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Benefits of a 102mm Achromat refractor over a 127mm MAK?

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#1 sojourneyer

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Posted 30 July 2021 - 09:36 PM

There had been a post created over a year ago about the benefits of an 80mm refractor over a 127mm Mak

but it left some elements out that were not discussed such as 80mm APO.  The topic primarily involved discussion an 80mm achromat.

 

So I will try to be more specific.  Since we are at the 102mm optics level the 102 APO is out of the picture as that definitely is in another league.

 

But what about comparing long and short tube 102mm achromats against the 127Mak?

 

I now only have a short tube (f/6.5) Celestron 102 with XLT coatings and I prefer it over my prior 127 maks.

For some reason the Mak levels out at about 120-130X when viewing the planets where I live. One reason is the limitations of the focuser.  The other is my location. My refractor gives me more clear viewing and I can reach higher magnifications as well.

 

For those reasons I sold my Maks. Yes, I purchased one and was disappointed with it and sold it. Then I had regretted selling it and purchased another one but sold it too and replaced it with a SV 80ED.  No regrets here.

 

Where I live and the EPs I use can  have an affect  on viewing experiences.

 

I only use the scope for visual and  not AP.  Unless I would be doing AP the achromat wins hands down overall-- planets, moon and DSO


Edited by sojourneyer, 30 July 2021 - 10:57 PM.

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#2 Hesiod

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Posted 31 July 2021 - 07:48 AM

My guess is that in such cases the optical quality of the single telescopes matters more than the other aspects.
A 5" MCT that levels at 130x is a truly poor sample, so you were right to get rid of it.
A good one should deliver well past 200x and in my experience a 5" can delve a bit more details than a 4" f10 achro, with a more evident advantage about color tones and hues.
On the other hand achros are cheaper and, as long as are willing to cope with their limits, more "flexible" due to the noticeably wider fov.
If somewhat on budget however my opinion is that a 5" f/5 Newtonian reflector gets the best from both worlds (and the ones with foldable tube beat the MCTs even for portability)
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#3 russell23

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Posted 31 July 2021 - 09:22 AM

Certainly the 102mm f/6.5 achromat will provide a much wider maximum TFOV.  So that is a huge advantage.

 

If the Mak has excellent optics and is in good thermal equilibrium then it should beat a 102mm f/6.5 achromat on the planets.  If it doesn't then there is a problem with the optics or it is dealing with tube currents.


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#4 sojourneyer

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Posted 31 July 2021 - 09:22 AM

My guess is that in such cases the optical quality of the single telescopes matters more than the other aspects.
A 5" MCT that levels at 130x is a truly poor sample, so you were right to get rid of it.
A good one should deliver well past 200x and in my experience a 5" can delve a bit more details than a 4" f10 achro, with a more evident advantage about color tones and hues.
On the other hand achros are cheaper and, as long as are willing to cope with their limits, more "flexible" due to the noticeably wider fov.
If somewhat on budget however my opinion is that a 5" f/5 Newtonian reflector gets the best from both worlds (and the ones with foldable tube beat the MCTs even for portability)

The funny thing Alberto is that I have had actually 3 127mm Maks (Orion and 2 Celestron) and a 90mm Mak.. The larger Maks all had that same problem.

 

The Maks certainly did not take any space in the house..LOL.  They were like a bad pair of shoes. You want to love them and keep them but they do not fit.

 

I am not really fussed about the CA and would rather contend with it than the cooling down as well.

 

I also do not have to contend with a dew shield as Maks do not have them unless you purchase one.


Edited by sojourneyer, 31 July 2021 - 10:32 AM.


#5 Echolight

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Posted 31 July 2021 - 10:07 AM

So how much does a 102 f6.5 achro weigh? And how does it compare to your SV 80ED visually?

 

I see a lot of love for the 127 Maks here. But I think I’d choose a C5 in this class for it’s shorter length and lower weight. And it’s potential for a 2.5 degree or more TFOV with a reducer. The C5 does cost more though.

 

I have a little collection of 90mm Maks. And they certainly are cute. So small and light. And cheap on the used market.


Edited by Echolight, 31 July 2021 - 10:09 AM.


#6 Rollo

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Posted 31 July 2021 - 10:17 AM

The 102mm Achro should cool down much faster than the 127 mak.     


Edited by Rollo, 31 July 2021 - 09:01 PM.

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#7 sojourneyer

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Posted 31 July 2021 - 10:54 AM

So how much does a 102 f6.5 achro weigh? And how does it compare to your SV 80ED visually?

 

I see a lot of love for the 127 Maks here. But I think I’d choose a C5 in this class for it’s shorter length and lower weight. And it’s potential for a 2.5 degree or more TFOV with a reducer. The C5 does cost more though.

 

I have a little collection of 90mm Maks. And they certainly are cute. So small and light. And cheap on the used market.

the Celestron 102 f/6.5 weighs 5 lbs

the Celestron 127 Mak weighs 6.5 lbs

the SV 80 Super ED weighs 5.5 lbs excluding rings and rail

 

Visually there is no comparison between a Super ED and the achromat  We are talking about Hoya FCD100 glass vs crown and flint.   Mercedes vs Yugo

 

I would love a SV102 ED but am happy with the two refractors I have.


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#8 rexowner

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Posted 31 July 2021 - 11:56 AM

I liked my Orion/Synta 127 Mak.  Supposedly these are really 118mm IIRC.  I had a good sample,

and it put up nice views.

 

Nothing wrong with it at all, but then I got a 102mm doublet refractor.  Equally as grab-and-go

as the Mak for me, and did everything better.

 

So I sold the Mak.  The buyer was happy.

 

Only reason I´d get a small Mak would be for camping.


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#9 AndresEsteban

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Posted 31 July 2021 - 06:17 PM

Certainly the 102mm f/6.5 achromat will provide a much wider maximum TFOV.  So that is a huge advantage.

 

If the Mak has excellent optics and is in good thermal equilibrium then it should beat a 102mm f/6.5 achromat on the planets.  If it doesn't then there is a problem with the optics or it is dealing with tube currents.

The problem here is that a 102 mm f/6.5 achromat has a CA index of 1,62... Too low even for the Sidgwick Criteria (CA>3) which, by the way, is personally consider low standard, being more a "Conrady guy" (CA>5). It simply won't work well at high powers on planets, doubles and the Moon. In that area MAKs and long focus achros (CA>5) will excel. BUT, yes, there's an area where a 102 mm f/6,5 achro will brightly perform and that is DSO!!!  a 102 
So, IMHO, you simply can't compare a MAK (127 mm for example) with a 102 mm f/6.5 achro. These scopes are totally different instruments for different purposes! BUT, being honest, I'd agree that a 102mm f/6.5 truly APO (not just an ED hybrid) would be a serious match to the MAK!
Just my 2 cents...

Celar skies for us all and less light pollution waytogo.gif Telescope.gif Telescope.gif Telescope.gif 
Andy


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#10 barbie

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Posted 31 July 2021 - 06:41 PM

I recently compared my USA made 90mm Mak to my 76mm fluorite apo refractor on the moon,planets and the brighter doubles and couldn't see any difference between the two. Both have s superb optics but I sold the refractor in favor of the more portable and compact 90mm Mak. The 90mm Mak is also lighter and can be carried outside on its tripod with one hand. I leave it set up in my home office and just grab the entire setup with one  hand and a few eyepieces with the other and I'm out the front door and observing within two minutes!! For my needs, the Mak is the better choice so I sold my refractor and now use my 90mm Mak as my only scope as I only observe the moon,planets and brighter doubles and couldn't be happier!! Also, my skies have gotten steadily worse over the last year and this summer in particular so much so that I can no longer justify owning more than one scope now. I've chosen the small Mak for these reasons.


Edited by barbie, 31 July 2021 - 06:52 PM.

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#11 sojourneyer

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Posted 31 July 2021 - 09:15 PM

I would still stack my SV80 Super ED up against the 127 Mak any day given that my Maks had big magnification issues.  And three of them? Seems like more than a coincidence.


Edited by sojourneyer, 31 July 2021 - 09:16 PM.


#12 RichA

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Posted 31 July 2021 - 09:46 PM

There had been a post created over a year ago about the benefits of an 80mm refractor over a 127mm Mak

but it left some elements out that were not discussed such as 80mm APO.  The topic primarily involved discussion an 80mm achromat.

 

So I will try to be more specific.  Since we are at the 102mm optics level the 102 APO is out of the picture as that definitely is in another league.

 

But what about comparing long and short tube 102mm achromats against the 127Mak?

 

I now only have a short tube (f/6.5) Celestron 102 with XLT coatings and I prefer it over my prior 127 maks.

For some reason the Mak levels out at about 120-130X when viewing the planets where I live. One reason is the limitations of the focuser.  The other is my location. My refractor gives me more clear viewing and I can reach higher magnifications as well.

 

For those reasons I sold my Maks. Yes, I purchased one and was disappointed with it and sold it. Then I had regretted selling it and purchased another one but sold it too and replaced it with a SV 80ED.  No regrets here.

 

Where I live and the EPs I use can  have an affect  on viewing experiences.

 

I only use the scope for visual and  not AP.  Unless I would be doing AP the achromat wins hands down overall-- planets, moon and DSO

You should wait for Questar's 5 inch to be released and try it.



#13 sojourneyer

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Posted 31 July 2021 - 10:06 PM

You should wait for Questar's 5 inch to be released and try it.

Drat, my pockets all have holes in them!



#14 treadmarks

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Posted 31 July 2021 - 10:26 PM

I have the same 102mm Celestron refractor as you. I can't directly speak to a 127mm Mak, but I can compare to my 102mm Mak. I've had them both out recently and did some comparisons. You mentioned high powers, but what I appreciate about my refractor over the Mak is its ability to do low powers. The reason for this is that, unless it's a very steady night, the low power view is going to be a lot sharper and more pleasing. When you view at higher power than the atmosphere supports, you're not seeing more detail, you're just seeing more blur. I have been repeatedly wowed by the view of the Moon in this refractor when I use it at low power.

 

The Mak beats this refractor on Jupiter. The CA in the refractor muddies the image too much, the Mak's view is more pleasing. The difference in detail levels is not huge though. On Saturn, I think achromats do a lot better. At least mine does. Saturn is not nearly as bright as Jupiter and CA is less of an issue. If anything, Saturn is too dim and the extra brightness a refractor gives over a reflector of the same aperture is helpful. I prefer my achromat over my Mak for Saturn.


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#15 sojourneyer

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Posted 31 July 2021 - 11:14 PM

I actually sold my Omni 102 f/6.5  when I got my Stellarvue.  I missed it and ended up purchasing  the 102 Celestron Starsense Explorer which actually is the Omni XLT 102 but with their tracking system.  That system is the bees knees. I love it. 

What more can you ask for... a good scope with fantastic tracking.....and the price I paid for the 1 month old scope made it even better.

 

Weather permitting I will use it Tuesday and compare with the SV.



#16 PowerM3

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Posted 31 July 2021 - 11:28 PM

Preferring a 102 short tube to a 5"Make for low power would be expected. But preferring it for high power views on the planets??? The only reason that the Achro would win is if the make is grosely not temperature equalized. 



#17 Hesiod

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Posted 01 August 2021 - 09:35 AM

I would still stack my SV80 Super ED up against the 127 Mak any day given that my Maks had big magnification issues.  And three of them? Seems like more than a coincidence.

In my opinion it is certainly so. Mind that, because of the large CO, those small MCTs need really good mirrors: a primary mirror which is barely diffraction limited by itself means a poor sample of MCT, well under the "diffraction limited threshold".

 

Cooling may be an issue, but one easy to discern and not much bothersome to handle; as for dewing, MCTs IME are very close to refractors, so not excessively prone to dew.

Most MCTs are not equipped with a dewshield, but it is easy and cheap to craft one from paper, plastic sheets or a gym mat.

 

Said so, were I asked for a cheap and versatile compact telescope would not recommend neither a MCT nor a refractor but a small Newtonian reflector



#18 sojourneyer

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Posted 01 August 2021 - 10:05 AM

In my opinion it is certainly so. Mind that, because of the large CO, those small MCTs need really good mirrors: a primary mirror which is barely diffraction limited by itself means a poor sample of MCT, well under the "diffraction limited threshold".

 

Cooling may be an issue, but one easy to discern and not much bothersome to handle; as for dewing, MCTs IME are very close to refractors, so not excessively prone to dew.

Most MCTs are not equipped with a dewshield, but it is easy and cheap to craft one from paper, plastic sheets or a gym mat.

 

Said so, were I asked for a cheap and versatile compact telescope would not recommend neither a MCT nor a refractor but a small Newtonian reflector

I actually made the dew shields for the Maks out of tar paper.



#19 barbie

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Posted 01 August 2021 - 09:48 PM

I made my dewshield from a photocopied star chart and had it laminated and flocked the inside. I works well and gives my classic ETX90 a "Questar type" appearance. This ETX90 rivals my now sold Tak FC76 apo on the moon,planets and double stars. It's SUPER sharp!!


Edited by barbie, 01 August 2021 - 09:52 PM.

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#20 Terra Nova

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Posted 01 August 2021 - 10:47 PM

I made my dewshield from a photocopied star chart and had it laminated and flocked the inside. I works well and gives my classic ETX90 a "Questar type" appearance. This ETX90 rivals my now sold Tak FC76 apo on the moon,planets and double stars. It's SUPER sharp!!

I’ve found my 1985 Questar with broadband coatings and my 1997 Tak FC76 F8 fluorite apo to give very similar views of Jupiter and Saturn in side by side comparisons. I really do love both scopes tho would hate to part with either one.


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#21 Jon Isaacs

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Posted 02 August 2021 - 07:34 AM

In my opinion it is certainly so. Mind that, because of the large CO, those small MCTs need really good mirrors: a primary mirror which is barely diffraction limited by itself means a poor sample of MCT, well under the "diffraction limited threshold".

 

Cooling may be an issue, but one easy to discern and not much bothersome to handle; as for dewing, MCTs IME are very close to refractors, so not excessively prone to dew.

Most MCTs are not equipped with a dewshield, but it is easy and cheap to craft one from paper, plastic sheets or a gym mat.

 

Said so, were I asked for a cheap and versatile compact telescope would not recommend neither a MCT nor a refractor but a small Newtonian reflector

 

I had an Orion 127 Starmax, I wasn't pleased with the images it provided but it was facing some tougher competition than a 102mm F/6.5 achromat.  

 

In terms of the thermal equilibrium, these days people are insulating SCTs and Maks with Reflectix,  that would be the first thing I would do. It seems that by insulating the OTA it slows down the heat transfer and essentially eliminates the tube currents.  It's a game changer.

 

https://www.cloudyni...with-reflectix/

 

I have had several 130mm F/5 Newtonians.. They have their virtues but they do have thermal issues and getting stable high power views comparable to a refractor takes an hour or more.  

 

Jon


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#22 Echolight

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Posted 02 August 2021 - 12:11 PM

My C8 has only had tube currents that one day that I left it out in the sun. But it has dewed over a couple of times.

 

So far my 90mm Maks have been immune to climatic conditions.
They don’t do anything my ED80 can’t do. Except be half as big and half as heavy, which is nice sometimes.


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#23 sojourneyer

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Posted 02 August 2021 - 12:55 PM

My C8 has only had tube currents that one day that I left it out in the sun. But it has dewed over a couple of times.

 

So far my 90mm Maks have been immune to climatic conditions.
They don’t do anything my ED80 can’t do. Except be half as big and half as heavy, which is nice sometimes.

I really would not think a 90mm Mak would have any major cooling down issues given their small size.   But you can not enjoy DSOs like you do with your 80ED



#24 Terra Nova

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Posted 02 August 2021 - 01:32 PM

I had a Celestron 127 for a while a few years back. On my Porta II it was a nice, compact package that was easy to pick up and move around anywhere on the deck or in the yard. I thought it would be the epitome of convenience. Dew and stray light were easy to manage with a homemade dew shield, but it had thermal issues that were far worse than the C5, and Meade 6 that I had at the time; even worse than either of the C8 SCTs that I had before and after. I gave up dealing with it in about a year and sold it. You could literally sense the heat plumes rising off the primary and pulsating through the air in the tube. It ruined detailed planetary view for me. I’ve never seen anything like that in my Questar 3.5”; it’s ready for viewing almost immediately after setup. Same with an old C90 Mak I had. Those two acted just like refractors of the same aperture. The 127mm Synta Mak was different for sure! It still wasn’t ready after an hour, and would sometimes have issues all evening. That’s what cured me of a desire for larger Maks.

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Edited by Terra Nova, 02 August 2021 - 02:15 PM.

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#25 barbie

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Posted 02 August 2021 - 01:57 PM

Those are many of the same reasons I've stuck with 90mm Maks and small scopes in general. I was very fortunate to get an outstanding ETX90 which was optically identical in performance to my former Tak FC76dcu on lunar, planetary and double stars. The 90mm Mak is more manageable for me now with my bad back and shoulders. My local weather conditions also no longer warrant me having more than one scope anymore.


Edited by barbie, 02 August 2021 - 02:06 PM.

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