Canon 7D focus issue-new observation

Started Mar 31, 2013 | Discussions thread
plugin Contributing Member • Posts: 806
Re: Show a video plus other thoughts

ldgehman wrote:

You mention in your post that it could be due to atmospheric conditions, and though it's hard to believe, I am beginning to see a pattern that supports that idea. I am consistently focusing on the same targets from inside the house through an open window. The last couple days in the morning and evening the jitter disappeared. Starting about late morning through the brightest part of the day I see the jitter. The objects I'm focusing on vary from 50 to maybe 150 feet away. I thought it was intermittent but now I'm thinking it may have been dependent on the conditions in which I was shooting. Some days when I was testing it was overcast with no sun and therefore I may not have seen the jitter. One of the objects I was focusing on today has out of focus blue sky in the background. If I looked really close I could see like a shimmery effect through the view finder that appeared like the magnified jitter that I see in LV. Could it really be atmospheric with these relatively short distances? I feel like I'm chasing my tail!

What you are describing does not require large distances.  When you have a warm area (inside) and a cool area, and air flows between them like that, it can cause the 'shimmering'.  Warm and cool air have different refractive indexes, so the turbulence caused by air flow acts like little lenses (but not in a good way), and since it constantly moves/changes, you see the shimmering, which will definitely affect image sharpness..

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