Dithering Aggressivity

[aaron]

I just did some research on dithering and thought I'd share my findings.

If you don't know already, dithering is a process that introduces some intentional, random movement in between your individual images. This movement shifts any camera dead pixels or hot pixels around, so they better average out when stacking. Also, dithering can produce rounder stars if you also drizzle, since stars are round and pixels are square

My question was, how much to dither? AstroImager can set the dithering aggressivity, but that value relates to the guiding scope & camera. Pixels are different for my imaging scope and camera. What's the relationship?

Here's how I figured this out:

1. I decided that I wanted to move the main imager in the range of 10 pixels.
2. I used astronomy.tools to calculate the ratio of my guide scope to imaging scope. This takes into account the focal lengths of the two scopes, and pixel sizes of the two cameras.
3. The tool calculated an imaging / guiding ratio of 1 : 1.66.
4. I divided 10 pixels by the ratio 1.66, to find a guider dithering aggressivity for my system of 6 pixels. I used this value in AstroImager.

In other words, if my guider moves 6 pixels, my imager will move 10 pixels. This value was MUCH greater than the 1.5 pixels I picked previously, for who-knows-why reasons.

I hope this helps someone!
Aaron