Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Zwo asi294mm pro flats

  • Please log in to reply
6 replies to this topic

#1 redfox

redfox

    Sputnik

  • -----
  • topic starter
  • Posts: 31
  • Joined: 26 Aug 2010

Posted 25 November 2023 - 08:53 AM

Hello have just gone from the asi1600mm pro to the asi294mm pro and i believe my flats need to be at least 4 seconds long with a mean adu of 30,000 problem i have the more sheets of white paper i add to get a luminance filter to 4 seconds makes my ha filter 80 seconds to get to 30.000 adu.

Any thoughts on why my luminance filter takes so much dimming down compared to ha etc,I'm using bin 2x2 for flats.



#2 Chrisofweden

Chrisofweden

    Messenger

  • -----
  • Posts: 401
  • Joined: 12 Mar 2021
  • Loc: Västmanland Sweden

Posted 25 November 2023 - 09:41 AM

The Luminance filter passes ALL the light thru to the sensor. The Ha filter only passes the light at (and around) the wavelength of Ha emission. This is the intended purpose of the NB filters.
The filters are doing their job, in other words, even though that in itself makes taking flats with NB filters (particularly SII and Ha) a bit of a challenge sometimes.
Hope this explains :)
/Chris
  • redfox likes this

#3 idclimber

idclimber

    Fly Me to the Moon

  • *****
  • Posts: 6,698
  • Joined: 08 Apr 2016
  • Loc: McCall Idaho

Posted 25 November 2023 - 10:37 AM

There is a lot of variability with that sensor. Try 2" exposures and see if they work. 


  • dswtan and redfox like this

#4 Drothgeb

Drothgeb

    Surveyor 1

  • *****
  • Posts: 1,705
  • Joined: 12 Jan 2022
  • Loc: Maryland

Posted 25 November 2023 - 12:04 PM

My most used camera is a 294MM. Before you decide that you need long exposures flats, try a regular short exposure flat and see how it works. You may find that you don’t need a long exposure. And if you can do short exposure flats, then you can use bias frames instead of flat darks. Although, flat darks still work best.

 

The 294MM has a few issues that affect some cameras. But the one you need to be particularly careful of, is how the camera’s software handles short exposure, then hands off to the imaging software a 1 sec for longer exposures. There is often a lack of linearity at this point. So calibration frames less than 1 second, don’t work properly with exposures of more than 1 sec. When that happens, the flats don’t correct properly. I see that every once in awhile, but not very often, with my camera. I usually use a light panel to do short exposure flats and equal length flat darks. If I have a problem with the flats correcting, then I’ll go back and shoot long exposure flats and flat darks. Out of all the imaging I’ve done this year with that camera, I’ve only had to do that once. 

 

Another thing I’ll mention is how that camera produces pretty ugly flats when used with Ha and Sii filters. That’s due to a poor job of coating the imaging chip. It varies camera to camera, but looks pretty bad with mine. If you notice it, don’t worry, flats will correct it.
 


  • redfox likes this

#5 redfox

redfox

    Sputnik

  • -----
  • topic starter
  • Posts: 31
  • Joined: 26 Aug 2010

Posted 25 November 2023 - 03:24 PM

Thanks all for your help. I did my Ha at 8 seconds,Sii at 12.7 seconds and Oiii at 1.74 seconds at roughly 30.000 adu each and all seems to have worked out i think when i do some luminance flats i will have to reduce the light strength more to get a longer exposure. 



#6 redfox

redfox

    Sputnik

  • -----
  • topic starter
  • Posts: 31
  • Joined: 26 Aug 2010

Posted 25 November 2023 - 03:28 PM

My most used camera is a 294MM. Before you decide that you need long exposures flats, try a regular short exposure flat and see how it works. You may find that you don’t need a long exposure. And if you can do short exposure flats, then you can use bias frames instead of flat darks. Although, flat darks still work best.

 

The 294MM has a few issues that affect some cameras. But the one you need to be particularly careful of, is how the camera’s software handles short exposure, then hands off to the imaging software a 1 sec for longer exposures. There is often a lack of linearity at this point. So calibration frames less than 1 second, don’t work properly with exposures of more than 1 sec. When that happens, the flats don’t correct properly. I see that every once in awhile, but not very often, with my camera. I usually use a light panel to do short exposure flats and equal length flat darks. If I have a problem with the flats correcting, then I’ll go back and shoot long exposure flats and flat darks. Out of all the imaging I’ve done this year with that camera, I’ve only had to do that once. 

 

Another thing I’ll mention is how that camera produces pretty ugly flats when used with Ha and Sii filters. That’s due to a poor job of coating the imaging chip. It varies camera to camera, but looks pretty bad with mine. If you notice it, don’t worry, flats will correct it.
 

As you said they sure are some ugly flats Ha is the worst,Sii and Oiii good.



#7 dswtan

dswtan

    Vanguard

  • *****
  • Posts: 2,060
  • Joined: 29 Oct 2006
  • Loc: Morgan Hill, CA

Posted 25 November 2023 - 04:16 PM

I can go below 4s with no issues for my LRGB. But others have had trouble as mentioned. Here are my current flats at unity gain on my two 294MMs at f/4.8 and f/7.

 

Note I'm down to 0.03 sec on the f/4.8 for my Luminance (Astronomik L2). I would *NOT* expect this to work on the much trickier 294MC, but I think there's much more leeway on the 294MM.

 

Flats UP 2023
 
Flats DOWN 2023

 


  • redfox likes this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics