The rings
These rings cost US$10, including shipment from China, which is very cheap. Upon arrival, I noticed that the quality did appear rather poor, in line with the price. The box is rather anonymous, with a "OM4/3" text and something in Chinese:
In the picture below, they are all screwed together, to give the longest possible extension:
And below, I have unscrewed them into individual components:
From left to right: The ring that goes into the adapter, or into a Four Thirds standard camera, and the first extension ring (1, 7mm), the second extension ring (2, 14mm), the third extension ring (3, 27mm), and finally the ring on which the lens is mounted.
By using these rings in different permutations, extensions of 17mm (just the front and rear ring), 24mm, 31mm, 38mm, 44mm, 58mm and 65mm (all the rings) are possible. The 24mm extension, using only the first extension ring marked with a 1, corresponds pretty much to the Olympus EX-25 Four Thirds extension ring at 25mm.
Operation
When using these rings, please note that they have are no electrical contacts at all. This means that the lens is "dead" when mounting it onto the macro extension rings, and you cannot operate the focus or the aperture.
I'm guessing that it is best to first extend the focus of the lens all the way, and then mount it on the extension rings. To do this, you must do a small trick, namely to first manually focus the lens to the minimum focus distance while it is mounted to the camera, and then unmount it without turning off the camera first. That way, you can mount the lens on the extension rings while the focus is already at the closest. Most likely, you'll want to use a smaller aperture than f/2, and again you must do the same trick: Change the aperture and unmount the lens without turning off the camera first. Of course, this process is rather awkward if you are going to experiment with different apertures.
The results
So how do these extension rings affect the close focusing possibility of the ZD50 1:2 macro lens?
First, let's see how close it can focus without any extra extension. Here the lens is mounted to the 4/3 to M4/3 adapter, on the Panasonic GH2 camera:
And the resulting image, at f/8, ISO 160:
24mm extension, 1:1 macro
Using the 24mm extension, corresponding roughly to using the Olympus EX-25 macro extension, the setup looks like this, note that the figure is closer to the front lens element:
With this resulting image, also at f/8 and ISO 160. This corresponds to around 1:1 magnification:
65mm extension, 2:1 macro
Finally, adding all the macro rings for a total of 65mm extension yields this setup:
Note that the figure is now very close to the front lens element. It is not easy to light the figure properly in this position, since the lens casts shadow over the subject. The resulting photo looks like this, at around 2:1 magnification, also written as 2x:
Conclusion
These macro extension rings were cheap, and not very good quality. Further, since they have no electronic contacts, they are very awkward to use. You must stop down the aperture before mounting the lens on the extension rings, which makes focusing harder. Normally, you focus at maximum aperture, and then stop down for taking the picture, which is handled automatically by the camera. But with no communication between the camera and lens, this is no longer possible.
The Olympus EX-25 extension rings allow for changing the aperture, and is probably much easier to use. However, it is also much more expensive.
At full extension, the macro rings allow for roughly 2:1 macro magnification, meaning that you can photograph an object with a diameter of half the diameter of the imaging sensor.
If you want to increase the magnification of a Four Thirds lens, but don't want to shell out the cash for the EX-25 extension ring, I would recommend that you simply crop the center of your images, rather than buy these cheap rings. The rings are not very fun to use, due to the lack of electronic contacts, and the poor quality. Keep in mind that since these rings are for the Four Thirds format, they cannot be used for Micro Four Thirds lenses. They can only be used for Four Thirds lenses.
