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- Shoot in Raw!
- A rule: never throw away data
- DSLR
- JPG conversion in camera throws away data
- Shoot raw and you get to control what data are used and when; data you don’t use aren’t thrown away, and you can try other decisions.
- This is not just an ideological debate; for astrophotos, your camera’s built-in JPG conversion will make wrong decisions. You need the raw files.
- CCD
- Most produce FITS files, which are a kind of raw
- If yours can produce JPG, don’t
- The Never throw away data rule will come back later, too, when we talk about post-processing.
- Taking multiple exposures
- Why do it?
- Is it equivalent to one long exposure?
- Noise reduction
- Error recovery
- Selecting exposure length
- how many exposures
- Rotate filters or combine sets?
- Why do it?
- Temperature stability
- Noise from your camera varies with temperature
- If you have a temp-regulated CCD
- Choose a maintainable temperature
- Choose a temperature for which you already have a collection of darks
- DSLR or non-regulated CCD
- Keep notes on the temperature
- Try to collect dark frames that roughly correspond to the temperature
- DSLR: if doing multiple exposures, don’t use built-in noise reduction – use separate dark frames.
- Don’t forget Flats
- Darks and bias can be collected separately
- Flats need to be done during image session, before anything moves
- Order of operations
- Darks and Bias Frames
- With temperature regulation, do these another time
- Otherwise, fit them in at a point of average temperature
- Focus on a suitable star near target
- Find and frame target
- Start autoguiding and wait for it to stabilize
- Take multiple exposures
- Take flats
- If filtered monochrome,
- take all exposures for a given filter together
- take flats with each filter, before changing filters
- Darks and Bias Frames