Dither settings


#1

With the goal in mind to create a dither that does the most good and requires the least time to settle, are there any guidelines for using the dither settings combined with the dither settings in Phd?


#2

Hi Marty,

It really depends on your guidance system whether it’s short focal length guide scope or long focal length main scope using OAG. Typically shorter focal length (or smaller image scale) the higher dither. That seems to work in theory but that has not been my experience. I started guiding with C-8 at 2000mm focal length with OAG so I thought I should start at small dither but I never saw any movements so I eventually increased dithering until High Dither to make a difference.

Sometimes if the image scale differences between main and guide scope is great (at least 3x difference) then you will have to experiment. For very short focal length guide scope guiding a long focal length main scope, sometimes a small dither in guide scope can cause excessive dithering in main scope’s images so you will have to find a compromise.

So, I suggest to start at High Dither and Settle < 1.0 pixel. If you see excessive dithering in between subs, then reduce dither by one step and repeat.

Peter


#3

Hi Marty,
Let me echo what Peter has said.
I also use High Dither and a Settle value of <1.0 px. And it’s recommended to use a 2x multiple of your guide exposure (in PHD2) for the “Settle For” time in seconds. In my case, I use 5s exposure, so I should be using 10s for Settle For. However, it’s best to play with these recommendations to see what works for you.
FWIW, I use a 12LX200 with a f/7.16 ratio through the main path and an additional f/5.0 through the guide camera path. If my math is correct, I’m guiding around 1100mm.
Good luck,
Mark


#4

Thanks for the replies.

I have two scopes presently, a 450mm fl @ f/5 and 910mm fl @ f/7 and use both with an OAG. using a Lodestar X2 guiding camera. Would you still start with High Dither and < 1.0 pixel?

I guess I was wondering if there is a measurable guideline we’re aiming for ( i.e. a star moves a certain distance) as opposed to a subjective quick look. Also should I assume you’re not touching the dither setting in Phd and leave it at the default of 1?


#5

I consider my mount somewhat settling challenged. Consequently the <1.0 works for me. But YMMV.
I leave the PHD2 dither at 1.
Hope this helps.

Mark


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