Focus adjustment in very dark environment

September 18, 2014  •  3 Comments

When we shoot the stars, Milky Way, northern lights, or subject in very dark environment, it is challenging to adjust the focus accurately. This note suggest several tips to obtain sharp focus in practical manner. Followings are the steps to adjust the focus to infinity (such as the stars, the moon etc.).

Step #1: Use Manual Focus mode and adjust the focus to the farthest object such as mountain in far distance while still enough sun (ambient) light remains. Then use a tape to prevent from movement. If you use a zoom lens, use the same focal length as your intended shooting. Use gaffers tape so than there is no sticky residues after removing.

Step #2: If Step #1 is not possible or you loose the Step #1 adjustment position, or change the focal length, you will need to do the followings.

Step #2a: Set the camera exposure as your intended shooting, and align the infinity symbol to the center of reference line. Then take one test shot. You may use 1-2 stops bright exposure setting for this adjustment.

Step #2b: Review the image with the LCD monitor in the back of camera by using 100% or larger view of your intended object such as stars. Observe if it is taken with accurate focus. If not, remember how it looks in the LCD with large size view.

Step #2c: Adjust the focus ring to right slightly so that left side of infinity symbol is aligned to the reference line. Then take a test shot and observe. Is the image better focus than Step #2b result? Then ideal focus point is in the left side of the infinity symbol. Remember how it looks in the LCD with large size view (same magnification to be used).

Step #2d: Adjust the focus ring to left slightly so that right side of infinity symbol is aligned to the reference line. Then take a test shot and observe. Is the image better focus than Step #2b result? Then ideal focus point is in the right side of the infinity symbol. Remember how it looks in the LCD with large size view (same magnification to be used).

Step #2e: Depending how the image shows in the LCD display, you will be able to mallow down to the ideal focus point by repeating above steps. Once you find the ideal focus spot, put a tape to prevent from movement and remember where the infinity symbol is aligned to the reference line. If you lost the adjustment for some reasons, you can adjust the infinity symbol to the ideal focus point (from your memory or memo). You may need to  repeat these processes if you change the zoom (focal length).

Step #3: Enjoy shooting.

Step #4: Enjoy the results.

Below images were taken with fine focus adjustment using above steps.

 


Comments

JoanaRobinson(non-registered)
I have been using a focus adjustment in very dark environment for years now. But I don't think it is necessary. Focus adjustment is only needed when you are shooting a subject that has a lot of contrast and there are several subjects that it can be used on. Visit this http://www.freecodecamp.org/news/how-to-use-on-page-seo-techniques-to-rank-on-the-first-page/ site to learn on page SEO techniques. The main reason why I use it is because it helps me get the depth of field right, and also works well with human faces.
Murali Narayanan(non-registered)
Considering the hyperfocal distance for a 14mm lens @ f2.8 is 7' 7", why not focus on an object 10 feet away (ask a friend to take a flash light and walk 10') and then shoot for the stars?
Bob Venezia(non-registered)
Thank you for your generous sharing of these ideas. Your focus is wonderful, but then everything about this image is superb. I am struck by how perfectly the mountain top is exposed, and the perfect amount of light on the trees in the foreground. There is so much more going on in this image than just the focus! Your planning is extraordinary.
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