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Celestron OAG on Edge 8"

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#1 zakry3323

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Posted 26 May 2020 - 06:52 PM

I've been dealing with tilt, and too many cloudy nights to do much about it. I finally narrowed it down the OAG. So I'm going to replace it with a more rigid Celestron OAG.

Whether or not I can get the backspace correct with that big OAG and filter wheel in front of the sensor remains to be seen. Either way, I'll post some results and maybe a pic or two, Zeus willing.

Edited by zakry3323, 26 May 2020 - 06:53 PM.


#2 zakry3323

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Posted 28 May 2020 - 06:51 PM

It looks like I've got enough room, with a few millimeters of backspace to spare. I'm very much hoping this will work out. This Celestron OAG is in a completely different class than the thin OAG's that I've been using. It's so nice to be able to rotate the camera and adjust the position of the OAG independently. It's also much easier to offset the off-axis weight of the filter wheel with the position of the guide camera. 

 

I thought that tonight might be the night to test things out, but the weather is against me. Sunday night, maybe :)

 

IMG_20200528_183000_01_resize_58.jpg



#3 KTAZ

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Posted 28 May 2020 - 08:11 PM

I’m looking forward to your report. Please keep the thread going.

 

I spent the last few weeks dong the painful research on OAG’s for my C9.25 and also settled on the Celestron OAG. It should be here in a few days. It just appears to be more stable and better designed than the others.

 

Let us know!


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#4 zakry3323

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Posted 28 May 2020 - 08:14 PM

I’m looking forward to your report. Please keep the thread going.

 

I spent the last few weeks dong the painful research on OAG’s for my C9.25 and also settled on the Celestron OAG. It should be here in a few days. It just appears to be more stable and better designed than the others.

 

Let us know!

I've seen some pretty long posts (at least one that is still going) about using the Celestron OAG with imaging trains regarding the larger Edge models, but not specifically with the 800.

 

These little guys have different backfocus requirements than their bigger brothers, so I believe this will be a different kind of challenge.

I'm using the .7x Reducer, connected directly to the OAG (it screws right onto the reducer's threads), followed by the EFW8 filter wheel (m42), then a 5mm extension, then my ASI1600mm.

Let me see if I can find a link to the thread I'm thinking of :)



#5 zakry3323

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Posted 28 May 2020 - 08:16 PM

Here it is :) 
 



#6 KTAZ

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Posted 28 May 2020 - 08:29 PM

Thanks for the link, but mine is not an Edge model, so I am not sure if it applies.


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#7 zakry3323

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Posted 28 May 2020 - 08:37 PM

Thanks for the link, but mine is not an Edge model, so I am not sure if it applies.

Ah, gotcha. For lighter loads the slim OAGs that I've used previously work just fine, but this Celestron is a beast by comparison. Much heavier and takes up much more space, but a great design overall. 



#8 bacon

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Posted 28 May 2020 - 09:33 PM

How much back focus did you end up with?  I ask because my setup is very similar and I landed at 106mm and the corner stars are not quite perfect.  Tolerance probably varies from reducer to reducer.  Also you should be able to use the Male M42 adapter directly into the EFW8.  It kind of looks like this is what you did based on your picture but you mentioned a 5mm spacer.  


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#9 zakry3323

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Posted 29 May 2020 - 07:41 AM

How much back focus did you end up with?  I ask because my setup is very similar and I landed at 106mm and the corner stars are not quite perfect.  Tolerance probably varies from reducer to reducer.  Also you should be able to use the Male M42 adapter directly into the EFW8.  It kind of looks like this is what you did based on your picture but you mentioned a 5mm spacer.  

I have yet to get it dialed in- looks like Sunday night is going to be my best bet. I'm measured out to 104mm presently with my calipers. My plan is to shoot test shots while increasing the distance until stars are tight. The Male M42 adapter does fit directly into the EFW8, I'd just otherwise be a little short on my backspace, so I used a 5mm spacer (included with the OAG) after the FW before the camera. 

IMG_20200529_082648.jpg


Edited by zakry3323, 29 May 2020 - 07:42 AM.


#10 kisstek

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Posted 29 May 2020 - 09:42 AM

A problem with putting spacers between the camera and the EFW is that the filters will start vignetting the sensor if there's too much space between them. ZWO recommends you attach the camera directly to the EFW. Just something to keep in mind.


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#11 bacon

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Posted 29 May 2020 - 10:26 AM

I agree with Mike about the vignetting but it may not be an issue at F7 or anything that flats can't take care of.  

 

Here is my setup.  I went with a spacer between the FR and SCT OAG adapter.  

 

 

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  • Edge8.jpg

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#12 KTAZ

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Posted 29 May 2020 - 11:42 AM

Joe; what is the power / comm hub that you are using on your mount?

 

Thanks



#13 bacon

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Posted 29 May 2020 - 12:38 PM

It's the Pegasus Ultimate Power Box v2. It's a quite nice piece of hardware--powers cameras, automates dew heater output, and drives my focuser.  



#14 zakry3323

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Posted 29 May 2020 - 04:23 PM

A problem with putting spacers between the camera and the EFW is that the filters will start vignetting the sensor if there's too much space between them. ZWO recommends you attach the camera directly to the EFW. Just something to keep in mind.

 

 

I agree with Mike about the vignetting but it may not be an issue at F7 or anything that flats can't take care of.  

 

Thanks folks!

 

I went with the rear spacer because.... I had an M42 spacer that I could use :) I'll post results here and we can take a look at the vignetting. Hopefully Sunday night!



#15 zakry3323

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Posted 01 June 2020 - 10:27 AM

Hey folks! 

 

Here's a frame and focus shot from last night. I actually didn't get the chance to look for a better star field to test it with, my pointing model was all messed up and my guide camera was having connection issues, so I bagged it a little early.

It looks like vignetting isn't too bad. Definitely some fall-off in three of the corners, but it doesn't look like anything is clipped, so it should be flats-fixable. Might even be that the filter wasn't aligned- I didn't calibrate the wheel like I should have after messing with the imaging train. Now to dial in the backfocus. It doesn't look like I'm off too much as it sits presently- I'll have a few spacers at the ready tonight and continue to make adjustments. Always welcome your insights and experiences!

 

frame_and_focusjpgg.jpg



#16 bacon

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Posted 01 June 2020 - 01:19 PM

That vignetting shouldn't be a problem at all, it's better than the light falloff I see in my frames.  The stars look good too, but yes PixInsight or CCD Inspector would definitely like more stars to analyze if you decide to dial in quantitatively.  Good luck!  


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#17 zakry3323

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Posted 03 June 2020 - 01:55 PM

That vignetting shouldn't be a problem at all, it's better than the light falloff I see in my frames.  The stars look good too, but yes PixInsight or CCD Inspector would definitely like more stars to analyze if you decide to dial in quantitatively.  Good luck!  

I added an additional 2mm delrin spacer and I think I'm pretty close to where I'd like to be now, probably one more millimeter might help. However, this spacing is coming between the sensor and the filter wheel, and vignetting is starting to become an issue. Would you share what kind of spacer you're using between your FR and OAG? 

I'm considering a baader clicklock, I LOVE them on my refractors, but I'm not sure how much backspace one would take up attached directly onto the SCT threads. 

This is a quick integration of 30 subs through a Lum filter. It became increasingly hazy (the Moon was no help at all), and I didn't get very much time before guiding failed altogether. No calibration frames, no cropping. The light drop off has become much more pronounced, and does clip to black in the bottom right corner completely. 

 

integration.jpg

 

integration_mosaic.jpg



#18 bacon

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Posted 10 June 2020 - 08:07 PM

I just saw your clicklock post and it reminded me about this post but your response got past me.  Apologies.

 

The spacing is detailed here by NuclearRoy:

https://www.cloudyni...00mm/?p=9649019

 

The spacer from Agena:

https://agenaastro.c...nsion-s-sd.html

 

Is it possible your frames are underexposed in the example?


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#19 zakry3323

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Posted 11 June 2020 - 02:06 PM

I just saw your clicklock post and it reminded me about this post but your response got past me.  Apologies.

 

The spacing is detailed here by NuclearRoy:

https://www.cloudyni...00mm/?p=9649019

 

The spacer from Agena:

https://agenaastro.c...nsion-s-sd.html

 

Is it possible your frames are underexposed in the example?

Thanks for the link bacon! I picked up a baader clicklock to see if I can't get adapted for easy removal of the imaging train, so that I can swap it out between different otas. Spacing will be close, I'll just have to keep you posted as to whether or not it works. 

Definitely underexposed. It was a cloudy night under a near full Moon, there's just a lot noise washing out the signal. Simple STF in PixInsight of a 20 minute stack of short subs, I wasn't expecting much, just wanted to get an idea of how bad the light fall-off was going to be. 


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#20 rishigarrod

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Posted 12 June 2020 - 04:26 AM

Here is my setup.

 

EdgeHD 8

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#21 zakry3323

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Posted 12 June 2020 - 07:45 AM

Here is my setup.

 

Thanks for sharing! How do you like that focus cube? Seems like it hangs out pretty far off-axis. Does it give you any balance issues?



#22 bacon

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Posted 12 June 2020 - 10:07 AM

I can offer my experience with the motor-only version (the one without the controller)..it works extremely well.  The bracket is slightly flexible but sturdy enough and the whole thing is too light to notice any affect on balance.  With backlash comp the setup gives very repeatable focus.  


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#23 rishigarrod

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Posted 12 June 2020 - 05:20 PM

I really like it. It was very easy to fit, as Job mentioned above there is a little flex in the bracket but it is OK. It's very fine grained, 11510 step per rotation! It has built in backlash compensations too. It does stick out a bit but I try to keep the guide camera roughly opposite to counter balance, not perfect but it does the job. My HEQ5 Pro doesn't seem to have any problems with it (as long is there is little wind!). I can get very nice 300sec subs and I can go further but in my Bortle 8 backyard there is not much point unless I am doing narrowband.


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#24 zakry3323

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Posted 13 June 2020 - 11:55 AM

Unfortunately, she went for a roll this morning: 
 

 

Right onto the floor. 

attachicon.gifIMG_20200613_112004_01.jpg

 

The irony is that I had brought it in to replace the vixen bar with a losmandy to improve stability. Hah. 

Well, the primary, secondary, and tube still look good. Nothing else appears to be broken. I guess I'll shoot Celestron an email and see if they'll repair it. 



#25 KTAZ

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Posted 13 June 2020 - 01:33 PM

Unfortunately, she went for a roll this morning: 
 

Oh man, I'm really sorry about that. I would NOT be in a morning mood after that.




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