This is a collection of notes supporting Paul Evans' talks "Getting Started in Astrophotography" given to the IAA in 2009, at Stargazing Live 2012 and to a number of Camera Clubs in Northern Ireland since, and "Beginners' Astrophotography" given to the IAA on 16th November 2016.
The more recent talk can be seen here.....
A photographic exposure is made up of three factors – Aperture, Shutter Speed and Sensitivity. A lens has a focal length and an iris to control the aperture. A telescope lacks the iris and is used at maximum aperture all the time. The magnification is the ratio of the focal length to the image diagonal.
Aperture = Effective diameter / Focal length, e.g a 50mm f2 lens has an effective diameter of 25mm
Magnification = Focal length / Image diagonal e.g 600mm telescope on a standard DSLR = 600/28 = 21.4x
Image diagonals – Full Frame DSLR or 35mm film – 43mm, APS-C DSLR – 28mm, Four-thirds DSLR – 21mm, Philips Webcam – 5.5mm
Shutter speeds – for hand holding a lens, the shutter speed should be shorter than 1 / focal length of the lens, so a 300mm lens needs a shutter speed of at least 1/300th sec. This is of more interest to sports photographers than astrophotographers! When mounted on a tripod, the Earth's rotation causes stars to trail after a surprisingly short time. The rule here is the maximum exposure time that can be used with an undriven mount is 600 / focal length (35mm equivalent). So for a 50mm lens, an exposure of 600/50 = 12 secs is possible.
Sensitivity – Modern DSLRs have very good sensors which control noise well, but still have limitations. Most will go up to ISO 6400, some even further, however for astrophotography the range ISO 800-3200 is generally the best, and even then there is much to be gained by taking many exposures and stacking them.
Tripod – make sure you have a sturdy tripod that keeps your camera absolutely steady. For astrophotography the required stability is greater than for observing.
T-Mount – connects the camera to the telescope via a 42mm thread (note not the same as an M42 mount!), A second adaptor may be needed to either screw on to the focusser or to mimic a 1.25” eyepiece. Note a DSLR or webcam will always need to be closer to the objective lens/mirror than a eyepiece, and adjustment may be necessary to achieve this.
Webcam – Usually one of the Philips Toucam range – very good for planetary, lunar and (with a filtered scope!), solar imaging. The SPC 900 is now discontinued but can be bought secondhand. Older models (740, 840) only work with Windows XP but can be flashed to work with Windows 7 as can the SPC 880 – google for details.
Intervalometer – very useful for setting a camera to take a number of images at set intervals. For example one could set a camera to take 20 frames of one minute each and leave it alone until the sequence is complete. A refinement is to leave some time between exposures to allow for sensor cooling which reduces noise. A selection of these is available on Ebay.
Though not essential, the use of a computer adds much to the experience. Here's some useful free software!
Autostitch - stitches adjacent frames together, particularly good at Moon Mosaics - http://matthewalunbrown.com/autostitch/autostitch.html
PhotoFilmStrip - Makes moving slideshows from a collection of still pictures using "Ken Burns effect", titles and music - http://www.photofilmstrip.org/
Stellarium - http://www.stellarium.org/ A fabulous desktop planetarium
WxAstroCapture - http://arnholm.org/astro/software/wxAstroCapture/ - webcam capture for Windows and Linux, and can also guide a scope!
Registax - http://www.astronomie.be/registax/ Stacking and Processing package for Lunar and Planetary images taken with a webcam
Startrails - http://startrails.de/ Take lots of pictures with short trails and this will add them all together to make long trails
Starstax.net - http://www.markus-enzweiler.de/software/software.html - Same idea as Startrails with slightly different options
Deep Sky Stacker - http://deepskystacker.free.fr/ - Stacking and Processing package for Deep Sky Objects taken with a DSLR
Virtual Moon Atlas - http://www.ap-i.net/avl/en/start - Detailed Moon simulation – essential for planning a lunar imaging session.
Paint.net - http://www.getpaint.net/ - Excellent free Photoshop alternative. Eventually you may buy Photoshop or its cheaper Elements version, but this is a great place to start!
The GIMP - http://www.gimp.org/ - very capable Photoshop alternative, also free. Probably a bit harder to learn than paint.net
Irish Astronomical Association - http://irishastro.org – Our own website!
Spaceweather - http://www.spaceweather.com/ NASA site giving warning of auroras, sunspot activity and much more.
Catching the Light - http://www.astropix.com/ Great site from Jerry Lodriguss with many very helpful articles.
This article written by Paul Evans (c) 2012 and updated 2016. All comments and questions welcome at firstname.lastname@example.org