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Help with autoguiding?

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#1 jmillsbss

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Posted 28 May 2024 - 09:16 PM

I'm having a hard time getting a guide star from time to time. I have the ASIAir Plus and the 174MM-Mini in the standard ZWO OAG. Current scope is the C8 at x6.3, camera is the 2600MCP. Last night, for instance, on M101 it could lock on a star. M13 it locked on a star. Go to the Virgo cluster region, no star. South of Virgo, no star. Back to M101, no star. (It was maybe 45 minutes after it locked on a star before?) I've got the prism just about as deep as it can go, without clipping the sensor on the 2600mc. Any ideas?

#2 hyiger

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Posted 28 May 2024 - 09:48 PM

I'm having a hard time getting a guide star from time to time. I have the ASIAir Plus and the 174MM-Mini in the standard ZWO OAG. Current scope is the C8 at x6.3, camera is the 2600MCP. Last night, for instance, on M101 it could lock on a star. M13 it locked on a star. Go to the Virgo cluster region, no star. South of Virgo, no star. Back to M101, no star. (It was maybe 45 minutes after it locked on a star before?) I've got the prism just about as deep as it can go, without clipping the sensor on the 2600mc. Any ideas?

Depending on the target you may need to rotate the OAG to find suitable guide stars. Also the C8 at f/6.3 has a very small image circle so it's going to be tough to find guide stars to begin with and the stars you do find will be severely distorted. The C8 (especially reduced) is not ideal for large sensors and guide cameras. 

 

That aside, try rotating. 


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#3 Tapio

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Posted 28 May 2024 - 09:51 PM

What's your guide exposure?
Can you increase it? Or gain?

#4 jmillsbss

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Posted 28 May 2024 - 10:32 PM

Ok. Are you saying rotate the camera in the holder? Did that. Helped once but not entirely. Would I want to go back to the 533MC-Pro with the C8 at x6.3 ?

#5 jmillsbss

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Posted 28 May 2024 - 10:36 PM

What's your guide exposure?
Can you increase it? Or gain?

You know what, I don't suppose I even thought about changing the gain settings on the guide camera!  I was only shooting witb 100 gain on the 2600MCP,  but I guess you're suggesting the guide camera gain cam be set to a different setting than the main cam? Of course! If that's do-able, and I guess it should be, perhaps that'd help!?!?



#6 powerslide

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Posted 28 May 2024 - 10:45 PM

I'm having a hard time getting a guide star from time to time. I have the ASIAir Plus and the 174MM-Mini in the standard ZWO OAG. Current scope is the C8 at x6.3, camera is the 2600MCP. Last night, for instance, on M101 it could lock on a star. M13 it locked on a star. Go to the Virgo cluster region, no star. South of Virgo, no star. Back to M101, no star. (It was maybe 45 minutes after it locked on a star before?) I've got the prism just about as deep as it can go, without clipping the sensor on the 2600mc. Any ideas?

Hi is it the OAG-L or the Standard with the smaller prism? You have the L in your signature but say its the standard. As far as I know the Standard Prism does not take full advantage of the larger 174mm sensor size. I recently got the OAG-L and 174mm Mini for my C8 and I am having no difficulty finding multiple stars. Having said that I am using it with a 533 at the moment but looking to upgrade to the 2600MM.



#7 powerslide

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Posted 28 May 2024 - 10:49 PM

Ok. Are you saying rotate the camera in the holder? Did that. Helped once but not entirely. Would I want to go back to the 533MC-Pro with the C8 at x6.3 ?

I think he is referring to rotating the OAG prism to the opposite side of the 2600 sensor. I would assume this is in case more suitable stars can be found there than current location. Be careful increasing gain, if it the SNR is reduced through additional noise you could get different issues. Your exposure around 3 seconds? 



#8 idclimber

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Posted 28 May 2024 - 10:52 PM

What's your guide exposure?
Can you increase it? Or gain?

You need to address both of these questions. I think the gain on my 174mm is 200, but I also use 2 to 4 second exposures if I am guiding. I also have mine paired with the OAG-L which also helps.

 

The main issue may be the C8 especially with common f/6.3 reducer. The image circle is just not that large and getting any OAG to fit is not trivial.


Edited by idclimber, 28 May 2024 - 10:53 PM.


#9 jmillsbss

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Posted 28 May 2024 - 11:01 PM

Hi is it the OAG-L or the Standard with the smaller prism? You have the L in your signature but say its the standard. As far as I know the Standard Prism does not take full advantage of the larger 174mm sensor size. I recently got the OAG-L and 174mm Mini for my C8 and I am having no difficulty finding multiple stars. Having said that I am using it with a 533 at the moment but looking to upgrade to the 2600MM.

Standard. Sig corrected!  I had the oag-L and was told it was overkill. Kept the standard I got in a lot purchase and sold the oag-L. Maybe I shoulda kept both! I may try with my 533 next time out and see how it goes. I really am enjoying the larger 2600mc though!!!


Edited by jmillsbss, 28 May 2024 - 11:05 PM.


#10 jmillsbss

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Posted 28 May 2024 - 11:07 PM

I think he is referring to rotating the OAG prism to the opposite side of the 2600 sensor. I would assume this is in case more suitable stars can be found there than current location. Be careful increasing gain, if it the SNR is reduced through additional noise you could get different issues. Your exposure around 3 seconds? 

I have been able to guide with 1.5 seconds but a couple of times last night I pushed to 4 secs and it wouldn't find a star.



#11 jmillsbss

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Posted 28 May 2024 - 11:17 PM

You need to address both of these questions. I think the gain on my 174mm is 200, but I also use 2 to 4 second exposures if I am guiding. I also have mine paired with the OAG-L which also helps.

 

The main issue may be the C8 especially with common f/6.3 reducer. The image circle is just not that large and getting any OAG to fit is not trivial.

Yeah it's entirely possible that I had the gain too low on the 174. That's the hope. I feel like it's not "seeing" stars if the gain is too low.

 

On a side bar, I understand the image circle is tight at 6.3x. I've been considering an update/upgrade from my standard, early 2k's C8 to a newer minted EdgeHD, but those reducers are .7x. Would that be more like the same issue or is there a work around or is there any difference at all?  Quite a few comments on various CN threads about the benefits of the larger OAG-L, some others about using the even larger Celestron OAG,  but there's still the small illuminated image circle....



#12 idclimber

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Posted 28 May 2024 - 11:53 PM

Yeah it's entirely possible that I had the gain too low on the 174. That's the hope. I feel like it's not "seeing" stars if the gain is too low.

 

On a side bar, I understand the image circle is tight at 6.3x. I've been considering an update/upgrade from my standard, early 2k's C8 to a newer minted EdgeHD, but those reducers are .7x. Would that be more like the same issue or is there a work around or is there any difference at all?  Quite a few comments on various CN threads about the benefits of the larger OAG-L, some others about using the even larger Celestron OAG,  but there's still the small illuminated image circle....

The 8" Edge uses the same SCT thread as the C8 and has much of the same problem. You can make sure you are using M48 adaptors instead of the SCT to M42 that many are using. This will open things up a bit. 

 

If you want to upgrade go with the 9.25" Edge which uses the much larger 3.28" threads all the larger Meade and Celestron SCTs have. 



#13 DuncanM

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Posted 29 May 2024 - 12:06 AM

I'm having a hard time getting a guide star from time to time. I have the ASIAir Plus and the 174MM-Mini in the standard ZWO OAG. Current scope is the C8 at x6.3, camera is the 2600MCP. Last night, for instance, on M101 it could lock on a star. M13 it locked on a star. Go to the Virgo cluster region, no star. South of Virgo, no star. Back to M101, no star. (It was maybe 45 minutes after it locked on a star before?) I've got the prism just about as deep as it can go, without clipping the sensor on the 2600mc. Any ideas?

Your guider prism should be centred along the long axis of the imaging camera.  Binning the guider camera will increase sensitivity.

 

The Starizona .63x SCT reducer is quite superior and should give better off-axis illumination:

 

https://starizona.co...-coma-corrector


Edited by DuncanM, 29 May 2024 - 12:07 AM.

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#14 ngatel

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Posted 29 May 2024 - 12:08 AM

I image a lot with a C8, 0.63 reducer, OAG-L, and a 174MM mini.

 

On some targets I can only get one guide star. On some targets several stars for multi-star guiding. I also really need above average seeing. Usually image with 2.5 sec exposures. I let PHD2 choose the gain.

 

The standard ZWO OAG pick-off mirror would be too small for my set up. Also I usually use a ASI533MC Pro that has a smaller sensor than your 2600 with a APS-C sensor. I have a ASI071MC Pro with the same size sensor and I have to raise the pick-off mirror higher than the 533 to avoid shadows, and this often really limits the number of stars for guiding to the point I no longer use the 071MC Pro with my C8 unless I switch to a guide scope. But instead of this I usually just do mosaics if I want a wider FOV than the 533 provides.


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#15 hyiger

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Posted 29 May 2024 - 12:11 AM

Hi is it the OAG-L or the Standard with the smaller prism? You have the L in your signature but say its the standard. As far as I know the Standard Prism does not take full advantage of the larger 174mm sensor size. I recently got the OAG-L and 174mm Mini for my C8 and I am having no difficulty finding multiple stars. Having said that I am using it with a 533 at the moment but looking to upgrade to the 2600MM.

How did you attach the OAG-L to the camera side of your image train? Mine has always been bolted to the filter wheel and can't remember if it came with a camera-side adapter to allow a threaded connection. 


Edited by hyiger, 29 May 2024 - 12:12 AM.


#16 powerslide

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Posted 29 May 2024 - 12:58 AM

How did you attach the OAG-L to the camera side of your image train? Mine has always been bolted to the filter wheel and can't remember if it came with a camera-side adapter to allow a threaded connection. 

Ah Camera is attached through the Filter wheel... but you could possibly use the tilter to bolt to the OAG-L and it has a threaded connection... 



#17 jmillsbss

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Posted 29 May 2024 - 09:32 AM

I image a lot with a C8, 0.63 reducer, OAG-L, and a 174MM mini.

 

On some targets I can only get one guide star. On some targets several stars for multi-star guiding. I also really need above average seeing. Usually image with 2.5 sec exposures. I let PHD2 choose the gain.

 

The standard ZWO OAG pick-off mirror would be too small for my set up. Also I usually use a ASI533MC Pro that has a smaller sensor than your 2600 with a APS-C sensor. I have a ASI071MC Pro with the same size sensor and I have to raise the pick-off mirror higher than the 533 to avoid shadows, and this often really limits the number of stars for guiding to the point I no longer use the 071MC Pro with my C8 unless I switch to a guide scope. But instead of this I usually just do mosaics if I want a wider FOV than the 533 provides.

I went from 1.5 up to 4 sec.  I really felt like that was as long of an exposure I should go.  I didn't know AA+ used the PHD2 that would select the gain.  I'm gonna have to look into this more.

 

After verifying the gain/exposure issue, if I still struggle to get usable stars, I'm gonna assume I need to go back to the OAG-L or switch to a different scope/camera combo.



#18 ngatel

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Posted 29 May 2024 - 10:42 AM

How did you attach the OAG-L to the camera side of your image train? Mine has always been bolted to the filter wheel and can't remember if it came with a camera-side adapter to allow a threaded connection.


You need a tilt adapter. The ZWO instructions show the part number and Agena Astro sells them. One issue is you cannot rotate the OAG-L in relation to the camera sensor (unlike the standard OAG) to get the pick off mirror parallel to the camera sensor. You have to use thin spacers to get the proper rotation. This is easier with the square sensor in the 533 camera.

#19 hyiger

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Posted 29 May 2024 - 11:18 AM

You need a tilt adapter. The ZWO instructions show the part number and Agena Astro sells them. One issue is you cannot rotate the OAG-L in relation to the camera sensor (unlike the standard OAG) to get the pick off mirror parallel to the camera sensor. You have to use thin spacers to get the proper rotation. This is easier with the square sensor in the 533 camera.

OK, so basically you would need tilt adapters on both side to get the threads. Yep, basically I end up rotating the camera as well. Fortunately though with the larger image circles on my 925 and 11 it's not much of an issue. 



#20 ngatel

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Posted 29 May 2024 - 11:34 AM

All of this was difficult with the OAG-L because I wanted to use a filter drawer. I had to buy a shorter T-adapter than the stock Celestron one and the filter drawer had to be backwards (filter is backwards) but it all works. The Celestron OAG doesn’t have have a helical focuser ring and IIRC it is wider. Also more expensive. I have my backspacing at 110 mm instead of 105 mm (1260 vs 1280 FL) and I get better stars with the extra 5 mm.

#21 Oort Cloud

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Posted 29 May 2024 - 12:01 PM

Do you have any other OTAs? If so, Id consider getting a 533 for the C8 and moving the 2600 to a scope with a larger image circle.

As others have noted, the reduced C8E image circle is barely large enough for APS-C, which doesn't leave much room for an OAG prism. A smaller sensor like the 533 would allow you to dip the prism stalk farther into the light cone.

As you've noted, it's not that it doesn't work...star dense areas (near the galactic plane) will not be a problem. It's when you turn away from the galactic plane, into the cost vastness of space, where there are far less stars to guide on.

Rotating the OAG is an option, but remember every adjustment means you need to recalibrate guiding.
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#22 Oort Cloud

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Posted 29 May 2024 - 12:08 PM

All of this was difficult with the OAG-L because I wanted to use a filter drawer. I had to buy a shorter T-adapter than the stock Celestron one and the filter drawer had to be backwards (filter is backwards) but it all works. The Celestron OAG doesn’t have have a helical focuser ring and IIRC it is wider. Also more expensive. I have my backspacing at 110 mm instead of 105 mm (1260 vs 1280 FL) and I get better stars with the extra 5 mm.


Not sure if your filter drawer is older, or non-ZWO, but I know at least the ones they currently sell have holes in them to allow bolting to the OAG-L. That would be the ideal way (and the intended way, by ZWO) to set it up so that you can maintain the 55mm spacing with an OAG-L and a filter drawer instead of the EFW. I realize yours works better at 110, but that may not be the case for everyone. Mine is perfectly flat at 105, so I'm guessing 110 would be worse for my OTA & reducer.
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#23 ngatel

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Posted 29 May 2024 - 01:42 PM

Do you have any other OTAs? If so, Id consider getting a 533 for the C8 and moving the 2600 to a scope with a larger image circle.

As others have noted, the reduced C8E image circle is barely large enough for APS-C, which doesn't leave much room for an OAG prism. A smaller sensor like the 533 would allow you to dip the prism stalk farther into the light cone.

As you've noted, it's not that it doesn't work...star dense areas (near the galactic plane) will not be a problem. It's when you turn away from the galactic plane, into the cost vastness of space, where there are far less stars to guide on.

Rotating the OAG is an option, but remember every adjustment means you need to recalibrate guiding.

Good observation. I have a C8, Esprit 100 and Zenithstar 61 along with ASI533MC Pro, ASI071MC Pro and a ASI183MC Pro. I also have two mounts and run two rigs every night. This provides a lot of options. Ever since I bought the 533 it is the only camera I use with the C8 and I use the C8 more often now.

 

Not sure if your filter drawer is older, or non-ZWO, but I know at least the ones they currently sell have holes in them to allow bolting to the OAG-L. That would be the ideal way (and the intended way, by ZWO) to set it up so that you can maintain the 55mm spacing with an OAG-L and a filter drawer instead of the EFW. I realize yours works better at 110, but that may not be the case for everyone. Mine is perfectly flat at 105, so I'm guessing 110 would be worse for my OTA & reducer.

The Gen 2 is ideal to bolt to the OAG-L, but I already had a collection of Gen 1s and several extra drawers, so switching over will be somewhat costly since I image with two rigs at once and need extra drawers for convenience. But I have been considering switching to gen 2 for a while. I never disassemble the imaging train for the C8 except the camera. Even when I travel I keep the T-adapter, OAG-L and the filter drawer connected. I do pack the FF/FR separately. 
 

I do have a 3rd smaller T-adapter that i can get 105mm back focus with all my components, but 110mm works better. Getting everything to work was time consuming and in the end worth the time invested.




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