This is a very wide rectilinear lens, but not quite as wide as you can get with other formats. For Canon Fullframe cameras, you can get the amazing EF 11-24mm f/4, and for crop DSLR cameras, you can get the Sigma 8-16mm f/4.5-5.6, with a 12mm equivalent wide end.
The Lumix G 7-14mm used to be the most expensive M4/3 lens. It is no longer, due to other more expensive lenses, but it is still the widest rectilinear zoom lens. But how does it compare with a fisheye lens, in terms of field of view? Here are some example images for comparison (click for larger images):
Lumix G 7-14mm f/4 @ 7mm
The fisheye image (right above) can be defished (click to see how it can be done using the free software Hugin). Defishing yields this result:
Samyang 7.5mm defished
Samyang 7.5mm desfished and cropped
When defishing using a rectilinear projection, like I did above, the image gets very stretched in the corners. To avoid this effect, some use the Panini projection in Hugin.
Comparing the two fields of view shows that you get a lot wider images using the fisheye lens:
As you can see, the fisheye lens gives you much wider images, but keep in mind that the corners are quite stretched, and you may not be able to use the whole picture when defishing. Still, even if you crop it a bit, it is way wider than what you get from the Lumix G 7-14mm f/4 ultra wide angle zoom lens.
Another very wide rectilinear zoom lens is the Olympus 7-14mm f/2.8 PRO. It is similar to the Lumix G 7-14mm f/4 in terms of field of view, but adds another stop of aperture, at the expense of a larger, heavier lens, and a steeper price tag. You shouldn't expect better images from this lens, but you get the possibility to use f/2.8. Also, the lens is weather protected, meaning that it is more likely to survive some water splashes.
The Samyang 7.5mm f/3.5 that I used above is a manual focus lens. There are also two autofocus capable fisheye lenses:
The Lumix G 8mm f/3.5 is one of the smallest autofocus capable fisheye lenses, but not any better optically than the Samyang lens, see a comparison here. The lens is still very good, but a tad expensive.
Olympus also has a fisheye lens, with a record large f/1.8 maximum aperture, the Olympus 8mm f/1.8 PRO. This large aperture is rarely needed for real life use, in my opinion. However, people who are interested in astrophotography will find it interesting. Also, it is good for use underwater, inside a waterproof housing.
|Lens||Lumix G 7-14mm f/4||Samyang 7.5mm f/3.5||Olympus 7-14mm f/2.8||Lumix G 8mm f/3.5||Olympus 8mm f/1.8|
|Pros||Small, light, not too expensive these days||Very good image quality, fantastic value for money||Fast aperture, weather protected||Compact, good image quality||Very fast for a fisheye, weather protected|
|Cons||Sharpness could be better at 7mm f/4, but improves when stopping down. Some purple flare||No autofocus||Large, expensive||Somewhat expensive||Do you really need a so fast fisheye?|