AF Extension Tubes

I figure that you know what they do so I'm guessing that you want an opinion of quality.

I had a set (Canon mount) but never felt 100% happy hanging a longer lens on them...something about the quality of the lock and build strength. I have since read on another forum that a well respected UK member had a couple of occasions where they detached spontaneously.
Canon's own are of superior build quality but vastly more expensive. I assume Nikon's will be have a similar price premium.

In short...hanging a "nifty" on them...no problem. Hanging a grands worth of classy glass on them....not for me.

Bob
 
I have a set of Kenko
very pleased with them
no sign of auto-detach! :nuts:
 
AFAIK
no effect on aperture
just affects the focussing
 
Joe T said:
Cheers Canon Bob, useful stuff.

I was tempted to try them on all three:

50 1.8
105 2.8
120-300 2.8

How does the 'effective aperture' change? Is it the same as any close-focusing lens? Or is it more like the effect of a TC?

Thanks
Click to expand...
Joe...you will lose a bit of light but the auto exposure will compensate for you. You'll also see various amounts of vignetting on a full frame body....greater tube length gives greater vignetting. The final drawback is a slight loss of image quality and sharpness. This is simply due to the increased magnification highlighting defects or shortcomings in the resolving power of the lens. Better lenses (esp. true macro's) cope quite well but consumer zooms are borderline at best.

HTH Bob
 
An additional bit of info...

The additional magnification you gain is ....length of tube / focal length of lens.
The formula is somewhat crude as it takes no account of the inbuilt extension pre-existing in the lens design. This figure can be calculated if the native mag at minimum focus is known.
In short, tubes will increase the mag far more on shorter f/l lenses (for the same tube addition). Tubes on "wide" lenses can actually put the minimum focus distance inside the lens.

Some lenses...eg Canon's 100mm macro....have a quite large change in focal length as the barrel extends. I believe that this one ends up below 70mm in theory.

Bob
 
Ooooh! are you now Joe? :naughty: would this be before or after my Birthday! :p
 
I've got a set of Kenko tubes and they are fine. I get 2:1 when fitted to my sigma 105 macro lens. Jessops had a sale on their tubes a while back £29.99 I think for a set so it may be worth checking there first ;)
 
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