To begin with the camera needs to be optimised for imaging the night sky. The following settings are based on my Canon EOS 650D but these settings will be on all other branded DSLR’s in one way or another. These are just the relevant settings and not all the settings on the camera:
•Image Quality: RAW
•Release Shutter Without Card: ON
•Image Review: OFF
•lens Aberration Correction: DISABLE
•Red Eye Reduction: DISABLE
•Auto Lighting Optimizer: OFF
•Long Exp. Noise Reduction: OFF
•High ISO Speed NR: OFF
•Live View Shoot: ENABLE
•Continuous AF: DISABLE
•Auto Power Off: DISABLE
•Shoot W/out Lens: ON (This needs to be enabled on some Canon camera’s to enable shooting through a telescope. If this setting is not in the menu, your camera allows shooting without the lens as standard)
The following settings are in the Custom Function (C.Fn) settings on a Canon Camera
C.Fn 1) User choice, pick what’s best for you
C.Fn 2) OFF
C.Fn 3) DISABLE
C.Fn 4) DISABLE
C.Fn 5) DISABLE
C.Fn 6) AF/AE Lock
C.Fn 7) User choice, pick what’s best for you
C.Fn 8) User choice, pick what’s best for you
Working out the correct exposure time and ISO setting for a target can be a bit hit and miss at times. The minimum exposure for bright galaxies and nebulae will be around 50 seconds (Orion being an exception) and this can go up to 30 minutes for a single exposure if imaging through a Hydrogen Alpha filter. The general rule is that the brighter the target the shorter the exposure should be. But to capture fainter objects the exposure needs to be a lot longer. You need to play about and mix the exposure lengths to find the best setting for the target being imaged.
There are also some targets that will require different exposure and ISO settings to capture it, For example: the Orion Nebula is one of the brightest in the night sky but a major part of the nebula are its faint wispy arms and gaseous outer regions. If you take short exposures then the bright core of the nebula will show up nicely but the fainter areas will not be captured.
On the flip-side any long exposures to capture the faint stuff will over expose the bright core. By using both exposure lengths and doing some creative blending in post processing you will create what’s called an HDR image (High Dynamic Range). By merging the two exposure lengths will give an image that shows the bright and faint parts of the nebula.
I know that you have spent a lot of time setting up and getting your mount perfectly Polar aligned etc…… but you also need to spend as much time as you can on getting the exposure and ISO settings right. Believe me, the blood, sweat and cursing will be worth it in the resulting final image.