Extension tubes: I am confused.....

[BanditPhotographyNW]

OK I have been reading about ways to extend the range of my Tokina 100mm macro lens, particularly extension tubes. However I am confused as to what they actually do. Do they simply take my 100mm lens and make it a 168mm lens (with a set of tubes) or is it just making whats already there at the same distance away look bigger? I'm trying to get further away but achieve the same magnification without buying a longer lens.

 

[amolitor]

The way a lens focuses is (well, roughly, details actually vary with modern lenses) is simply by moving the lens back and forth. When you look at something through a magnifying glass, there's a "right place" to hold it to focus on whatever it is, right? Then for bigger magnification, you move it further away from the thing.

In the same way, when you focus what you're really doing is moving the lens further away, or closer, to the sensor. The focusing mechanism generally goes from "focused at infinity" to "focused pretty close" within various engineering limits. If you have an 80mm lens, the focusing mechanism will move it from 80mm away from the sensor (infinity focus) to maybe 120mm away (focused "pretty close"). An extension tube just starts you out so-and-so many millimeters further away from the film plane. Say you've got a 50mm ring on. Now the focusing mechanism in the lens will rack the glass back and forth from 130mm to 170mm away from the sensor. You can't focus to infinity any more, 130mm is not close enough for that. You CAN focus down to pretty close to 1:1 macro, though, at that 170mm end of the scale.

 

[Edsport]

I don't think tubes is what you're looking for. Tubes just allows you to get closer than you can normally get and still achieve focus...

 

[BanditPhotographyNW]

OK so heres is what I gather, a teleconverter will allow me to step back further from my subject and tubes will make what I am already looking at without moving forward or backward more magnified.

 

[Edsport]

You have to be REAL CLOSE to the subject using tubes or you will not achieve focus, they allow you to get real close and still achieve focus. You can use Youtube and do a search for teleconverters to see what they do...

 

[KenC]

Extension tubes allow a very narrow range of focus, so you really need to get close to the exact length of extension for the magnification you want. You can't just throw on an extension tube and then decide how close you want to get. Best to read up on both extension tubes and teleconverters. Here's a link for extension tubes, but Google will get you lots more info on both:

Macro Extension Tubes & Close-up Lenses

 

[480sparky]

OK so heres is what I gather, a teleconverter will allow me to step back further from my subject and tubes will make what I am already looking at without moving forward or backward more magnified.

Yes... a teleconverter will allow you to move further away, but there's two penalties you'll pay. One is a much slower lens (in terms of maximum aperture). A 2x TC will convert an f/4 lens to an f/8, and an f/2.8 to an f/5.6. This will be a problem when it comes to focusing, since the viewfinder is much darker, and your in-camera AF may not function at all.

The second penalty is loss of image quality. TC's use glass to work their magic, and any added glass reduces IQ. Some TCs are good, some are bad, and some are useless. Like all things, the more you pay the better the quality. Just stick to name brands.

 

[BanditPhotographyNW]

Sorry for the late response been busy working on the house....Thank you all for the replies I now understand the difference quite well thanks to you. Just bought a Nikon 1.4 converter...seems to be the best IQ of the 3 nikon TC's for the gear I have..