Extension tubes

W

woollyback

Messages
1,417
Edit My Images
No
Folks,

Can anyone give me a simple explanation how extension tubes work re minimum focussing distance.

I am thinking of getting some for my 300f4 to do butterflies etc. Is there a simple formula for calculating and doesAF still work.

Cheers for any enlightenment

Rob
 
Dunno about a calculation for working out distances but you'll be pretty close to the subject. The cheaper tubes don't have electrical links in them so AF won't work. I think you'll get ones with electrics for about £70 or so. Better getting a dedicated Macro lens if you are serious. Hope this helps.
 
He's some numbers to play with....although the 300/4 is not the best lens for this type of shooting but butterflys should be fine at around 0.2x magnification.

12mm tube....0.18x at 1986mm (min focus) to 0.04x at 7786mm (inf focus). Working distance 1726-7526mm

25mm tube...0.24x at 1726mm (min focus) to 0.09x at 3925mm (inf focus). Working distance 1385-3649mm

Another table I have reports mag up to .3x but I can't confirm that one.

A 25mm tube will loose you about 1 stop of light so AF should still work,

Bob
 
I've used the 300mm f4'L' for shooting butterfly's and dragonfly's and its a cracking lens gives enough working distance, but still has enough quality and speed, I picked up a set of the Jessops auto extension tubes when they had them on special offer over Christmas and they do still give full auto exposure and metering, if you can pick up a set they are the ones to go for, I'm hoping to try mine later this year on the dragonflys.

Alan
 
Thanks for that,

I guess a macro would be best then, but just wanted to try a pseudo effort before committing to buying.
Do extension tubes work with macro (canon) lenses or is the mfd small enough not to worry about it?.

Cheers

Rob
 
Tubes will work to varying degrees with any lens. I have the Sigma 105. Depends how much magnifaction you need and that depends on the size of the subject. Here's a centepede's head I took with the 105, last week. Gives you an idea of what it'll do.

Bugs24April2008-16.jpg
 
woollyback said:
whoa, nice one.

Is that with just the 105 or with ext tubes?.

Cheers

Rob
Click to expand...

Just shot in RAW with the 105, then cropped in a bit in PP and sharpened etc.
 
You must log in or register to reply here.
Back
Top