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

Who makes the best 90mm SCT?

  • Please log in to reply
55 replies to this topic

#1 2696

2696

    Vostok 1

  • -----
  • topic starter
  • Posts: 132
  • Joined: 27 May 2019

Posted 21 August 2019 - 10:33 PM

I'm looking to buy my first SCT and a smaller, 90mm or so one is looking appealing to me. I wouldn't mind going up to a 102mm but for the sake of this let's say 90mm. I know a lot of companies sell 90mm SCT's and I don't know much about them, I was wondering if there was any certain one that's better or stands out over the others, (aside from Questars 90mm we all know it's great) if not and they're all relatively the same then which one would you personally recommend? Thanks.

#2 ShaulaB

ShaulaB

    Surveyor 1

  • *****
  • Posts: 1590
  • Joined: 11 Oct 2012
  • Loc: Missouri

Posted 21 August 2019 - 10:35 PM

Google Maksutov Cassegrain telescopes. Many 90mm and 100mm optical tubes that might look like Schmidt-Cassegrains are actually Maks. Example--the Celestron 4SE is not an SCT, it is a MCT.

Also, Questars are Maks-Cassegrain

Edited by ShaulaB, 21 August 2019 - 10:39 PM.

  • Gary Z likes this

#3 Gary Z

Gary Z

    Apollo

  • *****
  • Posts: 1395
  • Joined: 26 Jan 2012
  • Loc: New Mexico

Posted 21 August 2019 - 10:45 PM

Tell you what.  I recently was able to observe thru a 127mm Maksutov.  This particular one is a Meade from the Starnavigator NG Mount.  Well, I have to say, I love this little scope.  I recommend it and I believe the Skywatcher version is probably better.  I do apologize as you did specify 90mm, but I've only looked through the 127mm model.  As shaulaB indicated, there is a difference between the SCTs and Maks.  I have an 8 inch SCT, but now I'm looking for the 127mm Mak used....which so far, can't find any.  

 

Take care,

 

Gary


  • gfstallin and Chris Y like this

#4 Traveler

Traveler

    Gemini

  • *****
  • Posts: 3135
  • Joined: 19 Aug 2007
  • Loc: The Netherlands

Posted 21 August 2019 - 10:46 PM

All those 90mm Mak's are reasonble to excellent if...you don't use the mouts where they often comes with and if you can live with the long focallength and narrow field of view.The Questar is the best (newprice 5K)…

 

And as ShaulaB stated: most of the 90mm are not SCT's...



#5 SeattleScott

SeattleScott

    Fly Me to the Moon

  • *****
  • Posts: 5694
  • Joined: 14 Oct 2011

Posted 21 August 2019 - 10:46 PM

Personally I cannot think of any 90mm SCTs. And Questar has never made SCTs. I can think of many 90mm MCTs, including Questar. I have a Meade ETX90 that performs well, and they have an excellent reputation. The Celestron is well regarded too, as well as Questar obviously. There are some off brand ones that you don’t really hear about so not sure how they stack up. Hard to go wrong if you stick with Meade, Celestron or Questar. Meade and Celestron typically sell for about $90 used, OTA only. Questar a little higher..,

Orion makes a 4” as does Celestron. Both are current models. Meade used to make a 4” ETX. A bit further back, Meade made a 4” SCT. Smallest SCT I know of. There is actually one for sale near me. If you really want SCT instead of Mak, you could PM me about me buying it and selling it to you. Don’t see many around. The 90mm Maks are much more common.

Scott
  • Sarkikos, gfstallin and Joe1950 like this

#6 Joe1950

Joe1950

    Cosmos

  • *****
  • Posts: 9435
  • Joined: 22 Aug 2015

Posted 22 August 2019 - 12:16 AM

SCT:   Schmidt Cassegrain Telescope.    Celestron 5, 6, 8.  Has a flat looking front corrector lens.

MCT:   Maksutov Cassegrain Telescope.  ETX-90, Celestron C-90 Spotting Scope.  Has a deeply curved looking front corrector lens.

CAT:   CAtadioptric Telescope.   Both SCT and MCT are these.  It means it uses both a lens and mirror.

 

There are many sources of Maksutovs in the 90mm, 102mm, 127mm and so on. I think the Celestron NexStar 5 (127mm) is the smallest SCT currently sold new.

 

Astronomics, the sponsor of this website has a very good selection of Maksutovs, mounted and unmounted, as well as ALL other types and sizes of telescopes. As a member of CN you get a discount. 

 

Hope this helps!

joe


Edited by Joe1950, 22 August 2019 - 12:26 AM.

  • Jon Isaacs, Hesiod and gfstallin like this

#7 Stephen Kennedy

Stephen Kennedy

    Surveyor 1

  • *****
  • Posts: 1827
  • Joined: 03 Jul 2014
  • Loc: California

Posted 22 August 2019 - 01:15 AM

I have a 100 mm SCT made by Japan Special Optics (JSO) that I purchased in 1989 while stationed in Japan.  In my view it just does not have enough aperture to be a good astronomical telescope and I have actually been able to get more use out of it as a terrestrial telescope than an astronomical one.


  • gfstallin and Joe1950 like this

#8 Bowlerhat

Bowlerhat

    Ranger 4

  • -----
  • Posts: 332
  • Joined: 05 Jun 2019
  • Loc: Melbourne, Australia

Posted 22 August 2019 - 06:12 AM

I own a C5 and sold 80mm Skywatcher mak before. I think you're in for a treat with a small cat, although don't expect the image to be bright. There's a long thread here about Celestron C90:

https://www.cloudyni...-celestron-c90/

 

I believe in the robustness since the C90 uses a thicker cast for holding their primary at the back. However, I've been eyeing the Skywatcher Skymax 90. Same specs, different in form..since the skymax is even shorter and lighter (5cm in length difference, 400gr in weight difference). 

 

So far I think maybe C90 would be a good choice. I'd say C90, Meade 90, and Skymax 90 in that order.

And as others have said, these are not SCT. I've never heard of 90mm SCT before.


  • Joe1950 and davidparks like this

#9 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 30481
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 22 August 2019 - 06:38 AM

Are there any SCTs smaller than a 5"?  AFAIK, every CAT smaller than that is a Mak.

 

Mike


  • Joe1950 likes this

#10 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 78527
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 22 August 2019 - 06:49 AM

Are there any SCTs smaller than a 5"?  AFAIK, every CAT smaller than that is a Mak.

 

Mike

 

Back when, Meade sold the 2045 which was a 4 inch SCT.  But that's the only commonly available (at one time) smaller than 5 inch I can think of.

 Well the was the Criterion Dynamax 4000.

 

Neither are recommended by me.

 

Jon


  • Sarkikos, Boom and Joe1950 like this

#11 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 30481
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 22 August 2019 - 06:49 AM

The two commonly available types of Maksutov are

 

1) Gregory or "spot" Mak:  the secondary is a reflective spot on the inner surface of the Meniscus opposite the primary.  "This type of Maksutov-Cassegrain's high focal ratio and narrower field of view makes them more suitable for lunar and planetary imaging and any other type of observing where a narrow field high power view is a plus, such as resolving tightly packed globular clusters and double stars."

 

2)  Rumak (Rutten Mak):  the secondary is a separate mirror on the inner surface of the Meniscus.  "This provides an extra degree of freedom in correcting aberration by changing the curvature of the corrector and the secondary independently. Specifically it allows the designer to aspherize the secondary to provide a much wider flat field than traditional spot Maksutovs, with less off-axis coma."

 

https://en.wikipedia...sutov_telescope

 

 

"Due to design limitations imposed by the two surfaces of identical radius of curvature, the [spot Mak] has noticeably inferior off-axis performance: at 0.5° off-axis the wavefront error (best surface) is 0.24 wave RMS, mostly due to the coma, but also astigmatism. The design with separated secondary is highly corrected, with less than 0.025 wave RMS wavefront error at 0.5° off-axis. It is also better corrected axially (1/43 vs. 1/33 wave RMS), with lower field curvature due to both, lower astigmatism and larger secondary. Some lateral color (LC) is noticeable. Both  systems have very low chromatism"

 

https://www.telescop...n_telescope.htm

 

Mike


Edited by Sarkikos, 22 August 2019 - 07:00 AM.

  • eros312, gfstallin and Joe1950 like this

#12 2696

2696

    Vostok 1

  • -----
  • topic starter
  • Posts: 132
  • Joined: 27 May 2019

Posted 22 August 2019 - 07:23 AM

Thank you all for the responses, yes I know I made a mistake and I was actually talking about Maks, I just mixed them up hahah. But with all this being said I definitely will have to look into Astro-Techs Maks I would assume they're pretty good. I was originally looking at the Sky-Watcher models and they look nice and they are a reasonable price. I would have to get another mount of some sort since I'd want to use it for more of a grab and go set up for planetary viewing. If anyone has a decent but lighter mount in mind let me know!
  • Joe1950 likes this

#13 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 30481
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 22 August 2019 - 07:26 AM

You can look for a photographic tripod mount that has a fluid head.  These little C90's are short and light, so you can get away with a top-mounting video head.  The fluid head helps compensate for any imbalance.  I put my C90 on a 501HDV.  Works great.  You can probably find something decent used.

 

Keep in mind that the C90 has only a 1.25" visual back.  This will limit the weight of eyepieces.  No heavy 2" eyepieces.  And IMO a binoviewer would be a little crazy for such a small scope.

 

Stay away from GEMs.  You don't need a German Equatorial Mount for a C90.  That would be overkill.

 

An alt-az mount like the Voyager would also be bigger and heavier than what you need.

 

Mike


Edited by Sarkikos, 22 August 2019 - 07:34 AM.

  • Joe1950 likes this

#14 2696

2696

    Vostok 1

  • -----
  • topic starter
  • Posts: 132
  • Joined: 27 May 2019

Posted 22 August 2019 - 07:32 AM

You can look for a photographic tripod mount that has a fluid head. These little C90's are short and light, so you can get away with a top-mounting video head. The fluid head helps compensate for any imbalance. I put my C90 on a 501HDV. Works great.

Stay away from GEMs. You don't need a German Equatorial Mount for a C90. That would be overkill.

An alt-az mount like the Voyager would also be bigger and heavier than what you need.

Mike


Oh, I have a really cheap photographic tripod I suppose it could work, as long as the scope is within its weight limit. I'm going to have to keep my eye out for some C90's that pop up on Ebay they are pretty appealing as well.
  • Sarkikos likes this

#15 Bowlerhat

Bowlerhat

    Ranger 4

  • -----
  • Posts: 332
  • Joined: 05 Jun 2019
  • Loc: Melbourne, Australia

Posted 22 August 2019 - 08:01 AM

Is it lightweight tripod, or normal one? A tripod that's too light would increase the vibrations. Fluid head isn't really necessary although it's preferable. Other than that secondhand AZ mount would work too-this is a lightweight scope-so even AZ1 could be enough


Edited by Bowlerhat, 22 August 2019 - 08:02 AM.


#16 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 30481
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 22 August 2019 - 08:20 AM

Is it lightweight tripod, or normal one? A tripod that's too light would increase the vibrations. Fluid head isn't really necessary although it's preferable. Other than that secondhand AZ mount would work too-this is a lightweight scope-so even AZ1 could be enough

A fluid head isn't necessary.  There are a lot of things in this hobby that aren't necessary.  You could legitimately say the entire hobby isn't necessary!  grin.gif

 

But there are many things that make the hobby easier and more enjoyable. 

 

If the photo mount doesn't have a fluid head, chances are you'll have to clamp down hard on the altitude detention knob when you point the C90 near zenith, otherwise the scope will fall back.  That can be a royal PITA.  At least it was in my experience.  A fluid head will correct automatically for imbalance.  

 

Mike


Edited by Sarkikos, 22 August 2019 - 08:21 AM.

  • Eddgie and Joe1950 like this

#17 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 78527
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 22 August 2019 - 09:14 AM

A fluid head isn't necessary.  There are a lot of things in this hobby that aren't necessary.  You could legitimately say the entire hobby isn't necessary!  grin.gif

 

But there are many things that make the hobby easier and more enjoyable. 

 

If the photo mount doesn't have a fluid head, chances are you'll have to clamp down hard on the altitude detention knob when you point the C90 near zenith, otherwise the scope will fall back.  That can be a royal PITA.  At least it was in my experience.  A fluid head will correct automatically for imbalance.  

 

Mike

 

 

The alternative to a fluid head is mounting the scope "side saddle", alongside the mount head rather than on top. This is most easily done with a tilt pan 3 axis head. 

 

With the scope alongside the mount, it can be nalanced at all angles because the axis of the altitude axis can pass through the center of gravity of the scope.

 

5917534-SideSaddle ST-80 #1.jpg
 
Jon

  • Sarkikos and Joe1950 like this

#18 Cajundaddy

Cajundaddy

    Surveyor 1

  • *****
  • Posts: 1867
  • Joined: 27 Dec 2016
  • Loc: Cucamonga CA

Posted 22 August 2019 - 09:15 AM

Most of the current 90mm Maks are built by Synta in China, have reasonably good optics, and are branded by Celestron, Orion, and others.  The Celestron C90 spotting scope is a "best value" at around $150 with 2 eyepieces and throwaway tripod.

 

I have the C90 and enjoy it on a Twilight mount/tripod.  It was pretty unsatisfying on all of my photo tripods due to the wiggle at high magnifications.  For planetary viewing you will probably be at 120x - 150x and a rock solid tripod with slow motion will make viewing a pleasure.

 

** Planets are still pretty tiny in a C90 at 150x and that is a realistic limit for the scope.  They reveal a lot more detail with 250x so you may want to consider a 127 Mak instead.  I like the C90 a lot but am keenly aware of it's limitations.


Edited by Cajundaddy, 22 August 2019 - 09:19 AM.

  • Jaimo! and Joe1950 like this

#19 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 30481
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 22 August 2019 - 09:20 AM

 

The alternative to a fluid head is mounting the scope "side saddle", alongside the mount head rather than on top. This is most easily done with a tilt pan 3 axis head. 

 

With the scope alongside the mount, it can be nalanced at all angles because the axis of the altitude axis can pass through the center of gravity of the scope.

 

 
 
Jon

 

I've tried the C90 on DwarfStar and MicroStar Deluxe heads.  These are side-saddle.  But with these you can still have imbalance front to back if you switch between heavier and lighter eyepieces.  The short dovetail doesn't allow for much adjustment back and forth.  So for smaller scopes like the C90 or AT60ED, I prefer a top-loading fluid head.

 

Mike


Edited by Sarkikos, 22 August 2019 - 09:23 AM.

  • Jon Isaacs likes this

#20 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 30481
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 22 August 2019 - 09:25 AM

IME, the C90 is at its best for Moon viewing and double stars.  For many years, a 90mm Mak was my favorite grab-n-go Moon scope.

 

Mike



#21 Cajundaddy

Cajundaddy

    Surveyor 1

  • *****
  • Posts: 1867
  • Joined: 27 Dec 2016
  • Loc: Cucamonga CA

Posted 22 August 2019 - 09:26 AM

A nice backyard planetary package is the Celestron 127 SLT.  Larger aperture, a reasonably solid mount with motorized tracking, and a keen price at $389.  If I were shopping this would be on my short list.

 

https://www.amazon.c...B0038LX8XE?th=1


  • Sarkikos likes this

#22 Sarkikos

Sarkikos

    ISS

  • *****
  • Posts: 30481
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 22 August 2019 - 09:31 AM

A nice backyard planetary package is the Celestron 127 SLT.  Larger aperture, a reasonably solid mount with motorized tracking, and a keen price at $389.  If I were shopping this would be on my short list.

 

https://www.amazon.c...B0038LX8XE?th=1

Will the C127 OTA clear the mount when pointing near zenith?  If the scope can't clear the mount, I'd consider that a deal breaker for astronomy.  You want to be able to view the entire sky visible from your location without any no-go zones.

 

Mike


Edited by Sarkikos, 22 August 2019 - 09:32 AM.


#23 2696

2696

    Vostok 1

  • -----
  • topic starter
  • Posts: 132
  • Joined: 27 May 2019

Posted 22 August 2019 - 09:31 AM

Most of the current 90mm Maks are built by Synta in China, have reasonably good optics, and are branded by Celestron, Orion, and others. The Celestron C90 spotting scope is a "best value" at around $150 with 2 eyepieces and throwaway tripod.

I have the C90 and enjoy it on a Twilight mount/tripod. It was pretty unsatisfying on all of my photo tripods due to the wiggle at high magnifications. For planetary viewing you will probably be at 120x - 150x and a rock solid tripod with slow motion will make viewing a pleasure.

** Planets are still pretty tiny in a C90 at 150x and that is a realistic limit for the scope. They reveal a lot more detail with 250x so you may want to consider a 127 Mak instead. I like the C90 a lot but am keenly aware of it's limitations.


Right, I am very aware of what I should expect to see through something of this size. My current grab and go scope is only a 40mm and I'm even satisfied with the views I get from that.. so a 90-127mm would be more than enough for what I'm looking for. I may end up going with the middle ground here and go with something that's 102mm, I just have to keep looking around until I find something I like.

#24 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 78527
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 22 August 2019 - 09:31 AM

I've tried the C90 on DwarfStar and MicroStar Deluxe heads.  These are side-saddle.  But with these you can still have imbalance front to back if you switch between heavier and lighter eyepieces.  The short dovetail doesn't allow for much adjustment back and forth.  So for smaller scopes like the C90 or AT60ED, I prefer a top-loading fluid head.

 

Mike

 

A top loading fluid head has more imbalance and deals with it by friction.. fluid friction.  Properly balancing a scope may take some creativity, stock dovetails etc, don't always cut it. 

 

With a 90 mm Mak, there are no heavy eyepiece's..  

 

In terms of photo tripods, I am not talking about department store tripods. I'm talking second hand Bogen/Manfrotto heavy duty tripods. I find these on Craigslist etc. The tripod on the photo is a 3046 with a 3047 head. New this would be around $500, used, under a $100.

 

My favorite mount for a small Mak is the Vixen Portamount. 

 

Jon


  • Richard Whalen and Joe1950 like this

#25 Cajundaddy

Cajundaddy

    Surveyor 1

  • *****
  • Posts: 1867
  • Joined: 27 Dec 2016
  • Loc: Cucamonga CA

Posted 22 August 2019 - 09:40 AM

Will the C127 OTA clear the mount when pointing near zenith?  If the scope can't clear the mount, I'd consider that a deal breaker for astronomy.  You want to be able to view the entire sky visible from your location without any no-go zones.

 

Mike

I think it does.  I have the C90 on an SLT mount and have used a friend's 127 SLT.  I don't remember having trouble with mount obstruction.  Because it is a dovetail you have significant adjustment on the SLT to get clearance.

 

This is a pretty good demo of a C90 on the SLT mount.  A nice simple and portable setup for planetary or lunar observing:
https://www.youtube....h?v=Q8pCbZaWYz8


Edited by Cajundaddy, 22 August 2019 - 11:00 AM.

  • Sarkikos 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