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  #1  
Old 09-08-2018, 10:21 AM
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Outcast (Carlton)
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Meade UHTC pre ACF optics performance

I have the opportunity to acquire a 2004 Meade LX90 8inch Surplus a bundle for a very good price.

It has UHTC coatings but, is pre ACF. Should I be concerned by this?

Can anyone comment on the quality & performance of Meader UHTC pre ACF optics please
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  #2  
Old 09-08-2018, 10:37 AM
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Merlin66 (Ken)
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Over the years I've used many (!) Meade SCT's from 8" to 12".
From back in the LX5/6 days through to the Lx200 all pre ACF.

I didn't have any major complaints/ issues - always check the collimation and the tightness of the corrector retaining screws!

The only "area of concern" was the focusing mechanism....definitely not as robust as the Celestron but with practise can be mastered.

I'd probably still be using Meade were it not for the lack of rear access space (in the forks) for the larger spectroscopes...this lead to changing to a C9.25 and later a C11 on an NEQ6pro mount.
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Old 09-08-2018, 10:43 AM
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mental4astro (Alexander)
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Photo or visual applications?

The ACF system differs from non-ACF with a coma corrector built into the baffle tube of the ACF tube. This is only important when doing wide field photography as it will tighten up the stars along the edge of the FOV. When using a traditional non-ACF SCT, in order to achieve the same result you would need to make use of a focal reducer/corrector that is designed specifically for SCTs. You will also see that these same reducer/correctors cannot be used with ACF optics - you need to use a different focal reducer for these scopes.

For visual, ACF or non-ACF makes no difference. While there is a bee's dick amount of coma in non-ACF optics, you REALLY need to go looking for it while using the very lowest magnification and very widest TFOV the optics can give, and it will be at the very edge of the FOV, and it is not a place where any serious observing is done.

But everyone is different. Me, I only do planetary photography with my non-ACF SCT, so it makes no difference to me, and it I have never really noticed any ill effects those times I visually max out the TFOV of my SCT. But others wouldn't tolerate it, even if the way they use their SCT coma wouldn't be an issue.

In so far a optical quality goes, there are just as many dodgy ACF optics out there as non-ACF, regardless of when they were manufactured.

Ken mentions mirror shift, this is another matter, and the ACF instruments do seem to have this better controlled than cheaper non-ACF. Not perfect, but better, in both Meades and Celestrons.

Focusing tip if using a traditional Meade or Celestron SCT: Always wind the focuser knob in the same direction to achieve focus. This will also set the object back into the original position you had it in when you focus the object. Wind out, then wind in to focus. Wind out, then slowly wind in.

Also, this mirror shift will affect collimation. So when collimating your SCT with a star test, form your donut, then before analysing the donut, wind out a little then wind in, just like with focusing, and this will leave the primary mirror set in the same place as when you focus ACF scope or not.

Alex.
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Old 09-08-2018, 10:51 AM
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Thanks Ken,

Can you elaborate with respect to the focused not being as robust please

Quote:
Originally Posted by Merlin66 View Post
Over the years I've used many (!) Meade SCT's from 8" to 12".
From back in the LX5/6 days through to the Lx200 all pre ACF.

I didn't have any major complaints/ issues - always check the collimation and the tightness of the corrector retaining screws!

The only "area of concern" was the focusing mechanism....definitely not as robust as the Celestron but with practise can be mastered.

I'd probably still be using Meade were it not for the lack of rear access space (in the forks) for the larger spectroscopes...this lead to changing to a C9.25 and later a C11 on an NEQ6pro mount.

Last edited by Outcast; 09-08-2018 at 05:34 PM.
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  #5  
Old 09-08-2018, 10:52 AM
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Gday Alexander
Quote:
The ACF system differs from non-ACF with a coma corrector built into the baffle tube of the ACF tube.
Not sure this is correct.
The Celestron edges have a corrector in the baffle tube
but the Meade ACF uses a non spherical secondary, and IIRC, a slightly different figure on the corrector to flatten the field.

Andrew
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  #6  
Old 09-08-2018, 10:56 AM
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Hi Alex

Thanks for the info.

It would be used for 90% visual use with maybe a little dabble in short exposure planetary & maybe dso use with a dslr.

AP is not that important to me & as you say I can always use a corrector in the future if my needs change.

Cheers

Quote:
Originally Posted by mental4astro View Post
Photo or visual applications?

The ACF system differs from non-ACF with a coma corrector built into the baffle tube of the ACF tube. This is only important when doing wide field photography as it will tighten up the stars along the edge of the FOV. When using a traditional non-ACF SCT, in order to achieve the same result you would need to make use of a focal reducer/corrector that is designed specifically for SCTs. You will also see that these same reducer/correctors cannot be used with ACF optics - you need to use a different focal reducer for these scopes.

For visual, ACF or non-ACF makes no difference. While there is a bee's dick amount of coma in non-ACF optics, you REALLY need to go looking for it while using the very lowest magnification and very widest TFOV the optics can give, and it will be at the very edge of the FOV, and it is not a place where any serious observing is done.

But everyone is different. Me, I only do planetary photography with my non-ACF SCT, so it makes no difference to me, and it I have never really noticed any ill effects those times I visually max out the TFOV of my SCT. But others wouldn't tolerate it, even if the way they use their SCT coma wouldn't be an issue.

In so far a optical quality goes, there are just as many dodgy ACF optics out there as non-ACF, regardless of when they were manufactured.

Ken mentions mirror shift, this is another matter, and the ACF instruments do seem to have this better controlled than cheaper non-ACF. Not perfect, but better, in both Meades and Celestrons.

Focusing tip if using a traditional Meade or Celestron SCT: Always wind the focuser knob in the same direction to achieve focus. This will also set the object back into the original position you had it in when you focus the object. Wind out, then wind in to focus. Wind out, then slowly wind in.

Also, this mirror shift will affect collimation. So when collimating your SCT with a star test, form your donut, then before analysing the donut, wind out a little then wind in, just like with focusing, and this will leave the primary mirror set in the same place as when you focus ACF scope or not.

Alex.
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  #7  
Old 09-08-2018, 10:58 AM
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Thanks Andrew. If this is the case with the Meades, then I stand corrected. I'll have a look at a mate's to see Whichever the case, same things go for the reducer/corrector and dealing with whatever mirror shift the instruments may have.
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Old 09-08-2018, 11:05 AM
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The mechanical focusing mechanism used for the SCT's - both Meade and Celestron are used to move the main mirror up/ down the central baffle tube.
The very fine gap between the baffle tube and the mirror "boss" can cause some mirror flop - the is the same for both. Re-spreading the grease regularly by running the focus through the full travel a few times help reduce this flop.

In the Meade the focus knob joins the rear of the mirror support with a pin (the Celestron use a fixed threaded rod) and this can cause some extra focuser movement - you quickly learn to finally focus from one direction.

To ensure mimimum slop/flop (while using the spectrograph) I resorted to fitting a mirror lock (MAPUG design) which allowed the mirror/ focuser to be "locked" into position after focusing. This worked well for me, especially on the 12".

Nothing to be really concerned about, just need practise and you'll quickly come to terms with it.
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  #9  
Old 09-08-2018, 11:13 AM
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Merlin66 (Ken)
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https://en.wikipedia.org/wiki/Meade_Instruments

The Meade ACF design relies on a modified Hyperbolic secondary mirror for the "improved" performance.

Celestron just added a built-in corrector.
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  #10  
Old 09-08-2018, 11:26 AM
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Hmmm, easy enough to settle! Anyone have a Meade ACF and like to have a look up the bore hole of the primary? My friend can't have a look right now...
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  #11  
Old 09-08-2018, 11:32 AM
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Gday Ken
Quote:
on a modified Hyperbolic secondary
I read a paper once by a mob who got access to a brand new RCX and took it apart to put it on an optical bench.
IIRC, they mentioned the secondary was closer to an ellipsoid??
but that was also with F8 optics.
Not sure if the F10 ACF is similar to the newer F8 ACF, but there was a lot of discussuion back then on what figure it really was.
Have to see if i can dig out my old notes to see who published it.
Andrew

Last edited by AndrewJ; 09-08-2018 at 12:17 PM. Reason: changed from "bought" to "got access to"
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  #12  
Old 09-08-2018, 11:35 AM
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Gday Alexander

I have a 6" ACF on an LS mount and there is nothing but dust in the baffle tube.

Andrew
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  #13  
Old 09-08-2018, 11:43 AM
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Quote:
Originally Posted by AndrewJ View Post
Gday Alexander

I have a 6" ACF on an LS mount and there is nothing but dust in the baffle tube.

Andrew
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  #14  
Old 09-08-2018, 11:46 AM
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The Meade RCX didn't last long.....
http://www.star-instruments.com/images/MeadeRCX.pdf
Not sure it was similar to the "final" ACF design....
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Old 09-08-2018, 11:47 AM
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Just found my old files
It was done by a Paul Jones of Star Instruments back in mid 2006.
I cant find the post with the detailed optical bench piccies etc but did find this discussion on the original RCX which then became ACF

http://www.star-instruments.com/images/MeadeRCX.pdf


Andrew
Drat.

Ken beat me to it, but there is a folder out there on a website far away that had interferometry pics etc.

Last edited by AndrewJ; 09-08-2018 at 11:49 AM. Reason: ken beat me to it
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  #16  
Old 09-08-2018, 12:10 PM
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Merlin66 (Ken)
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Yeah but.....
The RCX design had a moving secondary for focusing....quickly dumped!
The later ACF design was more of a "conventional" SCT design......
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Old 09-08-2018, 12:22 PM
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Gday Ken
Quote:
The RCX design had a moving secondary for focusing.
Not quite.

It moved the whole corrector using 3 equidistance motors. ( IIRC, the secondary was actually glued to the corrector to hold position ).
Collimation was done by tilting the whole corrector and focussing by moving the whole corrector, ie "optically", no different to a moving primary. Users have actually retrofitted the dead RCX motors with a 3rd party controller using steppers and it appears to work very well.

Andrew
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Old 09-08-2018, 12:47 PM
Wavytone (Nick)
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Instead of speculating take a look at the spreadsheet “test results.xlsx” posted halfway down this thread:
https://www.cloudynights.com/topic/6...or-myth/page-3

You’ll find some ACF and non ACF Meade’s in there and the filters allow you to compare these.

In short there’s not much difference between ACF and non ACF. Meade’s quality as with Celestron is quite variable from scope to scope so you might be lucky, but most probably it will be fairly mediocre.

The Russian site from which the data is drawn is also linked - however if you are using a PC be careful as it attempts to install MALWARE on windows systems.
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Old 09-08-2018, 01:18 PM
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Thanks guys all good info to have that I did not have before.
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  #20  
Old 09-08-2018, 01:31 PM
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I have owned two Lx90s over the years both 8" one was UHTC and the other was EMD both were good scopes. I Sold the first I e to move to EQ G11 mount , bought the second one to have a easy alt AZ setup and sold that for the convenience of the Nexstar SE mount which allowed multiple OTA configs. But optica are on par with Celeatron Starbright and XLT. As already pointed out the focusing on Celestron is just a bit better. Dual arms are more stable but less flexibility in using other OTAs like a small refractor or smaller c6 or mak etc.
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