Lodestar vs self guiding

[LewisM]

Honestly, which is going to be the better system - a Lodestar through a PERFECT Takahashi finder (modified by me into a guidescope) solidly mounted on top (no flexure - I used Borg tube rings with a small aluminium custom milled set of spacers for a perfect fit), or the self guiding chip in the SBIG ST-8XE (which is now admittedly an OLD scope, but still fantastic in my opinion).

Is the chip on the ST-8XE sensitive enough to see well? I am thinking it may not be as sensitive as the Lodestar.

Seeing we still have horrendous cloud up here on the "Sunshine" Coast, got lots of time to sort things out.

Image of the current rig with the rigidly mounted guidescope arrangement (and the custom made light cone I had made to fit the 4" drawtube :) )

[Shiraz]

Lodestar and 237guider chips should be roughly similar in performance (similar pixel size/count and QE) - looks like the 237 is an oldy, but a goody.

An in-camera guider will not have any flex, so would be the better solution for broadband. For narrowband, the filters will vastly reduce the in-camera guider signal, so an external guider or OAG would probably be be better. The optical quality of the guide scope has almost no effect on performance - GSO ones work fine. Lodestar wins the guider sensitivity race by using big pixels - this is great for OAG or a long fl guidescope, but high QE guide cameras with smaller pixels may possibly be better alternatives for a small guidescope.

[multiweb]

Any flexure would come from the heavier scope moving in the rings while the guider is fixed. Doesn't matter if the guider is rock solid, what you have to watch out for is flex in the heaviest parts. If the guider was mounted directly on the refractor tube (in the available shoe) and not separate rings it would be best.

[gregbradley]

You should be fine with your guidescope as its a 4 inch refractor and not that demanding of guiding. Flexure is more of an issue in longer focal lengths generally speaking.

The Lodestar would be way better than the noisy 237 chip. I think also quite a bit wider FOV and you would almost always have a choice of guide stars.

I recently mounted an SBIG STi guide camera with the SBIG lens guiding kit which is all nicely made with very solid rings like that on my CDK17 at nearly 3 metres focal length. I was getting round stars at 15minutes in some orientations but flexure in other angles. I have since rebalanced my rig and perhaps it would work better now.

So the point being that sort of setup should work fine as long as your focuser for the ST8 is rigid. That may be the weak link.

Roland Christen recommends the guide scope being attached to the OTA tube not other attachments. But most likely you will get away with it here. But if you do get flexure that and the focuser would be the first 2 things to check.

Greg.

[LewisM]

Thanks for the help guys. I will try out the SG feature and see how it goes.

I have had nil issues with the Tak/Lodestar setup (used to be in a finder bracket! If anything was going to flex, THAT would!).

At least I can try things without having to unbolt anything :)

The focuser on these Greg is ROCK solid - it has 2 locking knobs, and NIL flex I can see. I didn't have to tension the grub screws providing pressure on the stabilising plate either (though have always had to with VC200L's)