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Guiding with RC6 or long FL scopes

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#1 KSPSteve

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Posted 30 May 2024 - 09:55 AM

I recently purchased an RC6 and I'm trying to dial in the guiding.  The best I can get at the moment is 3-4 arcseconds.

Here's my current setup..

>  iOptron RC6 (1370FL)
>  HEQ5 Pro
>  70mm/420FL refractor for guiding.  (Just because I have it.  I have a smaller 30mm/120FL guide scope, but as I understand this is too small for the RC6.)

>  Svbony SV905C 1280x960 for guide cam.

>  Using PHD2
>  Bortle 8  frown.gif 

I have another rig about the same weight, with the smaller guide scope, and I can usually get .5-1.0 arcseconds.

Given the above setup, should I be able to get guiding down to under 1.0?  If so, any suggestions as to where to concentrate my efforts?

If I were to go with an OAG, how much easier (or harder) would it be to achieve good guiding?

Would a filter of some sort (light pollution?) help on the guide scope?

Also, with both of these setups in the same weight range, my HEQ5 counterweights are near the very end of the bar.  Would it make any difference if I were to get an extension bar and move one weight farther down? (And the other one up.)

Any tips or suggestions appreciated, thank you!

-Steve


 


Edited by KSPSteve, 30 May 2024 - 09:59 AM.


#2 soojooko

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Posted 30 May 2024 - 10:02 AM

How much does your guide scope weigh? I cant remember the exact max payload for the HEQ5 - its around 10kg for imaging I think. Your RC6 must be around 5kg for the OTA only. Add the accessories, cameras, guidecope etc. You may find that weight is your problem here.

 

Whats the other rig made up of?


Edited by soojooko, 30 May 2024 - 10:04 AM.


#3 KSPSteve

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Posted 30 May 2024 - 10:13 AM

How much does your guide scope weigh? I cant remember the exact max payload for the HEQ5 - its around 10kg for imaging I think. Your RC6 must be around 5kg for the OTA only. Add the accessories, cameras, guidecope etc. You may find that weight is your problem here.

 

Whats the other rig made up of?

Thanks for the reply!  The other rig is a customized conglomeration with a 102MM/714FL as the main scope.  The weight is practically identical (coincidence) as I only need to move one weight like 7-8mm down for the RC6 rig.  So technically the RC6 rig is barely heavier.  So I'm doubting that this is the issue, but maybe?.. 



#4 Tapio

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Posted 30 May 2024 - 10:37 AM

I would try OAG guiding with that setup.
The attachment of your current biggish guide scope might be the problem.
Also above 1000mm imaging focal length the general advice is to use OAG.
Besides it's a lighter solution which is better for your mount.
Regarding your mounts counterweight - it's better to have bigger weight near the mount than lighter farther away - momentum arm you see.

As for OAG. There might be some tweaking in the beginning but once you get it sorted it's fine.
But with OAG you may need to get bigger sensor and mono camera.
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#5 bobzeq25

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Posted 30 May 2024 - 10:37 AM

I recently purchased an RC6 and I'm trying to dial in the guiding.  The best I can get at the moment is 3-4 arcseconds.

Here's my current setup..

>  iOptron RC6 (1370FL)
>  HEQ5 Pro
>  70mm/420FL refractor for guiding.  (Just because I have it.  I have a smaller 30mm/120FL guide scope, but as I understand this is too small for the RC6.)

>  Svbony SV905C 1280x960 for guide cam.

>  Using PHD2
>  Bortle 8  frown.gif 

I have another rig about the same weight, with the smaller guide scope, and I can usually get .5-1.0 arcseconds.

Given the above setup, should I be able to get guiding down to under 1.0?  If so, any suggestions as to where to concentrate my efforts?

If I were to go with an OAG, how much easier (or harder) would it be to achieve good guiding?

Would a filter of some sort (light pollution?) help on the guide scope?

Also, with both of these setups in the same weight range, my HEQ5 counterweights are near the very end of the bar.  Would it make any difference if I were to get an extension bar and move one weight farther down? (And the other one up.)

Any tips or suggestions appreciated, thank you!

-Steve


 

Tip and suggestion.  You won't like it, but it's honest and experience based (not theoretical).

 

The RC6 was my second scope, on a zeq25 (whoda thunk?  <smile> ).  Comparable to the HEQ5.  I gave up on trying to use that with the 1300mm scope (even reduced).  Got a CEM60 because I didn't want to go through that again.

 

Weight isn't the only issue.  Focal length counts a lot, it increases the demand on the mount, and the effect is non-linear. 1300 is more than twice as hard as 650.

 

Your problem is unlikely to be your guidescope.   It's likely a combination of the focuser flop (which suggests an OAG), and just too big a scope for the mount to handle.  Weight, focal length, slow optical speed.


Edited by bobzeq25, 30 May 2024 - 10:39 AM.

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#6 soojooko

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Posted 30 May 2024 - 10:40 AM

Thanks for the reply!  The other rig is a customized conglomeration with a 102MM/714FL as the main scope.  The weight is practically identical (coincidence) as I only need to move one weight like 7-8mm down for the RC6 rig.  So technically the RC6 rig is barely heavier.  So I'm doubting that this is the issue, but maybe?.. 

The thing with RCs is that they have a wide diameter compared to refractors; their centre of gravity is further away from the RA axis. So while its the same weight in total, the weight distribution is different. The fact you have to only move your CW 8mm tells us there's not much it it. But in this hobby "not much in it" can be a chasm!

 

To be clear - was your other rig tested on the same mount?


Edited by soojooko, 30 May 2024 - 10:45 AM.

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#7 KSPSteve

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Posted 30 May 2024 - 11:26 AM

Regarding your mounts counterweight - it's better to have bigger weight near the mount than lighter farther away - momentum arm you see.
 

Hmm...  Part of me thinks that moving the weights away from the axis would reduce the load on the axis, but if I'm understanding correctly this would also increase momentum on the counterweight side, which the mount would struggle to cancel out.  Does that sound right?

But if the weights are farther in, momentum increases on the scope side?..  So "ideal" weight location would be same distance from axis as COG of scope?..

My physics classes were a long time ago, lol...

Thanks!


Edited by KSPSteve, 30 May 2024 - 11:32 AM.


#8 KSPSteve

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Posted 30 May 2024 - 11:30 AM

The thing with RCs is that they have a wide diameter compared to refractors; their centre of gravity is further away from the RA axis. So while its the same weight in total, the weight distribution is different. The fact you have to only move your CW 8mm tells us there's not much it it. But in this hobby "not much in it" can be a chasm!

 

To be clear - was your other rig tested on the same mount?

Yes, same mount.

Good point on the RC COG.  I've seen a few rigs where the guide scope is under the large main scope instead of on top, like mine.  I might give that a try if I can MacGyver it.

Thanks!!



#9 Tapio

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Posted 30 May 2024 - 11:36 AM

Hmm... Part of me thinks that moving the weights away from the axis would reduce the load on the axis, but if I'm understanding correctly this would also increase momentum on the counterweight side, which the mount would struggle to cancel out. Does that sound right?

But if the weights are farther in, momentum increases on the scope side?.. So "ideal" weight location would be same distance from axis as COG of scope?..

My physics classes were a long time ago, lol...

Thanks!

Right on the first part and I think your second reasoning is true as well.
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#10 soojooko

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Posted 30 May 2024 - 11:36 AM

Yes, same mount.

Good point on the RC COG.  I've seen a few rigs where the guide scope is under the large main scope instead of on top, like mine.  I might give that a try if I can MacGyver it.

Thanks!!

Give it a go. But read and digest what Bobzeq25 says above. That focal length on that mount is not easy even before you consider the weight. But having said that, you should be able to better 3-4 arc seconds. How are you mounting the guidescope to the OTA right now? If its not super secure - flexure will also play its part.


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#11 KSPSteve

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Posted 30 May 2024 - 11:58 AM

How are you mounting the guidescope to the OTA right now? If its not super secure - flexure will also play its part.

I bought an identical dovetail bar (from FLO) and mounted it on top, then a spiffy Svbony dovetail handle mounted to that, then the guide scope mounted to the dovetail handle.  Works like a charm and seems pretty dang secure.  Was surprised to then find total weight almost identical to my other rig.

I also have the Rowan belt mod waiting for me to install one of these years...  I think the time has come, lol!

Thanks!    



#12 acrh2

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Posted 30 May 2024 - 12:10 PM

I recently purchased an RC6 and I'm trying to dial in the guiding.  The best I can get at the moment is 3-4 arcseconds.

Here's my current setup..

>  iOptron RC6 (1370FL)
>  HEQ5 Pro
>  70mm/420FL refractor for guiding.  (Just because I have it.  I have a smaller 30mm/120FL guide scope, but as I understand this is too small for the RC6.)

>  Svbony SV905C 1280x960 for guide cam.

>  Using PHD2
>  Bortle 8  frown.gif 

I have another rig about the same weight, with the smaller guide scope, and I can usually get .5-1.0 arcseconds.

Given the above setup, should I be able to get guiding down to under 1.0?  If so, any suggestions as to where to concentrate my efforts?

If I were to go with an OAG, how much easier (or harder) would it be to achieve good guiding?

Would a filter of some sort (light pollution?) help on the guide scope?

Also, with both of these setups in the same weight range, my HEQ5 counterweights are near the very end of the bar.  Would it make any difference if I were to get an extension bar and move one weight farther down? (And the other one up.)

Any tips or suggestions appreciated, thank you!

-Steve


 

 

Yes, it can be done.

 

HEQ5 can guide up to 28 lbs of equipment down to about 0.7" RMS typical, better with better seeing.

 

My Sirius EQ-G, which is a black painted clone of HEQ5 Pro, happily guides a 120 mm refractor with a full mono setup (22 lbs) to about 0.6" RMS.

In the past, I have guided a 1400 mm focal length Maksutov to produce reasonably round stars using ASI120MM-S (similar in performance to your Svbony SV905C) and a 30/120 mm guide scope. 

 

If you go to a Flickr gallery in my signature, you can see all of the early images I have taken with the Mak. All were guided with this mount and the guiding setup up I described above - 

Fireworks galaxy, Crescent nebula, M57, M27, Needle galaxy, M97, M63. The broadband targets used 2 min exposures, and narrowband targets used 4 min exposures.

 

If you want real tips/suggestions, you should post a guide log.


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#13 jml79

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Posted 30 May 2024 - 12:44 PM

Guide log would be helpful, another dumb question but is all of the error in DEC or RA and how is your DEC balance. The RC scopes have all of their weight at the back and then add a giant extension and camera behind that. Disclaimer, I don't own one but the few I have seen either have weight added to the front of the tube or a really long dovetail bar and the scope mounted somewhere close to the mirror in a really awkward way.

 

I would try to solve the problem before tossing money at it. Going from something that has worked well before to 3-4 arc seconds is a big change. I don't think an OAG is going to magically fix that. My OAG's improved my guiding by 0.2 - 0.3 arc seconds on average over a 30mm mini guide scope.


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#14 TXLS99

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Posted 30 May 2024 - 04:36 PM

 

Any tips or suggestions appreciated, thank you!




 

Just a thought, because I've seen others that have made the same mistake, but are you pointing your scope near the intersection of the southern meridian and the celestial equator during the guiding calibration? 

 

Is your actual guide scope focal length entered correctly in PHD2?

 

Did you create a dark library for the guide scope?

 

Are you getting at least 10-15 steps during the guiding calibration?

 

Some of these mistakes are more forgiving with a wider field setup, but at your focal length everything has to be spot on.

 

 

Just trying to eliminate all the variables


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#15 KSPSteve

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Posted 31 May 2024 - 11:43 AM

Just a thought, because I've seen others that have made the same mistake, but are you pointing your scope near the intersection of the southern meridian and the celestial equator during the guiding calibration? 

 

Is your actual guide scope focal length entered correctly in PHD2?

 

Did you create a dark library for the guide scope?

 

Are you getting at least 10-15 steps during the guiding calibration?

 

Some of these mistakes are more forgiving with a wider field setup, but at your focal length everything has to be spot on.

 

 

Just trying to eliminate all the variables


I haven't had to use a dark library yet, and I don't get 10-15 steps either.  Like you say though, I may need to address these now with the RC6.

 

Thanks!!



#16 Eric Dunn

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Posted 01 June 2024 - 03:16 PM

If you go to a Flickr gallery in my signature,...

I really enjoyed going through your gallery. Very nice stuff there. Thanks for sharing.


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