A newcomer to the Micro Four Thirds scene, the Chinese lens manufacturer 7Artisans recently released two inexpensive manual-focus prime lenses for the system: a 7.5mm f/2.8 fisheye and a 25mm f/1.8 lens.
Today we will take a look at the 7.5mm fisheye.
The lens was well-packaged, in an understated black box with a coated-on-matte black print design. It comes with a carrying bag, front and rear slide-on lens caps, and instructions in Chinese.
Manual focus is not really a detriment to this lens – it is probably the best choice for fisheyes anyway. When stopped down and set to the hyperfocal distance, fisheye lenses are pretty much “set it and forget it” as far as focusing goes. Also, there is typically so much information in a fisheye scene, most cameras would have difficulty deciding what to lock focus on.
Both the focus action and aperture adjustment are smooth and solid feeling.
The aperture ring has no hard stops – it can be adjusted from f/2.8 to f/22, but you must eyeball it when you line it up with the number markings.
Sharpness and Chromatic Aberration
To test the lens, I took a picture of a brick wall with sky and some leaves in the corner.
The pictures below are 50% out-of-camera JPEG crops at different apertures.
At f/2.8 through f/5.6, the lens is somewhat soft in the center and there is quite a bit of chromatic aberration in the corners, although sharpness starts to improve as you stop down.
At f/8, chromatic aberration slightly improves and the center becomes the sharpest.
By f/11, the center loses perhaps a little sharpness but the corners look the sharpest yet. Some of this could be attributed to the characteristics of the lens, but it could also be the result of increased DOF. The corners of a fisheye can end up resolving objects in widely varying focal planes, even when shooting a relatively flat scene. Chromatic aberration is also best controlled here.
By f/22, refraction kicks in badly and everything loses sharpness across the board.
I would guess the sweet spot of this lens to be somewhere between f/8 and f/11, which is surprisingly high for a Micro Four Thirds lens. Since there are no hard aperture stops, you could simply eyeball the spot between the f/8 and f/11 markings on the lens (approximately f/9.5), set focus to the hyperfocal distance, and leave it there for everyday shooting.
At f/9.5 on a Micro Four Thirds sensor, the hyperfocal distance is 0.4m, or 1′ 4″.
Pointing directly into the sun, this lens controls flare quite well, with minimal loss of contrast.
I did notice some internal reflections (red and cyan spots, perhaps from the lens coatings) in certain situations involving bright overhead sunlight. See the image below for an example.
More Sample Images
These images have undergone some minimal post-processing in Lightroom, mostly to demonstrate how much CA could be cleaned up (answer: quite a bit, but you will need to push the sliders to their maximum value).
This lens is not for everybody. If you are looking to get a wide fisheye at an inexpensive price point, and can look past its flaws, it could be for you. It works best under bright yet well-controlled lighting conditions.
With so much chromatic aberration at the corners wide open, this lens is probably of limited use for astrophotography — unless you are willing to stop it down, give up much of its light gathering abilities, and use it with a star tracker.
While it may not be able to compete with more expensive fisheye lenses, the 7Artisans 7.5mm f/2.8 is a decent value for the money. I did have more fun shooting with it than expected. At some point down the road, I may try the Rokinon 8mm f/3.5 or step up to the Olympus 8mm f/1.8 Fisheye PRO. For now, I plan to keep the 7Artisans lens in my bag – I expect I’ll see more opportunities to take advantage of its unique perspective in the future.