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Bried

A question about guiding

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Hello there,

At some point in the future I'm hoping to get my scope guided for astrophotography and I was just curious about some finer details.

I was wondering if a scope is guided is there still a need for the mount to be accurately polar alligned? My thinking is that if the mount is almost alligned but maybe slightly out, won't the guided tracking compensate for the error and keep everything tracked without any star trails occuring.

Regards

Brian

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Hi Brian,

Alignment is very important for you to get the most out of the guiding. The minimum amount of error you can put in to your setup, the better and easier your imaging session will be. Guiding will help to a degree, but guiding also has to cope with the errors in the mounts motor, and the environmental conditions, like weather, balance and vibrations. The more errors in your setup, the more dramatic the steps the guider has to make.

The more accurate your setup, and the more you can reduce the errors, the longer the sub length and the better the quality of sub (ie, nice round stars, not egg shaped).

I hope that helps

Keiran

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If you guide, then the star you picked for guiding will not move in the image (it may even be outside the image depending on how you have things set up) BUT if you aren't polar aligned then everything else will slowly rotate around that star - with the result that stars can turn oblong during long subs.

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there is an expression i read somewhere regarding guiding "the best guided scope is the least guided scope" having been through the trials and tribulations of guiding recently , the least of your worries will be polar alignment :grin:

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One caveat; a small error in PA (note small) can have two advantages. One, it means that DEC corrections tend to go in one direction only, so reducing the danger of oscillating across the backlash. It can even allow you to DEC guide in one direction only, so reducing the risk of over correction. Two, the small drift of the object over time introduces a little natural 'dither', meaning that the same pixels don't always sample the same bit of sky all through the run. If you have too much error in PA longer subs will show rotation. If, over a four hour run, your first and last subs are a few pixels out (as seen by the misalignment of their edges) then you are unlikely to have a problem.

In this case small does need to be small but I'm happy with good but not perfect PA. If you start trying to make a parallel rig of two imaging scopes then you enter a new world and PA really does have to be bang on the money.

Olly

Edited by ollypenrice

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The good news is that the software for auto guiding also makes it much easier to polar align your mount.

So while you really do need to get your mount polar aligned, it isn't a thankless tedious chore, and it will improve the quality of your images no end.

Cheers

Tim

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The good news is that the software for auto guiding also makes it much easier to polar align your mount.

So while you really do need to get your mount polar aligned, it isn't a thankless tedious chore, and it will improve the quality of your images no end.

Cheers

Tim

Your guiding with an EQ6 is legendary, Tim. Do you just get the PA as good as you possibly can?

Olly

Edited by ollypenrice

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