The planets
to 50% before merging them together to form the synthetic G. Common
notation shows the use of synthetic channels in brackets, for example R(G)
B. The advantage to this technique is that the overall capture time is shorter,
allowing you to complete a colour image in a third less time than it would
take for a full RGB set.
The individual RGB or RB captures need to be processed using a
registration-stacking program. The most commonly used applications for
this stage are the freeware programs Registax and AVIStack.
Once you have all three channels – RGB or R(G)B – use a graphics editor
to combine the channels. Each channel image must be loaded into the
individual colour channel of a blank RGB image, R being loaded into the red
channel, G or (G) into the green and B into the blue. The G/(G) and B channels
must also be aligned with the R.
Once done, the final result will be a full-colour rendition of Mars. Typically,
this will need to be massaged to a final end result using the editing
program’s levels, curves, contrast and brightness adjustment tools. A gentle
sharpening to the end result can be applied if appropriate to make detail
clearer to see.
Most of the planetary detail is recorded in the R channel, with the B
being particularly good at picking out any clouds present in the Martian
atmosphere. The use of an infra-red (IR) pass filter such as the popular
742nanometer (nm) "IR pro planetary filter" will produce a dimmer image to
work with, but often higher-contrast details.
A sharp R or IR image can be re-introduced to the main RGB result
by layering it over the main colour image and setting its blend mode to
luminance. Applied like this, the sharper R or IR image supplies the detail
to the image while the RGB result supplies the colour information. Such
images are normally labelled R-RGB or IR-R(G)B to indicate the use of a
luminance channel.
Mars has a somewhat frustrating rotation, taking almost 40 minutes
longer than an Earth day to rotate once on its axis. This means that if youdarker, exposed rocky regions. As these are primarily seen by virtue of the
light they reflect, they are known as albedo features. It is possible to image
more detailed relief features such as the larger craters, volcanoes and the
Martian equivalent of the Grand Canyon – the Vallis Marineris – but this
requires a big scope and extremely good atmospheric stability.
The best results with Mars are to be achieved by using a high-frame-rate
camera. Both colour and mono cameras can achieve excellent results, with
the latter being better suited to high-resolution imaging. A set of imaging
filters can be used to capture a red, green and blue (R, G and B) image set
which can then be recombined in a graphics editor to produce a full-colour
version of the planet.
Telescope optics should be properly adjusted (collimated) and the
telescope should be given sufficient time to cool outside so that it is in
thermal equilibrium with its surroundings. An hour or two outside will
achieve this for most telescopes, although large ones may need longer.
Point the telescope at Mars and insert the camera at prime focus (no
Barlow lenses). Focus and assess the atmospheric stability (seeing). If the
seeing looks good and the planet steady, consider inserting a Barlow lens
to up the image scale. Aim for a typical workable focal ratio for Mars of
f/25–f/40, achieved by multiplying the focal ratio of your scope by the power
of any Barlow used. For example, an f/10 instrument used with a 2x Barlow
will effectively work as an f/20 scope. Only consider going to the upper end of
the scale if the seeing is good to excellent.
Record a movie sequence using R, G and B imaging filters in turn. For
high-resolution work with focal lengths greater than 10 metres, do not take
more than 1–2 minutes per channel, otherwise the planet’s rotation will
cause motion blur. Interestingly, as Mars shows little useful detail through
a G filter, it is possible to use a technique for generating a synthetic G by
averaging an R and B result together.
This is done by loading both the R and B results into a
layer-based graphics editor and setting the transparency of the upper layer