How macro lenses work

[serid]

Hi All,

I am new to photography and am reading lots of documents / books about it
as I got fascinated totally ...

The only thing I am still getting confused of is this:

1) The closer subject to focal length point of a lens, the magnification is bigger
2) The closer the subject, the bigger focal length needs to be in order to capture
the image in good focus

One of the easiest way to convert a lens to a macro lens is to use an extension
tube - we extend focal length thus allowing closer distance to a subject (and bigger
magnification).

How about true ready made macro lenses ? How do they work ? I just cannot imagine
how they are constructed. How is the magnification achieved ?

I understand, that extending focal length doesn't mean that we need to physically
make a lens longer - that can be compensated by a set of additional set of lenses inside
it, but macro lenses with bigger focal length allow capturing subject with bigger magnification in bigger distance .... How is it done ?

Could anyone cast a light on this topic for me please ?


Thanks,

Adrian

[Tony-S]

Macro lenses simply extend the elements away from the sensor, enlarging the projected image. You can really see this on macro lenses that do not have internal focusing, such as the Sigma 105mm f/2.8 macro. The internal focus lenses (e.g., Canon 100mm and Sigma 150mm do the same thing but it's not conspicuous.