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In photography, 35mm equivalent reproduction ratio, or 35mm equivalent magnification, is a measure that indicates the apparent magnification achieved with a small sensor format, or "crop sensor" digital camera compared to a 35mm-based image enlarged to the same print size. The term applies to macro photography and is useful because most photographers are familiar with the 35 mm film format.     
Classically, a "true" macro lens is defined as a lens having a reproduction ration of 1:1 on the film or sensor plane. This remains the case, however now that small sensor format digital cameras are more prevalent than so-called "full-frame" 35mm cameras, an actual reproduction ratio of 1:1 is rarely achieved or needed to take macro photographs with these compact cameras. For example, the 12 megapixel Micro Four Thirds Panasonic GH1 camera with a 2x crop sensor only requires a 1:2 reproduction ratio to take a picture with the same subject size, resolution, and apparent magnification as a 12 megapixel "full-frame" Nikon D700 camera, when the images are viewed on screen or printed at the same size. Thus a Four Thirds system macro lens like the Olympus Zuiko Digital 35mm F3.5 Macro lens with a true maximum image magnification of 1.0x is rated by Olympus as having a "2.0x 35mm equivalent magnification". Similarly, Panasonic rates its Leica DG Macro-Elmarit 45mm F2.8 ASPH O.I.S. lens in the same fashion.
Calculating 35mm equivalent reproduction ratio
To calculate 35mm equivalent reproduction ratio, simply multiply the actual maximum magnification of the lens by the 35mm conversion factor, or "crop factor" of the camera. If the actual magnification and/or crop factor are unknown (such as is the case with many compact or point-and-shoot digital cameras), simply take a photograph of a mm ruler placed vertically in the frame focused at the maximum magnification distance of the lens and measure the height of the frame. Since the object height of a 1.0x magnified 35mm film image is 24mm, calculate 35mm equivalent Reproduction Ratio by using the following:
(35mm equivalent Reproduction Ratio) = (measured height in mm) / 24
Then to find the true reproduction ration of the lens, use:
True reproduction ratio = (35mm equivalent reproduction ratio) / C
Where C is the 35mm conversion factor, or "crop factor". Some common crop factors are:
|Type||Height (mm)||Crop factor|
|1/2.5" (Many Superzoom and point-and-shoot cameras)||4.29||5.6x|
|1/2.3" (Compacts and Superzooms like Canon Powershot SX Series)||4.62||5.2x|
|1/1.8" (High-end compacts like Canon Powershot G1 - G7)||5.32||4.5x|
|1/1.7" (High-end compacts like Canon Powershot G9 - G12)||5.70||4.2x|
|2/3" (Fujifilm X10)||6.60||3.6x|
|m4/3 · 4/3" (Four Thirds)||13||1.84 - 2x|
|Sigma Foveon X3||13.80||1.7x|
|General APS-C (Nikon DX, Pentax K, Samsung NX, Sony α & NEX)||15.60||1.5x|
- ↑ Digital Photography Review. Panasonic Leica DG Macro-Elmarit 45mm F2.8 ASPH OIS Review. dpreview.com. Digital Photography Review. Retrieved on 11 June 2012.
- ↑ Outdoor Photographer Staff. Choosing Your Macro. Outdoor Photographer. Retrieved on 11 June 2012.
- ↑ Pitts, Wes. Intro To Macro. Digital Photo Magazine. Retrieved on 11 June 2012.
- ↑ Arva-Toth, Zoltan. Zuiko Digital ED 50mm f2 Macro Review. PhotographyBLOG. Photo 360 Limited. Retrieved on 11 June 2012.
- ↑ Wetpixel: Underwater Photography Forums. Help with reproduction ratio. Wetpixel.com. Retrieved on 11 June 2012.
- ↑ 6.0 6.1 Wattie, John. Digital Stereo Macro Photography. nzphoto.tripod.com. Retrieved on 9 June 2012.
- ↑ Olympus Imaging Corp.. OLYMPUS : ZUIKO DIGITAL 35mm F3.5 Macro. Four-Thirds.org. Olympus Imaging Corp.. Retrieved on 9 June 2012.
- ↑ Panasonic Corporation. Leica DG Macro-Elmarit 45mm F2.8 ASPH O.I.S. lens. panasonic.net. Panasonic Corporation. Retrieved on 9 June 2012.
- ↑ Defined here as the ratio of the vertical height of a full 35 frame to that of the sensor format, that is CF=Height24mm / Height sensor.
- ↑ Depending on aspect ratio. 2x is most commonly used.
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