The baseline for camera orientation angle?

[choochoo_baloo]

Hello all,

I am a trifle confused about the baseline for camera orientation angle on a refractor imaging scope. 

This is having read the following from page 78 of the excellent Making Every Photon Count, 3rd edition: "in astro-photography, the baseline is the plane of the RA axis."

My confusion is that this definition doesn't tell me what plane is the baseline because the orientation of a plane is not known from knowing only one straight line (the RA axis here) that it passes through. Think of a paddle wheel on a paddle steamer. The plane of each paddle passes through a common straight line; the centre line of the driving axle. Hopefully this conveys my confusion with regard to the authors description above.

If anyone can clarify what the baseline/plane actually is for camera orientation used on a refractor, I would be grateful.

Thanks.

[PhotoGav]

I'll try and describe the plane referred to in words... might be tricky, but I have a feeling it will be better than my drawings!

Imagine the mount in the home position. You are standing behind it, looking up the RA axis as it points towards Polaris. Now imagine a plane that runs horizontally, cutting through the mount head from left to right. The plane is tilted up towards Polaris. That is the baseline plane.

When I'm setting up my camera on my scope, I find the best way to get things level, thereby helping with orientation from session to session, is to rest the scope on its dove tail plate on a table. I then attach the camera ensuring it is level with that, helped by the surface of the table.

When framing a target, I use two positions to make things easier if I come back to the object at a later date. First position as described above and the second position is at 90º to that. I then make a note with each target which orientation I have used.

Good luck and I hope you are enjoying some clear dark skies in Somerset!

[choochoo_baloo]

I'll try and describe the plane referred to in words... might be tricky, but I have a feeling it will be better than my drawings!

Imagine the mount in the home position. You are standing behind it, looking up the RA axis as it points towards Polaris. Now imagine a plane that runs horizontally, cutting through the mount head from left to right. The plane is tilted up towards Polaris. That is the baseline plane.

When I'm setting up my camera on my scope, I find the best way to get things level, thereby helping with orientation from session to session, is to rest the scope on its dove tail plate on a table. I then attach the camera ensuring it is level with that, helped by the surface of the table.

When framing a target, I use two positions to make things easier if I come back to the object at a later date. First position as described above and the second position is at 90º to that. I then make a note with each target which orientation I have used.

Good luck and I hope you are enjoying some clear dark skies in Somerset!

Very helpful thank you Gav.

So would I be correct in saying that the baseline plane is the plane where the female dovetail shoe of the mount (that screws onto the male dovetail bar of the scope) meets the the section housing the DEC axis. Would this be the same plane as the one you described? I have drawn a quick paint style sketch of what I'm describing. Is the top red plane the one you've referred to?

[choochoo_baloo]

didn't attach to previous post!

[PhotoGav]

Yes, it's that big top red plane, though I'm not sure it matters where it is exactly. The key here is that the camera is parallel to that plane.

Nice drawing by the way!

[choochoo_baloo]

Great, thanks. I didn't say it, but you're right, I meant that the baseline plane is parallel to the bottom surface 'plane' of the saddle piece.

Thanks for the help.