© 2018 Yorkshire Astronomy. 

One Small Step for Man One Giant Leap into Astrophotography

The Camera

First is to focus your camera at infinity, this is where the rays of light enter almost

parallel to each other. You can do this on auto by focusing on something a long way

away, when the camera focuses switch to manual. If the lens you're using doesn't

have an auto focus option. Zoom in as close as you can to a star and adjust the

manual focus until the star appears as a point. Your camera is now focused.

There are two things you'll need to look at, the exposure and the ISO. The exposure

is how long the shutter remains open. the ISO is effectively the sensitivity of the

sensor. Set the camera to manual (look for the symbol 'M' on the top of the camera)

when you look through the camera you will be able to cycle through the exposure

times using the scroller normally located on the top of the camera near the settings

wheel. the ISO needs some trial and error. but for Milky Way shots typically around

800 - 1200 works well.

The Lens

The Lens is the most important part of the camera! there are two aspects to search

for; how fast it is and the focal length. Typically the focal length gives you an idea of

the field of view. The shorter the focal length the more you can fit in the picture. for

Milky Way photos 14mm is perfect. For a deep sky shot of Andromeda or the

Nebula in Orion 135mm is ideal. Its also useful to have some lenses in the middle; a

50mm and 100mm would be perfect. These lenses are 'prime' they only have one focal length, they tend to be better for astrophotography than the variable telephoto-lenses which are

excellent for nature and day time photography.

The next thing is the speed. It will be labelled as a 'f number' this, in affect, tells you

how much light will be let through the lens when you open the shutter. Normal day

time lenses have an f value of around 4 - 6. for astrophotography anything less than

three is ideal!

Lenses I recommend are the Samyang 14 f2.8 - My go to Milky Way lens.

Canon 50mm f1.8 - a really good and cheap lens if you want to zoom a little on an

aspect of the Milky Way

Canon 135mm f2.8 - I use this for deep sky astrophotography.

The Rule of 500

Because the camera is on earth and the earth is spinning, the camera is therefore also

spinning now the stars you're trying to photograph are stationary, this means that

when the shutter is open the sensor will capture the light but as the earth moves the

stars will appear to move in the sky. the result on the photograph is 'streaking' the

stars appear to elongated. the rule of 500 is a rule of thumb and it allows us to work

out how long we can open the shutter without the stars streaking. take the focal

length of the lens and divide by 500.

For example the Samyang 14mm; 500/14 = 35.7

This means you can open the shutter for 35 seconds and the stars will still appear

as points of light.

an issue arises when we work with the 135mm Canon. 500/135 = 3.7. so the lens

can only be opened for 3.7 seconds before stars streak. to capture enough light to

make the deep sky objects pop out 3.7 seconds is not long enough, well need to

compensate for the earths rotation. you'll need a star tracker. I use a Skywatcher

Star Adventure. this is needs to be aligned to the pole star and then the camera can

be attached to it. exposures can run for up to three minutes.


Once you have your photos you'll need to process them. it may sound like cheating

but you aren't adding light to you photo. you've captured all the ancient photons its

just they aren't very concentrated so the light appears to be dim in comparison to the

light of closer objects e.g. light pollution. processing removes the unwanted photons

and allows the ones we want to be seen.

free online applications are Gimp and Photopea, although the easiest and best is

probably Photoshop which you unfortunately have to pay for a subscription to.

part of the processing is to 'stack' photos. This involves taking hours of short

exposure photographs and stacking them on top of each other. this reduces noise

and allows you remove photos with aeroplanes or satellites in. programs which can

do this for free are 'Starstax' and 'Deep Sky Stacker'

But above all get outside and look up, you don't need lots of expensive kit, a reasonable camera a tripod and you're away!! Good Luck and Clear Skies