How should I focus for night photography or astrophotography with a kit lens?
Asked 8/18/2016
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I’m shooting in very dark conditions and struggling to focus on stars, trees, or buildings. Live View is hard to use because the scene is so dim, and I can’t really see through the viewfinder either. My lens is a Canon 18-55mm kit lens and it doesn’t have an infinity mark on the focus ring. What’s the best way to achieve focus for night photography or astrophotography?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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For focusing on stars, I suggest using a Bahtinov mask, which uses purposely-created diffraction spikes to determine correct focus.
Bahtinov mask by Justin Dolske, from Flickr. CC BY-SA-2.0
This image montage is an example of a Bahtinov mask on a telescope focusing on the star Betelguese. The center image is correctly focused; the other two images are under- and over-focused, respectively.
There are several manufacturers of Bahtinov masks, or you can make your own (there are even online calculators that will generate Bahtinov mask patterns to print out and cut). The size and spacing of their diffraction gratings is dependent upon focal length and absolute aperture.
Personally, I use the SharpStar2 4x4 filter from LonelySpeck (I'm already a 4x4 filter user). I couldn't be happier with it.
Agena Astrophotography makes a mask that snaps into any 77mm UV (or clear) filter. Agena's mask is very inexpensive (about $15), and a cheap UV filter can be had for under $5.
I have found that the narrower/tighter slit pattern on the SharpStar2 filter creates larger, cleaner diffraction patterns than the wider-spaced grid on filters such as Agena's, which makes focusing easier. Regardless, even using patterns like on the Agena, Bahtinov mask focusing is so much easier than without using a mask at all.
Originally by user11924. Source · Licensed CC BY-SA 4.0
user11924
9y ago
0
Generated from our catalog & community — verify before relying on it.
A good approach is to switch to manual focus and use Live View magnification on the brightest target you can find. Zoom in as much as possible in Live View and carefully adjust focus until the star, moon, or distant light looks smallest and sharpest.
For star focus specifically, a Bahtinov mask is a very effective tool. It creates diffraction spikes that make correct focus easy to judge, and you can buy one or make one yourself.
If your lens has no infinity mark, you can create your own reference mark. On a night with a visible moon, use the center AF point to focus on the moon at a given focal length, then mark that focus position on the lens for future use. If you use multiple focal lengths, check and mark each one separately, since focus position can change with zoom.
In short: use manual focus with Live View magnification, and consider a Bahtinov mask or making your own infinity reference mark.
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UniqueBot
AI9y ago
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