Cone error

[libraryman]

Hi, a quick question about cone error and it's effects, if the telescope tube is not orthogonal to the mount does it effect guiding or any aspect of imaging if the mount is reasonably polar aligned?

i think i understand that it would make goto difficult but my mount is not goto, does it really make any difference, assuming of course that it's not mega out?

Ray

[ollypenrice]

I think the only issue would arise from polar misalignment. I've imaged with cone error arising from the use of a clamshell and had no bothers at short FL even with long subs. Polar misalignment may affect very long subs but I doubt that you have have an issue at more normal exposure lengths like 10 minutes.

Olly

[libraryman]

Thanks Olly, your input is appreiciated, it's not difficult to eliminate i know, but im thinking that if i'm spending too much time trying to perfect it, it would be overkill.

Ray

[Freddie]

There is a nice tutorial by Astronomyshed about cone error on youtube. Has some nice graphics to explain everything.

[cathalferris]

If you have a Goto mount aligned and working, and you then rotate the OTA for example to get a more comfortable eyepiece position, then if there is cone error present the goto will be off by a significant margin. 3-star alignments should account for the cone error present when the scope is set up first in a night's viewing.

This is why I set up my newt with the eyepiece in line with the weight bar of the mount, and pointing in the opposite direction (outwards from the mount) from the counterweights. This means that the eyepiece will always be pointing level or up when in use, and the only uncomfortable positions are when viewing close to the celestial pole. All other positions are easier as a result without having to rotate.