Slowly getting the hang of this DSLR astro imaging lark.

Lesson from last night: Remember to charge the batteries for the camera!! I'm using 6 x AA rechargeable batteries to run the camera, but I think i forgot to charge them because they ran flat around 12:30 this morning. I didn't change them because I was asleep in bed at the time!!

Anyhow, here is what you can do with a Canon 350d and an 8 inch Newtonian telescope in about 10 mins...A part of the M31 Galaxy...

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! :)

After spending a lot of time and energy getting the mini-WASP telescope array up and running at the New Forest Observatory, it was a pleasant change to do some imaging back at the Curdridge Observatory.

Last night a brief clear spell gave me time to dust off the homemade GEM telescope mount. Happily everything seemed to be behaving after few weeks of neglect. I was a bit worried the telescope was had got the hump with me running over to play at the NFO.

With the clouds starting to come in, I only had time to take 4 x 900s exposures of the very bright Bubble Nebula region with the Hydrogen Alpha filter in place.

For a change I decided to let Maxim handle the guiding the DIY mount instead of PHD guiding. Surprisingly it seems to work better than PHD guiding, which was unexpected. Using Maxim to do the guiding opens up the ability to dither the sub exposures a bit to handle the hot pixels and noise. The standard webcam settings in Maxim didn't seem to work for long exposure, but a bit of informed tweaking on my part got it working.

Maxim also supports plate solving: Quite nice to point the mouse at any star in the image and have it tell you the RA/DEC coordinates and the catalogue number automatically. Opens the door to a bit of asteroid spotting if I feel so inclined :)

Anyhow, here is the image: Pretty noisy because it is only 1 hour of data, but much better than nothing!

Recently Greg remarked that setting up a new astrophotography imaging system puts you right back at the beginning of the learning curve: How right he is! One problem after another needs solving, and you need a lot of discipline to focus on the problems and not fret about wasting good imaging conditions. Last Sunday we certainly did more than our fair share of problem solving in the twin domes of the New Forest Observatory. Multiple telescopes breed multiple problems!

However, I did my fair share of fretting about the wasted imaging time. This was the first time I'd actually been at the New Forest Observatory during a decent dark, clear moonless night. I was extremely impressed about the lack of light pollution: Much better than the skies at the Curdridge Observatory. The Milky Way was clearly visible overhead.

Once I'd got everything working, I was itching to try and image something. Lots of setup work remains (such as collimating the CCD cameras) but I was in a position to try some sort of imaging by about 11pm. The goal here was to prove we could synchronise and image with the two computers and two cameras at the same time, whilst using a dithering autoguider, calibrate the images (flat fields etc) and stack the data from both cameras together into a finished image.

The result was never going to be beautiful - both cameras are out of collimation, and the focusing wasn't great, but I was able to gather some frames from the IC1805 heart nebula region with both M26C cameras on the two Sky 90 telescopes with just the light pollution filter in place. The two telescopes weren't particularly well aligned either, but the image below consists of about 2 x 5 x 600s frames - i.e. five frames of ten minutes exposure contributed from each camera. This is where I was reminded of the shocking power of the mini-WASP parallel telescope array: 100 minutes of data in 50 minutes of imaging. Seductive stuff.

I also did a few frames in the M33 region which you can see underneath. This demonstrates the huge field of view of just one camera on the mini-WASP array.





Images reproduced by kind permission of The New Forest Observatory