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

StarPro 90 vs 102 Chromatic Aberration

  • Please log in to reply
17 replies to this topic

#1 Darli328

Darli328

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 18 Feb 2021

Posted 25 February 2021 - 01:14 PM

Beginner with my eyes set on a Meade StarPro 102 for all its simplicity, ease of use, grab and go convenience, etc.

Unfortunately I'm not in a position to be able to compare the 102 and 90 scopes first hand.

I've been doing a a fair amount of reading and am trying to figure out if the focal ratio of 5.9 (StarPro 102) vs the focal ratio of 6.67 (StarPro 90) in these telescopes would have noticeably less Chromatic Aberration?  And, if so is it really worth it to go with the smaller aperture?  My guess is larger aperture in most cases is more important than a longer focal ratio.  Really just trying to understand chromatic aberration and it's relationship to focal ratio.

Thanks 

 



#2 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 91,121
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 25 February 2021 - 01:25 PM

Darli:

 

Your question is a good one.  This is the way I see it:

 

Both scopes have a 600 mm focal length. The 102 mm will have more chromatic aberration but you are correct, in most cases, the 102mm aperture will provide better views anyway.

 

But here is the kicker:  Hidden inside every 102 mm F/6 telescope is a 90mm F/6.67 telescope as well as an 80mm F/7.5 telescope.

 

You can make a paper disk that fits inside the dew shield with an 90 mm hole and Your scope will now be an 90mm F/6.7.  This is called an aperture mask and is useful sometimes.

 

Jon


  • clearwaterdave, cookjaiii, vtornado and 1 other like this

#3 sg6

sg6

    Voyager 1

  • *****
  • Posts: 10,179
  • Joined: 14 Feb 2010
  • Loc: Norfolk, UK.

Posted 25 February 2021 - 01:45 PM

I have a Bresser 102/600, possibly the same scope as the Meade, and the CA is plain annoying.

Being me I would prefer the 90mm at f/6.67, but even that is I suggest is a little too fast for comfort.

 

Aperture is fine, it collects more light. And that is basically all it does. It is a nice easy simple measurement, and when you get to know other aspects its importance diminishes.

 

If you do not like looking through the scope you are not going to use it much, immaterial of aperture.



#4 cookjaiii

cookjaiii

    Apollo

  • *****
  • Posts: 1,028
  • Joined: 23 Nov 2015
  • Loc: Southeast PA

Posted 25 February 2021 - 01:59 PM

Jon beat me to it. Get the 102. You can always stop it down.


  • Jon Isaacs and PNW like this

#5 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 91,121
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 25 February 2021 - 02:03 PM

I have a Bresser 102/600, possibly the same scope as the Meade, and the CA is plain annoying.

Being me I would prefer the 90mm at f/6.67, but even that is I suggest is a little too fast for comfort.

 

Aperture is fine, it collects more light. And that is basically all it does. It is a nice easy simple measurement, and when you get to know other aspects its importance diminishes.

 

If you do not like looking through the scope you are not going to use it much, immaterial of aperture.

 

Aperture does more than collect light, it also provides greater resolution and fine scale contrast. 

 

I have owned a number of 4 inch achromats and ED/ apos including two 102 mm F/5s, three 100mm F/6s, a 102 mm F/6.5, and 102 mm F/7 ED doublet and a 4 inch F/5.4 dual ED app quadrupled. New, these cost from $200 to $4000.  They all provide meaningful enjoyable views.

 

At low to medium magnifications, the views are very similar. At high magnifications, the ED/apo scopes are definitely cleaner and sharper, not doubt about it. But even then, the basic planetary and lunar features are visible in the 100mm F/6 achromats.

 

There's a reason I've owned so many 4 inch achromats... they're good scopes, I buy them used, enjoy them myself for a while and give them to aspiring amateur astronomers in need of a good scope.

 

Optical perfection is not necessary to enjoy the wonders of the universe.

 

Jon


  • clearwaterdave, BFaucett, cookjaiii and 3 others like this

#6 sevenofnine

sevenofnine

    Viking 1

  • -----
  • Posts: 621
  • Joined: 16 Apr 2016
  • Loc: Santa Rosa, California

Posted 25 February 2021 - 02:17 PM

The C/N forum's sponsor (Astronomics) sells an 80mm ED refractor by Astro-tech for $400 and a ED 102mm for $600. Might be worth considering if CA is an issue for you. They get very good reviews. It's sure tempting to me ubetcha.gif



#7 Darli328

Darli328

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 18 Feb 2021

Posted 25 February 2021 - 03:08 PM

Darli:

 

Your question is a good one.  This is the way I see it:

 

Both scopes have a 600 mm focal length. The 102 mm will have more chromatic aberration but you are correct, in most cases, the 102mm aperture will provide better views anyway.

 

But here is the kicker:  Hidden inside every 102 mm F/6 telescope is a 90mm F/6.67 telescope as well as an 80mm F/7.5 telescope.

 

You can make a paper disk that fits inside the dew shield with an 90 mm hole and Your scope will now be an 90mm F/6.7.  This is called an aperture mask and is useful sometimes.

 

Jon

 

I honestly didn't even think about that, but that makes a lot of sense.  

Thanks!


  • Jon Isaacs likes this

#8 Tony Flanders

Tony Flanders

    Hubble

  • *****
  • Posts: 19,484
  • Joined: 18 May 2006
  • Loc: Cambridge, MA, USA

Posted 25 February 2021 - 03:09 PM

It seems worth noting that for the most part false color is only an issue for viewing the Moon and planets. (Also some daytime targets, but that's a totally different subject.) False color is very nearly a non-issue for deep-sky objects, for two reasons. First, you're usually viewing them at much lower magnifications, where the colored fringes are far less obvious. Second, they're too faint to stimulate color vision.


  • Jon Isaacs, BFaucett, aeajr and 4 others like this

#9 aeajr

aeajr

    Hubble

  • *****
  • Posts: 15,058
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 25 February 2021 - 04:05 PM

+1 for Tony's comments



#10 SeattleScott

SeattleScott

    Voyager 1

  • *****
  • Posts: 11,253
  • Joined: 14 Oct 2011

Posted 25 February 2021 - 04:23 PM

Neither is going to be good for planets anyway so get the one better for DSO, and stop it down if you like.

#11 oldtimer

oldtimer

    Vanguard

  • *****
  • Posts: 2,392
  • Joined: 13 Nov 2008
  • Loc: Lake County Illinois

Posted 25 February 2021 - 11:03 PM

+2 for Tony



#12 vtornado

vtornado

    Soyuz

  • *****
  • Posts: 3,515
  • Joined: 22 Jan 2016
  • Loc: Northern Illinois

Posted 25 February 2021 - 11:29 PM

One other area where CA is an issue is double star viewing.   If the pair is tight and one of the pair is much dimmer than the other, it can

get lost in the out of focus light.

 

I would go with the larger aperture and stop it down if the CA bothers you.  However ... stopping down a larger scope to get one with

less CA still means you have to mount that larger scope.   As an example, I had a 150mm f/8, it made a very nice 100 f/12, but boy

it was tough on the mount.


Edited by vtornado, 26 February 2021 - 10:27 PM.

  • BFaucett and cookjaiii like this

#13 oldtimer

oldtimer

    Vanguard

  • *****
  • Posts: 2,392
  • Joined: 13 Nov 2008
  • Loc: Lake County Illinois

Posted 26 February 2021 - 01:39 PM

If your just trying to 'split' double stars and not analyze the colors, a deep yellow filter Like a #12 will get rid of the CA


  • vtornado likes this

#14 PNW

PNW

    Ranger 4

  • -----
  • Posts: 389
  • Joined: 07 Sep 2017
  • Loc: Lummi Island, WA

Posted 26 February 2021 - 03:13 PM

I've got the Infinity 102 and it took me over 2 years before I noticed any CA. Yes there is a thin blue line on the bright edge of the Moon, but the clarity and definition of the craters is awesome. Same can be said about Saturn, but I'm looking at the Cassini Division anyway. But that's it. Star clusters and doubles show as pinpoints of light. I keep my Infinity next to a picture window for quick peeks at boats, birds, and stars on cold nights. At 12 pounds, it's easy to grab and go for longer outside sessions. 


Edited by PNW, 26 February 2021 - 03:18 PM.

  • clearwaterdave and JohnnyBGood like this

#15 Gary Riley

Gary Riley

    Viking 1

  • *****
  • Posts: 776
  • Joined: 01 Dec 2011
  • Loc: White Bluff, TN

Posted 26 February 2021 - 11:47 PM

I have the 90mm StarPro and I enjoy it as a quick grab-n-go scope. I am pleased with the quality of views for a refractor at such a relative cheap price. There is some CA around Jupiter. Saturn, Venus, Moon, and some of the brightest stars but I don’t find it all that annoying. I use my better eyepieces and diagonal than the ones that came with the scope which helps to give better views in my opinion. I think you could be happy with either one. The StarPro 90 weighs about 10lbs fully assembled.

Edited by Gary Riley, 26 February 2021 - 11:48 PM.

  • Darli328 likes this

#16 Darli328

Darli328

    Lift Off

  • -----
  • topic starter
  • Posts: 11
  • Joined: 18 Feb 2021

Posted 28 February 2021 - 03:43 AM

I have the 90mm StarPro and I enjoy it as a quick grab-n-go scope.

<...snip...>


Which diagonal and eyepiece(s) are you using?

I’ve read the ones that come with the scope are worth upgrading.

What about a Barlow, did you upgraded that too?



#17 PNW

PNW

    Ranger 4

  • -----
  • Posts: 389
  • Joined: 07 Sep 2017
  • Loc: Lummi Island, WA

Posted 28 February 2021 - 04:52 PM

My Infinity came with 3 eyepieces and a barlow. They were more than adequate for a beginners scope. Over time, I bought a 20mm Superview off the calssifieds for 20-30 bucks. WOW. That was the beginning of collecting eyepieces and telescopes. Considering most retailers are out of stock and backordered I'd say your money will be better spent on a Moon Filter. Get the metal framed one, the plastic frame is too easy to cross thread. Upgrades will come in due time. I'm beginning to realize this hobby is as much about collecting as it is in observing.....



#18 oldtimer

oldtimer

    Vanguard

  • *****
  • Posts: 2,392
  • Joined: 13 Nov 2008
  • Loc: Lake County Illinois

Posted 02 March 2021 - 05:16 AM

Collecting...............Eleven scopes, 6 mounts, 20+ eyepieces, 20 filters + 'spare' parts./   My wife doesn't read Cloudy Night and I keep some scopes in the Garage, some in the basement and some in the shed (HA)


Edited by oldtimer, 02 March 2021 - 11:15 AM.

  • PNW 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