Tuesday, April 29, 2014
Stacking Tele-Extenders • Power Pro • Straighten Up • Pay For Music
Q I want to use more than one tele-extender on my Canon telephoto lens, but my tele-extenders won't mate. How do you get yours to go together? When you do stack tele-extenders, do you stop them down for better sharpness?
A First of all, I only stack tele-extenders when I really have to—that is, when I otherwise can't get close enough to get the image I need. Some quality is lost when using even one tele-extender, and this problem is exacerbated when two extenders are stacked together. That said, stacking extenders can be a truly effective technique when a closer approach is impossible or unwise, and I'm always ready to try because there's nothing to lose and possibly great photos to gain!
Some tele-extenders will stack without a problem; the Canon Series II tele-extenders were made to stack, and as long as you place them in the proper order, they will mate and maintain electrical connections. The original Canon 1.4X and 2X extenders and the recent Series III extenders won't stack unless you add a 12mm extension tube between them. Surprisingly, they still focus to infinity even with the extension tube in place. If there's a way to stack Nikon tele-extenders, I don't know of it; their design precludes it. To experiment with other manufacturers' extenders, first try to stack them directly, and if that doesn't work, try the smallest extension tube between them.
When using two tele-extenders together, a few things need to be considered. Number one is that you'd better have an exceptional lens at the other end because, as noted above, extenders compromise image quality; this problem can be somewhat mitigated by an extra-sharp lens. Long lenses demand impeccable technique. Any missed focus or camera movement will be magnified at longer focal lengths. Work from a steady tripod and, if possible, use a fast shutter speed and stop the lens down by an ƒ-stop or two. Use expanded ISO (800, 1200, 1600) to help achieve the exposure you want, especially for early-morning and late-day shoots.
It doesn't hurt to take the quest for long-lens sharpness further, as I did last year when photographing a bald eagle nest over a period of months (see my project report in OP's April 2014 issue). To reach the nest, more than 200 feet away, I used either a Canon EF 500mm ƒ/4L or Canon EF 800mm ƒ/5.6L and one or two 2X tele-extenders. To control movement, I used a heavy-duty Really Right Stuff (RRS) tripod and RRS ballhead. I locked up the mirror by using Live View to minimize internal vibrations. Using a CamRanger wireless transmitter and my iPad 3, I controlled and fired the camera without touching it. If your camera has Live View Mode 1, which stops the movement of the last mirror in the shutter box, use it.
A note about focus: At 1000mm to 3200mm, the depth of field is minimal. If you miss the focus by just a few inches, the subject won't be sharp and you might attribute it to the lens combination, even though that's not the cause. I resolve this by using the CamRanger/iPad combination for focusing; with the magnification of the image on the iPad screen, the focus can be set dead-on.
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