Author: Richie Jarvis © 2020-07-09

Website: https://deepsky.org.uk

Contact: richie@deepsky.org.uk

Description of Parts

The camera is a peltier cooled CCD chip with a black and white Sony HDR sensor.  Made by Starlight Xpress Instruments, the model is the SX814 Monochrome camera.   To reduce electrical noise, it is cooled to -30 degrees below zero using an electrical cooler. Professional observatories use liquid nitrogen to do the same job.

Before I can start taking exposures, some initial calibration of the equipment is required.  The computer needs to know where it is on Planet Earth as well as what time it is. GPS can be used is used to get that information, or it can be entered manually, using Google Maps, or the Internet to find the correct Latitude and Longitude.  Once entered, the computer stores this information for future reference.

Initial Setup

Starting with the telescope in the home position, pointing North and with the weights down.  Using the computer sky chart to control the mount to move the telescope to a bright star, and line it up on the camera chip.  Repeat that three times and the computer knows how reality relates to its internal model of the sky.  Luckily, if I “park” the mount after use, and don't knock it, it keeps pretty good alignment night after night, so I only need to repeat the full Initial Setup procedure once or twice a year.

Focusing the Camera

Before taking any exposures for use in an image, the telescope and camera need to be focused.  Focus changes with temperature, this also means that each night the focus position will be slightly different.  To add complexity, as the equipment cools, and contracts, the focus point changes.  The automatic focuser I use, a Starlight Instruments (no relation to the camera manufacturer) Focuser Boss II Electronic Focusing Control and stepper motor.  This unit learns the change in focus over a 5 degree celsius temperature drop, and using that calibration compensates for changes as the temperature drops automatically.

Before any of that, I need to find a star, and carry out an initial focus run.  This is complicated further as each filter has a slightly different focus point.  Each time I change the filters in the filter-wheel, I need to recalculate the relative differences in position between the Red, Green, Blue, Clear, Hydrogen Alpha, Oxygen 3, Sulphur 2 and Hydrogen Beta filters.  Each one has a slightly different focus point.  More calibration, but the relative calculations stored. I usually redo that once a year, or if I change the filters around.

Slewing to target

Once the stars are focused, I pick a target, say a galaxy or nebula, and tell the scope to slew (move) to point at that location.

The guide camera (CCD2) now needs to be told how it is aligned.  This is a simple software routine which involves the computer making small movements to figure out which way the motors move in relation to the stars.  Once done, it locks on and removes tracking errors automatically.

CCD1 is then ready to take a long exposure.  At this point, CCD2 is taking pictures every second, sending commands to the mount motors to correct for errors.  This keeps the stars on the same pixels on CCD1 during a long exposure!  Otherwise you get lines, not points of light, and those do happen but go in the bin.

I take many exposures because the objects are so very very dim that long exposures to collect as much light as possible for a long time.  That also introduces random noise in the raw data.  To remove that, astrophotographers take multiple exposures for each filter. Some images require all the filters.

Example Results - Messier 51 - The Whirlpool Galaxy

Here is some more of my processed and published work:

https://deepsky.org.uk/astro-imaging.html

All images and text are licenced under the http://creativecommons.org/licenses/by-nc-sa/2.0/uk/

Contact: Richie Jarvis richie@deepsky.org.uk

© 2020-07-09

This episode of the Sky at Night was dedicated to the LCROSS lunar impact (http://lcross.arc.nasa.gov) event on the 16th October, and was broadcast in November 2009. I was asked to come along and setup my scope at the seaside to try and capture the impact, unfortunately, cloud prevented us from seeing anything. The good news was that no-one else did either, as the impact was not visible from Earth!

The Sky at Night - January 2010

This episode was filmed in December 2009. I was asked to come along and bring some imager friends, so I invited Neil Richardson, Stephen Green and Iain Melville. I also took Emily along as well.  We had a great time filming, and also got some imaging in as well. Iain taught Emily how to do Star Trails with my Canon 350D, and caught some beauties.  More of her work here: Emily's Star Trails

Here is the video, Emily and I are on at 1 minute 30 seconds: https://youtu.be/UbIcwvYTih8

You can listen to some of the old episodes here

Here is the result:

Full capture details & clickable large image available here

I have had some nice activity on it which looks good at 120fps

(note to self... Upgrade Joomla and get youtube support...)

Linky here:

https://youtu.be/EqNL-PYjchI

I've been playing for the last few nights with anything vaguely clear (its been shocking!).  Tonight I finally had a decent sky to play with for a little while, so went back to my old favourite Messier 51, the Whirlpool Galaxy (here for info and some of my other shots).  Mounted as usual on my EQ6 Pro and through the F/7 TMB 115mm running with a Televue TRF-2008 x0.8 Focal reducer.  The camera is mounted on the Starlight Xpress filter wheel via a T-adaptor screw fitting, then into the Focal Reducer, which fits the other side of the filter wheel using another T-adaptor thread.

I managed to get 12 x 10 minute exposures over the last 2 clear nights, and also have started on some 5 minute colour data for fun as well.  Here is the result so far.  That is a satellite in the Green data, giving the streak.  I am not sure which one, but might try and track it down.