Quick dash after astronomy meeting

Monday night was forecast to be clear until midnight, but Monday night was also this month’s meeting of the Eddington Astronomical Society, where I was scheduled to be a contributor.  The second hour of the meeting was a presentation by another member and it would have been rude to cut and run, so I arrived at my dark location at 9.30 pm.  It took until about 10.30 to set up.

My old notebook computer can just about run the guiding program PHD2 and the camera control program Backyard Nikon at the same time, but it is prone to falling over.  Those two programs can be set to talk to one another, so that the whole imaging system is able to “dither” the frames between exposures, with the result that each exposure is captured on a slightly different part of the sensor.  That helps with elimination of noise in the post-processing.  It took a couple of reboots and re-calibrations to persuade the system to run smoothly, but eventually I could start a sequence of five-minute dithered subframes of galaxy IC342 in the constellation of Camelopardalis.

I was also experimenting with using higher ISO settings, following the analysis available on the sensorgen website.  The Nikon D90’s read noise curve flattens out at ISO 800 and then again at ISO 3200 – a somewhat confusing result – so ISO 3200 was the choice for the evening.  That’s higher than I would normally use, and the loss of dynamic range was noticeable.  So was the amount of amp glow in the dark frames!

My four-hour plan for the whole session might have been optimistic, as the notebook battery wasn’t happy at -5° celsius, and only endured for about an hour.  The mist didn’t roll in until about 1am, but there is so much water in the ground in Cumbria that low level humidity is a real problem for imaging – even on an otherwise clear night.

So not the best session, but there have been so few this season and it was good to be catching a few photons under a dark sky.

Galaxy IC342 in Camelopardalis, magnitude 9.1
7 frames of 300sec, total 35min @ f/7, ISO3200

Backyard Nikon

I’m slowly moving towards full automation of my astrophotography.  My mount and camera form a stand-alone system which is more than good enough for me to take great pictures, but the addition of a computer-controlled guide system has drawn me into using the computer to manage taking the pictures themselves.

Canon users will be familiar with the well-known “Backyard EOS” programme that fully automates the capture of astrophotos using a Canon DSLR.  As a lifelong Nikon user, this option has not been available until now: those lovely people at O’Telescope have brought out the excellent “Backyard Nikon“.

Nikon have always been less comfortable with third-party external controls, so Nikon cameras aren’t quite as cooperative as Canon.  For example, my D90 will not accept the Backyard Nikon commands for exposures longer than 30 seconds – which rather defeats the object.  The shutter control for the D90 has to come from a serial port, which means a specialised USB-to-serial converter that fits the D90’s bespoke four-pin shutter release socket.

The internet is a great resource for sharing solutions, so I quickly found what was required, and eBay took me to the suppliers of the components.

After a session of gutting a cloned remote shutter release and wielding my soldering iron, this is the result:

It works!  In fact it works very well.

Now the clouds will be with us for the rest of the month…