Convection

PacificklausPacificklaus Major grinsPosts: 118Registered Users Major grins
edited November 6, 2016 in Technique
I recently encountered the issue of convection degrading my image quality when shooting birds with a really long lens. I could not find a lot of information on this issue online, so I wrote a blog post about it.

I'm curious for feedback, if that is useful information!

Here are some convection streams around a small fish, the story what's going on there is mentioned in the article:

16139547817_d88b8ba832_z.jpg

Comments

  • pathfinderpathfinder Drive By Digital Shooter western IndianaPosts: 14,358Super Moderators moderator
    edited December 7, 2016
    The issue of heated air rising and blurring images when using long lenses is very real indeed.

    One of the first times i really noticed it was photographing a launch at Cape Kennedy, Florida shooting out across the inland waterway. The warm, humid air, rising over the couple miles of water separating the mainland from the island, made it very difficult to capture a sharp image at all. Th image just swirled and danced due to the air convection currents.

    In Africa I noticed that I could capture very tack sharp images near sunrise, but by 11 am in the African savana, that the same lens was no longer sharp at all, due to the rising air from the heated ground. Cloud cover helps a great deal to prevent this, due to shading the equatorial sun.

    The time I got most surprised by convection currents was shooting in Yellowstone in February - we were hoping to capture images of the wolves - and hence were shooting with 500mm lenses across very long expanses of sunlit snow. I was really surprised to find major convention currents at mid day when the temperature was still near zero Fahrenheit, but that is indeed what I saw.

    The bottom line is that while long glass can help you capture images that you might not otherwise ever get, getting closer to your subject, and reducing the distance the light has to travel through the air from your subject to your sensor is always the better plan if you can do it. Overcast and clouds help prevent it a lot.
    Pathfinder - www.pathfinder.smugmug.com

    Moderator of the Technique Forum and Finishing School on Dgrin
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