Understanding macro with Olympus 3/4 system.

Started Mar 10, 2013 | Discussions thread
dave gaines
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Measuring macro with Olympus 4/3, Sigam 105, Olympus 50 mm & others
In reply to GrayPlayer, Mar 11, 2013

GrayPlayer wrote:

Need help understand macro image size with Olympus 3/4 system. Have E-620 and Sigma 105mm 1:2.8.

Macro lenses are designated by one of three measures of magnification: One is the macro ratio, such as 1:1 or 2:1. Another measure is magnification, such as 1.0 or 0.50, which means the same as the previous 2 measures. The other parameter usually given is minimum subject size when focused at the minimum focus distance. For Olympus 4/3 format the minimum subject size is 17 mm x 13 mm at 1:1 or 33 mm x 26 mm at 2:1.

Try focusing the lens on a metric scale. Move in close until you find the minimum focus distance of the lens, or set the distance scale to the minimum and focus by moving in. If it's 1:1 macro the smallest width you can focus on will be the same size as the sensor, or 17 mm x 13 mm for Olympus 4/3, m4/3, or Panasonic 4/3 and m4/3. Hold the camera somewhat square over the scale laying flat. Check the wide distance of the image against the horizontal scale and read the distance.

The Olympus 50 mm f/2 lens focuses in macro down to 2:1. The smallest image you can focus on, at the minimum focus distance, is 33 mm wide. Olympus gives the macro magnification in terms of a decimal, or 0.52. The inverse of that decimal number is close to 2, or macro at 1:2.

Adding the EC-14 teleconverter lens converts the lens to a 70 mm f/2.8. This allows you to focus from farther away. It will still focus at 2:1, providing nearly the same 33 mm wide subject size.

Adding the EX-25, the 25 mm extension tube, makes the 50 mm f/2 macro lens a closer focusing, 1:1 macro lens. It will then focus on a minimum subject size of 17 mm x 13 mm.

When comparing macro image size it's good to also compare it to macro on a 35 mm film plane (36 mm x 24 mm). People that I shoot underwater photos with compare macro to 35 mm, or the "full frame" sensor. Those folks think that anything smaller than 6:1 is still macro. This would be a subject size of 216 mm by 144 mm. That's a large subject in my mind. What's significant is that many people think of macro in terms of the subject size, and they also compare it to 1:1 on film.

A 33 mm x 26 mm minimum image size is approximately the same minimum subject size when compared to any 1:1 macro lens on 35 mm film cameras. Since 4/3 format has 4:3 frame proportions, not 3:2 like film, the difference is in the image proportions. That's why Olympus says the 50 mm f/2 lens is 1:1 macro in 35 mm film equivalents. But it's really 2:1 when compared to the 4/3 digital sensor, which is a truer macro measure.

I'm not familiar with the specs for the Sigma 105 f/2.8 macro lens and how that compares to the Oly 50 mm f/2 macro, but it will allow you to focus from farther away. This is good for skittish critters that won't let you get close, like butterflies.

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Dave

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