Focussing on the stars, obtaining sharp focus.
The topic of focus comes up consistently when talking about photographing the stars.
A lot of people find it confusing, complicated and difficult but it really doesn’t have to be. You will see that with how short this post is going to be. I will explain the two easiest methods I use, I’m sure there are other ways but these are simple and work well for me.
Firstly we need to set our lens to focus manually, the switch is generally found on the side of the lens, see picture. Some camera’s you may need to turn on manual focus on the body, refer to the manual for your camera/lens as it is quite different from system to system, but you do need to set the lens to focus manually. There is no need to change anything if you use a full manual lens. Some lens’s such as the Samyang 14mm 2.8 can only be focussed manually.
Note the switch changed to MF (manual focus) on lens barrel
I will first discuss using the infinity mark to set focus.
Not all lenses are created equal a lot of kit lenses do not have an infinity mark if you are using a lens without a depth of field scale and infinity mark you can read on but the second method, using the cameras live view is for you.
If you are using a lens with an infinity mark you simply set the lens to focus on infinity by rotating the focus ring on your lens lining up the mark on the lens barrel with the infinity mark on the depth of field scale (see pic) . Different lenses/makers do this differently some lenses you may need to line up two markers, some you may need to line up the mark on the barrel with the centre of the infinity mark.
Note the lines on the lens (centre) lined up.
With a lot of lenses this method will get you good results. If you find you are not getting perfect sharpness in your stars you may need to adjust by slightly moving the marker on the barrel to slightly after or before the infinity symbol or marker on the depth of field scale. If you do remember this for next time.
Second method is to use your cameras live view. This method can be used by almost all modern dslrs, mirrorless cameras and I’m sure compact cameras regardless of lens.
This is probably the best method as it can be fine tuned to give excellent results.
To use this method you simply,
- Turn on your cameras live view (with your desired exposure settings already chosen, see the basic night sky photography tutorial.
- Point your camera towards a bright star.
- Zoom in on the live view screen so you are magnifying a small section of the scene you are photographing. (On my canon this is as simple as pressing the magnifying glass button, the area and amount of zoom x10 is shown in the bottom right hand side of the camera’s live view screen in the example below)
- Now rotate the lens’s focus ring until the stars on your live view screen are sharp.
Done, now take a pic and adjust the focus if needed.
Your focus is now set! As long as your do not move the lens’s focus ring you don’t have to change this.
Note the live view screen zoom about x10 and area zoomed in on, bottom right of cameras live view screen.
The brightest star in the centre of the above image is the one we were zooming in on on the cameras live view screen to get focus. It is the resulting image after using the live view method, nice pin point stars.
But remember CHECK FOCUS OFTEN It is very easy to bump your lens out of focus while moving your camera, re-composing etc. I’d recommend that every time you re-compose or move your camera you also check focus or re-focus. Even if you don’t move it, check focus every few shots, there is nothing worse than ruining a nights worth of images because of poor focus.
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