Higher standards

One of the great things about digital astrophotography is the quality of the images we are getting. Look back at the images of 100 years ago taken with the great telescopes of the day and you will find they do not compare well with recent images taken with amateur ‘scopes today. You would be hard pressed even to find amateur exposures of any quality from those days.

We can ascribe the improvements in quality to several factors, but these spring to mind right away:

  • Emulsions back then were less sensitive than digital sensors are today (or, for that matter, than emulsions are today).
  • Long film exposures are subject to reciprocity failure, so that doubling the length of an exposure does not necessarily double the effect of the exposure on the film. Digital exposures do not have this problem, but they have poor dynamic range – which can be offset by careful use of software, bringing us to the next point….
  • Digital exposures can be stacked and manipulated in various ways to bring out detail. While you can scan analog exposures and then manipulate them, this is awkward, and certainly wasn’t available a century ago.
  • 100 years ago, all guiding was manual. Today autoguiding improves the reliability of guiding, and certainly removes the tedium. We are therefore less likely to find an image ruined by a lapse in attention.
  • With digital imaging, a bad subframe can be discarded immediately and a new exposure can be set up. 100 years ago you wouldn’t know for at best, an hour or so, and at worst, a couple of days, if your image was poor, and the problems in obtaining good images meant that marginal images would be retained instead of being discarded (or at least, set aside).

We can also point to the overall improvement in the quality of amateur instruments themselves. While a prowl of newsgroups will find many complaints, the fact is that modern scopes perform much better than scopes of old as a result of improved coatings and materials in general, and even mechanically there are many more good mounts available than was the case 100 years ago due to improvements in fabrication technology (leaving aside the issue of there being no commercial mounts 100 years ago, just considering custom mounts).

What’s next?

I replaced the objectionably flashy USB 2.0 hub (a multicoloured LED at each port, plus an overall flashing LED at the center – looked like a cheap Christmas tree ornament!) but the weather went sour pretty much immediately. More testing will have to wait for a clear sky.

At the moment almost everything is in place for remote imaging once the roof is pulled back. Wiring and cabling aside, I think all that remains is to add a focuser so that the camera can be focused from inside the house, and it would probably be good to dedicate a computer inside the observatory rather than carry my laptop back and forth as I have been doing. I may still have a problem with winter conditions but I will worry about that bridge when it falls down.

That should put me in position to observe over a longer season, and perhaps to observe during the week more often. With a cloud sensor and some way of opening and closing the SkyShed I could automate the observatory completely, but I’ve priced the components for that and — short of a lottery win — it’s not an option for the immediate future. A remote focuser will in itself eat my budget for quite some time (though I might be able to swing a dedicated reconditioned computer).

Eagle nebula

It’s amazing what can be recovered from even the worst of images.

Last night was clear with good transparency. I was having problems with my electronics – what comes of buying cheap USB 2.0 hubs [now replaced with D-Link (whew!)] – so guiding was erratic, and as usual, I had not solved my technical problems in taking decent flats and darks. On the other hand, late in the evening I upgraded my copy of Nebulosity and suddenly had a working image capture going (and promptly ran out of disk space). I tried imaging several objects, but have so far only processed one, the open cluster M16 and a greatly underexposed Eagle Nebula.

Eagle Nebula

FLT110, Canon 20D, reduced to 50%, Sum of 17 45-second images, no darks, no flats, summed in Nebulosity, processed further in Photoshop with Noise Ninja for cleanup.

Not a cloud in the sky…

The sky is absolutely clear right now. I’ve also finally got my cable issues straightened out, and my Gemini is updated to version 4.04. So why am I still inside?

Mainly, it’s muggy out there! I just took a step outside (it’s not particularly dark, thanks to my neighbour’s security lights) and it was like stepping into tepid water. Ugh! I looked for stars, and after a great deal of effort, found the Summer Triangle. With those conditions I figure it’s not worth trying anything. I’m just waiting for one of my fellow club members to tell everyone what a great night he had at his cottage….that’ll put the icing on the cake.

Bah! humbug! And Grump and Rassenfrassen too.

M57 revisited

Thursday night was a clear night with poor transparency and I didn’t expect to do much beyond check out autoguiding with the DSI Pro and PHD. I have been pleasantly surprised by the visual response of the DSI Pro – much improved over the unmodded ToUCam I have been trying to use (that is now strictly a planetary webcam). I stayed out much later than I expected, and eventually I paid a visit to my old friend M57, taking 17 images at 45 seconds each, then combining them in Keith’s Image Stacker, with post-processing in Photoshop CS2. During the exposures light clouds were drifting across the field, but the DSI Pro still managed to capture enough starlight that the PHD autoguiding software didn’t lose track. Unfortunately the capture software I intended to use, Nebulosity, kept informing me that my camera was returning errors — although there was no problem running a sequence for focusing. I reverted back to DSLR Shutter to control the camera and saved the images onto the in-camera card.

17x45s Canon 20D ISO 1600; FLT-110 at prime focus with autoguiding via Meade DSI Pro and PHD. No darks or flats.

Since I hadn’t intended to do any imaging I took no darks or flats and the original images show problems due to noise and dust on the sensor. This small crop has been cleaned up considerably — thank you, Photoshop!

If you go back a few months you will find a similar image of M57 without guiding which looks fairly close to this one. This time around M57 is off-center in the original photo and stars show distortion due to curvature of field (stars in the center of the original field are nice and round). It’s always something…

At some point I have to try a capture with a Barlow or Powermate between the camera and the scope in order to increase the image size. Resolution will not be improved, though, so perhaps I should be saving for another ‘scope to supplement the FLT-110. I’ll give that more thought after I make the experiment with the Powermate.