Samyang 7.5 mm f/3.5 fisheye
In 2009, Samyang introduced a relatively cheap, manual-focus 8 mm f/3.5 fisheye lens for APS-C cameras. I reviewed it here, and found it very satisfactory, although difficult to focus through the optical viewfinder of a DSLR.
I am now in the process of moving from APS-C DSLRs to the Micro 4/3 format (mainly with an Olympus OM-D E-M5). The Samyang 8 mm of course can be used, with an adapter, also om Micro 4/3 cameras, and in fact the image quality is remarkably good (see example above). However, the 8 mm covers an image circle quite a bit wider than the Micro 4/3 sensor. This has good effects (the peripheral areas of the image circle, which display the highest aberrations and distortion, are left out) as well as bad effects (the diagonal angle of view becomes significantly less than on an APS-C sensor). In addition, the Samyang 8 mm, although not a large lens compared to other APS-C lenses, is quite heavy, and cannot be called small (especially when mounted on an adapter, see picture below) compared with typical Micro 4/3 lenses. Since my principal reason for moving to the Micro 4/3 format is cutting down on size and weight, these things matter to me.
The above problems were removed by the introduction of the Samyang 7.5 mm f/3.5 fisheye for the Micro 4/3 format (and other mirrorless formats as well). This lens is also marketed under the Bower, Rokinon and Pro-Optic brands, like its 8 mm big brother. In comparison to the 8 mm, the 7.5 mm is moderately sized, even by Micro 4/3 standards. In fact, if one disregards its fixed lens shade, it might almost be regarded as a pancake lens.
However, the Samyang 7.5 mm is by no means a very small lens among those available for the Micro 4/3 format (above).
The good news is that the 7.5 mm is both better in terms of image quality (according to several online reviews, as well as my personal experience) and cheaper than the 8 mm. The 7.5 mm is even better than the much more expensive Olympus and Panasonic fisheye lenses, according to several online reviews (albeit these lenses do provide autofocus). The 7.5 mm is a complete optical redesign, not a modification of the 8mm. Except for increasing the DOF and lowering the already modest chromatic aberration, there are no particular reasons for stopping down the 7.5 mm. In fact, it is sharpest fully open, with minimal vignetting and low sensitivity to flare.
As typical of Samyang lenses, the 7.5 mm has fully manual focus and aperture and lacks a CPU (="chip"). This is not a problem on Micro 4/3 cameras, which can use CPU-less lenses (while low-range APS-C DSLRs sometimes cannot) and provide a high-zoom mode for manual focusing in live view. You still need to frame, switch to high zoom to focus, then (usually) return to normal view to verify the framing once more before shooting (and to verify that your feet, elbows and fingers are not in the picture). I don't find this to be a serious problem, since I typically don't use a fisheye when I am in a hurry. I use other non-CPU lenses on Micro 4/3 cameras, and the procedure is the same. It is essentially impossible to focus without zooming in live view.
It is feasible to shoot without precision focusing, by setting an approximate distance on the focusing scale and "shooting blind". At f/5.6, with the lens focused at 0.7 m (there is no such marking, but halfway between infinity and 0.25 m is a good guess), everything from 35 cm and farther is in focus. In this case, however, you need to test first if the focusing scale of your specimen of the Samyang lens is reasonably accurate. Many specimens of the Samyang 8 mm are not accurate in this respect, and landscapes may be unacceptably out of focus when the lens is set to infinity on the focusing scale (this is the only real fault I can find with these lenses). It may be necessary to mark the correct infinity or parfocal distance on the focusing scale with a permanent marker. The focus ring of the 8 mm is easily recalibrated with a small screwdriver, but this method does not seem to be applicable to the 7.5 mm. My specimen of the 7.5 mm focuses accurately, so I did not investigate further.
While previously I had to think twice whether to take along the 8 mm (which weighs close to 450g) in the DSLR camera bag, it is much easier to permanently leave the 7.5 mm (less than 200g) in the Micro 4/3 bag. In this way, it certainly will be used a lot more often.
The Samyang 7.5 mm is available in black or silver (actually silver-painted plastic). The lens mount and a portion of the barrel near the mount are chrome-plated metal in both black and silver versions. The red/orange anodized index ring and some internal details are metal as well.
The front lens cap of the Samyang 7.5 mm is proprietary and very similar to the lens cap of the 8 mm. It has the same fault: it is necessary to orient it with the two buttons at the top and bottom, or it will not engage the edge of the lens shade and will fall off. The petal lens shade is an integral part of the lens barrel, and its edges are reassuringly thick, suggesting that they will not be easily damaged during use. There is no way to mount a filter. The rear lens cap is a third-party item without Samyang markings. Unlike most third-party Micro 4/3 rear lens caps, which sit too loosely to be usable, this cap fits properly. I wish I could find a source for this cap and buy several, because the alternatives right now are to buy original caps at unreasonably high prices, or "fake" third-party caps that can fall off a lens at any moment.
The lens focuses down to 9 cm (at which point the image still looks like you are quite far from the subject, given the enormous angle of view, but nonetheless can produce interesting effects, see above samples). In comparison, the 8 mm focuses at a minimum distance of 0.3 m, which is not quite satisfactory (the Olympus 4/3 fisheye focuses down to 0.13 m and the Panasonic Micro 4/3 to 0.1 m). Be very careful when approaching a subject, because you may hit it with the front lens element if you only look through the viewfinder.
The front lens element of the Samyang 7.5 mm is much smaller than the one of the 8 mm. This results in considerable savings in weight and production costs. The front element of the 7.5 mm is also less convex, better sheltered by the fixed lens shade and less likely to be accidentally touched with a finger.
Handling a camera with this lens can be tricky. The lens barrel is just too short to keep the left hand under it, and any finger placed around the focusing ring is likely to be partly visible in a corner of the picture. It is probably best to move the left hand to a position under the camera body before shooting.
If you wonder how a difference of focal length of half a mm can account for the very different sensor area coverage (Micro 4/3 is half the sensor area of APS-C) and physical lens sizes, there are two answers:
Some users reported that their cameras have a tendency to underexpose with the Samyang 7.5 mm, especially in low-light and night shots. I did not notice this problem on my Olympus OM-D E-M5. This problem may have something to do with the small diameter of the rear lens element, which forces light to hit the peripheral sensor areas at an angle and may throw averaged light metering off. If this is true, using center or center-weighted metering may be a solution.
I found the Samyang 8 mm on a DSLR quite usable in several situations where a fisheye is not the most instinctive choice, as long as its curvilinear rendition is acceptable. The 7.5 mm is no different. For instance, people in the peripheral areas of a fisheye image (as long as they are not too close to the lens) look more natural than in the peripheral areas of a rectilinear super wideangle image. There are a few specific software tools, like epaperpress PTLens and Image Trends Hemi-Fisheye plugin, to "de-fish" or otherwise process these fisheye images to make them look more natural in post-processing (above example). PTLens converts the image into the equivalent of an image produced by a rectilinear wideangle. Perspective effects, or perceived perspective "distortions", are emphasized (geometric distortions are actually removed by de-fishing, but the perceived effect is often the opposite). Hemi instead straightens the vertical lines but not so much the horizontal ones, and achieves a subtler, more sophisticated effect that is aesthetically more pleasing in many cases (albeit not acceptable when a rectilinear rendition is required, like in conventional photography of buildings). Note, in particular, the appearance of the large curb stone at the lower left in the image.
Either software tool generates images with an angle of view that no current ultra-wideangle lens is capable of producing. The price to pay is a lower resolution in peripheral areas, especially when using PTLens (which is implicit in de-fishing to a rectilinear rendition and not a fault of this program). This can be partly compensated by cropping the edges of the image in PTLens, as I did in the above sample. The maximally uncropped PTLens image is shown below.
Natural landscapes shot with the Samyang 7.5 mm and the camera perfectly level, with the horizon running exactly across the center of the image, usually look fine if there are no nearby tree trunks or vertical buildings along the image sides. It is always possible to crop away uninteresting portions of the sky and/or ground in post-processing, so resist the temptation to tilt the camera up or down, and instead keep it strictly level. Use an electronic level display if your camera provides one. To include more of the sky or ground, shoot in portrait orientation instead of tilting the camera (but watch out for your shoes, hat and camera strap getting into the picture - it may be best to hold the camera far forward off your body like "chimping" P&S users do). Especially when the alternative is taking no picture, or taking only a narrow crop that misses much of the scene, I would encourage you to "think outside the box" with regard to fisheye lenses. They can be more than just "specialty" or "trick" lenses to take out for a spin only once a year.
Further examples of pictures recorded with the Samyang 7.5 mm f/3.5 can be seen here.
The Samyang 7.5 mm f/3.5 for Micro 4/3 is a manual-focus fisheye lens much cheaper than corresponding Olympus and Panasonic lenses. Its image quality is equal to or better than these more expensive competitors. Its modest size and low weight make it easy to carry at all times in a camera bag. A precise manual focusing requires zooming in live view.