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Has anyone tested the max load for astrophotography?

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#1 Wintersun

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Posted 23 February 2021 - 05:14 PM

I currently have an iOptron CEM25 mount and I will be using a EdgeHD 8 and guide scope with a small guide camera and a full frame DSLR. Total weight will be approximately 19.5 lbs for the payload supported by the mount. The CEM25 is rated for a payload of 27 lbs and so my planned payload is 70% of the mount capacity.

 

I am considering getting a iOptron GEM45EC to get a max payload of 45 lbs, or 22 lbs payload capacity for astrophotography, if it will be up to the job. The CEM70EC costs only $650 more but the head weighs nearly twice as much at 30 lbs. Moving the mount and tripod in and out of the house would be a bit of a pain with the CEM70.

 

I know about the "rule of thumb" with regard to reducing max payload by 50% for astrophotography but I wonder if this has been verified empirically by anyone in a controlled manner by gradually increasing load and then reviewing the resulting images. I should have a well centered load with the SCT and little leveraging of the load or torsional flexing as might be the case with a 100mm refractor telescope.



#2 photoracer18

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Posted 23 February 2021 - 05:37 PM

That is very borderline. Do you have any AP experience? If an 8" SCT is going to be your first AP setup I would advise against it as would most on this or another site. Regardless of load a 100mm refractor would be a much better choice than an 8" SCT. Much easier to learn with a 700mm FL than a 2000mm FL. Even an FR on the 8" only gets you down to 1400mm while a .8x on the 100mm gets you down to 560mm. Even that is too big to get all of M31 in the picture. The longer the FL the more magnified any vibration in the mounts drive train will be. On the other hand if you can do decently good M42 images with a smaller scope then you can get the 8" Edge, but I would recommend the GEM45EC then due to loaded weight.


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#3 imtl

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Posted 23 February 2021 - 05:51 PM

This is not just to keep the "50% rule". Weight is only one parameter. If you're going to be imaging at native FL of the Edge8HD then you are expecting a lot of your current mount even at 50% of the payload. You should also reconsider using a guide scope at those focal lengths. It's doable but quite difficult.



#4 bobzeq25

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Posted 23 February 2021 - 05:58 PM

Almost certainly not.  The mount is the most important part of a DSO imaging setup (NOT the scope or the camera).  Why would anybody in their right mind stress it to its limit?  It's a prescription for nasty problems.

 

Two further truths, as stated above.  Weight is by no means the only factor.  Focal length magnifies tracking errors.

 

And, if you're new to this, you're headed right for this situation.

 

"I regret spending the first 6 months trying to learn imaging with an 8" Edge, with that scope it was a losing effort. Fortunately got a nice little refractor, and not only have the quality of my images improved but I'm actually enjoying the process of learning how to do it!"

 

15 minutes spent watching this video can save you a whole lot of time (_many_ hours), and substantial money.

 

https://www.youtube....h?v=MNQU1hdqz4M

 

The problem you're having is.  Little about astrophotography is intuitive.  It takes real knowledge.


Edited by bobzeq25, 23 February 2021 - 05:59 PM.

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#5 Wintersun

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Posted 24 February 2021 - 01:07 AM

Bob - nothing about photograpy is intuitive and I have been involved for 55 years. Everything I learned with land photograpy did not apply at all when I started doing underwater photography. At least with digital cameras the effort and time involved to get up to speed is a fraction of what it was with film.

 

I guess no one seems to have a real answer in terms of the old rules of thumb. I learned years ago to experiment and find the "glass walls" in any endeavor. Hoping  to find individuals with hands on experience but evidently they are not participating on this forum. No worries.


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#6 Spacetravelerx

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Posted 24 February 2021 - 04:34 PM

@wintersun-

I am close to 95% capacity with my mount for astrophotography - nary a problem. My images come out fine. I have never run my mount at 50% - ever. Seems like an odd rule, or a rule made for poor mounts.
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#7 peta62

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Posted 24 February 2021 - 04:46 PM

You are absolutely right the short center balanced SCT is more mount friendly than long extremely front heavy refractor ( as much as I love my two refractors ), so you can load the mount more with SCT. I am sorry, no experience with iOptrons.



#8 FlankerOneTwo

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Posted 24 February 2021 - 05:02 PM

There is more than just total weight involved, even if the mechanicals are perfect, which part of what makes the assessment difficult. The more important factor is the moment of torque on the axis motors (which also corresponds to  stress on the gears and teeth), which is a function of both weight and distance from the axis. The distance obviously will depend on how you have the scope mounted, as well as number/weight/location of accessories also mounted on the scope/saddle.

Astro-Physics has a illustrative diagram here: (on the Mach2 specs page)

 

wt.jpg

 

And this is just at rest in a no-wind situation. Ultimately, it's easy to get poor images even with a good/adequate mount; there is a specific reason for the payload rating of the mount and to me not wasting my time is more important than the one time cost of purchasing a mount that is adequate and spec'd to the task. I have an CEM25 as well as a C8, and just personally there's no way I would mount that scope on it for serious long-exposure AP.



#9 bobzeq25

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Posted 24 February 2021 - 06:37 PM

Bob - nothing about photograpy is intuitive and I have been involved for 55 years. Everything I learned with land photograpy did not apply at all when I started doing underwater photography. At least with digital cameras the effort and time involved to get up to speed is a fraction of what it was with film.

 

I guess no one seems to have a real answer in terms of the old rules of thumb. I learned years ago to experiment and find the "glass walls" in any endeavor. Hoping  to find individuals with hands on experience but evidently they are not participating on this forum. No worries.

Honestly.  No serious imager wants to stress a mount to its limits.  That has nothing at all to do with "this forum".

 

Because we all struggle with tracking.  Because we all have "mount fever", the equivalent of aperture fever for imagers.

 

We all want a better mount.  I have an excellent CEM60, would really like a 10 Micron.  I can't afford it, and the old man couldn't carry it.  <smile>

 

The glass wall here is tracking, with any mount whatsoever.



#10 Spacetravelerx

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Posted 24 February 2021 - 06:52 PM

Honestly.  No serious imager wants to stress a mount to its limits.  That has nothing at all to do with "this forum".

 

Because we all struggle with tracking.  Because we all have "mount fever", the equivalent of aperture fever for imagers.

 

We all want a better mount.  I have an excellent CEM60, would really like a 10 Micron.  I can't afford it, and the old man couldn't carry it.  <smile>

 

The glass wall here is tracking, with any mount whatsoever.

@bobzeq25

I don't know - I have been running my mount, LX850, at 95% capacity for over 3 years now...and it has been outdoors that entire time...and I put it to use about 150/sessions a year (the joys of living in New Mexico).  The LX850 has worked perfectly the entire time.  Doesn't seem to stressed at all.  Long exposures? No problem.

 



#11 rdmarco

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Posted 24 February 2021 - 09:17 PM

I have an HEQ5 (rated to 30lbs), and I run a 127mm refractor with guide scope, and goodies at 19lbs. I can guide to <1 all night long. Nice, round stars.



#12 T~Stew

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Posted 25 February 2021 - 10:45 AM

I have an HEQ5 (rated to 30lbs), and I run a 127mm refractor with guide scope, and goodies at 19lbs. I can guide to <1 all night long. Nice, round stars.

I've seen HEQ5 carrying a steel tubed 10" Quattro newtonian astrograph (that is way over the HEQ5 limit) with superb images. Thats like 40 lbs or maybe more, plus a respectable 1,000mm and hanging all the focuser & camera weight way out there on the front and a huge wind sail, over 3 foot length. Basically worse case scenario. 
 
Sure it's a good rule of thumb to give plenty of margin, especially for someone who is new. But for someone who is experienced, they have patience and expertise to adjust and tweak things, have solid piers, observatories, etc. then they get better results at or even exceeding limits. I would never just expect to be able to push the limits with excellent results, but in some cases it has been done. I'm going to be thoroughly pushing the limits of my little Skyguider (maybe a little over, with a 125mm 'refractor') will definitely report back on that. Some here think the universe might collapse into a singularity if you approach the weight limit of a mount. lol.gif


Honestly.  No serious imager wants to stress a mount to its limits.  That has nothing at all to do with "this forum".

Bob, I know some serious images who may not like you speaking for them. You're a wealth of knowledge and expertise but might not want to make absolute claims speaking for everyone...

Edited by T~Stew, 25 February 2021 - 10:52 AM.

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#13 bokemon

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Posted 26 February 2021 - 01:12 AM

Go ahead and try with the CEM25.  It's a rickety little mount, but if you don't touch it in operation, it can give some stable results.  Since you are using a Full Frame DSLR, the requirements are less stringent because it has a bayer matrix, so effectively less strict resolution requirements than something like a mono camera.  Plus at that focal length, seeing is going to make everything blurry anyway.  You might have to tune up your mount (adjust some screws, etc) to get it working nice and tight.  Make sure your guide scope is rigidly attached to the telescope, or maybe switch over to off axis guiding.  Now that PHD2 has multi-star guiding, it should give some stable results.




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