Our closest star provides a unique opportunity for the amateur astronomer and astrophotographer to engage himself with
this wonderful hobby during the daytime. In fact, for the amateur whose nighttime activity is restricted due to family,
work or any other complication, the sun provides a viable alternative for the active pursuit of astronomy during the day.
Although the acquisition of images is very exciting, it really represents only one half the battle required to produce a
stunning result and which will reward the photographer for his efforts under the sun and, perhaps, during adverse
conditions. It should be emphasized that good technique is most vital during the acquisition of a GREAT raw image so
that the ensuing processing will be as trivial and least-evasive as possible. In order for this to become reality, we
need razor-sharp focusing, proper exposure and a suitable recording format.
Razor-sharp focusing can be influenced by a variety of factors including image scale, seeing and transparency (as usual),
the type of focuser used (ex. rack-and-pinion vs a feather-touch focusing device), the mount's stability etc. Rather
than delve into these technical issues, I would prefer to concentrate on the physical process itself where I seek out
the smallest possible sunspot visible on the solar disk and which I use to gauge my focusing. If we are poorly focused,
small details such as very fine sunspots will be lost from our field of view; in contrast, as we converge towards the
critical focus zone, smaller and finer detail will become available and which we can use to derive the optimal focus
point.
Once we are focused, we must establish the proper exposure. The availability of digital cameras has proven to be a
phenomenal tool for the astrophotographer, for testing and results are immediately available for perusal and study. My
preferred modus operandi is to use the lowest possible ISO setting (ex. ISO 100) so as to ensure that I have the lowest
possible electronic noise (this ISO setting may have to be increased upward if, for example, we have a windy day and we
require fast exposures to "freeze" the field of view as much as possible). I will then proceed to take 2-3 images of the
sun at various exposures which I consider to be possible candidate exposure times (for example, anything from 1/2000 to
1/250 sec). By looking at the histogram produced for each image on the camera's LCD, I will seek a histogram which has
as much dynamic range as possible and simultaneously covers approximately three-quarters of the maximum ADU (or the
horizonal distance of the histogram). Once I have narrowed down my available choices, I will use the zoom feature of my
EOS 300D to examine surface detail, for a properly exposed image will have indications of solar disk detail in the form
of grain and simultaneously record both large and small suspots and sunspot groups.
The third and final requirement for a great raw image is the recording format. Today's digital cameras have the consumer
in mind and, as such, their primary purpose is to perform software adjustments which should produce pleasant consumer
photos. One such software adjustment is the white balance which can prove to be detrimental to our solar images. In
order to ensure that we have the original image at our disposal with no software adjustment or intervention, it is
critical that we use the RAW image format when writing our images to the camera's flash card. Once downloaded onto our
computer, these images can be converted to TIFF format (16-bit !) using the camera's external software (usually
available on an accompanying CD) and proceed with our proposed processing.
Once a (good) raw image has been acquired, we are presented with the second challenge, namely the proper processing
which will maximize the amount of information that is hidden within our raw image file. Below I describe ten "easy"
steps which I use incessantly in processing ALL of my solar images. In fact, one could write a Photoshop script to
pursue the steps described below without any worry that human intervention would be required.