Hey everyone! I recently started to dive into the world of astrophography and have been loving it so far, I have a sky watcher adventurer GTI And a dslr. Theres a couple of things I’ve been running into that are causing me issues. First off, Before I had my star tracker I was taking one second exposures at 6400-3200 ISO and the background was completely dark, However now with these longer exposures with a star tracker (20-30 Second exposures) with an iso of around 400, after stacking and auto-stretching/background extraction with siril, I am seeing colored background (From what I presume is light pollution) How may I fix this? I’m using siril with background extraction and auto stretching. Another thing I’m uncertain of is, After I snap my photo, where should the histogram be? I don’t know if i’m under-or overexposing, Ill also attach a photo of my most recent orion nebula photo! I shot it at iso 400 with 20 second exposure.
Thank you very much for taking the time to read this! Have a great day :)📷 c791c5e2-106e-4a90-9c4e-88735f92d943.jfif
New to astrophotography! Trying to see how best to capture and edit DSO In bortle 8 class skies.
When you are shooting with such a wide angle lens, my first guess would be that there is some light source nearby that is causing the gradient. I’ve gotten them from things like running a little gas heater near my scope.
When I used a DSLR (Canon), I usually kept my histogram peak about 15% of the way from the left edge. What you want to avoid is saturating stars, as you lose the color and they start to bloat. So that little spike at the far right of your histogram is something to keep an eye on.
First off, don’t worry about the histogram. In astrophotography, sub exposure length is determined by read noise and light pollution levels. Go too short and you will have a buildup of noise, go too long and the image will be washed out and filled with gradients as you’ve seen. Under B8 skies, without filters there are going to be practical limits to sub exposure time, especially with a wide and I assume fast lens.
I would try shortening the sub exposure time. How deep you can go is determined by not how long your subs are but by the total amount of exposure you have. I would stay at ISO 400, make sure you’re shooting raw and try something in the 5 to 10 sec. range.
On gradients, the things that make them worse are light pollution including the Moon, wide field of views and shooting objects too low in the sky. Also, be aware of local sources of light. If there are light sources around you try to minimize that as much as you can.
@Tony Gondola , Thank you so much for your guidance! I will take this all in and try it for my next shoot.
Have a great rest of your day.
@John Tucker thank you very much for all the help. time is valuable, so I thank you for taking time out of your day to help me (:
Have a great day!
In Siril, there is a tutorial on background extraction:
https://siril.org/tutorials/gradient/
This may be very helpful in your situation, and since you’re dealing with B8 (usually linear) light pollution, you can reasonably extract the LP gradients prior to stacking. Scroll down the tutorial where it instructs you how to remove gradients as part of the subframe calibration process. Go to the heading:
📷 image.png
I hope that’s helpful!
CS,
Mark
Mark Fox · Mar 17, 2026, 07:10 PM
In Siril, there is a tutorial on background extraction:
https://siril.org/tutorials/gradient/
This may be very helpful in your situation, and since you’re dealing with B8 (usually linear) light pollution, you can reasonably extract the LP gradients prior to stacking. Scroll down the tutorial where it instructs you how to remove gradients as part of the subframe calibration process. Go to the heading:
📷 image.png
CS,
Mark
Awesome! I will look through that. Thank you so much, that is extremely helpful.
Clear skies!
- Horriblebaby
Just to reinforce the importance of editing, this was taken on a 87% moon night in a Bortle 7 location using broadband filters.
After editing
https://app.astrobin.com/u/chvvkumar?i=pxuzh4#gallery
The important thing is, especially for wide field set ups, prevention goes a long way. Aim to shoot the target when it is up high. Get away from bright sources of light and if you can’t, use longer dew shields on your lens to prevent stray light.
The better the original data, the easier it is to deal with it in post. I am not a Siril person but in Pixinsight, it is a matter of finding the right balance between gradient correction, curves and massaging the data.