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Old Jun 16, 2010, 1:38 PM   #1
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Default What does the macro switch do on my lens?

Hi,
I just bought a 70-300 Tamron Di LD lens, after asking everyone about a decent budget zoom.
Question is what does the macro switch really do?

Thanks
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Old Jun 16, 2010, 2:02 PM   #2
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If you're zoomed in towards the longer end of the lens (between 180mm and 300mm), it allows closer focus (so that a smaller subject will occupy a larger percentage of the frame for a given focal length).

See the Tamron's product information page here:

http://www.tamron.com/lenses/prod/70300_di_a017.asp

Here's a quote:

Quote:
Flipping a macro switch in the focal length range of 180mm to 300mm obtains a maximum magnification ratio of 1:2 at a minimum focus distance as short as 37.4", enabling close-up shots of flowers, insects, and other objects that normally require the use of a specially designed macro lens.
Basically that means that you can fill the frame with a subject that's twice the size of the camera's film or sensor (APS-C in the case of most dSLR camera models) when zoomed into 300mm and focusing at a distance of 37.4 inches (from the sensor or film, not the front of the lens), if you use the Macro switch after you zoom into towards the longer end of that lens.

To get better 1:1 (a.k.a., life size) magnification, which means you can fill the frame with a subject as small as the camera's film or sensor, you'd need a prime (fixed focal length versus zoom) macro lens rated at 1:1 Magnification (versus 1:2 as in that Tamron's specs).
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Old Jun 16, 2010, 2:07 PM   #3
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With the macro switch set to NORMAL, the minimum focusing distance is 1.5m and the lens has a magnification ratio of only 1:3.9. when the focal length is from 180mm to 300mm, and you move the switch to MACRO, the lens has a minimum focusing distance is 95cm and the lens has a magnification ratio of 1:2.
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Old Jun 16, 2010, 2:24 PM   #4
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So, I guess it is for of a distance shot, but wanting extreme close up on a bird, flower? Does it actually change the magnification that you see in the view finder, I am not home yet to test it?
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Old Jun 16, 2010, 2:41 PM   #5
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The magnification rating is representative of the smallest subject that can fill the frame at the closet focus distance and longest focal length (zoomed in more for more apparent magnification).

With a 1:2 Macro lens like that Tamron, if you zoom in to 300mm and use the Macro switch, you can fill the frame with a subject twice the size of the camera's APS-C size sensor in the case of most dSLR models.

IOW, a smaller subject takes up a great percentage of the image (your viewfinder view, how it looks on playback, etc.).

If you have a lens rated at 1:1 (no zoom lenses will do 1:1, so 1:2 is good for a zoom lens like that Tamron), then the the smallest subject size that would occupy the entire frame at the closet focus distance and longest focal length would be the same size as the camera's film or sensor.

Here's a .pdf brochure for that lens discussing that Tamron's 1:2 macro feature:

http://www.tamron.com/lenses/prod/as...Di_catalog.pdf
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Old Jun 16, 2010, 3:08 PM   #6
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I understand now. Thanks
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