Decided on the Vixen Atlux : is buying an autoguider (OT or Qguide type) overkill ?

[Ian Robinson]

I have decided on a Vixen Atlux with tripod.

I've seen claims of low single digit tracking error under tuned PEC when when polar aligned without autoguiding, which is pretty impressive and clinched it for me.

So since my biggest telephoto is 200mm fl using this with my trusty old Minolta XD5, and I am considering getting a 300mm fl lens with the Canon 40D then from another thread here :

200mm 6° 21’ 14" x 4° 14’ 17" with pixcel size 5.889" if I can get an adapter
300mm 4° 14’ 17" x 2° 49’ 34" with pixcel size 3.926" on a 40D

prime focus 1170mm 1° 5’ 13" x 0° 43’ 30" with pixcel size 1.007" on a 40D

If properly polar aligned as opposed to a rough polar alignment (two star computer alignment), will the Atlux better this once PEC has tuned the drive making autoguiding superfluous (and overkill in most cases) ?

[[1ponders]]

Ian even with plate scales (pixel scales) of 5.9 arcsec/pixel and 3.9 arcsec/pixel, and using an Atlux mount unless your polar alignment is very accurate you will still get Declination drift over time. How quickly your drift will become noticeable depend on the amount of the error in your altitude and azimuth misalignment. This is the value of the autoguider, not only to take care of periodic error but to correct for polar misalignment that would affect declination drift. Its a long call but I would say that any focal length over about 100-135mm would benefit from autoguiding, as a general rule.

[[1ponders]]

btw your alignment using either one star or two star will not make any difference. This alignment is only for your "pointing" accuracy not your polar alignment accuracy.

[Zuts]

Hi,

I am out there to take photo's. It takes me roughly 40 minutes to get a reasonable polar align on my scope/mount as I have to setup afresh each time in the park. Now, I could spend a few hours doing it and try and get it exactly spot on, but whats the point as after my imaging run i will just pack it all away; and with the autoguider I get nice round stars.

I rely on the autoguiding to allow me to do 5 to 10 minute subs on an EQ6 with a 600 mm FL scope. As Ponders says it corrects my polar alignment error and gives me more time to image. Maybe if i had a permanent observatory (and a better mount) i woud spend more time polar aligning.

You are already spending a lot on an Atlux, a QHY5 and a small guide scope isn't all that much more.

By all means though, try it first and see how you go, then decide if you want to get an autoguider.

Paul

[gbeal]

Nope, you'll be back for the auto-guider, like the knowledgeable posters have stipulated. You could try the shorter camera lens as a guide-scope though, if you can fit it to the scope/mount, and the Q to it.
Gary

[montewilson]

Actually the shorter the FL of the camera lens the more important the accuracy of your polar alignment also becomes. Sounds strange but its true. If you are even a bit off you will get field rotation in your shots. Guiding can't fix that either.

To get polar aligned well, you will need to do a decent amount of drift aligning but I think modern autoguiders can be used to speed up the process by showing the drift much faster than you can visually perceive it.

I spend about two hours getting the alignment right because rotation is really obvious with my FSQ and STL. In my case I use the super accurate Tak polar scope, TPoint and Automapper (which I am not saying you should) even then it takes me quite a while.

In short, yes you should get the guider but happily these days guiders are not expensive nor hard to use.

[g__day]

Without a tripod - so is it going to be permanently pier mounted?

The 3 star unaligned sky model - does give me pretty good results - but as said - great tracking won't help star field rotation if you're off target!

I auto-guide about 70% of the time!

[Ian Robinson]

Thanks all .... got some good food for thought.

I hadn't considered the field rotation issue in wide field long exposures, never noticed it , but never blown up more than to 4"x6" from 35mm negs and usually kept my astrophotos under 20min , manual guiding longer was way too tedious

[Ian Robinson]

Ordered it this afternoon :)

Under 7000 AUD w/ tripod and dovetail adapter + shipping. (NOT A FOREIGN DEALER).

No decision on the autoguider , or even if I need one.