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Guider recommendation

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6 replies to this topic

#1 niccoc1603

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Posted 12 June 2019 - 08:26 AM

According to my understanding the recommended ration between Imaging scale and Guiding scale should be <4

I just upgraded my scope and with the new configuration the Image/Guide ratio is 4.6

 

so now I have three options:

 

1) leave it as is, not a big deal

2) buy a cheap barlow and bring my 240mm guidescope to 480mm

3) sell my guide camera and buy one with smaller pixels

 

Which one do you vote for?

 

Thanks


Edited by niccoc1603, 12 June 2019 - 08:26 AM.


#2 Dynan

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Posted 12 June 2019 - 08:35 AM

From your image page, I see that you're guiding great!

 

I vote Choice #1...unless, of course, you're itching to buy something new. biggrin.png



#3 niccoc1603

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Posted 12 June 2019 - 08:37 AM

From your image page, I see that you're guiding great!

 

I vote Choice #1...unless, of course, you're itching to buy something new. biggrin.png

Thank you, this is for my new rig, which I haven't tried yet :)



#4 Tapio

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Posted 12 June 2019 - 08:37 AM

That ratio is not absolute truth.
I suggest you first how your guiding works and if it doesn't then you can try Barlow or something else.

#5 Gipht

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Posted 12 June 2019 - 08:42 AM

One factor might be how good your seeing is on  most nights.  With excellent seeing, you would be more likely to benefit from increasing the guide scope focal length.



#6 Ken Sturrock

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Posted 12 June 2019 - 09:42 AM

That ratio is not absolute truth.


Correct. There is no "magic ratio" (even though it *seems* to make sense). Rather, with any guiding routine written in the past 20+ years, what you need is a guide system that can adequately sample the guide star and generate a reliable sub-pixel centroid. That's it. If your guide scope was capable of keeping your mount on target with the old imaging train, it should be capable of doing so with the new OTA.

 

In other words, the imaging tube is independent and just along for the ride on a, presumably, well-guided mount.

 

Now, a different but related issue is that some users have lower resolution imaging rigs which are less sensitive to some guiding issues. If they buy bigger imaging OTAs then the OTA/camera is not only heavier (often with longer moment arms) such that it stresses the mount more, but it also captures the mounts tracking errors with higher fidelity. In that case, the mount was never guiding well - the user just happens to notice it more after the upgrade.

 

If it were me, I'd leave it alone and see how it does.



#7 t-ara-fan

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Posted 12 June 2019 - 12:53 PM

I just upgraded my scope and with the new configuration the Image/Guide ratio is 4.6

I have guided my EdgeHD-8 with a 0.7x reducer (1422mm FL) with an Orion MMAG (163mm FL).  It worked, I tried it once or twice. Might have been lucky.  It was on a HEQ Pro mount, so definitely nothing fancy.

 

True story: then I added a ShortTube80 guider. Which needed a 3 ring set to be solid. Which mounted on several pounds of a 14" Losmandy Dovetail.  Now we were getting heavy.  Too heavy. So I added a Mach1GTO.  Problem solved LOL, but not the cheap way.

 

I have a ZWO OAG on the way, that will be 4-5 pounds less than the ST80 described above.

 

TL;DR:  just try it.  I don't think you will have any problems.


Edited by t-ara-fan, 12 June 2019 - 12:54 PM.



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