Is My Guider Scope too small?

[kbrown]

So far I've been using a 50mm (180mm F/L) finder scope with a QHY5L-II as my guider setup. This gives me about 4.3" per pixel resolution. I've recently been using a ZWO ASI 183MC Pro as my imaging camera on my Sky-Watcher 250PX which gives me about 0.46"/px resolution with the 0.9x Coma Corrector in the train. My question is: Is my guider good enough any more?  I've been toying around with the idea of using my 72mm (500mm F/L) refractor as the guider scope which would give me 1.55"/px resolution but I'd be adding more weight on the system which is already at or near the limit of my NEQ6 Pro.

So far I've been using lin_guider as my guider software but will be trying out PHD2 soon as I just got it working with my QHY on my RPi3 which is controlling all the devices on my rig.

[discardedastro]

With a dob that big I'd be looking to move to an OAG, since at least some of your error is going to come from differential flexure and mirror support/positioning changes.

If you do go to an OAG then sensitivity is a key aspect though with a 10" dob you'll be doing alright for light to start with!

[Ronclarke]

If you struggle with PHD 2 give PHD 1.4 a try, it's almost bomb proof!!

[kbrown]

52 minutes ago, discardedastro said:

With a dob that big I'd be looking to move to an OAG, since at least some of your error is going to come from differential flexure and mirror support/positioning changes.

If you do go to an OAG then sensitivity is a key aspect though with a 10" dob you'll be doing alright for light to start with!

OAG did cross my mind but I don't think that's an option for me as there's no space for it in my rig (I think). I have a coma corrector in front of a filter wheel and the camera on the other side. I use barely any spacers to get to my desired back focus. The thinnest OAG I've found so far is 9mm. I have to double check but I think that's too much already. 

[discardedastro]

1 hour ago, kbrown said:

OAG did cross my mind but I don't think that's an option for me as there's no space for it in my rig (I think). I have a coma corrector in front of a filter wheel and the camera on the other side. I use barely any spacers to get to my desired back focus. The thinnest OAG I've found so far is 9mm. I have to double check but I think that's too much already. 

Ah, tricky. Have you looked at OAGs combined into filter wheels, or a Paracorr? The Paracorr has a mild barlow effect and so pushes the focal plane back considerably, which should then give you the required back focus.

[kbrown]

I have to look into the paracorr in detail. Might work albeit expensive solution. 

[michael8554]

Simplest, cheapest, and lightest solution would be to bin your guidecam 2x2, which would give an guiding image scale of 2.15 arcsecs/pixel.

Giving guide to imaging ratio of 4.7 : 1.

There's no definition of what the ratio should be , but 4 to 5 is often quoted, so worth a try !

Michael