Does polar alignment need to be more accurate when.....?

[starman1969]

Taking images of objects on the celestial equator? I am pretty new to this polar alignment gubbins, but I've got an astrotrac RA axis guider now so I need to refine my technique.

This was a recent 3 minute test exposure of Orions Belt etc using a dslr & 200mm lens. I know that Mintaka is very close to the celestial equator so any trailing I would have thought would be more obvious. There is trailing but that could either be my slippery polar alignment or maybe a bit of wind.

[BinocularSky]

Taking images of objects on the celestial equator?

Yes, but it is most critical for altitude misailgnment when the object is near the horizon, so start tracking a star near the eastern horizon. The drift is minimal if you start tracking when your star is on the meridian. To check for azimuth misalignment, choose a star near the meridian within a declination of around +/- 30deg. For a full account of the method, see http://astunit.com/a...php?topic=polar

[Welrod50]

Hi Starman,

I can see your point here with this question, but to my mind, if you are doing any AP, a solid polar alignment is really a must come what may. You may find you can get longer subs unguided depending on your target and where in the sky it sits, but I would always do a good polar alignment and three star align with the mount. To be fair, there is evidence of trailing in your shot, but not much. I'd be pleased enough with it myself! I wouldn't have thought this was down to wind, as things would be more blurry as the mount would move in various directions if wind. Looks like tracking error (being a 3 minute exposure) to me. But considering this, I think the shot is fine.

Have a good Chrimbo

[kirkster501]

A nice picture all the same may I say? Very nice.

[peem]

very nice , you can even see the horse head nebula

[JamesM]

Congratulations on your image and I was rather impressed when I enlarged it. In addition to posting your question here, you can also post it over on the imaging section too though the advice given above has probably nailed it for you.

James

[BinocularSky]

For a full account of the method, see http://astunit.com/a...php?topic=polar

I've just added a few images to explain the drift, and why you have to choose a star where you do. (14 years ago, when I first did that page, we were all on dialup modems and images made a page load slowly!).

[starman1969]

Thanks for the replies. I was quite pleased with the image, too. I've not had it long so I'm still getting to grips with it.

I used the mount to do a series of 30 second subs of various objects. Now I just have to process them.

[robbieince]

Excellent image. As others have already said, the drift is most at the equator and zero at the pole so this is one of the worst case scenarios.

However, it doesn't look like trailing to me, but it does look like coma on the left side - maybe the image train is a bit tilted?

best regards, Rob