- Roll back any roof or dome you may have (luxury items I know), or place the mount outside with a view of the North star and the sky area that you are targeting.
- Install the Optical Tube Assembly on the mount, and let it cool for at least 30 minutes.
- Make sure any counterweight is positioned correctly so that everything is in balance.
- Turn on any Dew Heaters you have and ensure they haven’t slipped down the tube.
Align the Mount
There’s a major banana skin opportunity here….
- With a Synscan GOTO setup (and with some other makes), the position of Polaris with be displayed on the handset during the alignment process. This tells you the expected position of Polaris with respect to the Pole Star, as if the Pole star was on a clockface. If your mount is on a tripod (rather than a permanent pier), perform a sanity check that the mount hasn’t been moved. Do this by looking through the polar alignment scope.
- Next use at least 2 stars to align the mount. Chose stars that are well separated in the sky.
- Perform a GOTO to a bright star or object, and check that the object is centred in the field when using a medium power eyepiece. If it isn’t, start again!
Focus the scope
Next banana skin here….
- Position the scope pointing at a bright star close to the intended target.
- Remove the eyepiece & diagonal and attach the camera.
- Select the LIVE VIEW option and look for the bright star on the laptop screen. You will probably only see one star; nothing else.
- Use the mount’s cursor controls to centralise the star.
- Use the coarse (and fine) focus on the scope to minimise the size of the star to a”dot”. You can use a contraption called a bahtinov mask – a piece of metal with a grid of slots cut in it which diffracts the starlight – but it isn’t essential.
- Select the “Zoom” icon and further refine the focus. If your focuser tube has a graduated scale, take a note of the position for future use. Then close the Live View window.
- Take a couple of 20s trial shots, in order to check the star is focused.
- If it’s OK, tighten the focuser tension knob so that nothing in the imaging chain can move.
Frame the target
- Position the scope pointing at the target.
- Take a 120s exposure and inspect the resulting image to check that you have recorded the target and that the stars are not trailing. Be hyper-critical at this stage. If the star images are not round then consider re-aligning the mount. It is better to start again at this point than to throw the whole session’s images in the recycle bin tomorrow. The following zoomed-in image suggests a problem…
- If everything looks good, centralise the image if it isn’t in the middle 30% of the frame.
Take the Light frames (i.e. the images with the lens cap off!)
- Configure the capture software to take about 10 to 20 short sub frames (exposures) of duration 60 to 90 seconds each. Use a delay of at least 15s between the end of one shot and the start of the next, to allow the camera chip to cool down. Set-up a delay of a few seconds between starting the sequence and the first exposure.
- Start the sequence.
- Step away from the mount and touch nothing! Just listen for the shutter’s click to make sure the first frame has started OK.
- Let the software do the work and keep warm whilst keeping an eye and ear on the progress of the session. Don’t be tempted to touch the laptop or tripod, or even get closer than a few metres; any vibration will ruin the image.
- Stroll around your location and soak up the starlight! Failing that drink tea or go back to the TV.
- Let the sequence complete. Open a couple of the images to check nothing is amiss with any bright stars that are visible. Don’t worry if the object itself isn’t obvious.
Take the Dark frames
- Put the scope’s lens cap on and grab another 3 to 5 frames at the same settings as before. Yes, they will be black, save for errant sensor pixels that are always on (“Hot”).
- Slew to the next target and repeat.
