Dithering

[Carole]

this has been an interesting discussion, 

drizzle during processing

But we need one now on Drizzling which I haven't a clue about. 
think we need to start a new thread for that, so will start one. 

Carole

[RobertM]

Hi,

Bit busy at the moment, but if you have undersampled a small star to less than one pixel, it does not make any difference what you do with it, its still the shape of the pixel. Which is one of the reasons I don't like uba wide field images, they just look like a field of little blocks, not stars.

Chris

P.S. http://www.ccd.com/ccd113.html

Sorry Chris, usually I agree with you but in this case that will  only be the case if all the light from a star falls exactly on one pixel (which is rare but maybe that's what you meant in which case I fully agree).  If it falls on more than one pixel then the star centroid is offset by a sub pixel amount and can therefore be derived at a greater accuracy.  It's this that we rely on for sub pixel guiding accuracy.

Robert

PS. Carole, you are a whole heap of trouble !!!

[Carole]

 

[MarkS]

Sorry Chris, usually I agree with you but in this case that will  only be the case if all the light from a star falls exactly on one pixel (which is rare but maybe that's what you meant in which case I fully agree).  If it falls on more than one pixel then the star centroid is offset by a sub pixel amount and can therefore be derived at a greater accuracy.  It's this that we rely on for sub pixel guiding accuracy.

Indeed, and this is why many people recommend guiding on a slightly defocused star - to ensure the star covers a greater number of pixels.

Mark

[Rocket Pooch]

Rob and Mark,

I agree with you both, if the star is on one pixel, as I suggest a larger box is a larger box. 

Still holding out on the defocused guide star, but I do understand why people do that as well, esspecially if they are guiding with a very short focal length guide scope, then spreading the star over at least 4 pixels is a good move.

Chris