Using extension tubes to reduce minimum focusing distance

alet

alet

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My 70-300 lens has a minimum focusing distance of 1.5 m or so. It's great for photographing my pet chickens, but at the moment i can't use the lens when they move too close to me.

I could change to my kit lens, which would work for such shots I guess, but there isnt always time for this in the moment.

From what I've read, it seems that extension tubes would allow me to focus closer. My question is, if I used an extension tube on the lens (perhaps a short one), would it still be possible to shoot a subject, say, 5 m away?
 
You lens has a minimum focus distance of 1.5m, so it should focus on anything 1.5m and greater in distance from you holding the camera and lens.

The extension tubes are a cheaper way of taking macro images. The tube contains no optical elements; its sole purpose is to move the lens farther from the image plane. The farther away the lens is, the closer the focus, the greater the magnification, and also the greater the loss of light (requiring a longer exposure time).

An extension tube increases lens magnification by an amount equal to the extension distance divided by the lens focal length. For example, adding a 25 mm extension tube to a 50 mm lens will give a magnification gain of 0.5X. Therefore, if the lens's original magnification was 0.15X, then the new magnification will be 0.15X+0.5X=0.65X. The closest focusing distance will also decrease to ~210 mm.
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http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm
 
It is unlikely that your lens will be able to focus that far with an extension tube attached. When shooting animals or anything where you cannot control their movements, it's always going to be a problem which lens to use. You can't really expect to be able to focus from your feet to 5m away and get frame filling subjects. A wide angle lens would focus very close, but the chickens would be very small in frame at any distance.
 
Use your kit lens, it can focus to 1:3 which is about the size of a 50p coin filling the viewfinder, I wouldn't have thought you'd need more than that?

Use the tele for 10mins then the kit lens for 10mins, that way you'll cover everything.

Extension tubes are not the way to go with these subjects.
 
alet said:
Thank you all for the helpful explanations. I'll just have to switch between lenses more often.
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I don't know where some of this advice is coming from. A short extension tube is just what you need to get the focus a bit closer - you just want to get down to a couple of feet rather than 1.5m, yes?

I do it a lot, usually with just a 12mm tube on a 70-200 lens, sometimes a 20mm. If you use the full set of three (say 12+20+36mm) it will get you very close indeed but as you add tubes you'll lose progressively more distance focus.

Try a 12mm tube, should do the trick and you won't lose a signifcant amount of light with just that. Or maybe a +1 or +2 diopter accessory close-up lens - cheaper, and will also do the job.

Edit: BTW, it's hard to say exactly what length of tube or strength of close-up lens is best. All calculations are theoretical and based on infinity as a starting point, but what you actually get also depends on the lens' minimum focusing distance and the actual focal length (which varies unpredictably with internal focusing zooms). Basically you just have to make a good guess, or best of all go into a shop and try it.
 
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HoppyUK said:
I don't know where some of this advice is coming from. A short extension tube is just what you need to get the focus a bit closer - you just want to get down to a couple of feet rather than 1.5m, yes?

I do it a lot, usually with just a 12mm tube on a 70-200 lens, sometimes a 20mm. If you use the full set of three (say 12+20+36mm) it will get you very close indeed but as you add tubes you'll lose progressively more distance focus.

Try a 12mm tube, should do the trick and you won't lose a signifcant amount of light with just that. Or maybe a +1 or +2 diopter accessory close-up lens - cheaper, and will also do the job.

Edit: BTW, it's hard to say exactly what length of tube or strength of close-up lens is best. All calculations are theoretical and based on infinity as a starting point, but what you actually get also depends on the lens' minimum focusing distance and the actual focal length (which varies unpredictably with internal focusing zooms). Basically you just have to make a good guess, or best of all go into a shop and try it.
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Hoppy.

The OP is chasing chickens, the autofocus will be compromised with extension tubes as will the minimum focus - even with the 12mm you would be starting at around 1:5 which is pretty restrictive.

In this instance without a fast focusing macro, the best option would be the kit lens at 1:3 which is more than enough...
 
Phil Young said:
Hoppy.

The OP is chasing chickens, the autofocus will be compromised with extension tubes as will the minimum focus - even with the 12mm you would be starting at around 1:5 which is pretty restrictive.

In this instance without a fast focusing macro, the best option would be the kit lens at 1:3 which is more than enough...
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The OP is not chasing chickens, but if he is that's a heck of a task under any circumstances. He just wants to focus a bit closer, with a tele-zoom. Sounds quite reasonable to me.

I've just tried a 12mm tube on my 70-200, which normally goes down to 1.2m. With the tube, focus runs from about 5m at 200mm down to about 0.6m from the front of the lens, or much closer at 70mm. AF works fine.

Just thinking about it, this is probably a better option than an accessory close-up lens - good for close, but you lose too much distance.
 
HoppyUK said:
A short extension tube is just what you need to get the focus a bit closer - you just want to get down to a couple of feet rather than 1.5m, yes?

I do it a lot, usually with just a 12mm tube on a 70-200 lens, sometimes a 20mm. If you use the full set of three (say 12+20+36mm) it will get you very close indeed but as you add tubes you'll lose progressively more distance focus.

Try a 12mm tube, should do the trick and you won't lose a signifcant amount of light with just that. Or maybe a +1 or +2 diopter accessory close-up lens - cheaper, and will also do the job.
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HoppyUK, this is exactly what I have in mind. Thanks for the advice. I have a set of macro diopter filters for my kit lens (annoyingly, I bought them before I got the zoom, which takes a much larger filter), which I could try out to see how it works in principle. Anyway, I've been looking for an excuse to get a set of tubes because I want to try out macro ... I will look into this when I get back from holiday.

Phil Young said:
I know he isn't really "chasing" chickens, that was a joke.
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Hehe, I try to avoid chasing chickens whenever I can; they are much faster than me. My preferred strategy is to try and outwit them, which works ... sometimes.

But you do make a serious point, autofocus is essential for photographing chickens.
 
alet said:
HoppyUK, this is exactly what I have in mind. Thanks for the advice. I have a set of macro diopter filters for my kit lens (annoyingly, I bought them before I got the zoom, which takes a much larger filter), which I could try out to see how it works in principle. Anyway, I've been looking for an excuse to get a set of tubes because I want to try out macro ... I will look into this when I get back from holiday.


Hehe, I try to avoid chasing chickens whenever I can; they are much faster than me. My preferred strategy is to try and outwit them, which works ... sometimes.

But you do make a serious point, autofocus is essential for photographing chickens.
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Good :) But note my comment above about using diopters - they will get you close, but you'll lose all focusing further than about 1m even with just a +1 diopter. On the other hand, you'll get several times that range with a short tube.
 
HoppyUK said:
Good :) But note my comment above about using diopters - they will get you close, but you'll lose all focusing further than about 1m even with just a +1 diopter. On the other hand, you'll get several times that range with a short tube.
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Also, you can expect some loss of IQ with a supplementary lens, there is NO IQ loss with extension tubes. This may or may not be important to you, because different people have different needs.
 
Garry Edwards said:
Also, you can expect some loss of IQ with a supplementary lens, there is NO IQ loss with extension tubes. This may or may not be important to you, because different people have different needs.
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There is a loss of quality with tubes too, by moving the lens a long way from it's optimum operating range, though usually less. Field curvature especially, so stopping down helps. The more tubes, the more it's affected, just as with stronger diopters also (though the higher quality Canon doublets and Raynox triplet designs are better).

But with both methods, it's the edges that go first so unless it's critical work, eg flat copying, it'll probably pass unnoticed.
 
HoppyUK said:
There is a loss of quality with tubes too, by moving the lens a long way from it's optimum operating range, though usually less. Field curvature especially, so stopping down helps. The more tubes, the more it's affected, just as with stronger diopters also (though the higher quality Canon doublets and Raynox triplet designs are better).

But with both methods, it's the edges that go first so unless it's critical work, eg flat copying, it'll probably pass unnoticed.
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Agreed, but the OP is only talking about a minimal amount of extension.
 
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