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CEM26 - first (cloudy) night

Astrophotography Celestron CMOS DSLR Imaging Mount Report Polar Alignment SCT Cassegrain
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115 replies to this topic

#101 nyx

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Posted 11 April 2021 - 02:34 PM

@nyx quite honestly, I am at a loss here. I think my brain is disconnecting slowly crazy.gif

If you don't have grub screws on the GEM28, I wonder why this is also happening on those mounts and if indeed tightening those 4 allen screws are sufficient or not. 4 allen screws should be sufficient to hold the two pieces together (not ideal, let's not go through that again grin.gif). Unless they did something equivalent the 4 allen screws of the CEM26... which I don't even want to imagine... On principle the less screws the better, so I would tend to favor the GEM28, but now I just don't know anymore.

I see what you are trying to do with the rings, and that sounds help fixing the issue.. but why is there any side-to-side play in the first place.. 4 holes, 4 screws, that should be rock solid. I am missing something here. I nearly want to dismantle the whole thing to understand what they did.


Judging from the video from the facebook group, the holes drilled on that nosepiece (GEM28) are not snug enough. Tightening the allen screws merely presses the nosepiece against the RA shaft.

What I don't get is, why doesn't the GEM28 have any grub screws?! The only reason I can imagine is that due to the extra 4 holes on the GEM28 "nosepiece", there wasn't any space left.

#102 YossiZ

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Posted 11 April 2021 - 03:15 PM

Continuing with the GEM28 DEC play issue:

 

I removed the saddle, opened the cover and checked according to the instructions from Ioptron.

The 4 socket screws were tight.

I found only one set screw (circled yellow). It was loose and I tightened it, but that wasn't the cause.

It seems that the whole sub-assembly marked in red moves axially as shown in the arrow in the picture added.

I asked Ioptron if there is anything to do about it. I guess I will not take apart the mount further than I already did.

 

It could be a problem with the goto accuracy when changing from targets on the north side to the south side, because the weight-shift might push that play to the other side. I think it won't affect tracking (or guiding).

 

Capture.JPG

 



#103 nyx

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Posted 11 April 2021 - 03:19 PM

Continuing with the GEM28 DEC play issue:

I removed the saddle, opened the cover and checked according to the instructions from Ioptron.
The 4 socket screws were tight.
I found only one set screw (circled yellow). It was loose and I tightened it, but that wasn't the cause.
It seems that the whole sub-assembly marked in red moves axially as shown in the arrow in the picture added.
I asked Ioptron if there is anything to do about it. I guess I will not take apart the mount further than I already did.

It could be a problem with the goto accuracy when changing from targets on the north side to the south side, because the weight-shift might push that play to the other side. I think it won't affect tracking (or guiding).

Capture.JPG


Is that the issue you are referring to:

https://youtu.be/LXrCpLOLnvU

?

#104 YossiZ

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Posted 11 April 2021 - 03:28 PM

Is that the issue you are referring to:

https://youtu.be/LXrCpLOLnvU

?

Yes, it looks exactly the same. Any known solution for that?

Anyway, it is definitely not mentioned in the GEM28 manual.



#105 nyx

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Posted 11 April 2021 - 03:33 PM

Yes, it looks exactly the same. Any known solution for that?
Anyway, it is definitely not mentioned in the GEM28 manual.


Now that sucks. Whatever screw is holding that worm gear assembly has come loose. I think you'd need to open it up further in order to fix this, but without instructions...

This is so frustrating and I haven't even received my GEM28 yet :/

#106 ppg677

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Posted 11 April 2021 - 04:23 PM

I'm likely to get a G11 - (I think I am fortunate to be in the US here). It looks like 3 pounds heavier than the CEM70 (33 compared to 30) which I am fine with. Still lighter than an EQ6R

Cost-wise, the G11G is a slight increase. I paid $3300 USD for the CEM70, extra weight and pier.
The G11G with an extra weight and shipping will be around $3585, although that doesn't come with the polar scope (I will use Sharpcap anyway)

There is a bit of a wasteland in the $2000-3000 range that the CEM70 seems to fit really well spec-wise

Good luck with your choices (I am still hemming and hawing)


I'm very happy I located a used GM-8. I was otherwise going to buy a GEM28 or CEM40.

Mechanically it just oozes quality.
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#107 crackout

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Posted 14 April 2021 - 07:02 AM

Any new findings?
I'm still particularly interested in the GEM28.

#108 nyx

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Posted 14 April 2021 - 07:12 AM

Any new findings?
I'm still particularly interested in the GEM28.

I should be receiving mine *soon*. I will of course check all the problematic spots and maybe even tear it down.


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#109 crackout

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Posted 14 April 2021 - 07:26 AM

Eagerly awaiting your feedback on this. smile.gif

#110 jdk

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Posted 14 April 2021 - 08:35 AM

mine is also on the way grin.gif hope to have it in use for the next new moon



#111 YossiZ

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Posted 14 April 2021 - 11:00 PM

Still waiting for instructions from Ioptron. In the meanwhile, the DEC play doesn't influence my unguided EAA results and I managed 60s and up to 90s exposures. Very satisfying.

 

20210414_194735.jpg

 

M82_10x90s.JPG

 

20210414_200940.jpg


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#112 Feccy

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Posted 15 April 2021 - 03:55 AM

Hey threaders...

 

As I have almost sorted my imaging train issues (back focus & collimation) I finally had time to see what the CEM26 was capable of without guiding. So here are the results of some single exposures on M51 taken on Monday night with each only having a slight tweak on PS Camera RAW to bring out the details a little. I have been doing 60 second exposures without any issues so I tried longer....

 

There's a scratch on my DSLR sensor which is responsible for the blotches - this was caused by a 'lack of talent' whilst modding the camera myself! Replacement sensor screen on it's way!

 

90 seconds exposure

M51 90 seconds
 
120 second exposure
M51 120 seconds
 
180 seconds exposure
M51 180 seconds
 
300 second exposure
M51 300 seconds
 
Next purchase is a OAG but I'm curious to see what everybody thinks?
 
Clear skies!

 

 

 


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#113 YossiZ

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Posted Yesterday, 12:35 AM

Another update:
Ioptron sent me a 4 pages document with instructions to solve the problem. It is a deeper surgery than I am willing to do myself.
For now I will try working with it like it is. Maybe unguided with good balance it will be okay.
If not, Ioptron suggested to send the mount for service.
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#114 iamfurgus

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Posted Yesterday, 02:53 AM

 

Hey threaders...

 

As I have almost sorted my imaging train issues (back focus & collimation) I finally had time to see what the CEM26 was capable of without guiding. So here are the results of some single exposures on M51 taken on Monday night with each only having a slight tweak on PS Camera RAW to bring out the details a little. I have been doing 60 second exposures without any issues so I tried longer....

 

There's a scratch on my DSLR sensor which is responsible for the blotches - this was caused by a 'lack of talent' whilst modding the camera myself! Replacement sensor screen on it's way!

 

90 seconds exposure

 
 
120 second exposure
 
 
180 seconds exposure
 
 
300 second exposure
 
 
Next purchase is a OAG but I'm curious to see what everybody thinks?
 
Clear skies!

 

 

 

 

There is some star trailing in all of them (90s looks best), but probably will stack just fine if there are some good and some bad subs, for me thats a good reason to keep the subs shorter as your more likely to have more good frames that way.  Galaxy looks fantastic though.


Edited by iamfurgus, Yesterday, 02:54 AM.


#115 nyx

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Posted Yesterday, 12:21 PM

A big thank you to @YossiZ for sharing this: https://drive.google...iew?usp=sharing

 

This shows how one can reach the DEC worm gear and, if needed, replace it. It *should* apply to both the CEM26 and the GEM28.

 

What blows my mind is how complicated tearing down a CEM26/GEM28 is when compared to working with a e.g. HEQ-5 Pro: https://youtu.be/hdS5Hisgats?t=247


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#116 dx_ron

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Posted Yesterday, 03:33 PM

Wow - that is also way more complicated than tearing down the CEM25P.




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Also tagged with one or more of these keywords: Astrophotography, Celestron, CMOS, DSLR, Imaging, Mount, Report, Polar Alignment, SCT, Cassegrain



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