Venus Laowa 25mm f/2.8 2.5-5X Ultra Macro,
tested at 4x
Very few current produced photomacrography lenses exceed a 2x magnification unaided (i.e., without using some kind of bellows, extension tubes, tube lens or add-on front lens). Among these, only three reach 5x:
All three lenses cover a full-frame sensor, and they share the same fundamental design, i.e. :
Manual operation of the "focus ring". In practical use, the focus ring is rarely used for focusing, and has instead the function of changing magnification. Autofocus would be largely useless in these lenses, since at these magnifications DOF is so shallow, that most of the time autofocus is likely to choose the wrong part of the subject to focus onto.
Using these lenses requires a mechanism (usually a focusing rack or a micrometric linear rail) to finely adjust the distance between the subject and the camera + lens assembly. With the possibly single exception of a legacy Minolta photomacrography lens, this mechanism is not a part of the lens.
Lens aperture is fully manual, except in the Canon lens. Automatic or preset aperture can be advantageous with the optical viewfinder of a DSLR, in order to provide as bright as possible a picture in the viewfinder. The Canon MP-E 65 and its automatic aperture were designed to facilitate framing and focusing in the context of this optical viewfinder. With live view now optional in virtually all current DSLRs, and obligatory in mirrorless cameras, an aperture that closes to the chosen value just before the exposure is no longer necessary for a comfortable framing and focusing of the subject, especially if artificial illumination is available. I prefer a fully manual aperture that shows me the actual DOF of the image, so that I can made the best use of it.
The Canon MP-E 65 has been around for quite several years, and its design has never been updated or improved. Canon is still offering it, in spite of past rumors that it had been discontinued. A problem with this lens is that it lacks a physical aperture ring. Adapting this lens for use on non-Canon cameras requires the use of a "smart" adapter capable of translating the electronic signals produced by the camera body into signals that the lens can understand, or tortuous shenanigans involving setting the lens aperture on a Canon camera, then moving the lens to the camera used to record images without the lens resetting its aperture. Another problem with this lens is that the front diameter of the lens barrel is so large compared with the diameter of the front optical element, and the working distance of the lens so short, that at high magnification the front of the barrel makes it difficult to suitably position the light sources.
The two remaining lenses are more recent offerings, and are available in a variety of full-frame lens mounts. While the Zhongyi lens has a built-in tripod collar, the Laowa lens does not come with one, and Laowa sells it separately as an option. This tripod collar, however, is insufficiently stiff, and I prefer to use the tripod shoe of a Metabones Nikon F to Sony FE adapter, further equipped with a long Arca-compatibe plate that adds a convenient way to coarsely adjust the distance to the subject (Figure 1, rightmost).
The Zhongyi 85 mm f/2.8 is a good idea crippled by a faulty design and a poorly thought-out fix of the fault. In 2019, this lens caught the attention of several photographers specializing in photomacrography when it became known that Zhongyi had sent test prototypes of a 1x-5x lens to a few professional photographers. Some of the latter, within the limitations of their non-disclosure agreements, expressed very high opinions on the performance of these prototypes. Once the first production batch of the lens reached buyers in late 2019, however, it quickly turned out that lens performance was quite poor in terms of both resolution and contrast. Clearly, Zhongyi had done some changes to the production batch that ruined the lens performance - one of the many examples of cost-cutting, corner-cutting practices common in Chinese companies and known as "quality fade". Typically, quality fade is a slow process that gradually takes place during the months or years a given item is being manufactured. In this case, quality fade seems to have been instantaneous, and to have taken place between the prototype manufacturing and the first production batch.
A quick fix of the problem with the original Zhongyi 85 mm f/2.8 came out in early 2020, and involved a much smaller front optical element and some internal changes. These changes did seem to partly solve the observed problems, but also reduced lens speed by about two stops, thus preventing the lens from producing its intended image resolution, especially above 2x. Making things even worse, Zhongyi never acknowledged this new problem. Zhongyi did not even change the pictures of the lens on their web site, which still (as of April 2022) show the initial, faulty version no longer available for sale.
Incidentally, this was not the first time Zhongyi had failed to produce a lens capable of providing its intended performance. The Mitakon Zhongyi 20mm f/2 4.5x Super Macro launched a few years earlier had apparently been designed to provide an extended magnification range, but prototype tests showed it was usable only within the very restricted magnification range of 4.0x to 4.5x. Rather than pulling the lens from production and heading back to the design board, Zhongyi decided to re-tool the production line to limit the travel of the focus/magnification ring, revise the nominal specifications, and go ahead with the sales anyway. This seems to indicate a toxic corporate culture where designs known to be faulty are not stopped from entering production. Instead, the worst of the faults are just plastered over rather than their root causes being corrected, and the still unsatisfactory products pushed onto unsuspecting customers.
Thankfully, Venus Laowa can design and build far better photomacrography lenses than Zhongyi, and is now known for products of high quality at reasonable prices. After the innovative but not fully satisfactory 60 mm f/2.8 2x, we have seen a quickly diversifying range of Laowa photomacrography lenses of better and better performance, as well as a few extreme lens designs previously unavailable in consumer products.
Laowa 25mm f/2.8 2.5-5X
In spite of providing only half the magnification range offered by its Canon and Zhongyi competitors, the Laowa 25 mm is remarkable for its good image quality, sufficiently fast lens speed, relatively narrow diameter of the front lens barrel, reasonable working distance even at the highest magnification, and solid construction. At 416 g, and considering this is a relatively small lens, it feels hefty and well-built. The magnification ring turns evenly and without wobbles, and the length of the lens in Nikon F mount increases from 82 to 137 mm thanks to a system of three snugly fitting coaxial barrels (including the fixed one carrying the lens mount). The front of the lens does not rotate when changing magnification.
The optical scheme uses 8 elements (one of which made from a low-dispersion glass) in 6 groups, and is therefore moderately complex by current standards. At least one floating group seems to be present at the rear of the diaphragm. All elements are thicker than usual, in spite of their small diameters. The 8-blade diaphragm sits behind the two first optical elements and is close to the front of the lens. In comparison, the Canon MP-E 65 uses 10 elements (of which one low-dispersion) in 8 groups and a floating subassembly, and the Zhongyi 85 mm uses an undisclosed optical formula with a floating subassembly.
A rectangular baffle flush with the lens mount is meant to eliminate stray light caused by unused portions of the image circle. This baffle moves within the barrel independently of the optical groups when magnification is changed, presumably in order to remain optimally placed at each magnification.
Some users reported an uneven vignetting in one or more corners when this lens was mounted on a T2 or M42 adapter. This was apparently caused by these screw mounts not perfectly aligning the rectangular baffle with the sensor. Although one user reportedly solved this problem by removing the baffle, I would suggest instead to properly align the baffle to the sensor by loosening the adapter's set screws and rotating the threaded mount of the adapter. This is possible in T2 adapters and most M42 adapters, but not in some T adapters.
The front element is mounted flush with the convex front of the barrel, and there is no front filter mount. If a filter is necessary, it should be mounted at the rear of the rectangular baffle.
A proprietary bayonet mount surrounds the front of the barrel. It is used to mount a proprietary front lens cap of metal-clad plastic. A small ring light, available at extra cost, can be mounted here. A tripod collar is also available. As mentioned above, I do not regard it as sufficiently stiff, and prefer to use an Arca-compatible plate integral to the Nikon F to Sony EF Metabones adapter.
The focus/magnification ring has a travel of approximately 100° and causes two coaxial sleeves to extend forward by about 55 mm. One of these sleeves is engraved with a magnification scale with markings at 2.5, 3, 3.5, 4, 4.5 and 5x that makes it easy to set the desired magnification. The aperture ring is located at the front of the barrel and has full-stop clicks between 2.8 and 16. It is useful to remember that E (effective aperture) is given by:
E = N (M + 1)
where N is nominal aperture (read from the aperture scale) and M magnification. Thus, taking the nominal aperture at face value, the effective aperture (rounded to the closest integer) at the magnifications available on this lens is:
Laowa provides essentially the same data of effective aperture in the user instructions of the lens, albeit only at nominal f/2.8 (rounded to the first decimal, which makes no practical difference).
Working distance is 45 mm at 2.5x and 40 mm at 5x. Thus, the working distance is much higher than the nominal focal length of the lens. The 14 mm diameter of the front element, for a lens with focal length 25 mm, would be enough to give a nominal f/1.8 speed (as calculated with the simplified formula N = L / d, where L is focal length and d the diameter of the front element), rather than the declared f/2.8. The high diameter of the front element is a result of several factors, including the optical position of the entrance pupil and the need to avoid vignetting and darkened corners at all available magnifications.
The relatively narrow (40 mm diameter) front of the barrel helps to illuminate the subject. However, an even narrower front diameter should be possible, and would further help. The main limitation is probably the diameter of the diaphragm housing, which is close to the front element, while the aperture ring could be moved a bit farther to the rear.
The following table shows the approximate field of view, in mm, recorded by this lens on a sensor of a given size (FF = 24x36 mm, APS-C = 18.7x24.9 mm, MFT = 13.5x18 mm). Be aware that there is no "standard" APS-C size, and APS-C sensors can somewhat vary in size among and within camera brands. Although easily computed, this table can be practical to have when setting an initial magnifications to use for a given task.
Robert O'Toole tested this lens at 2.5x and 5x (nominal magnifications), and reported that the actual maximum magnification is 4.82x. In order not to unnecessarily duplicate his test, I am presenting detailed results only at nominal 4x.
The subject of this test (Figure 3) is the tip of the tail of the same subject used for tests of the Laowa 100 mm f/2-8 CA-Dreamer Macro 2x. The cropped detail (Figure 4, 5, 6) is from mid-left to the image center. Image quality at nominal f/2.8 (effective f/14, Figure 4) is good but (as expected) slightly less excellent than with the best lenses at lower magnifications, with finest detail not much larger than one pixel in the areas in best focus. Some of the other areas, however, are blurred because they are out of focus, as a consequence of the low DOF. At nominal f/5.6 (effective f/28, Figure 5), the image is slightly blurred by diffraction, but DOF is significantly higher. Depending on the use of this image and the nature of the subject, an aperture in the interval between f/2.8 and f/5.6 could be the best compromise. At nominal f/11 (effective f/56, Figure 6) the image is significantly blurred and, unless the pixel count is substantially reduced, image quality is too poor in spite of the further increase in DOF.
If a low-resolution image for web publication is all that is needed, nominal f/8 and even f/11 might still be good enough. If the best image quality is required, f/2.8 should be used, probably combined with focus stacking if the subject is even slightly three-dimensional.
Figure 4 shows some axial chromatic aberration (green out-of-focus blobs, especially at the top and at the left of the subject), that becomes much less evident after closing the aperture to nominal f/5.6. This is a larger amount of this type of chromatic aberration than I have seen in other tests of the same lens. The color and relief of this particular subject may be partly resonsible for this.
Color, contrast and magnification range
With this lens, color and contrast are good at all magnifications. Color rendering is consistent with the Laowa 100 mm f/2.8 2x., so these two lenses can be used as a set covering the magnification range between zero (i.e. infinity focus) and 5x without significant interruptions. Probably, most of the other Laowa models of 2x macro lenses, especially the ones specified as Apo, are also suitable to complement the Laowa 25 mm f/2.8 2.5-5x (with the likely exception of the original Laowa 60 mm f/2.8 2x).
The necessity of swapping lenses at one point in this magnification range, and the physically very different sizes and working distances of these lenses, make bridging across the "break" in magnification range time-consuming, especially in the field. This is partly compensated by the fact that the Laowa 25 mm, coupled with one of the Laowa 2x lenses, provides a better image quality of both currently available lenses that offer a magnification range between 1x and 5x. In addition, these lenses provide a magnification range that does require lens swapping at 1x, instead of 2-2.5x.
A few specialized lenses, some of them individually even better than the Laowa lenses discussed herein, combined together can provide a reasonably full coverage of the same magnification range. However, each of these lenses typically excels only in a restricted range of magnifications, requiring frequent lens-swapping when changing magnification, and sometimes also color and contrast adjustments in post-processing to better match each other.
The Laowa 25 mm f/2.8 Ultra Macro is a versatile lens providing a good image quality already fully open, in a magnification range from 2.5x to (almost) 5x and at a reasonable price. This magnification range complements the several models of Laowa macro lenses capable of magnification up to 2x, and the magnification gap between 2x and 2.5x is not a significant drawback in practical use of these lenses.
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