Image orientation

[grimsay (Iain)]

Hello,

I have a question re. image orientation (if that's the correct term?). I was setting up my finder scope on my new SW 8 dob in daylight the other day and noticed that the image in the primary scope was not upside down as I expected. Rather is seemed to be angled at about 150 degrees.

The image in the finder scope was rotated a perfect 180 as I expected.

The result is that whilst trying to learn to track (? - navigate) in reverse would be confusing enough, doing so on angled axis is more so I believe.

Is the angle normal? And if not what can I do to adjust?

Cheers, Iain

[barx1963 (Malcolm)]

Iain
A very interesting question. The short answer is that it is caused by the fact that the eyepiece is not horizontal but at an angle. If you do the same thing with a big dob where the eyepiece sit on the side of the scope it sits at a different angle.
The critical thing is not to worry about it when using it for astronomical work. After all there is no up or down in space!!

When observing we quite often want to know what direction things are in relation to each other. For example if we find a bright star in the eyepiece and we know that a galaxy is 10 minutes to the east of it, how do we know where to look? For a newtonian like your scope a simple way is watch the star drift in the field of view, that tells you what direction west is. From that we now know east also and north always lies counter clockwise from west.

Cheers

Malcolm

[grimsay (Iain)]

Thanks Malcolm, feel a bit silly now seems rather obvious now.

I've had it out twice over the past 2 nights an I'm getting used to the movement already.

Cheers, Iain

Originally Posted by barx1963

Iain
A very interesting question. The short answer is that it is caused by the fact that the eyepiece is not horizontal but at an angle. If you do the same thing with a big dob where the eyepiece sit on the side of the scope it sits at a different angle.
The critical thing is not to worry about it when using it for astronomical work. After all there is no up or down in space!!

When observing we quite often want to know what direction things are in relation to each other. For example if we find a bright star in the eyepiece and we know that a galaxy is 10 minutes to the east of it, how do we know where to look? For a newtonian like your scope a simple way is watch the star drift in the field of view, that tells you what direction west is. From that we now know east also and north always lies counter clockwise from west.

Cheers

Malcolm

[csb (Craig)]

Thanks Malcolm

I never realised about watching drift direction. A great tip!

[Wavytone]

Originally Posted by barx1963

After all there is no up or down in space!

But... relative to earth (or the sun for that matter) there's a definite direction of rotation, defined by the polar axis (earth) or the axis perpendicular to the plane of the ecliptic.