extension tubes

[Dmitri]

For macro photography. Whats the deal?

What happens if you hook up a 70-250mm lens to it compared to a nifty 50? Does it get closer, further, no difference?

I'm thinking about getting the cheapy ones, but not sure if it would do anything that the reversed 50 trick can't do (other than stay on the camera).

 

[Derrel]

An 11,12,or 13mm extension tube hooked up to a 70-250mm zoom lens will give a much wider range of working distances than a reversed 50mm lens will,as well as a wider range of magnifications. This helps tremendously in lighting small subjects; with a reversed 50mm lens, the photographer is often only 2 to 4 inches from the subject, which makes it hard to utilize a lot of different types of lighting: daylight, OCF, on-camera or on-bracket flash,etc. By "cheapy" tubes, I hope you mean the $99 ProOptic-level, 3-tube sets that have electronic connectors for diaphragm control.

 

[Dmitri]

Actually I was looking at the $12 ones here: Amazon.com: Fotodiox Canon EOS Macro Extension Tube Set Kit for Extreme Close-up, fits Canon EOS 1d,1ds,Mark II, III, IV, 5D, Mark II, 7D, 10D, 20D, 30D, 40D, 50D, 60D, Digital Rebel xt, xti, xs, xsi, t1i, t2i, 300D, 350D, 400D, 450D, 500D, 550D, 100 lol. They don't have electric contacts so it's all manual, but I'm used to that anyway because of the reverse 50.

The pics that show how close it gets don't seem much better (if at all) than the reverse 50, so I'm wondering if sticking the 70-250 on it will allow for smaller macros - for example, getting just the eye on a dime rather than the whole face.

 

[Derrel]

What focal length do you think will have a higher image magnification? 50mm? 70mm? 135mm? 200mm? 250mm?

 

[Dmitri]

I don't know. I've never used extension tubes. All I have ever done macro-wise is flip my 50 around.

 

[djacobox372]

The zoom will be more convenient, however the image quality of the 50mm would probably be better.

 

[Overread]

The rough maths for using extension tubes is:

length of extension tubes in mm divided by focal length of the lens (for a zoom its the focal length its set to on the zoom ring) = magnification : 1

eg:
50mm of tubes on a 50mm lens gives: 50/50 = 1:1 (called "life size" or true macro)

50mm of tubes on a 200mm lens gives: 50/200 = 0.25:1 (or 1/4 of life size - ie less magnification).


So whilst the 70-250mm will give a wider range of possible magnifications, its strongest possible magnification (with a given length of extension tubes) is less than what is possible with a 50mm lens and the same length of extension tubes. Note that I've no idea what the magnification formula is for reversing lenses direct onto the camera body.
I can say that you can reverse a lens onto another lens and for that the formula is:
Focal length of the lens attached to the camera divided by focal length of the reversed lens = magnification : 1

Eg 250mm on the camera body and a reversed 50mm lens gives:
250/50 = 5:1 (ie 5 times life size - or equal to the greatest magnification possible with the canon MPE 65mm lens)

Working distances will of course be small, which makes lighting and focusing more tricky, but with practice and experience and playing around with stuff you can get some pretty impressive magnifications for not much cost.

 

[Dmitri]

Thanks Overread, thats exactly what I was asking! I also didn't realize I could use the reversed 50mm at the end of the 250... I will have to try that one!