BBC Sky at Night - UK (2021-08)

Step by step

STEP 6

Record in 30-60 minute blocks, using the transition period to

check for lens misting and that everything works. Post capture,

watch the result with video playback software. VirtualDub utility

(www.virtualdub.org) is perfect, allowing you to step through

each frame and copy any trails to an editor for later analysis.

August 2021 BBC Sky at Night Magazine 77

STEP 5
If your control software permits, take a calibration dark-frame
before recording. This requires you to cover the lens before the
software automatically takes a number of frames, which are
averaged and subtracted from the live video capture frames.
Ensure the field of view is obstruction-free, and hit record.

STEP 2

On a clear night, fit the lens and point the camera at a bright

star or planet. It’s a good idea to put the lens focus ring in the

middle of its range. Screw the lens adaptor in/out to achieve

rough focus; electrical tape can be used to secure the adaptor

in this position. Finally, fine focus using the lens ring.

STEP 3
Using your selected control software, adjust the camera to a high
gain setting. Start off at 50-75% gain. The final value will depend
on your sky quality and camera noise characteristics. Set the
exposure to say, 5 seconds, and take a test shot. Examine its
quality. If it’s really bright or noisy, consider reducing the gain.

STEP 4

Check your

computer’s power

settings and adjust

if needed so it will

remain on for at

least as long as the

session you intend

to cover. Choose

your exposure

setting. Here,

longer exposures

are simply to

reduce the frame

count overhead; 5

seconds generates

720 frames per

hour, 2 seconds

generates 1,800

frames per hour.

We’d recommend

somewhere in

this range.

STEP 1
You’ll need a fast, short focal length CCTV lens, available from
many online sources. A C-mount to T-thread adaptor will also
be required, the T-thread screwing into the camera housing.
Avoid screwing it completely into the camera to allow leeway
for any rough focusing. Ensure the lens aperture is fully open.

Improved test shots