Extension tube question.

[SealBeard]

Hey all,

I was just looking for some info/clarification on extension tubes...

Am I right in saying that with extension tubes in place, the minimum focusing distance of the lens will be closer, meaning less space between camera and the subject?

For example with a 70-200 2.8 the minimum focusing distance is 1.5m I think off the top of my head, fitting an extension tube(s) will reduce that right? but at the cost of 1-2 stops of light?

or am I totally off

 

[Chaz Photos]

That’s about it you will also get 1 to 1 or greater but not sure I put a70 -200 on a set
The number of stops will depend on how many tubes you fit

 

[SealBeard]

Ah cool thanks for clearing that up Chaz

 

[Slapo]

With a set of all three sections used, I get about 0.88 magification at 70 mm (being about 5-7 cm away from the subject) on my Sigma 70-300 mm APO DG macro and roughly 1:1 magnification (maybe a little more) when I mount a 500D screw on close-up lens on the Sigma while using the tubes, the front of the lens is about 3-4 cm away from the subject.

By the way, I'd suggest only getting the tubes if you the lens you want to use it on has a manual aperture ring. I can't really see much if the Sigma is set to F22 and it's not noon

 

[Canon Bob]

Rob,

Here are a few numbers to help you see what the extension tubes will do to your 70-200/2.8

With 12mm of extension, you'll have magnification between 0.22x and 0.17x through the focus range when set to 70mm focal length. Your working distance (lens objective to subject) will be 306 to 375mm.
At 200mm FL you'll have 0.22x to 0.06x with a WD of 914-3145mm

Going up to 25mm of extension gives 0.41x to 0.38x with a WD of 138-143mm at the wide end and 0.30x to 0.14x WD 694mm to 1466mm at 200mm FL

You focal range will shrink quite dramatically if more extension is used and it becomes a little impractical.

HTH

Bob

 

[SealBeard]

Thank you both, lots of very useful information especially the numbers I think I will try a set out and see if I get on with them, I think they may be pretty useful

 

[HoppyUK]

I use a set of Kenko tubes with a 70-200L 4. They work very well - full auto everything and £80 second hand from the For Sale section.

At 70mm I get within a fraction of 1:1. Used at different focal lengths and different combinations of tubes, you can get a wide range of magnifications and working distances.

The light loss is due to magnification, not focusing distance. At 1:2 is it one stop loss, and at 1:1 it is two stops.