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Old Sep 12, 2004, 6:30 PM   #1
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So, macro performance on a digicam seems to be measured by the minimum field you can capture (for instance, my c-4000 can capture a minimum field of ~1.7 x 1.25 inches) This make complete sense to me.

However, people don't seem to rate SLR macro lenses the same way. Instead they use strange alien dialects involving the words "life size" and "1:2 magnification." This makes no sense to me.

So my questions are. How can I tell just how small of an area a given lens can focus on? Is this 1:2 business somehow related to the focal length of the lens? Also, I noticed that in general, SLR macro lenses don't let you get all that close to your subject (typical focusing distance seems to be around 6-8 inches. compared to my c-4000's .8 inches.) Why can't I get closer with SLR macro lenses?


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Old Sep 12, 2004, 8:07 PM   #2
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The question isn't how close you can get, it's a question of how big the subject is in the picture. If you photograph bugs, you want them to appear big in the frame but not get that close. So close isn't always important.

This should explain what the 1:2 means:

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Old Oct 3, 2004, 10:15 PM   #3
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The system for describing macro performance dates back to film days when people made contact prints and were very aware of the size of their film. At 1:1 the image on the film was the same as it was in life. Digital cameras come with various size sensors as described by the 'magnification factor' or 'cropping factor'. Canon makes cameras with factors of 1 (same as film), 1.3 and 1.6. The same lens will provide the same size image of all three types of cameras but the 1.6 models will crop to the center of the image so it seems that you are getting a lot more magnification than you did with the same lens on film. Since the sellers of lenses do not know which of the sizes you will be using, it is easier to give the spec in the reproduction ratio format rather than saying that you can fill the frame with something 13mm or 21mm across (depending on the camera model).

If you have a 10D, 20D or Digital Rebel, the 15x22mm sensor means that a 1:1 rated macro (like the Canon 100mm f/2.8 will fill the frame with something 15x22mm in size. A 1:2 lens will require something twice as big to fill the frame. Of course, since the lens is interchangeable, you can always add extension tubes to get closer up to the point that you are focussed on the front glass. Before you get to that point you will run into problems like how to get light on the subject and how to focus with zero depth of field but the SLR system ismost flexible in the macro department.

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Old Oct 10, 2004, 10:03 PM   #4
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1:2 = about 2.75" x 1.75" (double the dimensions of a 35mm negative)

1:1 = about 1.38" x 0.38" (same dimensions as a 35mm negative)

2:1 = about 0.69" x 0.44" (half the dimensions of a 35mm negative)
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