Unguided dither scale

Hi everybody,

I am trying to get some unguided imaging going with my SB Myt + Tak FSQ106.

I am shooting the SMC with a very high DEC.

I am having good star shapes with exposures of up to 5min, actually maybe even better then with guiding. Guided dithering recovery is also a bit of a nightmare at this extreme DEC.

Just a question on unguided dithering scale… I see my dithers are much bigger than the expected max 3px specified in my sequence and when I dither guided.

How are voyager determining and issuing the dither sizes? It seems like the move command is overshooting the 3px scale max move. As far as I can tell my equipment, focal length and imaging scale is set correctly in Voyager.

I must note that I am seeing degrading pointing at the extreme DEC as well, so I dont know if the 2 is related. I am running TSX as telescope control.


Hi JDeacon,

i find the same problem…i setting 3 pixel of dithering but the immages are shifted moore of -+3 pixels!?

There is no problem with unguided dithering, simply the only way to dither is by using the movement of the mount. Despite the calculations for 3px, depending on your scale resolution, the place in the sky and the goodness of your mount and your model, you can have a greater or lesser deviation. The purpose of dithering is not to split the hair to get 3px but to avoid noise patterns. Remember to also use realign if you don’t guide to re-center the subject every X minutes. The X depend on your resolution and the size of your sensor.

Guiding, pointing (and dithering) is something really hard where you are nearest the celestial poles.


Yes there is nothing wrong with unguided dithering in Voyager… but it is something to be aware of that your unguided dither sizes can be different than what you are ‘used to’ with normal guided dithering. This also definitely seems to be influenced by where you are pointing in the sky. Like my case with a target pointing close to a celestial pole, you might see more severe differences.

This is also true for pointing accuracy, my Myt normally points beautifully, but close to the pole, it often needs a second or third pointing to get within tolerance.

I just did a few test runs testing different dither scales, until I am happy with the dither it gives me, I ended up using a small move only 0.7px, to give my a nice small dither. I usually use 2-3px when doing guided dithering.

I had my first session shooting the large mosaic over the SMC the weekend. Effortless with Voyager is all I can say! All Dragscripted and fully automated, I just get the telegram texts as it jumps from panel to panel! Going unguided on the project is also a first for me, and it is an absolute pleasure!

Maybe in a different thread I will share a bit how I tackled the project and my learnings.

Best Regards,

This should be part of every astrophotographer’s baggage when tackling complex or challenging projects.
Congratulations on your activities Jacques.

All the best