The Samyang fisheye lens is an alternative to the native Panasonic Lumix G 8mm f/3.5 fisheye lens, so it makes sense to compare them. Here they are, with lens caps:
They have different type caps. The Samyang, on the left, has a cap held in place with clips, operated by pressing the side tabs. The Lumix's cap is held in place with friction only. I prefer the latter, since the Samyang cap must be inserted correctly rotated, which is somewhat more awkward.
Removing the caps, reveals that the Lumix has a significantly larger front lens element. Both have the same type of integrated hood.
Looking at the rear of the lenses, we see that also the exit pupils have different sizes. The Samyang lens has the smallest exit pupil I have ever seen on a Micro Four Thirds lens. A large exit pupil is usually associated with a high quality lens, although there is of course no definite connection.
|Samyang 7.5mm f/3.5||Lumix G 8mm f/3.5|
|Number of aperture blades||6||7|
|Minimum focus distance||0.09m||0.10m|
Even though the Samyang lens is slightly smaller, and has smaller lens elements, it weights more. This is due to the lens being made from metal materials, in contrast to the Lumix lens, which has a plastic exterior.
The Samyang lens has a traditional mechanical focus ring, which moves the whole lens assembly back and forth. The focus ring is well dampened, and feels high quality. There is a distance scale, but sadly no depth of focus (DoF) scale.
Regarding the focus scale, I find it to be a bit lacking. It has no markings between infinity and 0.25m, as seen here:
There is some sense to this practice, of course: The focus is the most critical at shorter distances. Still, I'm guessing that quite many see the need to focus the lens to around 1-2 meter distance more often. So a distance marker at around 1-2 meters would be good. Of course, this lens has a quite deep Depth of Focus (DoF), so the focus is not much of an issue unless you are printing large copies of your pictures.
I solved this by adding a distance marker at 1m myself. It doesn't look very good, but it makes the distance scale much easier to use:
I found the infinity mark to be somewhat inaccurate. But I guess that is not uncommon.
The aperture ring also feels well made, and has clicks at full and half stops.
No electrical contacts
The Samyang lens is a purely mechanical lens, and has no electrical contacts. This means that the camera does not recognize that the lens is mounted at all, and certainly cannot read off information about the focal length or aperture.
It also means that you need to set the "SHOOT W/O LENS" option. Otherwise, the camera will not operate, as it believes that no lens is mounted at all. Here is the "SHOOT W/O LENS" menu option from the GH2 camera:
The camera will still store EXIF data in your image files, however, the information about focal length and aperture is never passed to the camera, and will be missing when using this lens.
Being a fisheye lens, of course you are going to get a lot of distortion. Still, there have been some rumors online that this lens has a stereographic projection, rather than a spherical projection, the norm for fisheye lenses. The stereographic projection is less distorted.
Comparing the distortion of the two fisheye lenses reveals that they are in fact quite similar. Here is a test image showing how a rectangular grid is projected to the sensor with the two lenses:
Read more about the study here. My conclusion is that the Samyang lens in fact features somewhat less distortion, but the difference is rather subtle.
When converting a fisheye image to rectilinear, a process called defishing, it is generally easier to defish the images coming from the Samyang 7.5mm f/3.5 than the Lumix G 8mm f/3.5 lens. The reason being that the Samyang lens has a more common projection model for fisheye lenses.
The Panasonic Lumix G 8mm f/3.5 fisheye lens, on the other hand, has more distortion that what is common for fisheye lenses, making it more difficult to use under certain conditions. Most of the time, this is a non-issue, but if you specifically intend to defish the images, I would go for the Samyang lens.
I have taken the same picture with both lenses, to examine their optical properties. Here they are, both at f/3.5, taken on a tripod. I used the base sensitivity of the GH2, ISO 160.
|Samyang 7.5mm f/3.5||Lumix G 8mm f/3.5|
To better examine the sharpness, here are some 100% crops from the upper right hand corner (click for a larger view):
It is quite apparent that the Samyang/Rokinon lens is surprisingly sharp in the corner. There are virtually no chromatic aberration (CA) artifacts. On the other hand, the Lumix fisheye lens has some residual CAs, even after the in camera CA adjustments.
Here is another sharpness comparison with the Lumix G 8mm f/3.5 fisheye lens. In this test, the lenses come out more alike in terms of sharpness.
The fisheye lenses cover a 180° diagonal field of view. So it can be quite difficult to avoid having the sun, or some other bright light source in the frame. Hence, the handling of flare is quite important. Does a strong, visible light source ruin the image?
Again, here are some comparison images, both taken at the same spot:
|Samyang 7.5mm f/3.5||Lumix G 8mm f/3.5|
|Samyang 7.5mm f/11||Lumix G 8mm f/11|
The Lumix lens gets the green ghosting in the opposite corner of the sun. The Samyang lens avoids this. Overall, I'd say the Samyang lens handles the flare better.
The Samyang lens has six aperture diaphragm blades, and hence, there are six rays around strong flares when stopping down. You can see this in the lower left example image, and even better in an article about the significance of odd and even aperture diaphragm blade numbers.
Here is a discussion about the possible use of a fisheye lens.
This lens can be used on any Micro Four Thirds camera, given that you enable the "SHOOT W/O LENS" option, as described above.
When used on the Panasonic GH2, it is possible to use the rear click wheel to enable the focus assist mode. Pressing the wheel once enables the magnified view. It can then be magnified even more by scrolling the wheel. To disable the magnified mode, half press the shutter, or press the click wheel once more. This GH2 feature is described here. All Micro Four Thirds camera have the magnified focus assist mode, but it may be more involved to enable it on some cameras.
To get the best focus accuracy, you should ideally focus manually using the largest aperture (f/3.5). When finding the focus range, you can then stop down the aperture to the desired size, and take the picture. Most system cameras handle this process automatically, however, since there is no signal connection between the lens and camera, the camera cannot help you with this process.
You can use the camera's automatic exposure with this lens. Just set the aperture you want on the lens aperture ring, set the ISO you want (or leave the ISO on auto), and the camera will set the appropriate shutter speed. This works well, in, e.g., the P and A modes.
The exposure is generally good in low contrast situations, e.g., in daylight. With high contrast scenes, though, the GH2 tends to underexpose significantly. This is strange to me, since using the Lumix G 8mm fisheye lens in the same way yields a good exposure.
At night, I must dial in approximately +1.3 EV compensation on the Samyang lens to get the same exposure as the Lumix G lens would have given. This is at full aperture, f/3.5. At f/5.6, the gap increases, and I must dial in +2.0 EV.
This behavior puzzles me. As the camera sees roughly the same image through both lenses, I would have guessed that it also exposes similarly. But it appears that using a non-electric legacy lens triggers a different exposure mode, which preserves highlights to a larger degree. Or, and I am just speculating here, since the Samyang lens features less flare, perhaps highlights are more defined with the Samyang lens, and hence the camera does more to preserve them.
The need for extra compensation with the Samyang lens can be illustrated with this example. The scene was shot with both lenses at f/5.6.
First, the Samyang lens without compensation:
The Samyang lens with +2.0 EV compensation:
And finally the Lumix lens with no compensation:
In my daytime outdoor sharpness example images above, I used no exposure compensation at all, and they all came out ok. So this is only a problem when the contrast is high, for example at night with artificial light sources.
Since the camera does not know that this is an extremely wide angle lens, it will assume that it has a focal length of around 50mm, and use a shutter speed of around 1/125s. This causes the camera to use too high ISO in some cases, as this lens can be handheld at 1/15s with few problems. Set the ISO lower manually to avoid this.
This image of Sergels Torgs was taken at f/5.6, ISO 160. Notice that straight lines which pass through the centre of the frame, are reproduced as straight in the image. The further from the centre a straight line passes, the more curved it is rendered. This is an important property of a fisheye lens.
Here are some 100% crops from the image, showing that the sharpness is very good throughout the frame (click to enlarge):
Another example, this one is from the Stockholm Old City:
The picture was taken by pointing the camera directly upwards inside a circular open yard.
And an example picture from the Rockefeller Center in New York:
This video was recorded with the Samyang lens at f/3.5.
The GH2 tends to underexpose when using this lens in high contrast situations, e.g., at night. Hence, I had to dial in +1.3 stops of exposure compensation. When using the Panasonic Lumix G 8mm lens, the exposure compensation is not needed, so it is clear that the camera treats them differently.
The first 20 seconds of the video below were filmed with the Samyang 7.5mm f/3.5 fisheye lens, using the Panasonic GH3 camera:
In this example, I filmed a firework display using the fisheye lens.
The process of making rectilinear, or at least near-rectilinear transformations from a fisheye image is commonly called defishing. I have written about this process here.
I have found that when defishing an image from the Samyang fisheye lens at 4:3 aspect ratio, you get a very wide rectilinear image. In my experience, it has a vertical field of view which is a little bit wider than the Lumix G 7-14mm f/4 lens at 7mm, and a much wider horizontal field of view.
Here is a real world comparison with the Lumix G 7-14mm f/4 ultra wide angle lens at 7mm.
Samyang also produce fisheye lenses for DSLR cameras, with the mounts of major camera manufacturers. You could conceivably buy e.g. the Nikon version of this lens, specified as 8mm f/3.5, and mount it to a Micro Four Thirds camera using an adapter for Nikon F on M4/3. This lens is also marketed as Rokinon, Bower and Vivitar.
However, I would not recommend doing so. The DSLR version of the lens is made for a larger sensor, and hence, when using it on Micro Four Thirds, you don't get 180° coverage in the diagonal. Also, due to the longer register distance of the DSLR systems, the 8mm fisheye lens made for these formats is much larger in size and weight. So if you can, go for the lens designed for Micro Four Thirds in the first place.
The Samyang/Rokinon 7.5mm f/3.5 fisheye lens has got impressively good optical properties. This makes it a good alternative to the Panasonic Lumix G 8mm f/3.5 fisheye lens, at a lower cost. You'll have to focus manually, though, which is quite easy for objects far away. When photographing close objects, though, it takes somewhat more effort to use the Samyang lens.
With the GH2 camera, I need to make exposure compensation during night photos with the Samyang lens, to get a sensible exposure. This is not needed with the Lumix fisheye lens. I'm sure this is a camera issue, though, and nothing I should blame the lens for.
I think the Lumix lens generally gives better colours. But this is a subjective matter, of course. As the Lumix lens is quite expensive, the Samyang lens is a good alternative, if you can live with using manual focus. The optical properties are certainly very good.
All in all, the Samyang/Rokinon 7.5mm f/3.5 fisheye lens is a very good lens, and provides good value for money. If you want to try a fisheye lens, it is a good choice.