Caveman Astrophotography

Through various circumstances I recently found myself deep in the mountains of Gippsland, Victoria, armed only with a pair of binoculars, the Canon 400D and a tripod. Dark, dark skies, so a great opportunity to get back to some tripod shooting.

Some limitations on tripod shooting:

A. Because you’re not tracking, you are limited in exposure times before the stars begin trailing. At 18mm, you can go for about 30 sec and still end up with a reasonably-sized image (say 800 pixel width) where the trailing is not obvious. You might be able to go a bit longer closer to the celestial poles. Of course if you zoom in, the exposure time becomes less because you are effectively magnifying the movement.

B. With limited exposure times, you want to shoot for brighter stuff in general, like the Milky Way, bright DSO’s, etc. No good shooting at ISO 400 or anything, use all you’ve got, ISO 1600 in my case. Of course dark skies help immeasurably. Keep the aperture wide too. The trick is taking lots of subs so you can swamp the inevitable noise in ‘stacking’.

OK, first shot, Sagittarius region of the Milky Way, shot though a gap in the trees. ISO 1600, F/3.5, 18mm in 18-55mm kit lens, 7 x 30 sec exposures, stacked in Deep Sky Stacker. Levels upped in Photoshop, and a bit of contrast. Nothing complex. The stacking ‘smears’ the trees!

Now, same set of 7 shots, this time stacked in Registax, aligned on the trees so the stars do trail. Nice effect I think, just shows how the same data can be processed another way to produce a completely different final image.

Next, try a bit of zoom, 55mm in 55-200mm Sigma zoom lens. Found by trial and error that I could go for about 15 seconds. Only took 4 subs, each at ISO 1600 and F/4, and stacked with Deep Sky Stacker. So ended up with quite an acceptable Eta Carinae Nebula widefield (better as a larger image, but reduced for blog entry). Note that the ‘added darklanes’ are just foreground trees and branches that have been ‘smeared’ in the stacking process, LOL.

Finally, go for 200mm zoom! Exposure times cranked right back, in this case to 3.2 sec before trailing shows. Target? Omega Centauri, the great globular cluster, nice and bright. Very little shows in each sub, but I have over 20 subs and stacking does its magic! Here’s a crop, with levels and contrast upped in Photoshop:

Just so you’re under no illusion about what’s coming out of the camera, here’s a full-frame of one of the Omega Centauri subs. Not much showing, a very faint blob only:

So that’s it! Had a great time, and shows you don’t even need a telescope to take "acceptable" astrophotos….