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

M81-M82 widefield - work in progress

  • Please log in to reply
1 reply to this topic

#1 LarsMalmgren

LarsMalmgren

    Ranger 4

  • *****
  • topic starter
  • Posts: 313
  • Joined: 22 Jan 2010
  • Loc: Denmark

Posted 26 March 2020 - 05:34 AM

Hi,

 

Decided to post a work in progress image of the M81-M82 area.

M81-M82.png?raw=1

 

Telescope is Takahashi FS-60CB + Takhashi Sky90 reducer/flattener

Mount is EQ6-Pro

Camera QHY-163M cooled to -20C, filter IDAS LPS-D2

22 frames 360 sec stacked in DSS, darks subtracted but no lights or bias (yet)

I live in suburban/smallish town - sky was mag 20.5  (city turns off street lights after 1 am)

 

Image is stretched and very little sharpening and cropped. That's it.

 

Ok, the goal of my project here is to capture the IFN but nothing is showing, even if i stretch very hard.

So i'd like your advice on how proceed.

The histogram show clear space on the left side of the peak, so i'm guessing that longer exposures wont help.

So is my sky just not dark enough?  Or do i just press on and get much more frames?

 

Thanks smile.gif


Edited by LarsMalmgren, 26 March 2020 - 08:04 AM.

  • zjc26138, elmiko, deepwoods1 and 7 others like this

#2 steinw

steinw

    Explorer 1

  • -----
  • Posts: 66
  • Joined: 07 Aug 2014

Posted 26 March 2020 - 09:57 AM

I think you just need more integration time. I started a another thread here a couple of days ago where I could see traces of IFN around M81 from a more light polluted sky. ( https://www.cloudyni.../#entry10063912 ).

 

I have two suggestions:

 

1) Try without the IDAS filter. I have stopped using mine, as I could not really see any benefit on broad band targets like galaxies. I just ended up needing more integration time. I tested this some time ago on pretty short integration times compared to what you need to pick up the IFN, so I might be wrong. But I haven't used mine in a long time, and my gut feeling is that for a 20.5 sky there would be no benefit. As the cities are moving to broad band LED lighting there will be even less use for a light pollution filter.

 

2) Do the calculations to make sure you are really swamping the read noise of the camera with your current exposure and gain. I you do that your sky noise will be the limiting factor and you can just keep stacking the frames to get better signal/noise ratio forever - or as long as you have patience.

 

The area to the left of the peak in your histogram, assuming you have subtracted bias and darkframes, does not mean that you dont have a small IFN signal. It just means that the IFN signal is riding on the general sky noise signal (the big peak), and still buried (if you don't see it) in the gaussian noise of the sky signal. 


  • LarsMalmgren 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