- For faint stars, you’ll want to use maximum gain, then raise the exposure until the spectrum starts to trail vertically. If the spectrum is close to being overexposed, you can lower either the gain or exposure.
Maximum gain may look like it’s noisier because it makes the noise look so much brighter on the preview screen, but in situations like drift scanning where you aren’t able to increase the exposure to collect more light from the target, maximum gain yields the best signal to noise ratio.
4. Position the star in the upper left corner of the field (or just above), so that the Earth’s rotation will carry both the star and spectrum across most or all of the sensor.
5. Start recording a .ser file once the zero order star and spectrum are both fully within the frame. Stop the recording before the zero order and spectrum start to run off of the frame. (It’ll make it easier later on if you don’t have to discard any frames due to the spectrum running off the edge.)
I use Sharpcap to capture my SER files. SER is an uncompressed video format; the quality is like FITS, but it’s much easier to process a single SER file later than it is several hundred FITS files.
6. If you’re using an uncooled camera, you should now cover the front of the scope, and without changing any settings, record another .ser file with anywhere between 10-100 frames. This second SER file contains the dark frames for this object. You’ll use these dark frames to remove false signals inside the camera, such as hot pixels and amp glow.
It’s important to record a new set of darks for every target because darks must be taken at the exact same temperature as the frames they’ll be used on, and with an uncooled camera, the sensor temperature is always changing. On the other hand, if you’re using a cooled camera, then you can keep your camera at a set temperature (for example: always capturing spectra at -10°C) and reuse the same darks over and over.