Samyang 8 mm f/3.5 fisheye
I often wondered whether a fisheye would come in handy in certain situations - in my case, nature photography (for instance, relatively small plants in their natural surroundings), cramped quarters (i.e., tight locations where I might want a wider angle of view than the almost 90° horizontal that the Sigma 10-20 mm gives me), rectangular rooms that I would like to cover in their entirety by shooting while standing in one corner, and a handful of other situations. However, given that these situations don't occur more than a few times a year, I have been unwilling to buy a Nikon or Sigma fisheye. Enter the Samyang 8 mm f/3.5 fisheye lens, which covers the APS-C (=Nikon DX) format corner-to-corner and costs one-third to one-half the above lenses.
The Samyang 7.5 mm f/3.5 fisheye is a completely different model, which I discussed here.
The Peleng 8 mm f/3.5 fisheye is another relatively low-cost lens. However, its price has steeply increased in the last few years, and it is now more expensive than the Samyang 8 mm. In addition, the Peleng is a circular fisheye designed for the full format (its design dates to the Soviet era). It does not cover the whole APS-C sensor area (the corners remain black). LensBaby makes a circle Fisheye Optic that is quite cheaper, but has several drawbacks (it is not a "real" lens with a real diaphragm, it has an angle of view of only 160°, image quality is low especially near the edge of the image circle, substantial internal reflections and flare produce odd results, and the edge of the circle of view is very unsharp and made even more so by a massive chromatic aberration). There are, of course, even cheaper "fixes" like using a fisheye "converter" mounted in front of an ordinary lens, or adapting a door peep-hole, but their image quality is usually horrible.
This Samyang fisheye has been availablesince 2009, and reviews and tests available on the Web do confirm its good image quality and solid construction. It is also marketed under the Falcon, Bower, Walimex and Rokinon brands. The Vivitar 7 mm f/3.5 looks identical, except for the rubber sculpture of the focusing ring. Opteka, on the other hand, re-brands it as a 6.5 mm f/3.5. There is an interesting page here about removing the lens shade of the Samyang 8 mm, using the lens for panoramic photography on a full-frame camera, and detailed geometric measurements.
The Samyang 8 mm f/3.5 is not designed to be used on full-frame (24 by 36 mm) sensors. However, it is in principle possible to do the latter. In this case, you do not obtain a circular image because the built-in, non-removable lens shade causes a roughly rectangular vignetting that leaves about one-third of the sensor area black.
The relatively low price is explained by the lack of autofocus and of any electronics in the lens - basically, what you pay for is only the optics and simple mechanical parts. Therefore, automatic exposure with Nikon DSLRs is only possible with the D200 and higher models. The lens does not identify itself to the camera, but some cameras allow the focal length and speed to be manually entered, and this data is then recorded in the EXIF headers of images. There are, however, a mechanical lever to close the diaphragm to the preset value during the exposure, as well as tags on the aperture ring to inform the camera body of the selected aperture.
In 2011, Samyang launched an updated version with a CPU (=chip) for Nikon cameras. This makes automatic exposure possible also on low-end Nikon DSLR bodies. This updated version does not autofocus. It is otherwise identical to the non-CPU version described in this page.
There is hardly any need for autofocus on this lens. Initially, I was surprised to find that manually focusing from infinity to the shortest distance of 0.3 m makes no visible difference in the viewfinder. In addition, the lens moves only about half a millimetre in and out throughout the whole focusing range. Therefore, the best solution is to focus at the parfocal distance (which depends on the selected aperture) and to leave the focusing ring untouched when shooting subjects located between half a metre away and infinity. At f/5.6, with the lens focused at 1 m, everything between 0.5 m and infinity is in focus. At f/8 or higher, it is even possible to set the focus at 0.8 m and forget about focusing. In practice, this means that focusing at the minimum distance of 0.3 m allows you to shoot a subject as close as 0.15 m, which is so close that you must take care not to hit it with the lens - especially since, in the viewfinder, it looks like you are metres away. One should remember that shooting a subject located at infinity with the lens focused at infinity wastes half of the available depth of field (specifically, the half that is located beyond infinity). Therefore, whenever practical, the parfocal distance for a given aperture should be set instead. Unfortunately, the depth of field is not indicated on the lens barrel. Hand-held exposures of 1/15 s are fully possible, especially if the subject is not very close.
Several users have reported that the focusing scale of their specimens of this lens is not properly calibrated (i.e., setting the focusing ring at the infinity marking leaves the image poorly focused at infinity). Recalibrating the focusing ring is easy, and is described, for instance, here.
The front lens element is large and convex (quite larger than the one of the Sigma 10-20 mm). The lens design uses 10 elements in 7 groups. One of the internal elements is aspheric. A built-in lens shade provides some protection against hitting the front element, but you must take care not to place a finger on it while handling the camera. My hands are of average size, but the left one ends up vignetting the image corners if I wrap it around the lens barrel when shooting. I have to keep it under the barrel and support the latter with two or three fingers only to avoid this. The lens barrel feels solid, except for a slightly plastic feel of the aperture ring (most of the barrel and focusing ring are metal, at least on the exterior). The aperture ring has clicks at half stops, except that it clicks directly from f/3.5 to f/5.6 - a gap of one and a half stops. This could be excused by saying that, for best image quality, you should not shoot below f/5.6 except in low light. The front lens cap is proprietary, and it slides onto the lens shade and clips inside it (the two clips must be approximately aligned vertically at the top and bottom, respectively, or the cap does not clip on). The rear cap is a third-party Nikon-fit type that does not sit on other lenses as well as an original Nikon LF-1 cap. You might want to use one of the latter instead. This is not an especially large or heavy lens compared, e.g., to the Sigma 10-20 mm models, although it is larger than some other fisheye lenses. There is no way to use filters, except possibly by attaching a small gelatin one around the rear of the lens barrel with biadhesive tape (not on the rear lens element itself!).
Half the fun of using a fisheye is that you can defish the images in post-processing. This operation removes the barrel distortion and transforms the image into the equivalent image produced by a rectilinear super-wideangle lens. I probably could not afford a rectilinear 6 mm f/3.5 lens (assuming one would exist, which it does not at present for the APS-C format). Instead, I can use software to achieve an equivalent result.
There are several types of fisheye lens designs, each producing a different type of geometric projection onto the sensor plane. Therefore, a single defishing algorithm cannot work equally well on all fisheye lenses.
Adobe Photoshop provides a Filter > Distort > Lens Correction tool that sometimes is used to defish images. However, it fails to properly defish images produced by this lens. A significant barrel distortion remains, no matter what settings I choose.
ePaperPress' PTLens does instead work very well on these images, in spite of its simple-minded algorithm and single correction parameter. It includes a standalone program as well as a Photoshop plugin. The sample below was defished with this program. Image Trends' Fisheye-Hemi plugin is designed to remove the barrel distortion mainly by making vertical lines straight, and its purpose is to render people in fisheye photographs in an acceptable way, rather than to remove geometric distortion. It succeeds well in its goal with images produced by this lens, and in fact the images of people look much more natural than those produced by extreme wideangles. I am told that DxO Optics does not recognize this lens and refuses to defish its images, but I am not certain that this information is updated. Other commercial and open-source packages likely do correctly process these images.
As a comparison, the first image above shows , and the second a defished image taken with the Samyang 8 mm, cropped to keep the maximum horizontal viewing angle (blue cropping frame above). The defished image cropped with the red frame displays an obviously much wider angle of view than the Sigma at 10 mm. The last image shows an obvious decay in image quality in the peripheral regions even at this small size (although an uncompressed image does look better). I would use an image cropped in this way only if it is essential to show as wide an angle of view as possible.
Images shot at f/3.5 show an overall relatively low resolution, distinct chromatic aberration and a slight softness in peripheral regions, but I have seen worse examples than these in third-party lenses of longer focal lengths. Stopping down to f/5.6 largely corrects these aberrations, and at f/8 images are as good as they can get. Defished images have a much reduced resolution in their peripheral regions, which is a natural consequence of the defishing process. There are quite enough full-size test images taken with this lens on the Internet, and I don't need to add mine.
This is a lens that provides good results at a very reasonable price. It produces sharp images that can be defished by cheap or free software and are equivalent to those produced by a hypothetical, but not yet available for the APS-C format, ultra-wideangle with a diagonal coverage of about 120°. If you crop the defished image only about the shorter dimension, you actually obtain a diagonal coverage in excess of 150° (rightmost, above). If, like I used to, you wonder about a fisheye but cannot justify its price, this is an ideal solution. With this lens, you can keep some change in your wallet, yet still go out and have fun. Just remember to shine your shoes, because you are going to see them in your pictures a lot more often than usual.
Do not shoot an approaching train or other fast approaching vehicle/animal with a fisheye by estimating its distance through the viewfinder - you will be in a hospital by the time it looks like it is time to pull yourself back.