How many extension tubes needed?

Started 6 months ago | Discussions
bruxi
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How many extension tubes needed?
6 months ago

I have a Canon 12 mm extension tube (EF II) and a Canon 25 mm EF II on order.  I like to shoot macro of coins and bugs.  I've noticed an online classified ad in my area for another 12 and 25 (same tubes) for an amazing price.  If I am going to be working with a 50mm lens, should I add to the 37mm tube length that I'll have?  I could buy either the 12 or the 25.  This deal won't last.

Thanks!

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SteB
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Re: How many extension tubes needed?
In reply to bruxi, 6 months ago

It depends on how close you want to get. In theory 50mm of extension tubes will give 1:1 on a 50mm lens at infinity, plus how close the lens focuses natively. Many lenses shorten their focal length at their closest focus, and therefore the extension tubes will have a greater effect than indicated by nominal values.

With 37mm of extension on a normal 50mm lens you should be able to get to just below life-size using the close-focusing of the lens itself. With the Canon compact EF 50mm f2.5 macro you would get over life-size. So the question is whether near to life-size is close enough for you. If it is you don't need more extension tubes, whereas you might need more extension if you want to get closer than that.

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Kraig
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Link to coin photo Articles
In reply to bruxi, 6 months ago

http://coinimaging.com/index.html

I came across this guy once and bookmarked him lots of good  macro info he is a coin guy.

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_sem_
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Re: How many extension tubes needed?
In reply to bruxi, 6 months ago

bruxi wrote:

I have a Canon 12 mm extension tube (EF II) and a Canon 25 mm EF II on order. I like to shoot macro of coins and bugs. I've noticed an online classified ad in my area for another 12 and 25 (same tubes) for an amazing price. If I am going to be working with a 50mm lens, should I add to the 37mm tube length that I'll have? I could buy either the 12 or the 25. This deal won't last.

The longer the extension, the higher the magnification, but also the shorter the free working distance. At a certain point, you reach the highest magnification as the subject hits the glass. Even earlier than this, it becomes difficult to illuminate the subject. There is also adverse impact of extension on image quality, but it tends to be worst at wide apertures, which are less used for macro due to thin DoF.

You could probably use another 25mm with a 50mm lens. Bellows are more convenient to operate than long stacks of tubes though. If you want to play with high magnifications, you should get a reversal adapter. Extension also increases magnification with a reversed lens; at higher magnifications this tends to produce a bit more working distance and better quality. For higher magnifications, you could consider reversing a lens with a shorter FL.

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Michael Benveniste
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Re: How many extension tubes needed?
In reply to bruxi, 6 months ago

The number of extension tubes you need depends on the lens you want to use and the magnification you want to achieve. I use this site to get a pretty good idea:

http://home.comcast.net/~nikond70/Tools/Simple_Close-up_Calculator/Simple_Close-up_Calculator.htm

With your 50mm f/1.4, with 37mm of extension you can reach magnifications of just under 0.75x. With 74mm, you can reach magnifications of just under 1.5x.

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