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Payload capacity / EdgeHD 11 on a CEM70

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#1 spiantino

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Posted 12 April 2021 - 02:52 PM

I'm curious if anyone has experience with using the venerable EdgeHD 11" on a CEM70.

 

Is this going to be too heavy? I did some rough calculations of that scope - with focal reducer, filter wheel, autofocuser, OAG and camera my total came to 34.6lbs, which is *just* within the budget of half the stated capacity of 70lbs. But I've also seen threads where people cite success with that scope on a CEM60, so maybe I'm being too conservative.

 

Plan B would be the EdgeHD 9.25 which saves ~7 lbs and should make the mount sweat a little less



#2 bobzeq25

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Posted 12 April 2021 - 03:13 PM

Either scope could work, but...

 

Only looking at weight is oversimplistic.  It's a crude measure of what "might" work.  What actually will work depends on focal length, a whole lot.  Focal length magnifies tracking errors.

 

F number and your skies play a role.  Faster scopes and/or brighter skies shorten subexposures.  My 400mm F2 RASA in my Bortle 7 skies works perfectly on the CEM60, I only guide to minimize eccentricity.  The weight is almost irrelevant.

 

So, forget the guesses based on weight.  Find people who've used those scopes on the mount, and see what actual experience is.   See what focal length they're working at, whether or not they use a focal length reducer.  That's the way to decide.

 

I've had a CEM60 for years.  A TS130 F7 (about 30 pounds total weight) works fine, but it's only 910mm.  It also supported a 6 inch Ritchey Chretien at 1360mm, but the total weight was only about 25 pounds.

 

This is typical DSO AP (and typical CN).  Theoretical analyses only take you so far, the situations are complex, results all too often are driven by what factors you put in, what you leave out.  Actual experience includes most all the relevant factors, it's much superior.


Edited by bobzeq25, 12 April 2021 - 03:19 PM.

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#3 pyrasanth

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Posted 12 April 2021 - 04:07 PM

I have a RASA 11 on a CEM70G and it handles the weight just fine- it weighs as much as the C11 so I beleive you would not have an issue if you pay attention to balance. The CEM70G for astro photography is happy at 50 pounds so I think you will be just fine.


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#4 Stelios

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Posted 12 April 2021 - 04:10 PM

I'm curious if anyone has experience with using the venerable EdgeHD 11" on a CEM70.

 

Is this going to be too heavy? I did some rough calculations of that scope - with focal reducer, filter wheel, autofocuser, OAG and camera my total came to 34.6lbs, which is *just* within the budget of half the stated capacity of 70lbs. But I've also seen threads where people cite success with that scope on a CEM60, so maybe I'm being too conservative.

 

Plan B would be the EdgeHD 9.25 which saves ~7 lbs and should make the mount sweat a little less

Go with plan B if you plan to image at the native focal lengths. The difference between an 11 and a 9.25" will be totally negligible in astrophotography, and at long focal lengths what matters is tracking--you want to help your mount as much as possible. 



#5 spiantino

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Posted 12 April 2021 - 04:13 PM

Either scope could work, but...

 

Only looking at weight is oversimplistic.  It's a crude measure of what "might" work.  What actually will work depends on focal length, a whole lot.  Focal length magnifies tracking errors.

 

F number and your skies play a role.  Faster scopes and/or brighter skies shorten subexposures.  My 400mm F2 RASA in my Bortle 7 skies works perfectly on the CEM60, I only guide to minimize eccentricity.  The weight is almost irrelevant.

 

So, forget the guesses based on weight.  Find people who've used those scopes on the mount, and see what actual experience is.   See what focal length they're working at, whether or not they use a focal length reducer.  That's the way to decide.

 

I've had a CEM60 for years.  A TS130 F7 (about 30 pounds total weight) works fine, but it's only 910mm.  It also supported a 6 inch Ritchey Chretien at 1360mm, but the total weight was only about 25 pounds.

 

This is typical DSO AP (and typical CN).  Theoretical analyses only take you so far, the situations are complex, results all too often are driven by what factors you put in, what you leave out.  Actual experience includes most all the relevant factors, it's much superior.

Maybe should have mentioned, this is to complement my existing setup which is an ED 127 refractor that I have lots of experience with at 952. I'm mostly looking to get better images of galaxies, so have done some of the homework on what FL will work best for me



#6 bobzeq25

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Posted 12 April 2021 - 04:18 PM

Maybe should have mentioned, this is to complement my existing setup which is an ED 127 refractor that I have lots of experience with at 952. I'm mostly looking to get better images of galaxies, so have done some of the homework on what FL will work best for me

No worries, my post would have been exactly the same.

 

Note the two answers above.  On a CEM60 someone is using a C11 on the mount at maybe 550mm, the other is concerned (theoretically) about using one at maybe 2750 mm.  Totally unsurprising.

 

You need more actual experience, less theory.  Why I made no specific recommendation, I have inadequate data.


Edited by bobzeq25, 12 April 2021 - 04:19 PM.


#7 spiantino

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Posted 12 April 2021 - 04:27 PM

Go with plan B if you plan to image at the native focal lengths. The difference between an 11 and a 9.25" will be totally negligible in astrophotography, and at long focal lengths what matters is tracking--you want to help your mount as much as possible. 

Oh interesting - I'd read some reviews of the 9.25 vs 11 and there wasn't much consensus on whether the 11 was worth it. But I agree that tracking is more important.

 

Any advice on focuser/autofocus? I'm getting moderate results with my current scope and the ZWO EAF, though I think most of my problems have to do with the ES focuser and not the ZWO EAF.



#8 spiantino

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Posted 12 April 2021 - 04:39 PM

No worries, my post would have been exactly the same.

 

Note the two answers above.  On a CEM60 someone is using a C11 on the mount at maybe 550mm, the other is concerned (theoretically) about using one at maybe 2750 mm.  Totally unsurprising.

 

You need more actual experience, less theory.  Why I made no specific recommendation, I have inadequate data.

 

What actual experience are you suggesting I need? I have read lots of user's experience with the Edge HD 11, and short of actually owning one I'm not sure what else I could do. I plan to image galaxies, likely at native FL. I'm not planning to use fastar. So the FL in question here is 2800.



#9 bobzeq25

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Posted 12 April 2021 - 10:28 PM

What actual experience are you suggesting I need? I have read lots of user's experience with the Edge HD 11, and short of actually owning one I'm not sure what else I could do. I plan to image galaxies, likely at native FL. I'm not planning to use fastar. So the FL in question here is 2800.

Talking to someone who's imaged with a C11 at native focal length on a CEM60.  It's not a decision that can be made on just the specifications, you're right on the edge with both weight and focal length.



#10 GaryShaw

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Posted 12 April 2021 - 10:41 PM

I talked to the folks at iOptron about a RASA11 (35#) on the CEM70 and they said that would be the upper limit they would recommend.....for imaging.



#11 pyrasanth

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Posted 13 April 2021 - 02:34 AM

I talked to the folks at iOptron about a RASA11 (35#) on the CEM70 and they said that would be the upper limit they would recommend.....for imaging.

Over 6 kilos can be shaved off the RASA 11 directly by using rings to mount the OTA. The ring assembly will add back a further 3 kilos so you probably get a net saving of 3 kilos by going for ring mounting- the rails on the RASA don't add to the structural integrety of the OTA (so i was told). I don't get any issues with my RASA on the CEM70G, I agree that I would not go any heavier however I think 50% of any rated mounts capacity for imaging is conservative or Ioptron don't stand by the assessment of their mount ratings.


Edited by pyrasanth, 13 April 2021 - 02:38 AM.

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