Flats not right-but why

[andrew s]

If this were my problem I would try the following.

Take a set of flats with the ota pointing up. Make a master flats. Then take a few flats in each filter and process them as if they were target images images.

Are the vignetting and dust motes removed? If no then either the filter wheel is not accurately positioning the filters or the processing is incorrect. 

If ok take flats with the ota horizontal in at least two ways to maximise and drop or flop. Again process separately as lights if vignetting and motes not removed movement may be an issue.

If vignetting and drop removed then my bet would be different light path through ota for sky and panel as I proposed before. I would investigate this next even if it's not a longterm option.

Regards Andrew 

 

 

Edited May 20, 2023 by andrew s

[Rodd]

11 minutes ago, andrew s said:

he filter wheel is not accurately positioning the filters or the processing is incorrect. 

I have eliminated the filter positioning as I always shoot flats before any filter change--so the filter wheel is removed from the equation.  Not sure I understand about different light paths.  I will try and collect flats at different elevations, including horizontal, though it wont be easy to devise a way.  

[andrew s]

11 minutes ago, Rodd said:

I have eliminated the filter positioning as I always shoot flats before any filter change--so the filter wheel is removed from the equation.  Not sure I understand about different light paths.  I will try and collect flats at different elevations, including horizontal, though it wont be easy to devise a way.  

I should have made myself clearer.  The light from the sky is essentially from infinity and follows the design light path through the optics. The light from the light panel is from just above the corrector and is somewhat diffuse this will will illuminate the camera field  and dust particles differently to the sky. 

This results in different vignetting as well as differences in how the dust shades the camera and hence differences in the motes.

I am not clear if you see shifts in the position of the motes or just not fully removed. 

I would still do the first test just to prove the processing worked as expected. Gumption traps abound in my world.

Regards Andrew 

[Rodd]

12 minutes ago, andrew s said:

I should have made myself clearer.  The light from the sky is essentially from infinity and follows the design light path through the optics. The light from the light panel is from just above the corrector and is somewhat diffuse this will will illuminate the camera field  and dust particles differently to the sky. 

This results in different vignetting as well as differences in how the dust shades the camera and hence differences in the motes.

I am not clear if you see shifts in the position of the motes or just not fully removed. 

I would still do the first test just to prove the processing worked as expected. Gumption traps abound in my world.

Regards Andrew 

So sky flats should be better.  Unfortunately, without a difuser for teh C11, skyflats downt work.  I dont need a difusser for teh FSQ.  A diffuser will act like the panel.  I will see if I can change the angle.  As far as the dust miotes--I think they are just not being fully removed.  I have had dust spoecs move between lights and flats--that is different and not much to be done except not having dust specs.  

[carastro]

To be honest, I took the sample images you posted and stretched them to extreme.  I found no evidence of flats not working, I saw neither dust motes nor vignetting, only the background nebulosity you referred to in your first post.

Carole 

Edited May 20, 2023 by carastro