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Sam

Drift Alignment for Dummies - with a webcam

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This might be a little presumptuous of me to post this in the tutorial section but here's my guide to doing drift alignment. I'm only doing this as it took me ages to work out how to drift alignment and as a relative newbie to astronomy I found the theory behind drift alignment a bit too much like mental gymnastics:

My description is based around the following bits of equipment:

8" Newtonian Reflector

Long Exposure modded webcam

HEQ5 mount (the basic version not syntrak or pro or anything fancy)

Step One - Balance the mount.

The mount has to be level. Point the mount towards the North as accurately as you can, no big deal if you can't see Polaris. I use a ball bearing on the equipment tray and keep adjusting the legs until it no longer rolls off - seems to be quite effective.

Step Two - Setting up

Point the scope towards a clear bit of sky. Fit the webcam to the scope - crank up the gain to maximum - gamma on minimum and set exposure to about 5 secs. Focus the scope as good as you can. Point the scope to the south along the celestial equator (90 degrees south of Polaris). Make sure the webcam is lined up properly. If you press the RA button (either left or right) the stars should moved horizontally across the screen - adjust the webcams orientation in the focuser until this occurs.

Step Three - Sorting out Left and Right

Now there should be a couple of stars on the screen - if not move the scope around a little bit until you find at least one (or increase the exposure a bit, that might work). For this step don't worry about left and right movement. If the star tends to move down the screen then the mount is pointing too far East so you need to move the mount to the West. You can either use the adjustment screws or physically move the mount. Check it again and keep moving the mount either East or West as appropriate until the stars on the screen don't move either up or down. Obviously when you move the mount the stars that were in the screen won't be there after the adjustment but with the gain set up nice and high there should be plenty of other stars coming into view.

Step Four - The Up and Down

Swing the scope around to the East, as close to the celestial equator as you can so the screen will still have stars rather than blurry trees or buildings. Same deal as the above except that the adjustments are in the up and down of the mount - which is only adjusted through the adjustment screws - now if your scope is level and the latitude is set quite accurately this will be pretty close. If the East isn't very visible then point the scope to the West and do the same process (just the adjustments will be the opposite).

Step Five - Adjusting some more

Repeat steps Three and Four until there is no movement in the stars on the screen. To test for movement reduce the gain on the webcam and lengthen the exposure to 45-60 secs. I normally have to do both adjustments twice until it's seems good enough.

Step Six

All done - enjoy

Hope that helps, seems to work pretty good for me.

Sam

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Sam, this is soooo helpful. Only today I've been reading about drift alignment and as you say, "mental gymnastics".

Although I got the jist of what I read, you have put it into "words of one syllable" so to speak.

I am certainly going to refer to your instructions the next time I go out.

The only thing that I need to sort out is, when lining up the webcam, pressing the RA button left should move the star which way on the screen?

An extremely helpful tutorial, thanks.

Steve

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Steve, since mine's a Newtonian when I press the right button the star will move right (I better check that though next time I'm out tough) because everything is upside down and backwards.

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Very interesting little tutorial. You make it sound nice and easy! :D

However......For about £20 you can get hold of WCS and it makes it a whole lot easier again! You will get a display showing where to move the Alt/Az screws and the whole process can be completed in about 20mins or so :lol:

BTW I am not knocking your tutorial, ifI had not bought WCS I would be giving it a try myself. WCS basically works the same as you guide but works out what the correction should be for you.

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Very interesting little tutorial. You make it sound nice and easy! :(

However......For about £20 you can get hold of WCS and it makes it a whole lot easier again! You will get a display showing where to move the Alt/Az screws and the whole process can be completed in about 20mins or so :p

BTW I am not knocking your tutorial, ifI had not bought WCS I would be giving it a try myself. WCS basically works the same as you guide but works out what the correction should be for you.

A handy thread and one that I shall save - but - what is a WCS when you have one? ;)

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Cheers Dante, WCS is an application that works out the drift and how much you need to correct. Guidemaster does a similar thing and is free.

Sam

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Sam,

thanks for taking the time to write down your instructions. Just one point for the sake of clarity, once you have completed step 4 you need to repoint your telescope back South or North (I think),

cheers

Alan

cheers

Alan

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Sam,

thanks for taking the time to write down your instructions. Just one point for the sake of clarity, once you have completed step 4 you need to repoint your telescope back South or North (I think),

cheers

Alan

cheers

Alan

Good point Alan - cheers:)

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