Guide scope alignment

[Sirius Bizness]

I am in the process of building my imaging setup and I am looking where to attach my guide scope. I am going with a 50mm finder and have a question around its positioning. Are there any issues with placing the finderscope off axis (to the main imaging scope) in both directions? Obviously all finderscopes are off axis in one direction but is it ok to step the guide scope out to the side? I am looking to attach the finder offset on the imaging scope tube rings. Would this cause any additional issues during guiding?

Any advice greatly appreciated.

[FarSide]

What scope are you imaging with?

[malc-c]

What scope are you imaging with?

I'm assuming its a Equinox 120ED or an Orion ED80 looking at his signature

[FarSide]

Thanks a lot.

Why don't you use the ED80 on top of the 120ed? I'm assuming you're not going to be using both at the same time?

[Sirius Bizness]

Will be the 120ED. I am going down the route of a finder guider to minimise total weight on the mount plus the effort and time needed to set up each night. If the finder guider doesn't work then the ED80 is the back up option.

Any ideas around my original query or am I over thinking it.

Ps. Is there a way to get signatures to show up on the mobile version. May be useful.

[Zakalwe]

I am in the process of building my imaging setup and I am looking where to attach my guide scope. I am going with a 50mm finder and have a question around its positioning. Are there any issues with placing the finderscope off axis (to the main imaging scope) in both directions? Obviously all finderscopes are off axis in one direction but is it ok to step the guide scope out to the side? I am looking to attach the finder offset on the imaging scope tube rings. Would this cause any additional issues during guiding?

Any advice greatly appreciated.

It doesnt matter...as long as it is roughly pinting in the same direction as the imaging scope. If you are using PHD, the orientation doesn't matter a jot either. And a finderguider works well with a widefield rig (I use one on my Equinox 80).

[swag72]

I use a 10x60 finderscope piggy backing on top of my SW120ED and it works fine.

[ollypenrice]

I think that how much the orientation of the finder guider matters is related to how good your polar alignment is. The better it is the less your finder guider has to be on axis. Also if the cone error of the the guider and the main scope were considerable and diverging, then that, too, would make demands on your PA. I don't think the answer to this one is dead simple. I'm no genius when it comes to this kind of stuff so I pass on my thoughts. As ever, the shorter the FL and the shorter your subs the less any of this matters.

Olly

[Zakalwe]

Craig Starkey of PHD Labs

".... that PHD doesn't give a hoot about the orientation. Setting it up "square" can help you read the log file a bit (in particular the calibration section) but PHD's guiding accuracy isn't affected.

During calibration, PHD determines two vectors - one for RA and one for Dec. For any error (displacement from the lock position) we have another vector. You can ask how much of that vector lies along the RA and how much along the Dec (you just calculate the dot product of the vectors). So, RA/Dec becomes a pair of axes just like X and Y. The fact that they're rotated relative to X and Y doesn't matter as, by doing this dot product (or "projection") you get into RA/Dec "space".

[adamsp123]

I have a couple of photos that I have posted before but I post here that may help.

In the close up you can see I have added a upper dovetail to the main rings and then added a small set of scope rings I got from sky and scopes astroboot, I drilled and tapped the dovetail to take the mini scope ring shoe, then nip everything up nice and tight.

I am using a QHY5V with the Modern Astonomy adaptor.

The second shot shows it all mounted on a 120ED scope.

Works a treat!

HTH Pete