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Which is the most afordable mount which is able to carry a 12" truss tube RC telescope

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#1 Ayaan Hashim

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Posted 20 June 2021 - 01:39 AM

Just a question asked out of curiosity,

If I were to image with a 12" Ritchey Chretien with an ASI 071MC camera hitched on the back with a reducer(unbinned), which the mount for the least money required to carry this load when imaging 3 minute subs guided during AVERAGE seeing conditions? Maybe if I mounted a Hubble Optics UL12 on a GEM45 when imaging 2 minutes subs with an ASI 071MC pro, it would worklol.gif .

Thanks all for replying,

clear skies,

Ayaan



#2 Astrojensen

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Posted 20 June 2021 - 02:34 AM

 

which the mount for the least money required to carry this load when imaging 3 minute subs guided during AVERAGE seeing conditions?

This is the wrong way of thinking. No matter where you're located, there will be nights of excellent seeing, and you will be EXTREMELY unhappy, if your mount and scope can't take advantage of it, when it happens. 

 

And that superb seeing might even happen on a windy night! 

 

In astrophotography (or indeed also visual, but particularly in astrophoto) it never pays off to settle for average. You want to maximize your chances of success, in order to reduce frustration - and to make sure the money you spend are not wasted. 

 

To go for a 12" and a mount that barely holds it, is asking for trouble and frustration. If you can't afford a mount that can hold a 12" and guide it effortlessly for as long as you need, it's better to go down to a 10" or even 8" scope on the same mount. 

 

A friend of mine has used a C14 for quite a few years now, first on a EQ-8, which worked okay-ish, but always seemed to require some fiddling here and there (and is insanely stupidly designed in some places). He eventually bought a 10 Micron GM 2000. It completely changed EVERYTHING for him. He doesn't even guide the C14 anymore, it can take exposures of many minutes without any guiding at 3900mm focal length. Stars are always perfect pinpoints, every single time, all night long. 

 

 

Clear skies!

Thomas, Denmark


Edited by Astrojensen, 20 June 2021 - 02:37 AM.

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#3 Ayaan Hashim

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Posted 20 June 2021 - 03:22 AM

Hey Astrojensen,

Thanks for replying to my post. How come 10 microns don't need to be guided? I know that they have encoders on both axes, but I thought mounts sort of run head-first into a wall when the encunguided?ounter the seeing. If resolution is limited by seeing, how can you image at 3900mm-But  I actually don't know what his pixel scale was, nor the seeing conditions, or his exposure timegrin.gif. Sorry if this is a Newbie question, which I amlol.gif .


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#4 jeffcrilly2

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Posted 20 June 2021 - 05:04 AM

The 10micron has absolute (presumably high resolution) encoders.   The RA encoder is part of a closed loop system to remove periodic error.   There's no need to guide out the periodic error.

 

Guiding to chase the seeing is (in my view) a losing battle.   Some sort of tilt-mirror "adaptive optics" (e.g. SBIG AO) may help.

 

I've recently started using an AP Mach2 with unguided exposures; this mount also has closed-loop absolute encoders.

In addition to near zero periodic error (from the absolute encoder), software is supplied to create a sky model of pointing error (e.g. due to small polar mis-alignment and system flex) and apply the pointing error model to any gotos in addition to "tracking".   I use a "medium" sized sky model of about 71 points which takes about 35 minutes to run.  I'm primarily portable and have been running the sky modeling during astronomical twilight.

I've not tested it extensively for "how long can I expose without error", but recently I've been experimenting with 5 minute unguided exposures at ~2200mm using a Meade 12 ACF with Lumicon GEG reducer and QHY268M binned 2x2.  Results are promising, even with Meade 12 (I'm not convinced the mirror lock is sufficient).


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#5 Spikey131

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Posted 20 June 2021 - 07:13 AM

I think the words “affordable mount” and 12” cannot be used in the same sentencelol.gif


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#6 WadeH237

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Posted 20 June 2021 - 09:18 AM

Personally, the smallest mounts that I would consider for a 12" RC would be an Astro-Physics AP1100, a 10Micron HP2000HPS or Software Bisque Paramount MX+.  Thomas is spot on with his comments.

 

Regarding 10Micron and guiding, I believe that you have a misunderstanding.  It's not correct to say that they don't require guiding.  I'm not a 10Micron owner, and I'm not familiar with all of their publications, but I believe that even they tell you that beyond a certain image scale and exposure length, they recommend guiding their mounts.

 

There is much mythology here on Cloudy Nights regarding encoders.  The correct way to think about encoders is that they are simply a mechanism to achieve a desired level of accuracy in positioning of the mount's axes - and nothing more.  They are also not the only way to achieve accuracy.  It can be done with mechanical quality and tolerances as well.  Beyond providing for accuracy, they do nothing to help with unguided imaging.

 

In fact, if you had a mount, with absolutely perfect tracking, you would get poor unguided results with high resolution imaging.

 

Why is that, you ask?  The reason is that the apparent motion of the sky varies with both position in the sky and with environmental conditions.  We think of stars moving at sidereal rate in the sky.  In theory, if your mount can track perfectly at sidereal rate, that would be all you need.  The problem is that all of us with ground based telescopes are imaging through a giant lens called "the atmosphere".  On your other thread, we've talked about seeing, which is the effect of scintillation.  But that's not the only effect.  The atmosphere also refracts light.  Because of that, the apparent motion of the sky is only at sidereal rate at the zenith (directly overhead).  As you point the mount lower, it's looking through more atmosphere, and that slows down the apparent movement.  And at high resolution scales, this effect is not subtle at all.  So if you want to accurately track, your mount needs to consider the altitude at which it's pointing.  Fortunately, this is just math.  Some mounts have a tracking rate called "King Rate".  King rate is like sidereal, except that it accounts for altitude.

 

So for unguided imaging, you just need King rate, right?  Wrong!

 

The problem is that the refractive properties of the atmosphere are affected by temperature, pressure and humidity.  So for effective, high resolution imaging without guiding, you need to consider these factors as well.  To do that, you need environmental sensors and tracking correction that account for them.

 

Even when you have that nailed down, you still have other problems to deal with.  Telescopes, especially as they get larger, are rubbery things at the microscopic level.  The bend and flex as they point in different directions.  Optics shift.  The refractive properties of lenses change as the temperature of the glass changes.  Mirrors shift.

 

So how do you deal with all of that?

 

What you need - and this is the "secret" of the 10Micron mounts - is a way to sample points all across the sky (or at least in the parts of the sky where you will image) and compare the actual pointing position, versus the expected position.  You can then use that data to build a model that accounts for all of the above factors.  The mount can use that model to continually adjust the tracking to accommodate over a dozen factors.  10Micron includes this capability in their hand controller.  It's important to note that this is not unique to 10Micron.  Both Astro-Physics and Software Bisque (Paramount) also have this capability.  The difference is that AP and Bisque use software running on your computer, instead of the hand controller, to do this.  Astro-Physics uses software called APCC Pro to do the same thing, and Software Bisque's is called ProTrack.  It's also worth nothing that the latest mount from Astro-Physics (the Mach2) includes this capability built into the mount, and will be porting it to their other current mounts as well.

 

Finally, there are two caveats to keep in mind.  Any modeling is only as effective as the behavior of the entire system is repeatable.  For example, SCT's focus by moving the primary mirror.  Since the primary mirror needs to be free to move, it can shift around somewhat randomly.  This random shifting cannot be modeled.  For this reason, not even a 10Micron mount can imaging with an SCT unguided.  The second caveat is that the real world never completely conforms to our attempts to model it.  For this reason, once you reach a certain level of resolution, or try to expose for long enough, the model will diverge from reality.  At that point, you need to guide.

 

I hope that this helps to give a background for understanding the factors involved in answering your questions.

 

-Wade


Edited by WadeH237, 20 June 2021 - 09:36 AM.

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#7 rgsalinger

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Posted 20 June 2021 - 10:56 AM

which the mount for the least money required to carry this load when imaging 3 minute subs guided during AVERAGE seeing conditions?

 

The CEM120 will easily carry that load and costs about 4400 dollars. You also need a pier. Nothing wrong with more expensive recommendations, but the OP is asking about the least expensive option. I've had a CDK12.5 and an Edge HD 11 on my CEM120 and it worked just fine. 

 

The EQ8 mounts are in the same price range - under 5k and should do the same job. I don't have one so that's just a suggestion about something else to look at. 

 

I do not consider either of these to be good portable mounts. They are heavy and bulky. Still, for 5K you have a mount that will carry pretty much anything you can lift. 

 

Rgrd-Ross



#8 WadeH237

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Posted 20 June 2021 - 11:06 AM

The CEM120 will easily carry that load and costs about 4400 dollars.

Thanks for adding this one.  The EQ8 is probably another candidate.

 

I tend to forget about those mounts, especially when the discussion includes unguiding imaging with large scopes (and the OP in this case has another thread specifically about very high resolution imaging).  But they are certainly worth considering.



#9 teashea

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Posted 20 June 2021 - 09:49 PM

Just a question asked out of curiosity,

If I were to image with a 12" Ritchey Chretien with an ASI 071MC camera hitched on the back with a reducer(unbinned), which the mount for the least money required to carry this load when imaging 3 minute subs guided during AVERAGE seeing conditions? Maybe if I mounted a Hubble Optics UL12 on a GEM45 when imaging 2 minutes subs with an ASI 071MC pro, it would worklol.gif .

Thanks all for replying,

clear skies,

Ayaan

The mount is as important as the telescope.  Don't cheap out and undermount the telescope.  So many people do and regret it.  You are going to need a very good mount for that load.  Think north of $10,000.



#10 teashea

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Posted 20 June 2021 - 09:51 PM

Personally, the smallest mounts that I would consider for a 12" RC would be an Astro-Physics AP1100, a 10Micron HP2000HPS or Software Bisque Paramount MX+.  Thomas is spot on with his comments.

 

Regarding 10Micron and guiding, I believe that you have a misunderstanding.  It's not correct to say that they don't require guiding.  I'm not a 10Micron owner, and I'm not familiar with all of their publications, but I believe that even they tell you that beyond a certain image scale and exposure length, they recommend guiding their mounts.

 

There is much mythology here on Cloudy Nights regarding encoders.  The correct way to think about encoders is that they are simply a mechanism to achieve a desired level of accuracy in positioning of the mount's axes - and nothing more.  They are also not the only way to achieve accuracy.  It can be done with mechanical quality and tolerances as well.  Beyond providing for accuracy, they do nothing to help with unguided imaging.

 

In fact, if you had a mount, with absolutely perfect tracking, you would get poor unguided results with high resolution imaging.

 

Why is that, you ask?  The reason is that the apparent motion of the sky varies with both position in the sky and with environmental conditions.  We think of stars moving at sidereal rate in the sky.  In theory, if your mount can track perfectly at sidereal rate, that would be all you need.  The problem is that all of us with ground based telescopes are imaging through a giant lens called "the atmosphere".  On your other thread, we've talked about seeing, which is the effect of scintillation.  But that's not the only effect.  The atmosphere also refracts light.  Because of that, the apparent motion of the sky is only at sidereal rate at the zenith (directly overhead).  As you point the mount lower, it's looking through more atmosphere, and that slows down the apparent movement.  And at high resolution scales, this effect is not subtle at all.  So if you want to accurately track, your mount needs to consider the altitude at which it's pointing.  Fortunately, this is just math.  Some mounts have a tracking rate called "King Rate".  King rate is like sidereal, except that it accounts for altitude.

 

So for unguided imaging, you just need King rate, right?  Wrong!

 

The problem is that the refractive properties of the atmosphere are affected by temperature, pressure and humidity.  So for effective, high resolution imaging without guiding, you need to consider these factors as well.  To do that, you need environmental sensors and tracking correction that account for them.

 

Even when you have that nailed down, you still have other problems to deal with.  Telescopes, especially as they get larger, are rubbery things at the microscopic level.  The bend and flex as they point in different directions.  Optics shift.  The refractive properties of lenses change as the temperature of the glass changes.  Mirrors shift.

 

So how do you deal with all of that?

 

What you need - and this is the "secret" of the 10Micron mounts - is a way to sample points all across the sky (or at least in the parts of the sky where you will image) and compare the actual pointing position, versus the expected position.  You can then use that data to build a model that accounts for all of the above factors.  The mount can use that model to continually adjust the tracking to accommodate over a dozen factors.  10Micron includes this capability in their hand controller.  It's important to note that this is not unique to 10Micron.  Both Astro-Physics and Software Bisque (Paramount) also have this capability.  The difference is that AP and Bisque use software running on your computer, instead of the hand controller, to do this.  Astro-Physics uses software called APCC Pro to do the same thing, and Software Bisque's is called ProTrack.  It's also worth nothing that the latest mount from Astro-Physics (the Mach2) includes this capability built into the mount, and will be porting it to their other current mounts as well.

 

Finally, there are two caveats to keep in mind.  Any modeling is only as effective as the behavior of the entire system is repeatable.  For example, SCT's focus by moving the primary mirror.  Since the primary mirror needs to be free to move, it can shift around somewhat randomly.  This random shifting cannot be modeled.  For this reason, not even a 10Micron mount can imaging with an SCT unguided.  The second caveat is that the real world never completely conforms to our attempts to model it.  For this reason, once you reach a certain level of resolution, or try to expose for long enough, the model will diverge from reality.  At that point, you need to guide.

 

I hope that this helps to give a background for understanding the factors involved in answering your questions.

 

-Wade

Very excellent explanation.



#11 rgsalinger

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Posted 21 June 2021 - 01:35 AM

Well, if you want to spend a lot of money on a mount then get a Planewave L350. Since there's no worm or ring gear, there's no periodic error. That will easily handle an RC12 since PW sells them complete with a CDK14. I just wish I had room for one in the observatory. The PWI4 modelling software combined with the high resolution encoders is a really elegant solution for an observatory. 

 

If one wishes to answer the OP's question then I think that the two mounts I mentioned fit the bill. If anyone wants to come the observatory one night toting an RC12 (or a C14), we can put it up on the CEM120 and do the experiment. There's always coffee and cookies out at the observatory. So, far mine is 3.25 years old and going strong. (Full disclosure - I did spend the money to have it serviced by iOptron because I just didn't want to do it myself.)

 

Rgrds-Ross



#12 jgraham

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Posted 21 June 2021 - 07:02 AM

I use my trusty old Atlas EQ-G (EQ6) with my 12" Meade SCT from LX850 production and ASI071MC Pro or QHY 168c. I have a _lot_ of experience with this mount and I have pushed the edge a bit over the years and to be honest I was surprised at how well it works. I would not recommend this for the faint hearted, but if you pay attention to the details, watch you balance, and remove any extra weight it works quite well. My standard subs are 4 minutes and guiding is excellent. The biggest problem that I have is that my local seeing rarely supports the image scale of this system and I'm better off using a smaller scope. But when the seeing cooperates this is a wonderful system.

 

Atlas LX850 (12-22-2020)-1.jpg

 

Food for thought.

 


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#13 t-ara-fan

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Posted 24 June 2021 - 06:25 PM

OP don't forget good sequencing software so your scope can slew to different targets automatically - even after your bed time.

 

First scope?  A quality 80mm refractor on an awesome mount, with a mono camera and filters so you can cut through that Bortle 9 light pollution.


Edited by t-ara-fan, 24 June 2021 - 06:26 PM.

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