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(More customer reviews)Acronyms used: DOF = depth of field, FOV = field of view
This lens is a full-frame fisheye with 180 degrees diagonal FOV that is available under a variety of brands with a declared focal length varying between 6.5mm and 8mm - there's this Opteka 6.5mm, a Vivitar 7mm, and a Bower 8mm. I own the Bower, not the Opteka, but from the picture, they look identical - only the Vivitar is different in the exterior finish. All these lenses appear to be made by Samyang, a South Korean company that puts out several mirror and normal tele-lenses, and that more recently came out with two higher quality prime lenses - this 8mm f/3.5 and an 85mm f/1.4 (Opteka 85mm f/1.4 Medium Telephoto Portrait Lens for Pentax K7, K200D, K20D, and K2000 Digital SLR Cameras)
First, a note on the lens pictured here: the amazon photo probably displays a Canon/Nikon version, because for Pentax, the aperture ring also has an automatic position - A - allowing control of aperture within the camera. This is very convenient and an exclusive feature on the Pentax version! Note that as far as focus is involved, this is a manual focus lens - don't let this scare you though, because the FOV of this lens is very large, so you won't spend much time focusing it.
The lens comes with a clip-on front cap, a screw mount cap, and in addition to those - a pouch, which I thought it's a really nice touch. The caps are of light plastic that feel fairly cheap. The front cap clips to the inside of the petal hood, similar to how front caps usually clip to the filter thread. The mount cap is actually not covering the mount contacts - poor decision. The pouch is made of a thick cloth that feels like velour on the outside and synthetic material on the inside - it will protect the lens from scratches but not from shock. The lens is very well built - the mount is metal and the rest is plastic, but the plastic feels good. The focus ring in particular feels pretty smooth - not that you'll get to use it much, but it is nice. The aperture ring works fine too, but I haven't really used it after setting it to A.
A note about filters - this lens doesn't take any - you'll understand why when you'll see the front element. Also, minimal focus distance is 0.3m/1ft. And, finally, my Bower didn't come with any serial number marked anywhere, which makes it the first lens I have without a S/N.
So, how about the optical performance?
A few reviews online have suggested that this lens uses a special projection of the image, called stereographic (check it on wikipedia where they have some nice images showing the result of several types of projections) - it appears to be the only lens to do so. What this means practically is that the edges of the frame are less distorted as in other fisheyes - in fact, this seems to be the only lens available that uses such a projection, which automatically makes it pretty special. From my use so far, I can confirm indeed that the curvature at the edge of the frame is less pronounced than I've seen in photos produced by other fisheyes.
The resolution is good all across the image and only at the extreme borders the image gets a bit softer. Best performance is reached around f/8.
With a lens covering such a wide FOV, flare can be an issue because the sun can easily shine in your lens. Fortunately, Samyang has done a pretty good job controlling this aspect - it can still happen, of course, but it's fairly rare.
Chromatic aberations (green-magenta) can show up often and they are mostly visible at the left and right borders. This sadly appears to be a general issue with wide-angles - Pentax's 10-17 is also reported to suffer from CAs. Purple fringing can also appear in regions with high contrast, but this effect is not very pronounced - it's pretty similar to what could also be obtained with the Pentax 18-55 lens - maybe even a bit better.
So, in conclusion, this is a fisheye lens that doesn't have any major weakness - whatever negative comments I wrote above can probably be made about any other fisheye lens. The build quality is good and the lens is unique in its use of stereographic projection which makes it suitable for more general photography scenarios than are usually associated with the use of a fisheye. Combined with the lowest price for a fisheye lens right now, all this makes this Samyang/Opteka/Bower a very attractive proposition.
Score explanation: 5/5 - it doesn't mean it's perfect, but I can't find a major flaw worth taking a star off. Samyang has produced a good value lens and I hope they'll follow up with more such products.
Click Here to see more reviews about: Opteka 6.5mm f/3.5 Manual Focus Aspherical Fisheye Lens for Pentax and Samsung Digital SLR Cameras
The Opteka 6.5mm f/3.5 Fisheye Lens is an excellent addition to any photographer's collection, giving users the ability to expand their creativity and capture incredible scenes from a truly unique perspective. The special fisheye design allows maximum creative expression.This lens, when used with cameras with an APS-C image sensor, creates images with an expanded perspective, including images with a creatively deformed outlook and a sharp pan focus that extends throughout the entire frame. By offering a 180-degree angle of view, this fisheye lens can be used to create amazing image expressions that cannot be seen by the human eye, such as exaggerated perspective and distortion. The minimum shooting distance (just 12 inches) and large depth of field also provide amazing close-up shots.Opteka's super multi-layer lens coating reduces flare and ghosting, a common problem with digital cameras and also creates an optimum color balance.
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