Electronic Viewfinder Interchangeable Lens cameras (EVIL) are gaining popular acceptance in the world of underwater photography. Manufacturers are responding to the new popularity with new lenses, housings, domes, and other accessories. In this article we will investigate the macro-photography capability of a micro-four-thirds camera.
This article will:
-
investigate the macro-photography capability of a micro-four-thirds format digital camera.
-
demonstrate the difference in a 'regular' lens and a 'macro' lens.
-
explain the importance of minimum focus distance.
-
photograph the smallest possible subject using a 14-42mm zoom lens with and without a +10 diopter.
-
photograph the smallest possible subject using a 45mm macro lens.
-
explain reproduction ratio.
-
demonstrate the importance of reproduction ratio.
-
demonstrate how cropping reduces resolution.
Reproduction Ratio
Reproduction ratio is a method of comparing apples to apples amongst differing camera formats. It is defined as the ratio of the size of the subject photographed to the size of the image of that is projected onto the image sensor (or film).
When photographers refer to reproduction ratio, neither the size of the camera display, nor the computer screen, nor the size of the print, is considered. Reproduction ratio, by itself, will tell you nothing about image resolution; a 4:1 reproduction ratio with a 36 megapixel sensor will not have the same resolution as a 1:1 reproduction ratio image on a 10 megapixel sensor.
Reproduction ratio is a statement of information that tells you about the optical system, from the subject you photograph, through all lenses, to the image sensor or film.
Comparing apples to apples?
A 1:1 reproduction ratio
-
Large Format Camera 4 x 5 inch; a subject 5 inches wide will result in an image 5 inches wide on the film.
-
Medium Format Camera 6cm x 6 cm; a subject 6cm wide will result in an image 6cm wide on the film.
-
FX Format Digital Camera or 35mm Film Camera 24mm x 35mm; a subject 35 mm wide will result in an image 35mm wide on the film (or sensor).
-
DX Format Digital Camera 23.7mm x 15.5mm; a subject 23.7mm wide will result in an image 23.7mm wide on the image sensor.
If you know the focal length of the lens and the physical size of the camera sensor (or film), can you calculate reproduction ratio? No! You also need to know the distance from the lens to the subject being photographed.
Reproduction ratio is determined by the focal length of the lens and the distance to the subject.
What do all these different camera formats have in common when using a 1:1 reproduction ratio? A 10 mm subject will make a 10 mm image on the film, or the digital sensor, regardless of the film or sensor size, regardless of the focal length of the lens! Cropping the image does not change the reproduction ratio.
Minimum Focus Distance
You might think that a 14-42mm lens, when zoomed to 42mm will be "almost as good" as a 45mm lens. Is this true? Definitely "maybe". A very important factor which we have not yet discussed is minimum focus distance. Why? Because the distance from the lens to the subject will determine the size of the image of that subject. Therefore, simply moving closer to the subject, will get your reproduction ratio closer to 1:1. So it is possible that two lenses with the same focal length could have different reproduction ratios.
Pixels and Resolution
It is the relationship of reproduction ratio to sensor pixels that will determine the maximum possible resolution of an image (for the purposes of this article, we will not be interested in interpolation, aliasing, etc.). The Panasonic GF2 uses a 12 megapixel sensor. It is arranged with 4,000 pixels horizontally and 3,000 pixels vertically. Knowing that the sensor width is 17.3 mm, we can calculate the size of each pixel. 17.3mm / 4,000 = 0.004325 mm, which is equal to 4.325mm. That is 0.0000043 meter (or 0.0002.1 inch).
Lens Tests
For these tests we compared the Olympus M.Zuiko 14-42mm lens to the Leica 45mm lens. Each lens was also tested with the Subsee +10 diopter. The camera was a Panasonic GH-2 in a Nauticam NA-GH2 underwater housing. The camera was handheld in a utility sink filled with potable water.
To speed up these tests, we installed the Reefnet SubSee +10 diopter onto a Saga Dive Flip Lens Holder for 67mm lenses. Using the Saga Dive Flip Holder we can change the diopter in and out in less than a second.
First, let's see how the Olympus 14-42mm lens does. Looking at the shot below, we see that the frame is filled by the marks on the scale at 226mm through 305mm. The size of the subject appearing on the 17.3mm wide sensor is 79mm wide (8+7/8 inch through 12 inch = 3+1/8 inch wide). The reproduction ratio is then calculated as 17.3 / 79 = 1 : 4.6
1 : 4.6 Reproduction Ratio
Olympus 14-42mm at 42mm
For the next test we flipped the Reefnet Subsee +10 diopter into position, and again, moved the camera as close as we could get focus lock. The resulting image is shown below. In this image we see from 233.5mm through 268.5mm on the scale, which tells us that a 35mm wide subject will fill the 17.3mm wide sensor. In the 35mm film world, this would be called a 1:1 reproduction ratio. To get the true reproduction ratio we calculate the 17.3 / 35= 1 : 2.
1 : 2 Reproduction Ratio
Olympus 14-42mm at 42mm With SubSee +10
Now let's look at the Leica 45mm lens.
1 : 1 Reproduction Ratio
Leica 45mm Lens
We can see the marks on the scale from 230mm to 247mm; a distance of 17mm. In this case the reproduction ratio is 17 / 17 = 1:1. You may also see that getting closer means it is more difficult to light the subject.
But can't I just crop my photograph?
Computers and some really nice software make it very easy to crop your photos. So why spend the money on a good macro lens when you can just crop the photo? Here is the same 1 : 4.6 photo we showed above, but cropped to show only 17mm across, to fool ourselves that this could be a 1 : 1 photograph.
1 : 4.6 Photograph Cropped to 1 : 1 Dimensions
In the cropped "1:1" photograph we see that chromatic abberation is more obvious (it should be, we 'magnified' the image 20x larger [4.6 times in each direction]). Also when you compare this image to the uncropped photograph, it seems as if most of the dust on the ruler has somehow disappeared in the cropped image. The reproduction ratio was not good enough to make an image of the dust.