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Drizzle test on undersampled images
My currrent (relatively inexpensive!) CCD, an Orion StarShoot G3 Mono, has 752 x 582 pixels, with a pixel size of 8.5 microns. When fitted to a short-focal-length ED80T with a FR (FL = 384 mm), the image scale works out to be 4.65 arcseconds per pixel. Quite undersampled!
The obvious solution is to use the Hubble method - Drizzle. Nebulosity 3 software provides a good algorithm for this. So, taking 25 x 5 min subs (dithered), I had a play around with various settings to see what suited my gear best.
Attached are snapshots of a zoomed in part of an image, ordered as follows:
1. Single frame
2. Traditional align + combine stacking
3. Drizzle with pixel reduction = 0.6, image scale = 1.5 (Nebulosity default)
4. Drizzle, PR = 0.5, IS = 2
5. Drizzle, PR = 0.4, IS = 2.5
All have been pre-processed (bias, darks, flats) so they are clean.
In theory, provided I have enough subs, the PR = 0.4 and IS = 2.5 should be about optimal -- but a coarser Drizzle would be required if I had fewer subs, to avoid leaving holes in the image.
For reference, PR = 0.4 and IS = 2.5 gives me an effective resolution for the camera of 1880 x 1455, and a simulated pixel size of 1.85 arcseconds/pixel.
Comments?
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