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Old Feb 29, 2012, 10:08 PM   #1
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Default magnification factor

hello
is there an easier way to figure out the magnification factor of a lens when doing macro esp. if you dont have a dedicated 1:1 macro lens.
for example what does .19x mean.
i think it means 80% of the original size of the thingee your shooting.
or its covers 80% of the sensor.
whatever,
is there a quick easy way to convert these .19x specs. without doing complicated math in your head or on paper.
thanks in advance for any responses.
spring is almost here
cheers
pete

Last edited by deterpawson; Mar 2, 2012 at 8:56 AM.
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Old Mar 1, 2012, 6:33 AM   #2
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Some manufacturers quote the magnification factor as a ratio (i.e.: 1:1, 1:2, 1:2.7, etc.) while some use the decimal equivalent (i.e.: 0.25, 0.22, 0.34, etc.)

They are the same, just from a different perspective.

A magnification ratio of 1:4 is the same as the decimal equivalent of 0.25x. Think of the ratio as a fraction (instead of 1:4, think 1/4.) To convert a decimal equivalent to a ratio, divide 1 by the decimal equivalent. A decimal equivalent of 0.19x is 1/0.19 or 5.26, which means a magnification ratio of 1:5.26.

The magnification ratio is generally used for genuine macro lenses, while the decimal equivalent is generally used for non-macro lenses.
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Old Mar 1, 2012, 7:27 AM   #3
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That was informative and easy. Good question and answer, thanks to both the OP and the answer.
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Old Mar 2, 2012, 8:57 AM   #4
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thank you kindly TCAV
fabulous
now i can work it out whenever i dont have a macro lens
using tubes really cant afford macro yet
enjoy
peace and happiness
pete
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Old Mar 2, 2012, 10:13 AM   #5
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If you want to figure out the magnification ratio when using extension tubes, or any macro configuration, take a photo of a ruler (A metric ruller would work best. That will eliminate the necessity of any English to Metric conversion, etc.) at your system's closest focusing distance. Compare the length of the scale on the ruler to the width of your image sensor, and you've got the magnification factor for that system.

For instance, the following image was created using a 50mm lens at its minimum focus distance, on an extension tube on an APS-C dSLR. The scale in the image is about 11/16 inch long. An APS-C image sensor is roughly 24mm wide. So the magnification ratio can be calculated as follows:

11 / 16 = 0.6875 inches

0.6875 * 25.4 = 17.4625 millimeters

(Does anyone see the advantage of using a Metric scale instead of an English scale?)

24 / 17.4625 = 1.37

... or a magnification ratio of 1.37:1, which is greater than 1:1. That's better than most Macro lenses.
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Last edited by TCav; Mar 2, 2012 at 10:15 AM.
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Old Mar 2, 2012, 10:29 AM   #6
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If the image had contained a length that was longer than the width of the image sensor, the result would have been a little different. For instance, suppost the length was 1 3/16 instead:

1 3/16 = 19/16 inches

19 / 16 = 1.1875 inches

1.1875 * 25.4 = 30.1625 millimeters

24 / 30.1625 = 0.80

... which is the decimial equvalent of the magnification ratio (0.80x). To calculate the magnification ratio, divide the length of the scale by the size of the sensor:

30.1625 / 24 = 1.25

... or a magnification ratio of 1:1.25 , which is less than 1:1.
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Last edited by TCav; Mar 2, 2012 at 4:58 PM.
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