Imaging
If Imaging is a subject
you've only heard of in passing, or maybe have read a little about but
were put off by talk of auto-guiders, Peltier coolers
and not to mention large sums of cash, then worry not.
You may well have heard of
webcams being used in astro imaging, as well as digital cameras - both
compacts and SLRs - and the 'older' film cameras. These can all
provide an excellent introduction to the subject at economical prices.
Once you've experienced the satisfaction of creation your own astro
images this way, you may well feel justified in spending a little more
on more complex and challenging solutions but let's walk before we can
run...
Throughout the years a lot
of experimentation by amateur astronomers and general photographers
alike, has gone into photographing celestial objects. The moon is an
easy target and one everyone is likely to cut their teeth on and is
probably the best one to start with. It's big and bright and could,
with a decent quality telephoto lens and fine film or
medium/high-Megapixel digital camera, be imaged without any telescope
at all. Similarly with the correct filter on the front of the lens,
the Sun can be imaged (it's the same apparent size in the sky as the
Moon) and you can probably manage star-field pictures on a 'fast' film
with exposures of a minute or two, without getting star streaks. But
that's about the limit.
Indeed, with the most
basic of equipment, some fantastic results can be achieved so we'll
try to cover them all, including film cameras, digital cameras,
webcams and to a lesser extend, CCD cameras. We'll try to approach it
chronologically too ie. In the order that things have developed (no
pun intended!)
Film versus Digital
Who'd have thought, 20
years ago, that digital cameras and webcams would emerge and be so
popular as they are today? Whereas back then it was commonplace for a
family to possess maybe a little Instamatic-type roll-film camera and,
if there was a 'real' photographer in the family, a SLR (Single Lens
Reflex) camera, today (much like televisions!) everyone seems to
possess at least one digital compact camera. Furthermore, because of
reduced real-costs, ownership of a digital SLR is no longer
necessarily dictated by the photographic prowess of its owner or the
size of their wallet. Film
cameras which may well have been terrific pieces of equipment in
their heyday, are now relegated to the dusty depths of
bottom-drawers in storerooms or garages, which is sad because they
still have a lot to offer.
But it doesn't have to end
like that and we'll explain why...
If you possess an 'old'
SLR camera, it's a great way to get you into astro imaging. If you
don't have one, you can pick them up for pennies at boot sales and on Ebay,
for example. The reason why the SLR is preferable over the
'Instamatic' type is that the lens is removable. This means
that with a little 'T2' adapter ring, easily obtainable through many
on-line photographic shops or Ebay again, for example, you can
interface the camera body to a telescope eyepiece and put it straight
onto your telescope. Because an SLR also provides through-the-lens
focusing you can still use the viewfinder to see and focus on your
target (although the focusing will physically be achieved by adjusting
the telescope focuser unit, not the camera).
Film itself has advantages
over digital techniques insomuch as long exposures are not prone to
the electronic 'noise' of a CMOS or CCD chip, so what you get on the
film is exactly what the camera is seeing, not some spurious,
self-induced speckling/hazing of the image. You also have the choice
of black-and-white film or colour, in various 'speeds' (levels of
sensitivity to light) and if you are even just a little bit
interested, black-and-white development & printing is well within
the scope of most peoples' abilities, without expensive equipment or
really strict processes. (Colour is very much more demanding a
process). Overall film is a very flexible system and if you want to
experiment, it's an interesting hobby to get involved in as obviously
it isn't restricted just to astronomical subjects.
There are a few
disadvantages though, it has to be said (or digital would never have
caught on!); You have to wait for a laboratory to process your film
when you're finished, if you aren't going to do it yourself, and that
will cost a few pounds/dollars depending on where you go and what size
prints you want. One issue you may have is finding a processor who
understands that your pictures will be mainly black (clear on the
negative) and that he should nevertheless 'print all' regardless.
(More on that later). Unless you're using slide film which tends to
reproduce colours more faithfully, colour reproduction on your prints
may not be as you expect. Once you've got the prints, you'll then have
to scan them to be able to share them with people across the internet
(but at least you can then alter the colours to correct them if they
came back a bit 'odd' with applications such as Photoshop or
Photostyler) - You may well want to submit them to galleries or
magazines, for example. Well why not?
So let's look at the
practical side of imaging in
astronomy - how you get set up and the first fruits of your
labours...
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