Canon 100mm 2.8 macro

[Alex53]

I am getting a Canon 100mm 2.8 macro lens for my macro photography, however, knowing that maybe larger than 1:1 will be tempting in some circumstances, I was wondering whether its worthwile to throw in a set of kenko extension tubes.

How much extra magnification will these give me?

Also, how will they affect the working distance?

It is 1ft/31cm to start with, to get 1:1. So say the extension tubes gove me 1.4:1 or something, would I still have to get closer to benefit from that extra magnification?

[Jesper]

Good choice, the Canon 100mm f/2.8 Macro is a great lens, not only for macro photography.

The working distance is 1 foot, but this is the distance from the sensor (or film) to the subject. At 1:1, the distance from subject to the front element of the lens is about 1/2 foot.

Sorry, I can't answer your questions about how extension tubes exactly change the magnification and working distance. But if you search for "extension tubes" with Google, you'll find some interesting pages:

http://www.shutterfreaks.com/Tips/ExtensionTube.htm
http://www.toledo-bend.com/gallery/index.asp?request=ExtTube
http://www.imaginatorium.org/stuff/tubes.htm (online calculator to calculate the effective f-stop when using ext. tubes)
http://www.camerahacker.com/Auto_Manual_Lens/Auto_Teleconverter_Manual_Lens.html

[ScottE]

I occasionally use my Kenko extension tubes with my Sigma 105 mm macro lens for very tiny subjects. Other than cropping the photo it is the only way I have to get photos of very tiny details. Be aware that depth of field is very limited and you should use a tripod, mirror lock-up and cable release because any camera movement will compromise the picture at that much magnification and short working distance.

I use the extension tubes more with other lenses to get closer focusing distances. Most of the use is for things like butterflies and dragonflies so I can use a long telephoto lens and keep enough working distance to avoid chasing the insect away.

[Jon]

The basic lens extension formula is 1/f = 1/i + 1/o where f is lens focal length, i is image distance (from nodal point of the lens) and o is subject distance (again, from nodal point). i/o will give you magnification as well. In general, to get a higher magnification, you'll have to move closer to the subject.