The Laowa 25mm f/2.8 Ultra Macro lens has good image quality overall, but it’s not perfect. I’ll go through the different image quality considerations below.
Assuming that your chosen aperture doesn’t have too much diffraction, you can get excellent sharpness with the Laowa 25mm f/2.8. For instance, here’s an image taken at 2.5× magnification and f/2.8 (so, f/9.8 effective), plus a 100% crop:
Although some parts of the image look pretty soft, that’s because they’re out of focus rather than because of a blurry lens. The tiny slice that’s in focus looks good to me (and some sharpening will obviously improve it even further). Still, it’s worth noting that an effective aperture of f/9.8 is the least diffraction you can get on this lens. If you go beyond 2.5× magnification or beyond a stated aperture of f/2.8, you will substantially increase the level of diffraction with the Laowa.
You can see the decline in sharpness clearly in the 100% crops below. These are at 2.5× magnification. The apertures written here are what the aperture ring said; to get the effective apertures, multiply the f-numbers by 3.5. Click to see full size:
And the following are 100% crops at 5× magnification. To get the effective apertures, multiply the f-numbers by 6:
When focus stacking with the Laowa 25mm f/2.8, you can maximize your image quality by sticking to the widest aperture value. However, that gives you such shallow depth of field that you’ll probably need to capture dozens of photos (at least) in order to get a good focus stack.
Still, this lens is capable of very impressive sharpness. If you’re not getting sharp enough images, it’s likely because you’re using an aperture with too much diffraction, such as an effective aperture of f/45 or f/64. No matter how sharp a lens is, it can’t beat the laws of physics.
Bokeh is the quality of background blur in a lens, and it’s a pretty important topic for something like macro photography, where you’ll almost always have some out-of-focus areas in the photo. The Laowa 25mm f/2.8 lens has pleasant bokeh to my eye. If you have obvious specular highlights in the background, they can look a bit busy with a ring around the outside, but it’s no worse than most lenses. And if your background doesn’t have such obvious specular highlights, the bokeh on this lens is nice and soft.
Take a look at the background blur in this photo:
I think it looks very good overall – not too busy, with a gentle falloff from focused to out-of-focus. Here’s another real-world sample that I think shows the transition well:
Overall, the background blur on this lens is quite nice. There is a bit of longitudinal chromatic aberration – out of focus regions behind the subject turning green, while out of focus regions in front of the subject turning magenta – but it’s very minimal. (A worst case example is the image of the coin in the “sharpness” section above.) It’s hardly noticeable and I have yet to see it harming a real-world image. That’s better than with most macro lenses out there, many of which have very high chromatic aberrations at close focusing distances.
The biggest optical problem with the Laowa 25mm Ultra Macro is the strange vignetting pattern it exhibits, especially at its widest aperture.
Most f/2.8 lenses have some level of vignetting when shooting wide open, but that’s not the concern here. Take a look at the following image, shot at 5× magnification and a written aperture of f/2.8:
If it’s not clear like that, let me put the image against a gray field:
What the heck is that? Rather than ordinary vignetting where the corners gradually darken, there’s rectangular vignetting around the whole frame!
I believe the culprit is this (non-removable) structure at the back of the Laowa 25mm f/2.8, which looks like it could cause mechanical vignetting in the shape we’re seeing:
In case you don’t think this has a real-world effect on your photos, take a look at the following shot (I know, not totally in focus, but it shows the vignette issue very clearly):
The photo above is exported directly from a raw file in Lightroom, where I didn’t do any edits aside from a +0.8 exposure adjustment and a bit of noise reduction. Not only is there an obvious dark line across the top of the image, but there’s even a brighter line beneath it as well. (Some sort of flare effect? Just an optical illusion from the dark line above? I really don’t know.)
If you’re wondering when this vignetting issue causes the most problems, take a look at the following sample images at various apertures and magnifications. Note that the aperture values in this diagram are the stated values on the aperture ring, not the effective apertures:
As you can see, the rectangular vignetting issue doesn’t disappear until you’re at a stated aperture of f/8, regardless of magnification. It’s especially noticeable at f/2.8 and f/4.
There’s also a bit of “normal” vignetting on this lens as well, which is strongest at 2.5× magnification and f/2.8. However, this isn’t something I consider objectionable. The rectangular mechanical vignetting is a much bigger problem.
So how do you fix it? The good news is that you won’t notice it most of the time, even if you’re at f/2.8. That’s because most real-world subjects have enough variation to hide subtle gradients like this. For instance, although the real-world photo I showed a moment ago has clear mechanical vignetting along the top, it’s hardly visible along the bottom of the frame because of the subject’s details.
But if you do encounter it, you’re stuck with either cropping the photo or spending the time to do manual corrections in post-processing. Suffice to say, that’s not ideal.
Does this make the Laowa a bad purchase? I wouldn’t go that far. Of the dozens of sample images in this review, I only had to correct this issue twice: once for the image I showed a moment ago, and once for the damselfly focus stack on the previous page. It’s annoying that the issue exists at all, but it hasn’t ruined any of my photos yet – just made the process more inconvenient.
And that’s it for image quality! On the next page of this review, I’ll compare the Laowa against other macro lenses and summarize its biggest pros and cons.