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

First time Astrophotography.

  • Please log in to reply
6 replies to this topic

#1 Stumyatt76

Stumyatt76

    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 30 Mar 2018
  • Loc: Gloucester UK

Posted 24 October 2021 - 09:20 AM

Hi. 

 

I have decided to get my first telescope and mount and really keen to start Astrophotography. I have spent a few weeks getting to know the rig and setup sequence generator pro. 

 

Quick question. I’m keen to do deep sky imaging but unsure how long the exposures should be for and how many to do. Is it just trial and error or is there a rule of thumb. Also i have a ZWO ASI1600. For the gain settings is there any presets listed anywhere or again in this all trial and error?

 

many thanks in advance and apologies if i sound completely out of my depth. 

 

Thanks 



#2 B 26354

B 26354

    Vanguard

  • *****
  • Posts: 2,252
  • Joined: 05 Jan 2017
  • Loc: Southern California semi-desert (NELM mag 5.3)

Posted 24 October 2021 - 09:29 AM

https://www.amazon.c.../dp/0999470906/

 

grin.gif



#3 jonnybravo0311

jonnybravo0311

    Mercury-Atlas

  • *****
  • Posts: 2,951
  • Joined: 05 Nov 2020
  • Loc: NJ, US

Posted 24 October 2021 - 09:37 AM

Exposure length varies greatly depending on the optics, the sky conditions, the camera settings, etc. The general rule of thumb is to ensure you swamp the read noise by a significant amount. Applications like SharpCap and NINA provide tools to calculate "optimal" exposures.

 

Bracken's book (linked in the post above mine) will help you understand these concepts and more :)


  • Stumyatt76 likes this

#4 DirtyRod

DirtyRod

    Ranger 4

  • *****
  • Posts: 343
  • Joined: 23 Mar 2021
  • Loc: Arizona

Posted 24 October 2021 - 09:40 AM

Good book. I can't remember if the book covers it but often your exposure length is limited by your mount. In my case, I've struggled to get consistent guiding and 120s is my limit with 60s being optimal. Longer than 120 and I'm throwing out most of the data due to elongated stars. This is why you hear so many people talk about the importance of the mount. 

 

So, being that I'm limited on exposure length, often the gain is set higher that recommended to compensate for the shorter exposures. I always start by looking that the optimal camera setting that provides the least amount of noise with the best dynamic range and start from there. 


  • Stumyatt76 likes this

#5 bobzeq25

bobzeq25

    ISS

  • *****
  • Posts: 26,278
  • Joined: 27 Oct 2014

Posted 24 October 2021 - 09:41 AM

Hi. 

 

I have decided to get my first telescope and mount and really keen to start Astrophotography. I have spent a few weeks getting to know the rig and setup sequence generator pro. 

 

Quick question. I’m keen to do deep sky imaging but unsure how long the exposures should be for and how many to do. Is it just trial and error or is there a rule of thumb. Also i have a ZWO ASI1600. For the gain settings is there any presets listed anywhere or again in this all trial and error?

 

many thanks in advance and apologies if i sound completely out of my depth. 

 

Thanks 

(Sub) exposure.   Like much in AP. you really need to understand the theory.

 

Too short subexposure, and too many subs, and you get too much read noise, which accumulates per sub.  Too long, and too few subs, and you saturate the camera, ruining star color, and blurring highlights.

 

You need to balance those things.  There are some different methods.  I like this.  Easier than it may sound.

 

Take a light and a bias.  Subtract the average ADU (digital units), get the corrected light adu.  This essentially measures your light pollution level and optical speed, both of which greatly affect subexposure.  This is why what others use is usually of no importance to you.

 

Using data on the ZWO webpage, convert to electrons.

 

Take the read noise, also on the ZWO webpage, and square it.

 

You want the first number to be 5-10X the second.

 

Number of subs.  More is better, and this is more important than the above.  What counts is the total number of photons you collect, how you break that into subs is less important.  At least one hour total imaging time.

 

Key mistakes to avoid.  Skimping on the all important mount.  It's not intuitive how good a one you need, or what it costs to make a mount that good.  Getting too big a scope.  That makes a difficult task much harder.

 

If you're spending more on the scope than the mount, that's a red flag.


Edited by bobzeq25, 24 October 2021 - 09:42 AM.

  • Stumyatt76 and jonnybravo0311 like this

#6 kathyastro

kathyastro

    Soyuz

  • *****
  • Posts: 3,838
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 24 October 2021 - 09:44 AM

The most important piece of equipment is the mount.  Don't skimp on it.  The rule of thumb is to get a mount that has a weight rating of double the weight that you intend to put on it.

 

Exposure times will vary a lot, depending on sky conditions, target brightness, mount stability, focal length, focal ratio, camera performance.  Too many variable to give a quick answer.  For DSO imaging, you should probably aim for a total integration time (i.e. total of all your subs) of 30-60 minutes.  And then go up from there depending on results.


  • Stumyatt76 and jonnybravo0311 like this

#7 Stumyatt76

Stumyatt76

    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 30 Mar 2018
  • Loc: Gloucester UK

Posted 24 October 2021 - 10:23 AM

Thanks all for the advice. I have purchased the book. Hopefully it will point me in the right direction


  • bobzeq25 and B 26354 like 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