Dithering

[Darkstar_1]

is it possible to use dithering on a mount that is only driven in RA? thanks.

[Darkstar_1]

I would have thought someone would have known.

 

[Davey-T]

Only in RA I guess, don't know if PHD or maybe APT supports dithering on one  axis, have a browse of their instructions.

Dithering is one of those things that you don't need to try until everything else in your imaging set up is working.

Dave

[Oddsocks]

Yes, you can dither in RA only.

In some guiding software packages you are given the option of deselecting dither in DEC and only dither in RA to counter large backlash in the DEC gears that causes residual movement in DEC long after the dither command has completed.

If using a manual mount that is not auto guided it can be a little tricky to "blip" the RA drive using the motor keypad, you need to be random in the ammount the mount moves each time and only move the target object by a few pixels.

If there is a large backlash in RA you need to pause for at least ten seconds or more after issuing a dither command and before starting the exposure to allow the RA worm to catch up with the gear otherwise you will have oval stars.

[ChrisLX200]

On 02/02/2016 at 11:43, Darkstar_1 said:

is it possible to use dithering on a mount that is only driven in RA? thanks.

Well no you can't, at least not in both axies (and doing it only one would leave you with smudgy lines). Dithering means to randomly move the FOV around a given radius from a centre point so hot pixels and clumps causing colour blotching are evened out. Dithering is very useful for DSLR imagers as it does reduce the colour blotches significantly, but you must use a larg-ish dither radius (and both axies..)

ChrisH

[Darkstar_1]

Thanks for that.

[ollypenrice]

In reality you won't be perfectly polar aligned and this misalignment will give you a natural dither. If you're not guiding in Dec then you are sure to get some dither from this misalignment. Besides, you don't have to dither via the guiding/capture software. You can stop the guider for a few moments between subs, or give the mount a little nudge from the handset, and you'll still get a huge benefit in terms of noise reduction. Even if it isn't nudged between every sub you'll see a benefit.

Olly