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Meade ACF 10" f/8 vs RC 10"

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#1 Yoddha

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Posted 06 January 2020 - 06:29 PM

Hello,

 

I want to make an upgrade in the next half year or so and for some time am reading opinions in the net, however can't get clear direction and will be very thankful to hear your opinions :)

 

Here is the background. I'm pure imager (once or twice per year am making short visual walkthrough for friends that has no experience at all). The setup which am building is permanent located in a small obsy - a 2.2m Uniwesal dome (don't mess with them unless you like big troubles). The mount is CEM60 and my primary camera is QHY22 with set of Astrodon filters - 3nm narrowband and LRGB. For many years am a refractor guy flowerred.gif In a parallel world where money are not a factor would like something like 180mm of that kind and bigger dome, but I am here and now... It is not possible to house/afford something bigger than 150mm which is not significant step over the 130mm I have... So am looking for alternatives :)

 

There are two options that tear me apart and still can't find stable direction:

 

1. GSO clone RC 10" f/8 truss tube, detached focuser, with reducer that will make it ~ f/5.4

2. Meade ACF 10 f/8, possibly additional focuser, with reducer that will make it ~f/5.4

 

Both will be used with OAG. The collimation should not be a big issue - it is permeant setup and in worst case will require tuning once-twice per year... Am I right?

 

My research started and continues with real images hunt in Astrobin (in addition to reading everything that can find in the forums). There are some spectacular images taken with both scopes! 

 

My considerations so far are: 

The RC pros with truss version - the cooling will be faster because the open design and fans, the temperature shift should be smaller. The cons are bit bigger stars, spikes.

The ACF pros are the smaller obstruction, bit smaller stars and no spikes. The cons are slower cooling, bigger temperature shift, mirror flips ??? May need additional focuser, bit bigger price.

 

In long term I want to use the scope for astrophotography for smaller targets. In very long term if one day I find myself tired of astrophotography shocked.gif am thinking for supernovas search or variable stars photometry...

 

As I started will be very thankful to hear your opinions for those two models, for the links that I have missed, as well as the points and considerations I don't see or know  bow.gif bow.gif bow.gif 

 

P.S. I have excluded the RASA models because are not compatible with the filters I have and because they require manual filter change. Fast Newtonians are excluded because are also too fast for Astrodon and because it is hard to put Corrector + OAG + Filter wheel.



#2 DuncanM

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Posted 06 January 2020 - 07:07 PM

I have two Meade 10in F10 OTAs and two Meade 10in F6.3 OTAs  Both work well with Starizona SCT reducers and the 10in F10, works exceptionally well and rivals an Edge HD OTA and Edge reducer. I get ~F6.9 with a 10in F10 and a Starizona .63x SCT reducer and  ~F5 with a Meade 10in F6.3 OTA and a Starizona .75x SCT reducer.

 

My point is that a used 10in F10 (or C-9.25 /C-11 non-Edge) and a new Starizona .63x SCT reducer might be a much lower cost alternative.

 

Example images:

 

https://www.cloudyni...m/10884-images/


Edited by DuncanM, 06 January 2020 - 07:27 PM.

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#3 jrcrilly

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Posted 06 January 2020 - 07:25 PM

The F/8 Meades are a whole different class from the earlier F/10 (and F/6.3) designs. Greatly improved focuser, flatter image plane, etc. I owned and used both the 12" GSO RC and the 12" F/8 Meade (and a few 12" F/10 Meades) so I can describe my experiences with both. Overall, I preferred the F/8 Meade. Only downsides were the losses and potential dew involved in having a corrector plate. Build quality was a notch or two above the GSO RC. Both captured pleasing images; either would do the lob you want. My astrobin gallery should have examples from both.


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#4 Spacetravelerx

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Posted 07 January 2020 - 01:43 AM

I can second the Meade f/8 ACF - the optics are excellent and NO mirror flop with the f/8 ACF.  No noticeable image shift when focusing.

I too have noticed a flatter image plane with the f/8 ACF vs f/10 models.   I have been using the Astro-Tech 2" field flattener recently, which is intended for refractors, on my 14" f/8 ACF.  Shockingly, the views are coming off quite flat on APS-C chips (I can't speak for full frame sensors).

Overall I give my vote for the Meade f/8 ACF.


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#5 Yoddha

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Posted 07 January 2020 - 08:45 AM

Thank you very much!

Are there observations how slower is the cooling of SCT vs RC? My place has a fast ambient temperature drop immediately after the sunset and after that it is quite slow. The dome is buffering the conditions but still has to consider the initial cooling...



#6 jgraham

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Posted 07 January 2020 - 03:36 PM

I use a Lymax cat cooler on my 8" and 10" SCTs. I'm not sure that they are still available, but there are several DIY versions floating around.
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#7 Peterson Engineering

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Posted 07 January 2020 - 03:52 PM

Hi Yoddha,

 

A 2.2 m dome is indeed a tight squeeze.  Your IOptron CEM60 is an expensive mount and I assume that you're just talking about an optical tube here. Which is sort of a shame, because a fork mounted scope provides a lot more working space than an GEM.

 

If a scope lives in an ambient temperature dome setup cooldown isn't an issue.  But depending upon the temperature gradients you experience scope design certainly is.  I've been using Meade's LX200 line for 20 years, the last 13 in a dome.  I've never noticed temperature associated problems with tube currents on my LX200GPS 14".  Thermal expansion is far more significant than tube current.

 

Because temperature early in the night is higher than when I shut the scope down late at night when I last used it, early evening Initial startup focusing is always necessary. And focusing is guesswork for an hour after sunset due to thermals.  So a second focus is preformed about an hour after sunset.  And the scope is subsequently refocused with every subsequent 3°C temperature change.  Now the 14" has a long aluminum tube and the 10" you're looking at will be a bit more forgiving.  

 

So if temperature change is really important I'd go with a carbon fiber tube.  Or add a temperature compensating focuser to your setup.

 

Clear skies,

 

Pete


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#8 Spacetravelerx

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Posted 07 January 2020 - 04:00 PM

Thank you very much!

Are there observations how slower is the cooling of SCT vs RC? My place has a fast ambient temperature drop immediately after the sunset and after that it is quite slow. The dome is buffering the conditions but still has to consider the initial cooling...

Being in New Mexico I get significant temperature changes.

For focusing I use the Meade Microfocuser, however I am moving to a temperature controlled focuser next to automate the process.

Also, for my dome (if I ever get it built), I was looking at adding A/C to thermal control the inside of the dome.


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#9 Yoddha

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Posted 07 January 2020 - 04:36 PM

Hi Pete,

 

Thank you!

 

I have chosen CEM60 because it allows me to use the other OTAs :)



#10 Yoddha

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Posted 07 January 2020 - 04:38 PM

Hi Andrew,

Interesting idea :) I already have humidity control, but maybe have to put some isolation on the walls before thinking in A/C... 



#11 Yoddha

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Posted 10 January 2020 - 06:32 AM

Thank you very much!!! The things are starting to incline towards SC :)

 

Bit more feedback for the RC10"? The RC8 has good optics but 10" bigger and harder to make... 



#12 Stephen Kennedy

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Posted 12 January 2020 - 03:02 AM

I have a GSO RC6 and have been extremely pleased with the optics,  While the mirrors are smaller than those on an RC10, I am confident that the mirrors on an RC10 are made with the same high quality as those with smaller apertures.    The RC design is a completely reflective one which unlike the Meade SCT with its corrector plate and coma corector lenses in the baffle tube will never suffer from false color, spherical aberration, dew, light loss or any of the other deficiencies a reflector/ refractor hybrid  can be expected to display.  Why do you think that nearly all research astronomers use RC telescopes while none use SCTs?                                                                              



#13 DuncanM

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Posted 12 January 2020 - 03:24 AM

Meade ACFs and Celestron Edge SCTs have a corrector plate but only the Edge SCTs use baffle tube optics.


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#14 Yoddha

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Posted 12 January 2020 - 07:45 AM

Hi  Stephen,

 

You are right that almost all research scopes are RC, however their optics are on other level of production ;) The ASA, RCOS, Officina Stellare RCs will provide way other image than GSO... So having in mind that SCT are easier to be produced and their mass production is longer than GSO RCs is making me wondering which is the better choice for 10" range :)



#15 Benni123456

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Posted 14 January 2020 - 01:15 PM

I have a GSO RC6 and have been extremely pleased with the optics,  While the mirrors are smaller than those on an RC10, I am confident that the mirrors on an RC10 are made with the same high quality as those with smaller apertures.    The RC design is a completely reflective one which unlike the Meade SCT with its corrector plate and coma corector lenses in the baffle tube will never suffer from false color, spherical aberration, dew, light loss or any of the other deficiencies a reflector/ refractor hybrid  can be expected to display.  Why do you think that nearly all research astronomers use RC telescopes while none use SCTs?                                                                              

this seems purely repetition of advertising.

 

the rc has field curvature and like in a refractor one needs to insert a good flattener.

the flattener, if not good, can be a source of ca and other image errors.

 

an edge hd has the flattener within the scope.

 

professional astronomers like rcs just because they give a larger field of view without coma.

 

when you use fullframe and larger sensors, this is of course important for amateurs.

 

Most important however, is that rcs can have a smaller f number. 

 

an sc works mostly at f10-f7 and not below that.

 

an rc works at f8 natively and you can still add a reducer.

 

professional rcs have much faster fnumbers than these amateur things. astronomers like things in the f2 range. an sct is not suitable for that.


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#16 rockstarbill

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Posted 14 January 2020 - 02:19 PM

this seems purely repetition of advertising.

 

the rc has field curvature and like in a refractor one needs to insert a good flattener.

the flattener, if not good, can be a source of ca and other image errors.

 

an edge hd has the flattener within the scope.

On a tiny 1" sensor (ICX694 in this case) the RC10 will have a perfectly flat field with no field corrector required.


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#17 DuncanM

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Posted 14 January 2020 - 02:47 PM

The smaller size and weight of an SCT must also be considered. Larger size and equal weight means a larger observatory and a larger mount for equal wind tolerance.


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