Do I need to dither lights darks flats bias and dark flats or just my light frames?

[Quetzalcoatl72]

I think i know what dithering is but i've only been doing that with lights during the sequencing in nina, do i need to do that for all my other calibration frames?

[tooth_dr]

No, you just need to dither lights.

[teoria_del_big_bang]

3 hours ago, Quetzalcoatl72 said:

I think i know what dithering is but i've only been doing that with lights during the sequencing in nina, do i need to do that for all my other calibration frames?

As @tooth_dr says just dither for lights.

The idea is that whilst the camera is taking an image the scope follows the target perfectly (or as well as it can within the limits of your guiding) but then for the next image it just moves the scope a little so that the next image is a few pixels over one way, then the image after that it will move it a few pixels  in another direction. 
So over a session it will keep dithering around a position never moving more than a few pixels from where you took the first image but not taking all images in exact same position.
So when it comes to stacking the pictures together it will line up all the stars but any hot or cold pixels will not all be in same position on all the frames and so the software in the stacking program can remove them.

When taking darks or flats you are imaging either darkness or a light source at the end of the scope so dithering would not do anything. 
I guess the only time taking flats may have an issue is if you were to take them using a white T-shirt method and the dawn sky and kept tracking on the scope if it caught a few of the brighter stars or a planet but most people use a flat panel of some description, and dithering would probably not really help that in any case.

Steve

[ollypenrice]

Darks can't see out of the scope so there's no point in dithering those!  As Steve says above, if using a fixed light source for flats you don't need to dither. If you're at all worried that your light source is uneven you could move it around a little or rotate regularly during the capture sequence but that's unlikely to be necessary. However, picking up stars is indeed a risk if doing twilight flats. Leaving a few seconds between flat exposures will, if the mount is undriven, give you natural dither as the stars move. It will also stop your chip heating up which can sometimes happen with flats.

Olly

[alacant]

3 hours ago, ollypenrice said:

 

Edited January 9, 2022 by alacant

[alacant]

Phew. Never come across that. Use a light source other than the sky?

Edited January 9, 2022 by alacant

[Quetzalcoatl72]

On 09/01/2022 at 16:19, ollypenrice said:

Darks can't see out of the scope so there's no point in dithering those!  As Steve says above, if using a fixed light source for flats you don't need to dither. If you're at all worried that your light source is uneven you could move it around a little or rotate regularly during the capture sequence but that's unlikely to be necessary. However, picking up stars is indeed a risk if doing twilight flats. Leaving a few seconds between flat exposures will, if the mount is undriven, give you natural dither as the stars move. It will also stop your chip heating up which can sometimes happen with flats.

Olly

My flats are done with the screen and t-shirt method, the dust picked up looks like rings, the pictures are still dark gray, i've seen a lot of light greys or even other colours like pink. I don't know what the deal is with that, and I hope my flats are addicuate.

[Quetzalcoatl72]

On 09/01/2022 at 09:34, teoria_del_big_bang said:

As @tooth_dr says just dither for lights.

The idea is that whilst the camera is taking an image the scope follows the target perfectly (or as well as it can within the limits of your guiding) but then for the next image it just moves the scope a little so that the next image is a few pixels over one way, then the image after that it will move it a few pixels  in another direction. 
So over a session it will keep dithering around a position never moving more than a few pixels from where you took the first image but not taking all images in exact same position.
So when it comes to stacking the pictures together it will line up all the stars but any hot or cold pixels will not all be in same position on all the frames and so the software in the stacking program can remove them.

I thought that was the case, I'd like to keep the images centered especially if i want to capture multiple objects at once like galaxy clusters

[ollypenrice]

On 09/01/2022 at 21:19, alacant said:

Phew. Never come across that. Use a light source other than the sky?

Play nicely.