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EAA Payload Capacity - GEM

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11 replies to this topic

#1 telco507

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Posted 08 May 2021 - 10:04 AM

Greetings guys,

 

Its quite common to mention that for AP you should not go more than 50% of the payload capacity while using a GEM.

It also depends if its a SCT or a Frac.

 

In the case for EAA what would be that %?. Also what would be this number in the case for a SCT or for a refractor (F6 or 7)?.

 

Let me get your expertise on this.

 

 

 

Telco507

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#2 GaryShaw

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Posted 08 May 2021 - 10:41 AM

Hi, pretty subjective territory but, FWIW:

 

If you’re an EAA ‘observer’, you can likely load to just below the stated rating and be fine. If you’re an EAA ‘imager’ (mostly interested in capturing images) or  someone wanting to do AP ‘lite’, observe the 1/2-2/3 rule. 



#3 bips3453

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Posted 08 May 2021 - 12:12 PM

+1,

EAA can be done with shorter exposures, hence allowing higher weight to be put on the mount as mount is less prone to tracking errors with-in a single exposure. 


Edited by bips3453, 08 May 2021 - 12:12 PM.


#4 Spacetravelerx

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Posted 08 May 2021 - 08:58 PM

Greetings guys,

Its quite common to mention that for AP you should not go more than 50% of the payload capacity while using a GEM.
It also depends if its a SCT or a Frac.

In the case for EAA what would be that %?. Also what would be this number in the case for a SCT or for a refractor (F6 or 7)?.

Let me get your expertise on this.



Telco507
Orion 6 inch Dob
15x70 Oberwerk



Ehhhh it is common to mention not to go above 50% payload capacity for AP or anything however it is a false statement. I have been doing EAA and Astrophotography and easily go to 95% payload capacity with refractors and ACF OTAs on a GEM with nary a problem.
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#5 cmooney91

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Posted 25 May 2021 - 08:28 AM

My poor old Super Polaris gets overloaded to ~160% and it works fine for 8-16s EAA exposures. It has ~40 arc-sec P.E., but it doesn't really matter for EAA live stacking.


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#6 Ptarmigan

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Posted 25 May 2021 - 06:43 PM

EAA is not astrophotography. It should not be an issue to go over 50% of the mount's rated weight limit. The 50% for astrophotography is a rule of thumb.


Edited by Ptarmigan, 25 May 2021 - 06:43 PM.

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#7 GaryShaw

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Posted 26 May 2021 - 07:08 AM

EAA is not astrophotography. It should not be an issue to go over 50% of the mount's rated weight limit. The 50% for astrophotography is a rule of thumb.

Well, take another quick look at Post 2 and think whether the above is right for you.

 

It all depends, since EAA involves differing degrees of gear for different folks. I’m an EAA observer yet I have several cameras, a filter wheel and auto focuser- all on a 203mm F4 Newtonian with a dew/light shield. This all supports my needs for decent image quality ‘live’ observing. About all I don’t have that an AP person would have is a heavier, cooled camera and a heavier guiding setup.
 

I think the OP, or others, need to be clear that EAA can entail virtually the same payload weight as full AP does. I felt my gear was close to overloading my AZ Mount Pro, hence the new iOptron 70 has arrived. 
 

Its  all good, just be aware of the issues and trade-offs and make decisions accordingly. A slightly over-sized mount is not likely to be one of my ‘regrets’ in life. 
cheers

Gary


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#8 dcweaver

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Posted 31 May 2021 - 11:25 AM

Socrates coined the phrase:  Know thyself.  In this case, it can be modified to:  Know thymount.

   

How heavy you can load it depends on how smooth it's tracking is and how that changes with payload weight and weight distribution.  Long exposure astrophotographers, who measure exposures in terms of hundreds of seconds, find that loading a mount to 1/2 of the rated payload gives better odds of not having a wiggle or jiggle than the odds with more payload.  So this "rule of thumb" may or may not apply to your situation.  Each mount and payload has its own character.  Just like individual people, you have to get to know the mount and learn what works.

 

For EAA, exposures are measured in terms of 10s of seconds or less.  The odds of having a tracking hiccup are much lower with those small durations.  In addition, you can set a FWHM filter in SharpCap to discard smeared subs.  In the worst case, just start over because you aren't dealing with hours of integrated exposures.  You are likely dealing with 5 minutes.  So while the basic principle behind the 50% rule applies (keep the weight down to increase your odds of getting good subs), the load limit that achieves this for a 10-30 second exposure may be higher than 50% of rated capacity.

 

What happens at a dark site, stays at a dark site... Just like Vegas, it's all about the odds.


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#9 Spacetravelerx

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Posted 31 May 2021 - 11:38 AM

Socrates coined the phrase:  Know thyself.  In this case, it can be modified to:  Know thymount.

   

How heavy you can load it depends on how smooth it's tracking is and how that changes with payload weight and weight distribution.  Long exposure astrophotographers, who measure exposures in terms of hundreds of seconds, find that loading a mount to 1/2 of the rated payload gives better odds of not having a wiggle or jiggle than the odds with more payload.  So this "rule of thumb" may or may not apply to your situation.  Each mount and payload has its own character.  Just like individual people, you have to get to know the mount and learn what works.

 

For EAA, exposures are measured in terms of 10s of seconds or less.  The odds of having a tracking hiccup are much lower with those small durations.  In addition, you can set a FWHM filter in SharpCap to discard smeared subs.  In the worst case, just start over because you aren't dealing with hours of integrated exposures.  You are likely dealing with 5 minutes.  So while the basic principle behind the 50% rule applies (keep the weight down to increase your odds of getting good subs), the load limit that achieves this for a 10-30 second exposure may be higher than 50% of rated capacity.

 

What happens at a dark site, stays at a dark site... Just like Vegas, it's all about the odds.


Like I said earlier, with my mounts - the LX850 (both of them) and the LXD75 - I have gone close to 100% load for EAA AND Astrophotography...long exposure astrophotography for 100s of seconds.  Nary a problem.

 

It purely may be related to the brand, but I have I never ever experienced a problem fully loading my mount for Astrophotography on a Meade mount.

EAA...no need to worry about loading to 100% at all unless perhaps the mount is flimsy or something.



#10 dcweaver

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Posted 31 May 2021 - 12:06 PM

Andrew -

 

The LX850 is a good looking mount.  Don't see too many of them in service, but not surprising it can take the full load.  A real beast!



#11 alphatripleplus

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Posted 31 May 2021 - 12:32 PM

I have two mounts that I use:  a Mach 1 and an old Vixen/Celestron Super Polaris. For EAA,  the Super Polaris is "usually' adequate even for my C8 (which is an older version and it slightly exceeds Vixen's conservative payload capacity estimate). I have not come close to testing the Mach 1 payload capacity.

 

 

One other comment: Most EAA subs are indeed short for me, except if I am trying to capture emission nebulae in H-alpha, I will use longer subs  -  sometimes up to 45 secs or longer.



#12 galacticinsomnia

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Posted 02 June 2021 - 05:58 PM

If you can balance your gear, there is no reason you can't get to your payload limits.  That is what it is rated for, that is what it can do.
How well it does it, well you should try and find out, and report back :)

Clear Skies !!


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