Macro filter and focusing


TPF Noob!
Oct 11, 2007
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Will a macro lens or even an extension tube change the distance of how far I have to be before the camera/lens will focus? I searched the forums about macros filters, extension tubes and read something about bellows, but I saw nothing about the miniumum focal distance if it is increased or decreased at all. And just for clarification a macro is not necisarrily a magnification of the image/zoom, but more the magnification of the light allowing more details to be captured on the subject right? Sorry if this has been asked a million times, but I am currious.
I can't speak to the filters, I've never used one. A macro lens simply allows you to focus more closely. Other than that it's a normal lens with the same challenges.

Extension tubes can be even more challenging and do not allow infinity focusing. In fact, there is a very small focus area at any given focal length with it decreasing at shorter lengths. When using extensions it's often times best to set the lens (focal length and manual focus) for the magnification you want (especially if attached to zoom lenses) and physically move back and forth form the subject to focus.

Focusing so close introduces many challenges, Two very important ones are are a very thin DOF and lighting.

hope that helps

you may find this little booklet from canon useful:
Auxiliary close-up lenses (or macro filters as many people call them) do permit you to focus more closely - ie they decrease the minimum focus distance. They do not alter the effective aperture of the lens in most cases.

They work by producing an effective focal length that is shorter than the focal length of the main lens ("prime" lens, "prime" having two different meanings nowadays) - ie the lens becomes more powerful and hence focuses more closely. You lose infinity focus.

Auxiliary close-up lenses are not very well corrected for aberrations, and you need to stop down to get decent image quality. Some of the manufaturers, including Leica, Nikon and Canon, produce a more expensive line of close-up lenses that have at least two elements. These have some degree of correction of aberrations. The Nikon two-element versions are suffixed with a 'T' to show that they are mainly intended for use with telephoto lenses, but they can be used with other lenses.

A similar effect is used with some true macro lenses. Some of them achieve their close focusing ability by shortening the focal length as you focus more closely. True macro lenses not only allow you to focus more closely but they are also corrected for close-up use, which normal lenses aren't. They often achieve that at the expense of their ability to perform as well at greater distances.

Here is an earlier thread on close-up lenses that has a little more detail: link.


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