summer, I was either using Vixen Zooms and matching image size or using the Vixen LV Lanthanum fixed eyepieces and getting as close as possible by dividing focal length by eyepiece focal length (example: SW80ED at f/7.5 got a 6mm for the 600mm focal length to get 100 power, SW100ED at f/9 got a 9mm to match the 900mm, 6 inch, 152mm, at f/8 got a 12mm for the 1200mm, 8 inch Meade SCT at f/10 with the 2000mm got a 20mm {actually, because I have a 2 inch diagonal with a longer light path, I had to use the zoom at about 22mm because the f/10 is closer to f/11}, and so on). My conclusion is that the inexpensive achros did "well enough" for what they are and what they do best. Using the Vixen LV eyepieces took the eyepieces out of the comparison. I also used inexpensive Celestron Plossls and Televue Plossls as well.

 

I can't be more clear: I know that the sky conditions are another BIG VARIABLE too. I got much pleasure from the scopes with the few Televue eyepieces I used, but the inexpensive plossls did fine UNDER THE SKY CONDITIONS THAT DOMINATED this summer from my yard.

 

I am looking for a weather window (here in the NW USA) to drive to dark, clear skies at altitude to get a good chance at "BEST" seeing Mars this year. I'll take the 8 inch Meade SCT for sure, but If I can, I'll consider either the SW100ED or the 6 inch achro too. AND I will take the 100mm or 80mm f/5 along. At least it will be a finder, sweeper. If I have time, I'll compare Mars in the f/5 as well if time permits ?!?!?

 

Now sojourneyer asked about "achros (moderately fast) and eyepieces" and used the word "considerably" which I will point out is a subjective word, so my best answer is it depends (MOSTLY ON sojourneyer's tastes) !!! If the targets are planets and moon, why not consider a 100mm f/9.8 achro like the Celestron C-102 that I still own, but has mostly been gathering dust now that I have the SW100ED ???

 

Thanks for your patience in reading my long post,

 

Ed (aka eblanken)


Edited by eblanken, 16 October 2020 - 02:20 AM.

  • Rollo likes this

#10 Mitrovarr

Mitrovarr

    Gemini

  • *****
  • Posts: 3,217
  • Joined: 12 Sep 2004
  • Loc: Boise, Idaho

Posted 16 October 2020 - 02:10 AM

Both will improve your experience in different ways.

Most of the advantages of better eyepieces are absolutely relevant to achromats.

Better AFOV? Yep.
Better eye relief? Absolutely.
Better edge correction? Sure.

They will not to anything whatsoever to improve the chromatic aberration, of course, beyond not contributing any themselves.

A better scope is also better, of course. It will be sharper and have less/no CA. Different improvements.

Both are worthwhile. I'd probably go for the eyepieces first myself.
  • Astrojensen, BigC, eblanken and 1 other like this

#11 eblanken

eblanken

    Vostok 1

  • *****
  • Posts: 153
  • Joined: 21 Mar 2020
  • Loc: Portland Oregon Area NW USA

Posted 16 October 2020 - 02:34 AM

Hi again,

 

Mitrovarr makes good points.

 

This question applies to standard Meade, Orion, Celestron, etc 4 inch achromats (focal length between f/ 6.5 to  f/7.5) found on the market and not to APOs.

 

Will a better eyepiece make a considerably better viewing experience with a standard achromat scope or will a better scope make a considerably better viewing experience with a standard eyepiece?  Or both.

 

By standard eyepieces I am alluding to those such as Orion Sirius Plossls, Celestron Omni, etc. 

 

Viewing would be associated with the moon and planets.

 

Obviously a better eyepiece and better scope is the way to go.

Sojourneyer, now for some questions:

 

(1) Why f/6.5 to f/7.5 ? Why not f/9 or f/10 ? The mount ? Transportability ? Buying new or used achro ?

 

(2) Why achro and not ED ?

 

(3) Why Celestron or Meade or Orion ? Why not Stellarvue used ?

 

(4) Do you own already or just contemplating a purchase of an achro ? Eyepieces ?

 

Best regards,

 

Ed (eblanken)



#12 photomagica

photomagica

    Ranger 4

  • *****
  • Posts: 330
  • Joined: 23 Jun 2013

Posted 17 October 2020 - 02:13 AM

I have both achromats and now a 127mm Explore Scientific Triplet Apochromat (the first type FCD1 Glass). By chance I have the Apo with me but am separated from my best eyepieces by the pandemic, so I've been using the Apo with a Celestron 8-24mm Zoom, a Celestron 40mm Plossl, a Nagler 10.5mm Plossl and an Orion Stratus 3.5mm. OK eyepieces but nothing to get to excited about. Even so the telescope is very satisfying to use and the views of Mars at opposition have been impressive. Am I unhappy I'm separated from my 82 degree Naglers? Not that much. As others in this thread have said,  a better eyepiece will only take so so far. I'm very impressed by the performance of the Apo Triplet - even though it is by far from being considered the best - compared to the achromats.

Hope this helps.

Bill


Edited by photomagica, 17 October 2020 - 02:22 AM.


#13 sojourneyer

sojourneyer

    Apollo

  • *****
  • topic starter
  • Posts: 1,114
  • Joined: 07 Sep 2019

Posted 17 October 2020 - 12:05 PM

Hi again,

 

Mitrovarr makes good points.

 

Sojourneyer, now for some questions:

 

(1) Why f/6.5 to f/7.5 ?      Why not f/9 or f/10 ? The mount ? Transportability ? Buying new or used achro ?

 

(2) Why achro and not ED ?

 

(3) Why Celestron or Meade or Orion ? Why not Stellarvue used ?

 

(4) Do you own already or just contemplating a purchase of an achro ? Eyepieces ?

 

 

Hello Ed,

Thanks for the queries.  It is a general question I was asking.

I have a 102mm Achro f/6.5

I have a 127mm Mak f/12

I have Celestron scopes

Stellarvue is too costly and would not provide me value for the money as I do not use the scopes a great deal and for a short period of time observing the skies

 

Was contemplating purchasing better EPs but I do not think they will improve my viewing significantly.. Thus the question.

 

Thanks

 

 

 

 


Edited by sojourneyer, 17 October 2020 - 12:30 PM.

  • eblanken likes this

#14 Mitrovarr

Mitrovarr

    Gemini

  • *****
  • Posts: 3,217
  • Joined: 12 Sep 2004
  • Loc: Boise, Idaho

Posted 17 October 2020 - 02:36 PM

I mean, you don't upgrade eyepieces past the level of basic plossls because you want sharper eyepieces (usually). You upgrade because expensive eyepieces have a much larger field of view, are sharp all the way to the edge, and don't have uncomfortable tiny eye relief in use in short focal lengths.

 

In these ways they improve the views through any telescope, even a poor one.


  • stevew, Bonco2 and eblanken like this

#15 sojourneyer

sojourneyer

    Apollo

  • *****
  • topic starter
  • Posts: 1,114
  • Joined: 07 Sep 2019

Posted 17 October 2020 - 03:17 PM

My EPs are 68 degree ultra wide angle except for the Zoom



#16 eblanken

eblanken

    Vostok 1

  • *****
  • Posts: 153
  • Joined: 21 Mar 2020
  • Loc: Portland Oregon Area NW USA

Posted 17 October 2020 - 05:31 PM

Hi sojourneyer,

 

You already own (according to your later answers) more than I thought you owned in your original post.

 

Your question was a good one and there have been some good answers already.

 

All-the-best,

 

Ed (aka eblanken)


  • sojourneyer likes this

#17 sojourneyer

sojourneyer

    Apollo

  • *****
  • topic starter
  • Posts: 1,114
  • Joined: 07 Sep 2019

Posted 17 October 2020 - 06:43 PM

Hi sojourneyer,

 

You already own (according to your later answers) more than I thought you owned in your original post.

 

Your question was a good one and there have been some good answers already.

 

All-the-best,

 

Ed (aka eblanken)

Ed,

The relevant part is that while my EPs are wide angle they are not in the  Baader,

Televue, Explore Scientific, etc range. They are svbony wide angles.

thanks for your input


Edited by sojourneyer, 17 October 2020 - 07:15 PM.


#18 Astrojensen

Astrojensen

    Voyager 1

  • *****
  • Posts: 13,371
  • Joined: 05 Oct 2008
  • Loc: Bornholm, Denmark

Posted 18 October 2020 - 02:10 AM

Ed,

The relevant part is that while my EPs are wide angle they are not in the  Baader,

Televue, Explore Scientific, etc range. They are svbony wide angles.

thanks for your input

Again, it depends on what you observe. On-axis, your Svbony eyepieces are probably just as sharp as anything else, more or less, it's in the off-axis performance you'll find the greatest differences between them and more expensive makes. Also, Svbony has several different eyepiece lines, so it would be interesting to know exactly what you've got. 

 

 

Clear skies!

Thomas, Denmark


  • eblanken likes this

#19 Bomber Bob

Bomber Bob

    Hubble

  • *****
  • Posts: 18,123
  • Joined: 09 Jul 2013
  • Loc: The Swamp, USA

Posted 18 October 2020 - 09:07 AM

This question applies to standard Meade, Orion, Celestron, etc 4 inch achromats (focal length between f/ 6.5 to  f/7.5) found on the market and not to APOs.

 

By standard eyepieces I am alluding to those such as Orion Sirius Plossls, Celestron Omni, etc.

 

Viewing would be associated with the moon and planets.

 

A 4" F7 achromatic is gonna have obvious CA / false color.  It wouldn't be my choice for a lunar / planetary scope...

 

The closest I have is a vintage Celestron (Vixen / Japan) C-102 F10.  With this achromatic, the quality of the diagonal & eyepieces definitely affects the views, especially at 40x per inch & higher.  For planetary, I use a 1.25" Baader prism + UO HD Orthoscopics or Tele Vue Naglers & Radians.



#20 sojourneyer

sojourneyer

    Apollo

  • *****
  • topic starter
  • Posts: 1,114
  • Joined: 07 Sep 2019

Posted 18 October 2020 - 10:55 AM

This question applies to standard Meade, Orion, Celestron, etc 4 inch achromats (focal length between f/ 6.5 to  f/7.5) found on the market and not to APOs.

 

By standard eyepieces I am alluding to those such as Orion Sirius Plossls, Celestron Omni, etc.

 

Viewing would be associated with the moon and planets.

 

A 4" F7 achromatic is gonna have obvious CA / false color.  It wouldn't be my choice for a lunar / planetary scope...

 

The closest I have is a vintage Celestron (Vixen / Japan) C-102 F10.  With this achromatic, the quality of the diagonal & eyepieces definitely affects the views, especially at 40x per inch & higher.  For planetary, I use a 1.25" Baader prism + UO HD Orthoscopics or Tele Vue Naglers & Radians.

I have a 127Mak for lunar, planetary viewing.



#21 Bomber Bob

Bomber Bob

    Hubble

  • *****
  • Posts: 18,123
  • Joined: 09 Jul 2013
  • Loc: The Swamp, USA

Posted 18 October 2020 - 12:43 PM

I have a 127Mak for lunar, planetary viewing.

Okay... if you're intending the 4" F7 for deep-sky, you don't need expensive accessories.  If it'll accept 2" stuff, a mirror diagonal + the China-made Celestron / Orion / SVBONY wide-field eyepieces will give good views at low to medium powers.


  • BigC likes this

#22 sojourneyer

sojourneyer

    Apollo

  • *****
  • topic starter
  • Posts: 1,114
  • Joined: 07 Sep 2019

Posted 18 October 2020 - 01:25 PM

Okay... if you're intending the 4" F7 for deep-sky, you don't need expensive accessories.  If it'll accept 2" stuff, a mirror diagonal + the China-made Celestron / Orion / SVBONY wide-field eyepieces will give good views at low to medium powers.

Yes Bob, the 102 Achromat is intended for DSO. I have svbony 68 degree wide angle EPs but will stick to 1.25 " EPs etc. It has a GSO dual crayford focuser on it. 

The Mak will be the planetary, lunar scope..

 

My question originally asked if I needed better EPs for the Achromat but apparently I am okay and would not really get any value for money by purchasing any high end EPs.  Only visual no AP.

 

thanks



#23 BigC

BigC

    Fly Me to the Moon

  • *****
  • Posts: 5,922
  • Joined: 29 Sep 2010
  • Loc: SE Indiana

Posted 18 October 2020 - 05:29 PM

Sojourner,

 

 As one who has eyepieces in the $5 to $300 range I can also verify the extra $$$ get you a wider FOV and possibly (usually) greater eye relief. 

 

Some people claim the old Huygens actually corrects or mitigates CA although that I can't confirm.

 

It sounds like you already have what you need(want) given your observing goals .


  • sojourneyer 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