6 replies to this topic

[brebisson]

Hello,

 

I am trying to add guiding to my setup: EQ3-2, 66ed with 400mm focal (no corrector), zwo178 (2.4µ pixels).

 

Guiding will be done with another zwo178 and PHD2.

 

 

I have scrounged an optical divider, and I have also a 30*120mm guide scope (svbony)...

 

Which one will be the best for guiding?

It seems to me that:

 

Optical divider:

Pro: less extra HW

Pro: same resolution as the main imager

Con: the stars on the edge of the field, where the pickup occurs are just BAD (very elongated, definitely not point like)... which can not be good for guiding...

 

Guide scope (30*120):

Pro: correct stars for guiding

Pro: more lights on the guiding stars

Con: 3.3 times "larger" pixels in arc seconds... How will that affect pointing precision?

 

Guide scope option 2: use an old, crappy, 40*300 scope:

Pro: focal lenght and pixel size closer to main imager.

Con: much larger on the scope.

 

 

In your experience, what is the best way to guide? and why?

What would you advice?

 

Thanks,

Cyrille

 

[Tapio]

I guess you mean Optical divider = OAG off axis guider?

 

In your case with small refractor I recommend the small guidescope option.

Pro: more lights on the guiding stars

Con: 3.3 times "larger" pixels in arc secon

Your con - your guide scope works fine with your small imaging refractor.

[michael8554]

"Guiding will be done with another zwo178"

 

Colour or Mono ?

 

Colour one may not be sensitive enough for OAG.

 

"very elongated, definitely not point like)... which can not be good for guiding.."

 

PHD2 seems to cope.

 

Prism must be low enough to just not cause a shadow on the main camera's Flats.

 

And adjacent the long edge of the main camera's sensor.

 

For guidescope:

 

"3.3 times "larger" pixels in arc seconds.."

 

PHD2 does sub pixel guiding, so an image scale of 4.13arcsec/pixel is not a problem.

 

I would keep the OAG for a later long FL scope acquisition.

[matt_astro_tx]

Your main scope is only 400mm focal length.  Just use the 30mm guide scope.  The OAG (optical divider) isn't worth the trouble and since you don't have a flattener it may not work all that well with the stars being so misshapen at the edge of the field.

 

I use the same guide scope and it works great.

 

Save the OAG for when you get a bigger scope.

Edited by matt_astro_tx, 20 September 2024 - 08:55 AM.

[brebisson]

Hello,

 

So the consensus seems to be 30*120 guide scope...

 

Everyone seems to agree! this feels strange, as if I have suddenly be transferred in a parallel universe :-)

 

Thanks everyone.

Cyrille

[PIEJr]

When starting out (Over 10 years back) I tried to use an OAG with my 80mm 480mm telescope.

Back then, OAG were considered only for the big reflector telescopes.

I tried two different ones.

Finally, I tried a guide scope and found instant success with my guiding.

And I've never looked back.

 

That first Orion Star Shoot autoguider system served me well up until the camera finally died.

I replaced it with an ASI 290MM, then replaced the 50mm guide scope with an Svbony 60mm guide scope. For my larger refractor telescope.

 

But smaller refractor telescopes like my 80mm work best with Guide Scopes and cameras.

[astromusic]

Guide scope will be a lot less frustrating for you, I believe! OAG's are a lot more finicky; mind you, they do have their uses, but for a beginner, they are a lot more fiddly to get right.