Monthly Archives: January 2014

More DSLR disasters

Such amazing night skies with the weather, I pointed my DSLR up. 28mm fixed lens, ISO 800, f/2.5, exposures of 10-30s. Nothing great came out of it (no surprise), but some photos on Flickr (lower res images below). I’m amazed at how big a difference having the moon up makes, even when it’s a very dry night and I’m shooting photographs 150° away from the moon.

This old Canon Rebel XT is probably past its prime, I bet I could get much better results with a newer sensor. I’m tempted to try my little pocket Canon S100 tonight; it’s a tiny sensor, but it’s new and good at low light and CMOS might do interesting things the old CCD won’t. Worth a try at least. I did at least solve the lens focus problem on the last two shots; I focussed on the edge of the moon! There’s nothing bright enough for the autofocus to grab onto without the moon though.

Wide angle shots of the night sky are not particularly interesting without context, I understand why all the arty shots involve something in the foreground like a picturesque barn or something.


Milky Way (with moon)
Orion (moon up)
Milky Way (no moon)


DSLR focus for astrophotography

Playing with astrophotos with the DSLR again, focussing remains a problem. One solution is a Bahtinov mask, a little plastic screen doohickey that does some magic diffraction stuff so that when the lens is in perfect focus, you can easily see because the image lines up. Good discussion on Stack Exchange.

New eyepiece

So after a few months’ enthusiasm I lost interest in the backyard astronomy. Through the summer, sadly. As warm as it is it doesn’t get dark until late, and it’s still hard to find stars and see things and I got frustrated. But then we had perfect weather and a friend of mine got a scope and that inspired me to bring out the 8″ Dob again and hey look, there’s some stars!

To bolster my new-found enthusiasm I succumbed to the nagging desire I’ve had since I got the scope to buy a fancy eyepiece, in particular a Televue Ethos 8mm with a 100° apparent field of view. I got sucked in by the marketing and reviews about “falling into the dark sea of stars” when looking through the thing.

It is quite nice, although it’s not as transformative as I’d hoped. There’s still the uncomfortable feeling of squinting through a tube with one eye closed. But boy it’s wide and bright and zoomy. I like it quite a bit and it will instantly replace my old 7.5mm Plössl. I’m also hopeful it can replace the 25mm Plössl for many things.

Objectively, on the 8″ Orion Dob the Ethos gives me 150x magnification with a 0.7° field of view. Compare 160x and 0.3° with a 7.5mm Plössl, or 48x and 1.0° with the 25mm Plössl. Subjectively, the Ethos feels like I can look around about as well as I did with my old 25mm Plössl eyepiece. I’d given up on the 7.5mm Plössl; so narrow, so zoomed in, even when I found the object I wanted to see it was out of view too fast to enjoy. I was able to quickly find Jupiter and the Orion Nebula with the Ethos, something hopeless with the high zoom Plössl. The Pleiades weren’t so impressive though, just too narrow a view to see the 1.5° square cluster.

My main complaint is it’s so heavy and expensive I’m a bit nervous. Orion’s Dobsonian mount is stiff enough the scope is still stable, but I’m scared I’m going to drop the thing. Also the way it sits in the 1.25″ focusser with a single lock screw feels flimsy. (Despite having a 2″ fitting the eyepiece is truly a 1.25″ bit of optics.)

It took me awhile to pick the right eyepiece; I knew I wanted a fancy Tele Vue wide FOV eyepiece but wasn’t sure what their products really were until I found the specifications page. The advice for Dobsonians page was also useful. I picked the $550 Ethos over the $300 Nagler / Delos because every review I read said the extra FOV was worth it. I considered getting the 10mm instead; the field of view is closer to the 1° I’m used to with the 25mm Plössl. But the advice page made me think ahead to when I get the next eyepiece, and the 13mm is an appealing increment over the 8mm. Also the 10mm is a relatively new and unusual product, I figured the 8mm had the kinks worked out and more resale value.

So after 20 minutes using it too look at easy targets, yeah, I’m impressed with the Ethos eyepiece. If I were worried about money I’d consider the Naglers instead; slightly less FOV but half the price! But the Ethos is lovely and I imagine I will quickly be spoiled by its generous view.

Next up on the gear lust list: a GoTo mount. I know finding stars manually is half the fun in backyard astronomy but I just don’t like it. Need to read up more on whether stepper motors on a simple Dobsonian really tracks reliably. It seems like it should, but so much development is behind equatorial mounts I have to assume they are better. Alternately I’d like a better finder scope for manual finding; the reflex sight is just not good enough. At about $40 for an 8x spotter scope it seems like a simple upgrade compared to motorized mounts.