Image Acquisition: Hunting for Photons in the Backyard
Processing is the part where your photo looks amazing but acquisition basically, the time under the stars is actually the most important. If you don’t capture it, you can’t process it! So this is how we enhance our signal to noise ratio and gather a lot of hours of quality data for those dim deep sky objects.
To achieve the finest data, a method of work must be established, and I will explain to you the equipment and the methods that turn a clear night into a fruitful imaging session.
The Essential Gear Checklist
First of all: tracking the sky is a must. If you are doing long exposures, then your equatorial mount is by far your most valuable piece of equipment.
The Mount: Here, Polar Alignment is a must. Our tutorials demonstrate how you can accomplish this alignment quickly and accurately by using devices like a PoleMaster or SharpCap. When your mount is spot on, the stars remain exactly where they have to be, thus you are able to take those long, stunning exposures without star trailing.
The Camera: In any case, if you use a stock or modified DSLR, a mirrorless camera, or a cooled astronomy camera (OSC/Mono), the aim is one and the same: to take the shots in RAW format. This allows for the maximum amount of data and dynamic range to be saved, which is very important for the later processing.
Guiding System: Beyond two minutes, a guide scope and a guide camera must be used. This arrangement makes the smallest, continuous, automatic corrections to your mount’s tracking so that your stars are perfectly round even if you use a high magnification. Basically, it is a must have upgrade that gives you instant return on its investment.
The Capture Process: Hours Make the Image
Astrophotography requires a lot of patience and the image with the highest exposure time is always the winner. In fact, you are not taking one photograph, but are accumulating hundreds of images, which are called subframes.
Framing and Focusing: To get our target absolutely centered, we employ plate solving. Next, a Bahtinov mask or similar tool is used to get focus that is as sharp as possible. This step should be carefully considered, a soft image means soft details, no matter how much processing time you apply!
Taking Light Frames: These are the main exposures. Usually, we go for the longest exposure possible maybe two, three, or five minutes after which the background sky is too bright (in case you are in a light polluted area) or your stars start to trail. In fact, the best way to do it is to have at least 3 5 hours of total exposure time on your target in order to be able to extract those faint details.
The Calibration Frames: These are the characters behind the scene of a clean image. They are necessary to get rid of the imperfections that are inherent in the sensor of your camera:
Dark Frames: They are taken with the cap on and are intended to remove thermal noise as well as “hot pixels”.
Flat Frames: When they are taken against an evenly lit surface, they remove vignetting, dust spots, and very slight light falloff.
Bias Frames: It is the shortest exposure possible, with the cap on, and is meant for the removal of readout noise.
Right after your session, make sure you pick up these frames, and you’ll be thanking yourself when it’s time to click the Stacking button. It’s precisely this careful gathering of data that provides you with that perfect, noise free base for a breathtaking final image!
→ Must-Watch Acquisition Guide: 80% of Astrophotography Basics in 20 Minutes!