E-M1.2: Single Point Focus Accuracy with Birds in Shrubs using the 300mm F4+MC14

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drj3 Veteran Member • Posts: 7,973
E-M1.2: Single Point Focus Accuracy with Birds in Shrubs using the 300mm F4+MC14

There have been numerous posts concerning focus inaccuracy of the Olympus E-M1.2 especially in lower illumination. While I had not noticed this as a problem, I wanted to do a simple test of real birds in shrubs to see how the camera performed. I could have been ignoring the number of situations where the camera failed to focus.

The temperature finally warmed to 35 degrees F, so I decided it was time for a quick little experiment. It was overcast and about one hour before sunset, so the illumination was relatively low. My evaluation was simple, was the bird or the branches in focus, the image did not need to be “tack sharp”. Since the shutter speeds varied between 1/13 and 1/80 second at 420mm, there was obviously going to be some blur in some of the images due to bird/photographer movement (if I do another test I will try to remember – warm coat – gloves).

The depth of field for the images varied between .95 - 1.26 inches or .48 - .63 inches beyond the focused point on the bird making it fairly easy to evaluate focus. I shot a total of 80 images on four birds (first four images). I varied the focus point on the bird by either using the center focus point and moving the camera or by moving the focus point itself so that I would sometime focus on the head or chest or side of the bird. I would simply point the camera at the bird, half press the shutter and then move the focus point to the desired position and let the camera auto focus in CAF mode. Total time for the experiment, a little less than 9 minutes, or about 9 images per minute.

A single focus point was used for all images, camera Aperture Priority at f7.1, AF Lock +2, CAF, Rls Priority S = On (I often do not wait on the camera to confirm focus – it is a little slow with the confirmation and birds move).

In 73 of the 80 images, the focus was on the bird. In 7 images focus was not any better on the bird than the branches. This could be due to either the camera missing focus or due to user error (I do sometimes accidently fully press the shutter instead of a half press, so nothing is in good focus). I made no attempt to be extra-careful. Basically, I just pointed, half pressed and then fully pressed, then changed the focus distance forcing the camera to fully focus each trial. I also moved the focus point around between trials so that the focus point was not always on the birds head/chest.

The final image is an example of a bird where the camera could not auto focus. I manually focused the camera since the camera focused on the large and small branches/vines in front of the bird. However, even had the camera been able to focus on the bird, I would certainly have deleted the image (unless it was an Ivory-billed Woodpecker). All images other than the last one are full resolution.

The results of this simple test are very much like my experience with the camera’s autofocus. The accuracy is very good in situations like those of the attached, where the bird is behind branches. Would it have performed better with a smaller focus point? Maybe, if the above 7 misses were camera related, no if they were simply user error.

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