@Waddizzle wrote:
Why would there be a loss of light? Surely, not because it has further to travel.
Yes, that's exactly why there's some minor (usually) light loss to macro extension tubes... light fall off.
Keep in mind that light diminishes exponentially. If a lens is 3" long and you add 3" of extension behind it, you've doubled the distance the light has to travel, so theoretically would lose a stop of light.
However, it's not a lot when using a single tube... even with a relatively long 25mm or 36mm tube it's less than a stop of loss when using them with short telephoto lenses.. The more extension, the higher the magnification, but the more light loss. Not to worry if you are using the camera's internal meter, it will take into account any light loss to extension(s).
Loss of image quality is another matter. Some lenses work better with extension than others. Loss of IQ mostly occurs when using extension tubes with non-macro lenses.... lenses that aren't "flat field" designs, aren't optimized for close focusing... have difficulty focusing across the entire frame when "forced" to focus closer than intended. As a result, they tend to be softer in the corners and at edges when extended. There also can be some vignetting. I find telephotos usually tolerate extension better than shorter focal lengths.
But the vignetting and softening can be useful. For the following image I deliberately used a combo that I knew would cause some of both... a Canon 50mm f/1.4 at large aperture (f/2, I think), with 20 or 25mm extension.
Macro lenses work great with extension tubes. In fact some macro lenses are 1:2 on their own and require some extension to reach full 1:1 magnification. There are "matched" extensions just for those type of lenses. But the "universal" extensions work just as well.
I always have some extension tubes with me. They come often come in handy for unexpected opportunities. All the following were done with extension tubes on various lenses. The first is with a 20 or 25mm extension on a vintage 1:2 Tamron 90mm macro lens.
These berries were shot with a Canon EF 85mm f/1.8 with 20mm extension.
Extensions can work well on zooms, too... This spider was shot with Canon EF 70-200mm f/2.8 and a 25mm extension.
And even longer lenses, such as this tiny fence lizard shot with a Canon EF 300mm f/2.8 with 36mm extension.
In fact, extensions can be very helpful when telephotos minimum focus distance just isn't close enough, as was the case with this little bush **bleep** at its nest shot with a Canon 500mm f/4 IS and 36mm extension.
EDIT: I almost fell out of my chair laughing when I saw the bird's name was "bleeped"! You'll just have to figure it out, I guess!
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & ZENFOLIO
