NorthernMonkey
enthusiast
Reged: 01/05/2007
Posts: 271
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Hi all.
I've been trying to shoot a few macro pics with my canon 100mm on a 400d body, but sometimes I find I'd like to focus just a little closer, so was thinking of getting one fo the extension tubes.
I know I'll loose the ability to focus to infinity, but how much will long distance focus will I loose with them attached. With the 25mm tube, will I still have focus within the range I am likely to use while crawling about, say up to 1m, of will I be better off with the 12mm tube.
Is it worth the extra for the canon ones, or are the kenco ones just as good?
Cheers
NM
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daft_biker
Action Man!
Reged: 11/10/2006
Posts: 7966
Loc: Doon the glen
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Quote:
With the 25mm tube, will I still have focus within the range I am likely to use while crawling about, say up to 1m, of will I be better off with the 12mm tube.
Is it worth the extra for the canon ones, or are the kenco ones just as good?
Yes, no, no, yes 
Yes you'll still have a useful range of focus but I wouldn't worry about adding just 12mm of extension to the 100mm as it won't do much.
I have the kenko set and they work fine....that and they come in a set of 3 and you can use all 3 together(68mm)  With all 3 Kenko tubes on the 100mm you get about 2:1 without sacrificing much working distance....just stay away from the smaller apertures as things go fuzzy.
The more extension you use the more light you lose....if you have problems getting enough DoF normally the tubes will make life even tougher! (fun tho  )
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Andrew (BSRIPN) ... Pics.
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OneTen
'Two Breakfasts'
Reged: 23/06/2003
Posts: 2661
Loc: Devon
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I have the EF 25 for use with the 100mm macro. To be honest I haven't used it that much and tend to use the 100mm without the tube.
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Richard .......... My Website - My Flickr
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NorthernMonkey
enthusiast
Reged: 01/05/2007
Posts: 271
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Quote:
Yes, no, no, yes
Thanks, you've just saved me a pile of cash not buying an EF12.
I decided that I needed one this morning when a Tiny black and white spider crawled across my front door, and the 100mm wouldn't focus closely enough.
Could I use 1.4tc-EF25-100mm macro to get even closer?
The tc would phsically fit behind the 100 macro with the extension tube in place.
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Malcolm_Stewart
Carpal \'Tunnel
Reged: 11/07/2005
Posts: 2727
Loc: Milton Keynes, UK
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Quote:
Could I use 1.4tc-EF25-100mm macro to get even closer?
The tc would physically fit behind the 100 macro with the extension tube in place.
No.
But the image captured would be larger. Whether the AF (or focus confirmation) would still work I've no idea.
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Malcolm Stewart
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daft_biker
Action Man!
Reged: 11/10/2006
Posts: 7966
Loc: Doon the glen
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Quote:
Quote:
Could I use 1.4tc-EF25-100mm macro to get even closer?
The tc would physically fit behind the 100 macro with the extension tube in place.
No.
But the image captured would be larger. Whether the AF (or focus confirmation) would still work I've no idea.
I've never tried it but I would have thought the answer was yes because the TC essentially eats into the working distance while increasing magnification.
Regardless of the 25mm+TC thing I expect the Kenko tubes stacked together will give higher magnification, lose less light(change the effective aperture less), give higher quality results and may even cost less than just the 25mm Canon tube . Teleconvertors become more useful with longer lenses where extension tubes are not as effective.
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Andrew (BSRIPN) ... Pics.
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Malcolm_Stewart
Carpal \'Tunnel
Reged: 11/07/2005
Posts: 2727
Loc: Milton Keynes, UK
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To me "working distance" in macro is measured from the front edge of the macro lens, rather than from the film plane which is normally used for the distance settings on the lens' focus scale.
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Malcolm Stewart
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9541
Loc: Sussex-by-the-Sea
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According to the formula given here 100mm of extension would reduce effective aperture by 2 stops (2.8 x (100 + 100)/100). Thus doubling the focal length of the lens by means of extension tubes has exactly the same effect as using a 2x converter.
There's no getting away from Newton.........
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Nigel
Completely BSRIPN 
ElSid Gallery
A camera in the hand is more fun than one in the cupboard........
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MickLL
Two Grand Man
Reged: 01/08/2004
Posts: 2716
Loc: SE England
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Quote:
To me "working distance" in macro is measured from the front edge of the macro lens, rather than from the film plane which is normally used for the distance settings on the lens' focus scale.
That is correct for you - but everyone else counts working distance as being from the 'film' plane to the subject. It's that distance that's used in all the formulae.
It's also because of the above that the working distance (by your definition) isn't as much more as one might think when swapping from, say, a 100mm lens to a 200mm. The extra length of the longer lens eats into 'your' working distance but not into 'mine'.
Hope that's clear
MickLL
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NorthernMonkey
enthusiast
Reged: 01/05/2007
Posts: 271
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Quote:
There's no getting away from Newton.........
Damn him. I was getting the 1.4TC for something else anyway (to use with my 300 f4) So ill try it sometime.
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beejaybee
Marvin
Reged: 18/07/2007
Posts: 5267
Loc: Really Here In Name Only
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Quote:
Quote:
To me "working distance" in macro is measured from the front edge of the macro lens, rather than from the film plane which is normally used for the distance settings on the lens' focus scale.
That is correct for you - but everyone else counts working distance as being from the 'film' plane to the subject. It's that distance that's used in all the formulae.
The distance set on the distance scale on the lens is indeed from subject to film plane, but I agree that "working distance" is the distance between the subject and the front of the lens - it's that which determines e.g. shading of the subject by the lens hood.
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daft_biker
Action Man!
Reged: 11/10/2006
Posts: 7966
Loc: Doon the glen
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Bummer! Not sure why I was thinking the effective aperture was a stop and a bit down with the tubes on regardless of lens used...does make more sense the way you put it Just aswell for AE!
However, doubling focal length with tubes should still give better quality than doubling with a TC....tubes just magnify "flaws" (abberations?) already in the lens compared to a TC which magnifies the same flaws and also adds some new ones. Hope I at least got that right 
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Andrew (BSRIPN) ... Pics.
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El Sid
Going potty
Reged: 14/04/2003
Posts: 9541
Loc: Sussex-by-the-Sea
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Quote:
However, doubling focal length with tubes should still give better quality than doubling with a TC....tubes just magnify "flaws" (aberrations?) already in the lens compared to a TC which magnifies the same flaws and also adds some new ones. Hope I at least got that right
Weeeeeellllllll............some might argue that doubling the distance that the light cone spreads over will magnify any aberrations present in the lens. On the other hand using a TC will do the same AND quite probably add a few of it's own.... so on the whole I'd say you're right...
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Nigel
Completely BSRIPN
ElSid Gallery
A camera in the hand is more fun than one in the cupboard........
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