SCT collimation (indoor vs outdoor)

[Nightingale]

I realised that indoor collimation using the hubble artificial star never matches up with a star test outdoors.. ie. When i collimate indoor, i get perfect donuts.. but when i take it outside, the doughnut is skewed.. and the images from my single shot dslr shows more rounded stars with the real star collimation.. my question is; is the indoor collimation the correct method and am getting skewed donuts outside due to atmospheric conditions? Or is the outdoor collimation the one to use as the stars are at infinity rather than the 30 feet artificial star?

[StuTodd]

The reason you get "good" collimation indoors and it changes when outside is because the scope isn't thermally stabilized.

This is possibly the most important step so always collimate outside after the scope has been sat for an hour or so.

[multiweb (Marc)]

Depending on the FL and aperture of your SCT you might have to add extension tubes at the back to try to keep the primary in its ideal position when using an AS indoors because of the short distance. AS are good to get you close as you're less affected by seeing but to finish off do it on a real star.

[Nightingale]

Err.. checked it again tonight.. extremely pristine skies and no wind.. i think it was all atmospheric to begin with.. but i still need to do a fine tune.. thanks for all yr thoughts