So this was a bit hard to capture and quite time consuming.
Because I was photographing it at 300mm, I could only have an exposure time of 1.6 seconds, before you get any star blur due to the rotation of the earth. (this is worked out by 500 divided by the mm your shooting at)
So I had to take many photos, then stack them, to be able to bring the detail out. All the photos were taken in RAW.

300mm | ISO 1000 | 2min 18s combined | ƒ5.5
Nikon D5200 | 70-300mm AF-S Nikkor FX

How it was taken
Every 10 photographs, I had to realign the the camera so the nebula was in the centre of the image. I took 180 photographs doing this. The are called 'light frames'.
I then took 20 photographs, with the same settings, but this time with the lens cap on. These are called 'dark frames'. (its extremely important that these are taken with the lens at the same temperature as the light frames.
Then another 20 photographs with lens cap on, but this time with the shutter speed set to that fasted setting. These are called 'bias frames'.

All of these photographs were then put into a program called 'Deep Sky Stacker' which, because the distance between the stars are the same on each image, realigns each images over the top of each other. I then turned on a setting which quarters ever pixel, for even more detail, and what your left with, is a very dark looking TIFF file with a ridiculous amount of data in it.

With this TIFF file, I put it into Photoshop and then set to work 'clipping' and pulling the data out that I want. The image then slowly starts turning from solid black, to seeing an outline of the whites of the stars. I probably did this for about 30 mins until I was left with the image above.

There are many sites online that go into depth on the whole process, explaining what setting you need - this is how I learned how to do it.

Light frames
This is the actual image data of the object you are photographing. There's lots of imperfections in light frames which need to be removed before they can be stacked.

Dark frames
Each pixel on the camera is slightly different. Some read the signal hotter, and some read the signal colder. Dark frames are subtracted from the light frames to get rid of this grain/noise.

Bias frames
Imaging sensors in cameras will have noise that is produced by the electrical system itself. Most of the time this will have a fixed pattern.This pattern is subtracted from the light frames.

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