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Flats, Narrowband & general (ex.DSLR now CMOS)

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Apologies but I have done a search but can't quite find what I need.  My new setup is the ASI1600mm-cool with FW etc and having established that it all seems to work, based on some feedback from the people at Star Tools, it appears flats are NOT optional, though I was hoping to get some half decent results without them while i learned the setup, but no I now need to tackle them due to the absolutely vicious gradient and vignetting that seems to be blowing away any data particularly in my OIII and SII (and to a certain extent LUM) stacks.

I have a Neumann flat panel, and with my DSLR it was easy to just position the histogram peak 1/3 away from the left (or whatever it was) but I plan on using SG Pro's flat wizard, and it wants a target ADU:

Screen Shot 2017-01-29 at 09.30.50.png

So can anyone help with:

a. What this target ADU should be, and what is it a function of (e.g. Camera, light source etc)

b.  Should it be the same for each filter?

c. I've heard it said (written) that one flat can suit all, e.g one LUM can be applied to RGB as well, and one HA can do OIII and SII.  Any thoughts?  I assume this would depend on spotlessly clean filters

Many thanks, Andy

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Hi Andy

ADU is a function of camera but I believe SGPro converts the real ADU into a 16 bit equivalent. 

I aim for about 1/2 on the histogram so the default 30k works well (65k being max reading) with the 500 tolerance. 20k would give you about 1/3rd  

You want the same value for each filter. SGPro will try various exposures to achieve this. I find for LRGB I have exposures of 1s or less but my Ha filter takes about 12s. I use sheets of paper to diffuse the light source so I reduced the number of sheets to reduce the exposure for the Ha filter. 

If your filters give any vignette then you want to be sure it's the same for each filter. I'd recommend taking flats with each and seeing if they are the same. As you say, you need to be sure your filters are clean. 

Edited by Filroden
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I agree with that. In my case filters are a good way from the chip and are not the cause of dust bunnies, usually. These come from the chip window most of the time so I can often get away with 'one flat fits all.' If I can't I can't. You have to experiment - but flats are vital. If you don't have good flats, processing is a nightmare.


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I should have added that in the wizard, make sure to use the current sequence as the profile and have that set up to connect to camera and filter wheel. SGPro will then bring in both filters and bin mode into the wizard (in your screen shot it isn't showing the filters).

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