Drift alignment on a AVX mount

[gonzostar]

Hi I have a 8"SCT on a AVX mount. I try to do some imaging but restricted to 2 minute subs due to a unguided set up.

Would you recommend drift alignment with this mount also. The reason to ask is that you can do 2 star alignment then 4 calibration stars. Aswell as a facility ti align  the mount 

Is it still necessary to drift align for 2 minute subs after doing all of the above?

Cheers

 

Dean 

[Joel Shepherd]

The 2x4 alignment procedure makes GOTO -- the initial aiming of the scope at your target -- more accurate. It doesn't help much with polar alignment which is what you need as a starting point for accurate tracking while making exposures. For that you should use the "All Star Polar Alignment" routine built in. Essentially (assuming you're in the northern hemisphere), find a "named" star to the south and near the meridian, center it, push the Align button, select Polar Align and Align Mount. It'll back off and slew to the star and you'll center it again. Then it will back off and slew a final time: this time instead of using the hand controller to center it in the eyepiece, use the mechanical altitude and azimuth adjustment knobs (you're shifting the position of the mount itself). I usually repeat that whole procedure twice: if the scope is very far out with regard to polar alignment, then aligning it will throw the GOTO alignment off: you just shifted the whole sky as far as it is concerned. At that point you can consider drift alignment though I've never found it necessary (for unguided exposures up to 90 seconds or so: two minutes will be a stretch). For longer exposures, I'd invest in guiding: the mount probably has a lot of periodic error that no amount of drift alignment will correct but which autoguiding can manage.

[gonzostar]

Thanks for this information Joel. Will do the procedure twice. How much notice do you give when it gives you alt, azm readings in the polar alignment?

[Joel Shepherd]

Well, I'm happy with zeroes straight across, or a one at the very end. :-)  I've heard that isn't in fact perfect: you could do better if you then went on to drift align, but it's definitely workable. A more error on the first alignment is fine; it's the second one that matters.

[gonzostar]

Never quite managed zeros across the board yet!

[Joel Shepherd]

Do you have a reticle eyepiece like http://www.amazon.co.uk/Orion-Illuminated-Reticle-Telescope-Eyepiece/dp/B000J5OTBM ? It's a huge help for making sure stars are consistently centered in the eyepiece, which could help get to a better alignment.

[orley]

18 hours ago, Joel Shepherd said:

Do you have a reticle eyepiece like http://www.amazon.co.uk/Orion-Illuminated-Reticle-Telescope-Eyepiece/dp/B000J5OTBM ? It's a huge help for making sure stars are consistently centered in the eyepiece, which could help get to a better alignment.

It certainly does help! However, FLO sell a SkyWatcher reticle eyepiece that's a lot cheaper.

[fwm891]

You can also do the procedure photographically with liveview and use cross hairs on the image to centre on

[gonzostar]

Quote

 

Thanks for the advice i do have now a reticle eyepiece. It certainly does make things easier the a 7mm eyepiece and a barlow lens!

Do you still use barlow with the reticle eyepiece to decrease the FOV? Does it make centering the target star more accurate? 

[Davey-T]

7mm on it's own should be fine.

I usually do a ten minute last drift to check its OK you can see it wandering with PE.

Dave