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Which guide scope for Deep Sky AP

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#1 crozen

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Posted 04 January 2021 - 09:06 AM

Hi,

This is my setup :
Scope : TS Optics AP 102/520 6-Element-Flatfield Imaging Star OTA
Mount : Skywatcher NEQ-6 Pro Goto
Imaging : modified EOS Rebel T4i DSLR
Autoguiding : ZWO ASI 120 MC Color camera.

Question : What good guide scope do i need for autoguiding with the ASI 120 MC ?

Thnx !



#2 meansrt

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Posted 04 January 2021 - 09:22 AM

You've not got a huge focal length so you can easily get away with the ZWO mini guide scope or maybe one at 250mm focal length like the Evoguide 50ED. If I were you I might switch to a monochrome guide cam though I'm sure the color will work just fine. 



#3 jonnybravo0311

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Posted 04 January 2021 - 09:40 AM

Here's a formula to help you determine whether your main cam/scope and guide cam/scope will work well together:

 

(FL_main/FL_guide)*(PX_guide/PX_main) where FL = focal length and PX = pixel size.

 

Get an answer < 3 and you're in a good spot.

 

Example:

 

WO GT81 with 0.8x reducer = 382mm

WO 50mm guide scope = 200mm

ASI 294MC = 4.63

ASI 120MM Mini = 3.75

 

(382/200)*(3.75/4.63) = 1.55

 

Therefore, the above is a great combination.


Edited by jonnybravo0311, 04 January 2021 - 09:45 AM.

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#4 crozen

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Posted 04 January 2021 - 10:53 AM

Here's a formula to help you determine whether your main cam/scope and guide cam/scope will work well together:

 

(FL_main/FL_guide)*(PX_guide/PX_main) where FL = focal length and PX = pixel size.

 

Get an answer < 3 and you're in a good spot.

 

Example:

 

WO GT81 with 0.8x reducer = 382mm

WO 50mm guide scope = 200mm

ASI 294MC = 4.63

ASI 120MM Mini = 3.75

 

(382/200)*(3.75/4.63) = 1.55

 

Therefore, the above is a great combination.

Will this be good ?
TS Optics 102/520 = 520mm
TS Optics 80mm guide scope = 328mm  https://www.teleskop...al-focuser.html
DSLR = 4.29 µm
ASI 120 MC Color = 3.75 µm

(520/328) * (3.75/4.29) = 1.385


Edited by crozen, 04 January 2021 - 10:54 AM.


#5 jonnybravo0311

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Posted 04 January 2021 - 11:32 AM

Will this be good ?
TS Optics 102/520 = 520mm
TS Optics 80mm guide scope = 328mm  https://www.teleskop...al-focuser.html
DSLR = 4.29 µm
ASI 120 MC Color = 3.75 µm

(520/328) * (3.75/4.29) = 1.385

Just purely by the numbers? Yes, that's a good combination.

 

Most of the time people go with mono cameras for guiding (120mm mini and the like). You could use a smaller guide scope if you wanted. A 50mm would be fine as well.



#6 Rasfahan

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Posted 04 January 2021 - 12:44 PM

I have good success with a 30mm guidescope and the 120mm (mono) for my apo (100/550 mm). The 50mm on the mc should work just fine.


Edited by Rasfahan, 04 January 2021 - 12:45 PM.


#7 SonnyE

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Posted 05 January 2021 - 12:53 AM

I've been using my same Orion 50 mm guide scope all along.

I had the Orion SSAG camera for a lot of years.

But recently got a ZWO ASI290MM Mini. More stars, more detail.

I find that the telescope is one part of the equation, but the camera can make a big difference.



#8 moxican

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Posted 05 January 2021 - 02:25 AM

Here's a formula to help you determine whether your main cam/scope and guide cam/scope will work well together:

 

(FL_main/FL_guide)*(PX_guide/PX_main) where FL = focal length and PX = pixel size.

 

Get an answer < 3 and you're in a good spot.

 

Example:

 

WO GT81 with 0.8x reducer = 382mm

WO 50mm guide scope = 200mm

ASI 294MC = 4.63

ASI 120MM Mini = 3.75

 

(382/200)*(3.75/4.63) = 1.55

 

Therefore, the above is a great combination.

This is spot on...

 

With a main/guide scope ratio that low, color or mono will not make any difference. I would not sweat it. Set up next time you have clear skies and shoot awaycool.gif



#9 Stelios

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Posted 05 January 2021 - 03:01 AM

Cheapest guidescope I know is the Orion 50mm. $79. Works fine too... Paying more won't get you more.



#10 sbharrat

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Posted 05 January 2021 - 07:15 AM

I've been using my same Orion 50 mm guide scope all along.

I had the Orion SSAG camera for a lot of years.

But recently got a ZWO ASI290MM Mini. More stars, more detail.

I find that the telescope is one part of the equation, but the camera can make a big difference.

Happy with the Orion 50mm? Thinking of that as it is a bit lighter than some other similar choices but was wondering if any flex with the way it attaches. Thinking of pairing this with a ZWO ASI120MM...



#11 crozen

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Posted 05 January 2021 - 07:29 AM

Cheapest guidescope I know is the Orion 50mm. $79. Works fine too... Paying more won't get you more.

You are wrong. 
There are other things which are also important. Having a focuser in front of the scope (the cheap Orion 50 mm) is really a hell ! Also that mount is not accurate.



#12 meansrt

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Posted 05 January 2021 - 09:51 AM

You are wrong. 
There are other things which are also important. Having a focuser in front of the scope (the cheap Orion 50 mm) is really a hell ! Also that mount is not accurate.

I dont think the focuser will be that much of a problems since Ideally you can just set it and forget it. The accuracy of the mount ( I assume you're talking about the thumbscrews? ) shouldn't actually matter very much. This is because the guiding software will account for the guide scope being slightly out of line with your telescope anyway when it does calibration. 



#13 jerr

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Posted 05 January 2021 - 10:58 AM

There are even cheaper clones of tiny ZWO guidescopes available straight from China:

 

https://www.aliexpre....75334f1501UB2B

Shipping cost is nothing or close to nothing depending on a vendor. I’ve ordered one and waiting for delivery. Should be with me tomorrow after 18 days of waiting. I plan to us it with my ZS66 but will give it a try also with APO127 - fl.950 even though pixel scale calculation gives me result slightly above 5.



#14 charlieb123

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Posted 05 January 2021 - 11:36 AM

SVBony 50mm guide scope is the same as the Orion 50mm scope.

 

As long as all the thumbscrews are locked down it works well. Make sure it's solidly mounted.



#15 crozen

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Posted 09 January 2021 - 03:45 PM

Guys, what do you thing about going this way for more tracking precision : OAG with the ASI 120MC ?
The bad thing is that the camera is not monochrome, so, less sensitive but maybe it works !

Has anyone tried ?
I'm in Bortle 6.


Edited by crozen, 09 January 2021 - 03:47 PM.



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