Question. When getting a 12, 20, 25, 36 mm extension tubes...what exactly does the number represent? Does a 12mm tube allow the camera to be 12mm closer to the subject at it's minimum focusing distance and still be in focus? Same thing for the rest, 36mm tube mean 36mm closer minimum focusing distance?
Question. When getting a 12, 20, 25, 36 mm extension tubes...what exactly does the number represent? Does a 12mm tube allow the camera to be 12mm closer to the subject at it's minimum focusing distance and still be in focus? Same thing for the rest, 36mm tube mean 36mm closer minimum focusing distance?
It's simply the tube thickness, a 12mm tube moves the lens 12mm farther from the camera than it's designed to go.
It's possible to work out the theoretical increase in magnification. Say you have a theoretical 100mm lens that focuses to 1:1 macro. If you were to extend it 100mm from the camera, you would now have a 2:1 lens that is less bright (can't remember the numbers for light loss). 12mm on a 100mm lens should yield a 12% increase in magnification, if I've remembered correctly. On a 50mm lens the same 12mm tube would give you a 24% increase in magnification.
Of course, a lot of lens designs use built-in extension in their optical formula, others focus by extension, so the numbers are not as simple as the formula above. Still, with prime lenses it should be a decent approximation. The only practical way I know of to measure magnification is by focusing on a ruler as closely as you can, then comparing that measure to, for example, the horizontal width of your sensor (eg. for 35mm full frame, 36mm across, 24mm vertically)
Comments
And it costs a ludicrous amount of money, but shows that macro at comfortable working distances is possible.
The man who owned it had bought the lens for birding and since he was also interested in bugs and already had the tubes and all...
http://pyryekholm.kuvat.fi/
Wow, yeah the things $$$ can do. Oh that would be nice...
OneTwoFiftieth | Portland, Oregon | Modern Portraiture
My Equipment:
Bodies: Canon 50D, Canon EOS 1
Lenses: Canon 10-22mm f/3.5-4.5, Canon 24-105mm f/4L IS, Canon 50mm f/1.4, Canon 100mm f/2.8 Macro, Canon MP-E 65mm f/2.8
Lighting: Canon 580EXII, Canon 420 EX, 12" Reflector, Pocket Wizard Plus II (3), AB800 (3), Large Softbox
Stability: Manfrotto 190CXPRO3 Tripod, Manfrotto 488RC4 Ball Head, Manfrotto 679B Monopod
OneTwoFiftieth | Portland, Oregon | Modern Portraiture
My Equipment:
Bodies: Canon 50D, Canon EOS 1
Lenses: Canon 10-22mm f/3.5-4.5, Canon 24-105mm f/4L IS, Canon 50mm f/1.4, Canon 100mm f/2.8 Macro, Canon MP-E 65mm f/2.8
Lighting: Canon 580EXII, Canon 420 EX, 12" Reflector, Pocket Wizard Plus II (3), AB800 (3), Large Softbox
Stability: Manfrotto 190CXPRO3 Tripod, Manfrotto 488RC4 Ball Head, Manfrotto 679B Monopod
It's possible to work out the theoretical increase in magnification. Say you have a theoretical 100mm lens that focuses to 1:1 macro. If you were to extend it 100mm from the camera, you would now have a 2:1 lens that is less bright (can't remember the numbers for light loss). 12mm on a 100mm lens should yield a 12% increase in magnification, if I've remembered correctly. On a 50mm lens the same 12mm tube would give you a 24% increase in magnification.
Of course, a lot of lens designs use built-in extension in their optical formula, others focus by extension, so the numbers are not as simple as the formula above. Still, with prime lenses it should be a decent approximation. The only practical way I know of to measure magnification is by focusing on a ruler as closely as you can, then comparing that measure to, for example, the horizontal width of your sensor (eg. for 35mm full frame, 36mm across, 24mm vertically)