How do I find infinity focus on a kit lens that has no distance scale?
Asked 4/25/2012
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My kit lens has no focus distance markings, and I want to shoot distant subjects at night. Since it may be too dark to focus through the viewfinder, what’s a good way to find and set infinity focus on a lens with no markers?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
14y ago
2 Answers
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Another possibility is to make a hartman mask for the lens. This method is used to find infinity focus for astrophotography.
In use, you'd point it at the night sky so that you'll see trails of stars. Slowly rack the focus and take a long exposure to test that setting. As you approach infinity, the two star trails will merge into one line.
Be sure to look at a single and not a double star!
Once you find focus, mark that point and note the local temperature as this will change depending on the materials the lens has and its focal length.
You may want to bring some gaffer tape to secure the focus ring once you've found the right spot so that it won't move if you touch the camera.
Hope this helps!
Originally by user5675. Source · Licensed CC BY-SA 4.0
user5675
14y ago
0
Generated from our catalog & community — verify before relying on it.
A practical method is to use Live View and manual focus on a very distant bright object, such as the moon. Magnify the Live View image as much as possible, then adjust focus until it looks sharp. For normal photography, the moon is effectively at infinity. Once you find the spot, mark it on the lens and consider taping the focus ring with gaffer tape so it doesn’t move.
Another option, especially for astrophotography, is a Hartmann mask. Point the camera at a bright star, take a test exposure, and adjust focus until the separated star images or trails merge into one. Then mark that focus position.
Keep in mind that the exact infinity-focus point can shift slightly with temperature and lens construction, so it’s smart to recheck focus if conditions change significantly.
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