With a big thanks to Andrew Wall (Astroman) for writing this tutorial for AP members.

Astrophotography with a camera and tripod.

Although there are many different aspects of Astrophotography, I thought I would just stick with those that use a standard Digital Camera or DSLR and a simple tripod. Astrophotography is generally thought of as a part of photography that requires a mount that tracks the stars or some form of sophisticated telescope system. This is not necessarily true; Astrophotography can be done with a simple point and shoots Digital camera and/or a DSLR. Depending on what type of Camera you have the results and your subject matter will be different. For instance, with a simple point and shoot digital camera, wide angle shots of a starscape are possible, making it possible for anyone to take images of the constellations. I will go into more detail on how to perform this later.

The equipment, besides the camera can be as cheap as a camera bag to a stable tripod, both these can be used to hold your camera in the correct position for your photograph. I will be discussing mainly tripod mounted Astrophotography as this is what most people will have. With a DSLR a cable release is a must, or if you do not have one, exposures of up to around 30 seconds are possible in most DSLR cameras. Even simple point and shoot cameras sometimes have the ability of going up to 30 seconds. This is more than adequate for simple Astrophotography. If you do not have a cable release you will be restricted to the longest exposure of the camera and you will have to use the cameras timer delay function if it has one, to prevent and movement of the camera at the start of the exposure.

Focusing your camera is pretty much up to you, there are many different ways of achieving infinity focus with your particular lens system, if your camera has a live view function, such as the Canon 40D, you can set this to on and use this method for focusing. I had a quick play with a friends live view function on the Canon 40D, and found it more than adequate to reach perfect focus every time. With other cameras sometimes it takes a little longer, before I started using software to help me focus. I found the easiest way was to look through the view finder at a reasonably bright star or the moon and focus the best you can. If you are taking an image of the moon exposures of around 1/60th – 1/500th are generally enough to capture detail. After the image has been taken, preview it and zoom in on it, if the craters look out of focus, try again after tweaking the focus. Keep note of which way you turned the dial or knob only by a very small amount. Then shoot again, and check. Keep doing this until you find the optimum focus position. You can use this same method to focus on a star, the smaller the star the more in focus it is. Don’t be turned off if the stars do not look like pin point when zoomed up, this is perfectly normal in digital cameras. The main aim if you are shooting stars is to make them as small as possible.

Can you use Autofocus? Sure! You will have to find a pretty bright object though as the in camera auto focusing system requires a fair amount of light to work. A very bright star or planet or the moon can be used. This sometimes may not work and a little tweaking by the photographer is used for optimum results. Using the above methods is only a guide, many people find their own way of doing things, but these methods have worked for me in the past.

I am going to assume that the user is using a Tripod and a DSLR as I am most familiar with this type of photography. Choosing what you want to photograph is purely up to you, if you want to take a star trail photo for instance, to show the rotation of the earth you would use exposures more than 30 seconds so a cable release is required. For a more general image showing the stars as points of light, an exposure of 30 seconds or a bit more is enough before trailing is noticeable in a 50mm lens. So some nice wide field shots can be done by just pointing the camera up and shooting away.

Star trail pictures are very popular amongst people, but how do you find the South Celestial Pole or where the centre of rotation is? The easiest way is to find your latitude of where you will be taking the photograph from, this will be anywhere from 12 degrees if you are in Darwin to 42 degrees in Hobart. This is the angle above the horizon you need to set your tripod to. You will also need to find True South, there are a number of ways to do this, but the easiest is to use a magnetic compass which will put you reasonably close. This will give you a good reference to where the centre of rotation will be so you can frame a subject in the foreground to make the image more appealing.

Once the camera is set in a position and you have a full battery or an AC adapter connected, set your camera to M (manual) and turn the dial until the exposure is set to Bulb. Also be sure your aperture is set to your widest setting. If you have a hard wired cable release, you will be able to keep the shutter open until you either run out of battery or you turn it off yourself. Please note the longer you subject the sensor to light the more light that it will record, so if you live in a city your exposures will become quickly saturated with “light pollution” This is light that is given off by Sodium Vapour and Mercury Vapour lights in cities, this is a big problem for a photographer as it reduces the about of time you can expose for. In the country however, away from the cities, you can sometimes take exposures of over 3 hours with minimal fogging, the only thing that would affect the image is sky glow, a natural effect which is dependant of the weather conditions at the time of the exposure.

ISO levels at the time of the exposure is completely up to you, the lower the ISO level the less grainy and less light that the sensor will pick up, but you will get an increased saturation of colour, which can look very nice especially if the background is dark. Higher ISO levels will increase the amount of noise that will be picked up, this noise can be due to the camera being warm or amp glow. If it is a warm night you choose to do the imaging then you will have more noise, than a night that is cold.

Stars around the SCP

The above image was taken a different way to capture the rotation of the earth; I took this by taking a series of images of shorter exposures and adding them together in Photoshop, using the apply image command. This method is useful if the area you image from is saturated in light pollution or where longer exposures are not possible. The effect of the windmill being lit was done with a simple LED torch, being shined on to the windmill during a couple of the exposures. I had my ISO levels set at 400 so it was a little grainy. Total exposure time was only about 45 minutes, reasonably short time but the effect is there.
For images that you have taken with short exposures, showing little or no trailing in the stars, they may look reasonably grainy if a high ISO was used and not very special. To enhance this type of image, Astrophotographers use a processing technique called stacking. This method of processing stacks a series of images on top of one another to reduce the amount of noise in the final image. It also enhances the signal or the object you are trying to take a photo of. There are a few ways of doing this, the simplest way I found was using a program called deep sky stacker, which is a free program, which enables the user to select the images you want to stack together. Once completed the process you can save the image as a TIF and then do the final adjustments in Photoshop or editing software of your choice. Deep Sky Stacker can be found at http://deepskystacker.free.fr/english/index.html

Stacked image using a Fuji Finepix S-7000 and deepsky stacker.
From a Suburban backyard. 5 images, 15 second exposure, ISO400
There is a number of software packages which can be bought over the internet which can help the user to focus, take images, and process those images in easy steps, most of these you have to buy, but some are free. If you’re serious, it’s a small price to pay.

Some to look out for are:
Images Plus - http://www.mlunsold.com/
Registax - http://www.astronomie.be/registax/
DSLR Focus - http://www.dslrfocus.com/

I hope this small tutorial will help some members being able to photograph the night sky.

Andrew (astroman)