OAS NOVEMBER 20013 ASTRONOMY EZINE VOL 2 | Page 31

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To produce a successful mosaic it is vital to make sure that as the telescope is
traversed across the face of the Sun and carefully ensure that the whole disc is
covered with the photos taken. If an area is missed this is like trying completing a
jigsaw only to find a piece missing! When I am making a mosaic I ensure that I
have plenty of overlap with successive photos on all sides of the images. I normally
start at the left side of the top of the Sun and traverse right while shooting 500
frame video sets and then move down working to the left and so on.
The next stage is to process all the images to the same standard, this is fairly easy
if the seeing is consistent and there are no thin cloud present but more difficult if
not. I use Photoshop CS5 to construct my mosaics and I presently have no
experience of other programs but there are many that are suitable.
I start by opening a new document and initially select the International paper
option [a large size sheet]. I then default the background colour to black using two
brightness/contrast background masks and then I click on “layer” and “flatten
image”. I import the first photo and set it in position, I then select and import the
second photo and use the “move tool” and make it 50% transparent in “layer” this
allows for fine positioning of one photo over the other [zoom in a few times to
check for exact alignment]. Turn the layer back to 100% [fully on] and then select
the eraser tool to merge the two together and remove any hard edges that show a
clear indication that they are separate photos.
Some of my friends use this process to build ¼ of the image as separate pieces and
then at a later stage put the four quarters together to achieve full disc.
Once the full disc is fitted together it may still look patchy with areas of dark and
lighter tones. This can be smoothed out by selecting the eraser tool again at a low
percentage say 2% and gently work on the darker patches to blend them lighter so
that the image acquires a more even appearance. The colour layer can then be
added after this stage. When I add the colour to my photos and movies I always
use the colour balance mask with three separate layers for shadows, mid tones and
highlight colours. I try to recreate an impression of the colours that I see in the
eyepiece.
The photographic equipment available and the image processing techniques are
continuously changing and improving as technology advances. I personally am not
expert in computing or advanced image processing techniques but I am always
experimenting, willing to learn and also share my experiences and mistakes.
Mistakes are a very valuable part of the learning process so just analyse what went
wrong and then find the solution.
The internet and particularly solar observing forums are an invaluable link to tap
into the experiences of lots of expert amateur solar images and everyone is welcome to join in. I would recommend joining SolarChat and the solar section of the
Cloudy nights forum.
One expert solar imager Ken Crawford has posted an absolutely brilliant tutorial on
solar image processing in Photoshop CS5 here is the link. I would recommend you
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