Polar alignment using OAG instead of Guide Scope

[bluesilver]

HI, First sorry if have this in the wrong section, wasn't too sure which one to go with.
So i was looking at changing my setup from a guide scope to an OAG.
My scope is a Skywatcher Esprit 150 ( I have a .77 reducer, but to keep things easier, just referring to it without for now )
My guide camera is ZWO asi290mm mini
Guide scope is Orion 60mm
Everything works well, guides well polar aligns well, ( if i setup close to being right, have had a few times when i was too far out and it wouldn't polar align )

I picked up a standard ZWO OAG and tried it out, but no hope of polar aligning, I am thinking with the narrow field of view of the asi290mm mini working through the OAG, it isn't getting a wide enough field of view.
Is this correct?
Should i be looking for something like asi174 with a wider field of view?
Or should i be looking for a camera with a similar field of view as my main imaging camera?

This is the first time working with a OAG, and just trying to get it to work with the polar alignment setup.

Any advice would be appreciated.
Thanks.

[admin]

Hi,

yes, your problem is going to be the field of view - the small sensor of the 290MM combined with ~1m focal length of your main telescope gives an FOV that is just too small (by probably a factor of about 3) for the polar aligning to work.

I would imagine that a bigger guiding sensor may not cure the problem - the issue will be that it may not be possible to illuminate all of the bigger sensor from the OAG prism, so you may get very bad vignetting and still only see stars in quite a small area of sky.

Why not just run the polar alignment on your main imaging camera? I presume that has a decent size sensor and so gets an FOV of more than 1 degree in each direction.

cheers,

Robin

[SteveInNZ]

I put a par-focalizing ring on my QHY5L-ii so I can swap it between the OAG and the finder/guidescope. In the OAG it bottoms out before the ring makes contact and in the finder, the ring stops it. The downside is that I have to do a calibration run in PHD2 each time but that's a small price to pay.

Steve.

[bluesilver]

Appreciate those replies,
I didn't think of using the main camera and scope for polar aligning, good pick up there.
Using Astronomy.tool, the field of view is pretty much the same, but that i mean, using the Esprit 150 and asi2600, the field of view is very similar to using my Orion 600m guide scope and asi290mm mini.

I am now thinking that the field of view being soo small using a asi290mm mini in an OAG with the Esprit 150, I won't really be able to pick up many stars to guide on due to such a narrow field of view, Might have to re look at the guide camera for a larger field of view if i go down this track