|Lenses for underwater use|
These lenses are non-fisheyes, and gives you straight lines and can be used both under and above water with great success. You can read about fisheyes for underwater use on this site as well. There are both zooms and prime lenses in this category and they range from 10mm and up. The picture to the right is taken with a Sigma 10-20mm at 10mm of 2 divers repairing some equipment at 35m depth in Saltstraumen, Norway. This is actually the worlds strongest Maelstrom.
As you can see, there is not too much distortion. It is a lot easier to take good pictures of people looking natural with these lenses than with a fisheye. Be aware that there is still some distortion due to the extreme wide angle, but again these do not show very well under water.
If you want one wide zoom for a digital Nikon to use both under but mostly above the surface, you should go for a 12-24mm. The Tokina is the best buy. It covers a very useful area. If it's mostly for underwater use, go for the Sigma. The is no other lens that goes this wide, except for the fisheyes.
Nikkor/ Sigma/ Tamron 14mm f2.8
Nikkor: It is as wide as you get with a Nikon lens on a full frame camera. From the tests I have read it is not superior to many of the zooms optically, but it is faster. It gives an extra stop comparing with the zooms, but other than that it doesn't really have any advantages on the DX format cameras. I have not tried this one myself. They can all focus close enough for using in a dome port.
Both Sigma and Tamron have similar lenses that are somewhat cheaper. If you have a digital camera with the cropped sensors you will be better off going for a zoom lens unless you really need that extra stop. If you want to go wider you should have a look at the fisheye's.
Sigma 20mm f1.8 (24mm f1.8)
These lenses are very special. They are wide and really fast. On a DX format camera you use the sweet spot of the lens which give acceptable results. It gives some softness wide open, but sharpens up when stopping down. It's main advantage is the max aperture which can allow you to take pictures when other lenses don't. This is one area where the zooms are not working to well. For example, like at the picture above, using the Sigma 10-20mm at 20 gives you f5.6. The shutter speed was 1/80 so I could have gained more ambient light with somewhat slower shutter. If I wanted more than that, I would need the f1.8, which is 3 1/2 stops faster than the zoom.
The focal lengths are good for large fish close portraits of divers. Being so fast it helps you out taking wide angle shots when it is overcast, deeper waters, Norwegian winter light etc. I really wish I had this lens when I was swimming with Killer whales in the northern part of Norway a couple of years ago. It was simply too dark for the other lenses.
You can use filters on the lens, but be aware that it has a 82mm threading for filters. If you already have lots of 77mm filters for your lenses, then you might want to consider the 24mm f1.8 from Sigma. It has a lot of the same advantages, but you "lose" 4mm.
Nikkor f4/ Sigma f4.5-5.6/ Tokina f4 12-24mm
These lenses all cover the same area. The Nikkor and the Tokina lens can only be used on the DX format cameras, while the Sigma also can be used on the good old film cameras or the new D3.
The Nikkor and the Tokina are comparable when it comes to image quality as well. The price difference makes the Tokina an attractive deal. The Sigma has a slightly worse reputation. The Sigma lens is quite big and might not fit in your port.
The picture to the right here is taken at 13mm. No, he's not making sushi, but simply opening av sea urchin to feed some hungry fishies. For taking closeups of people you should not go wider than this without being careful. As you can see it is starting to look distorted. This effect is stronger when the distance to the different parts of the body is varying. In this picture the hands are in front of the diver and the head is tilted forward. This is also where the distortion is strongest. Why is this important? My point is that the 12-24mm lenses cover a really nice area. You don't really need a wider lens unless you take wreck shots or would like a silhuette picture of a diver. The 12-24 lenses can also take these pictures really well, but require more distance to the object. If you are to use the lens both under and above water these are great choices.
If you want to read how others reviewed these lenses you can have a look at Popular Photography reviewing the Tokina, the Sigma lens, Ken Rockwell's digital wide zoom overview and Photozone's tests of all three lenses.
Sigma 10-20mm f4-5.6 EX DC HSM
This is the widest you can get without looking at the fisheye lenses. It is smaller than the the other lenses and works really well for underwater use. At 10mm the distortion can be a little obvious if you use it close on familiar objects. It works really well on bigger things like wrecks, a diver at a little distance, sharks etc. On the really big thing like the wrecks you should consider the fisheyes. This picture was taken at Sipadan with the Sigma lens at 13mm. My wife wanted to experience beingin the middle of this wirlpool of barracuda and left me on the outside documenting it. I could have benefited of being a little closer and zoomed out to 10mm. One of the main advantages of this lens is it's versatility with the zoom. You can use it for really wide pictures, but also for turtle portraits. At places like Sipadan the speed of the lens is usually not a problem.
The lens is sharp, gives bright colors and lets you focus as close as you wish. The only thing that could be improved is the speed. Diving in Norway, especially when the sun is not at it's brightest, it forces the ISO up if you want to use ambient light. If you are going to use the lens mostly under water, then this is the one to get.
I have used it quite a bit above the surface as well, which works really well even though I wish I could get a little more on the long end. This cover at the norwegian magazine Dykking was taken with the Sigma lens allowing me to stand close to the diver while taking this shot.
The lens teams up really well with the 20mm f1.8, which is almost 4 stops faster. This lens will work for most wide angle shoots, while the 20mm will help out when the light conditions bad.
You can read test and reviews on this lens at Photozone, Popular photography and a review of the wide zooms at Ken Rockwell. Neither of these focus on under water use. You want to go even wider? Take a look at the widest.