A Little Bit Out of Focus

Last night I made a second set of test shots of the Thai moon over Bangkok. This time I tried manually focusing on the moon with my Canon 75-300mm lens set at 300mm.

Although the pictures looked all right in the viewfinder and on the LCD display, when I got them into Lightroom they were unacceptably blurred.

Moon Out of Focus

Moon Out of Focus

My first attempts when I let the camera auto-focus were much better. I was surprised that it could focus, but it did and it did a better job than my 53-year-old eyeballs.

I remember my Canon A-1 film SLR camera had two optical devices in the viewfinder to help you focus. (This was the 1980s before auto-focus was available).

The first were micro-prizms. They disappeared when the picture was correctly focused. The second was a split prism. This worked better in low light. You adjusted focus until the top and bottom half of the picture was aligned. This article talks about them and this article explains the optical theory.

I don’t think there’s a technical reason cameras no longer have these aids. They are available on professional cameras like the Canon EOS-1 series. I suppose manufacturers believe that autofocus works 99% of the time so they are no longer necessary for amateurs.

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4 Responses to “A Little Bit Out of Focus”

  1. Arthur Says:

    You could do better.

  2. Michael Willems Says:

    Autofocus with one focus spot should be great at f/8. So is it motion blur, in your other images? Or the warm atmosphere? I’d certainly try to stick with 1/00th second, that kind of shutter speed order of magnitude, and use a steady tripod.

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