We're trying something new for the Curdridge Observatory: Colour imaging with a Canon DSLR camera! For many years my astrophotography has been dominated by monochrome hydrogen alpha imaging with the odd tri-colour narrowband image thrown in for good measure. I've never seriously used my Canon 350d DSLR on the telescope. Previous explorations of traditional RGB imaging have never come to much: Normally due to the difficulty of flattening 4 different images taken through filters with a mono CCD camera.

Some recent weekends spent down at the New Forest Observatory playing with Greg's 10 mega-pixel colour CCD cameras have inspired me to see what can be done with my 8 mega-pixel Canon 350d DSLR. Some years ago this digital camera had its internal infra-red filter swapped for the Baader replacement with a view to doing some astrophotography. The occasional dabble aside, I've never really attempted any serious work with it.

The goal here isn't to produce any jaw-dropping images. There countless Canon DSLR cameras strapped onto the business end of 8 inch Newtonians out there. It isn't anything new. Think of it more as an exercise in preventing stagnation. Variety to regenerate the soul a bit.. Hopefully I might end up with something to stick on the wall which prints out in a format larger than a postage stamp.

Truth be told, I like a new bunch of problems to solve.

So how does one do this DSLR Astrophotography business?

Step 1: Get your DSLR modified with a replacement internal IR filter that lets light through at common astronomy wavelengths (i.e. Hydrogen Alpha and Sulphur). I'd already done this years ago.

Step 2: Attach your DSLR to the telescope. This required a serious bit of hunting around my house to find the Canon-M42-T adapters. Alas, when attached the Baader MPCC the spacing was all wrong. A bit of lathe work soon had the camera attached to the coma corrector with the correct spacing. This then fits the 2 inch focuser on the scope.

Step 3: Make the DSLR camera talk to Maxim. Easy enough The maxim EOS II driver works splendidly and soon I was operating the DSLR camera just like real ccd camera.

Step 4: Make your shutter release cable. Cheap serial USB converter and an opto-isolator and that problem was solved. Maxim can now make the camera do long exposures over 30s.

Step 5: Figure out the calibration process. Turns out you need nice high value flats and you MUST have bias calibration of the flats. Other than that I found dark frames useful to knock out the amp glow. Dithered guiding via maxim removes most of the hot pixels without a darkframe.

Step 6: Power the camera. This was fun. Using the built in rechargeable battery for a night of astrophotography is a bad idea, so first I see a very cheap Canon mains adapter on Amazon. Turns out it has the wrong shaped plug on it. A bit of Cathartic negative feedback results in a replacement that fits and powers the camera. However, this seems to have created a monster earth loop somewhere turn the DSLR camera on and the telescope mount starts doing random slews - I joke not!!! Resigning myself to using batteries of some sort I buy 6 decent rechargeable AA batteries and a 6 batter holder instead.

Step 7: Filter out the light pollution. No money this month due to car tax. No money next month either due to new mirror. Put either a Hutech LPS or a Astronomik CLS filter on the note to Santa. Donations welcome. 2 inch or DSLR clip please :)

Step 8: Focus it. FocusMax and Maxim all work together with my ASCOM electric focuser and the DSLR to get a good focus. Slow, but it works. Getting decent focus was one of the horrors that put off DSLR imaging for a long time.

Step 9: Find out the collimation is terrible with the larger sensor and phaff about with optical alignment for a few nights.

Step 10: Run off 20 x 180s frames and see what you get!

Here is the Bubble Nebula and M52 region. Click for full sized version. Still need to tweak the collimation a bit. M42 here I come! :)

M52 and bubble nebula region with Canon 350d DSLR camera