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                   Tuesday, July 21, 2009 - 4:58PM

660mm test with 2.2x teleconverter

By DAN ROBINSON
Editor/Photographer
25 Years of Storm Observing
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In my quest for ever-closer lightning imagery, I decided to dig out an old piece of equipment that I haven't used for years - my Raynox 2.2x teleconverter. I realized that the threads were the same size as my Canon DSLR lenses, and upon testing it out today discovered that it will work well enough for the upward lightning documentation project. The teleconverter cost me a little over $200 when I bought it - that sounds expensive, but as far as teleconverters go this is a pretty cheap low-end one (good ones run around $1,500). Its drawbacks are 1.) autofocus will not work with it, 2.) a painfully small depth of field, making focusing tedious and softness-prone, 3.) its large size - even though it is fairly lightwieght, it makes the camera very front-heavy, 4.) the long focal length amplifies vibrations, yet another source of softness, and 5.) chromatic abberation is pronounced. The results, as I said, are OK for the application, but far from ideal. If I had funding sources for this project, I would rent or buy a longer high-quality lens - but since that is not an option now, I just have to work with the tools I've got. Although these test shots are not too bad, I'm somewhat concerned at how the extra glass layers will respond to bright lightning channels at close range.

EDIT: Since making this post, I have done some shopping around for telephoto mirror lenses - an 800mm runs about $250 at B&H, and some of the 500mm models come with a 2x teleconverter for a 1000mm effective length. Apparently the low cost is due to these lenses being slow (usually fixed F8), no autofocus, and weird ring patterns in any out-of-focus areas. In theory, none of those should be a problem for the close lightning application. My current setup is manual focus anyway; close lightning needs a small aperture, so a fast lens is actually less ideal; and there should be no 'hard' objects out of focus in the background behind the lightning (only flat gray sky). Mirror lenses are also smaller, which would make the setup less cumbersome. I don't have the extra $250 to spend at the moment, but I think if a mirror lens improves the image at all over what I have, it may be worth it. I have several pending invoices that as soon as one or two are paid, I may have some cash flow to give this a shot - stay tuned!

The following sets of shots are comparisons between the 70-300mm lens at 300mm, and the same lens with the Raynox 2.2x teleconverter installed (for an effective 660mm image).


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I have used this teleconverter in the past on the VX2100 video camera for a couple of upward lightning shoots at the WVAH tower - some images from that are below.


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