Zhongyi (Mitakon) 20mm 4-4.5X F/2 Super Macro Lens
Overview & First Impression
Zhongyi Optics of Shenyang, Liaoning China has introduced an exciting new super macro lens with 20mm focal length and 4-4.5X magnification range and a FAST aperture of F/2.0. I am very lucky to get an early copy of it and started stacking some images.
When I received it, the impression was good, unlike other Chinese lenses, it is well packed with customized protective foam all around it. Build quality is very impressive, it feels heavy given its small size and there is definitely this "all metal" feeling! Coupled with superb surface finish, it gives you the impression of quality. Here are some pictures
The next thing I tried is to turn the focus ring (or rather the magnification ring) and it is smooth and silky with right amount of dampin. I can turn it fairly fast, not that one would do so in actual usage, I was just trying to feel how smooth it is. Because of excellent first impression of its build quality, this is somehow what I expected to be. Next I turned the aperture ring, to my surprise, it is continuous, no clicks sound for each marked stops. It is just as silky as the magnification ring with right amount of damping.
Technical & Details
The lens is a manual focus lens with continuous aperture from f/16 to f/2, compatible with full frame camera, though I have only tested it on my APSC Canon 550D, I have no reason to doubt it will work with full frame. Minimum focus distance, or working distance as most extreme macro photographer call it, is 20mm as specified. Actual tests show it is 21.67mm at 4x magnification and 16.82mm, This might disappoint many photographer used to normal lens, but it is a decent working distance compared to many 4X to 5X microscope objectives, so as an extreme macro photogrrapher, there is no complain from me at all, in fact quite happy with it.
Here is how I measured it -- put it on my Canon 600D and put it on my stacking rail, then move them so the front of lens just make contact with a flat object, then move it back until I get sharp focus. My stacking software will show me the distance it moved.
The lens just touched a flat object, error could result if it is not "just touch" the flat object.
Lens is moved back and I have obtained a sharp focus
My stacking rail control software shows 21672um or 21.672mm. This is for 4x magnification.
Inside group of glass elements, there is this 3 blade iris. At first this is not a big deal, again as an extreme macro photographer, I have never used a microscope objective with an iris. Here is a picture of the iris shot from front with iris set to f/16
However, things get a little weird when shooting a subject with out of focus highlights -- triangular bokeh appeared as shown below.
The above image showed up when I was doing a focus stack, it is the #63 image and images around. If you are shooting with single images, this probably will not be acceptable. However, when I finished stacking, this is gone as shown below.
As shown above, the triangular bokeh is gone in final stacked image. This is because stacking software (in this case Zerene Stacker) will only pick sharpest part of the image and the bokeh is not part of it.
The issue with weird out of focus bokeh also shows up as doughnut shaped artifacts. Here is a video that shows what happens when camera is moved in and out of focus, you can see doughnut shaped bokeh show up and disappear as focus moves along the subject (small part of hind leg of a beetle)
Of course, as demonstrated before, this is not a problem if you intend to do focus stacking and final results are excellent.
Having 20mm focal length has one advantage over longer focal length lenses -- increasing its already super magnification to even higher magnification by adding extension tubes. Because it short focal length, adding every additional 20mm extenson will increase magnification by 1X. So by adding a 100mm extension tube, which is routine in extreme macro work, you can achieve 4.5+100/20 = 9.5x. The company hinted to get to 13X, I only tested it up to 10x by adding 120mm extension tubes. The shorter the overall length of lens, the less vibration issues and the easier to make. To compare it with a standard 100mm 1X macro lens like Canon EF 100mm macro, to achieve 9.5x, you would need an extension tube of 850mm or 2.79 feet, that is impossible.
Another good point with this lens is that it is relatively fast, with maximum aperture of f/2 This is important because as magnification increases, by adding more extension tubes, the effective aperture gets smaller. For example, without any extension tube, the effective aperture is f/8 at 4x. When increased to 6x, the effective aperture is f/12, even for APSC cameras, this is still outside diffraction limited range. For full frame cameras, even if you increase magnification to 10x, the effective aperture is f/20, still outside diffraction limited range.
As an extreme macro photographer, this lens offers me the following advantages:
1. Shorter focal length makes extending it easier
2 Fast aperture make its easier to achieve higher magnification with decent effective aperture
As discussed above, some disadvantages:
1. Triangular iris and doughnut shaped bokeh, but not a problem if you are stacking.
2. image quality is a little soft, especially pushed up to higher magnification, but I think it is still acceptable, particularly for casual users and stackers.
The following are some stacked ima