Essential Guide to Wideangle lenses
The other type of wideangle lens we're yet to mention are fisheye lenses. These tend to be a bit more niche, partly because they're known to produce stronger signs of distortion. If a wideangle zoom doesn't give you the field of view you're after and you'd like to squeeze even more in the frame the other option you have is a fisheye lens. The angle of view fisheye lenses offer varies between 100 and 180 degrees and in the case of the latter it can save you having to merge a series of shots together to create a panoramic image.
There are two types of fisheye lenses available - circular and full frame. The differences between the two are that circular fisheye lenses offer a 180 degree hemisphere view and the prominent black corners at the edges are created by the image circle failing to cover the entire sensor.
Full-frame fisheye lenses are quite the opposite and they enlarge the image circle to cover the entire rectangular frame. Fisheye focal lengths vary just like wideangle primes and wideangle zooms. One of the widest currently available is Sigma's 4.5mm f/2.8 EX DC circular fisheye for APS-C DSLRs. While they're fun to experiment with and use occasionally, fisheye lenses do have more limited use and it's one reason why wideangle zooms are considered better value for money.