View Full Version : Standard (Prime) Lens Underwater

04-09-2010, 12:33
I've been reading about standard lenses for "terrestrial" photography particularly for the benefits of "faster" exposure and better control of shallow depth-of-field.

For example, a 50mm standard lense typically has a larger aperature and allows more light to pass. I'm wondering if this has an added benefit for marine photography. I've never taken an underwater photo but it seems in this case, a standard lense would be a great fit.

From what I've read about marine photography, it's typically hard to avoid backscatter and darn near impossible to get a decent photo without a great strobe due to both particulate matter suspended in the water and poor light transmission at depth.

It seems to me that a big aperature would be ideal for reducing back scatter because of shallow depth of field and would also make great use of available light at depth.

Yet, it also seems that I can't find information on standard lenses for marine photography, save for macro-zooms and fisheye lenses.

Does anyone have any experience with using a standard lense rather than a zoom at depth? I'd like to get this figured out before I sink a bunch of cash on a housing for my D60.


04-09-2010, 13:13
The issue that I've learned about lenses underwater is that because of the diffraction of light you tend to lose field of view so the effective length of a lens is about 1.3x of what it is on land. So a 50 mm lens will have a FOV underwater (using a flat port) of around 65mm, which is getting a bit narrow. And then if your talking a "real 50mm" lens, i.e. a 50mm lens on a full frame DSLR, on your D60 which has I think an APS-C sensor you have to cut the field of view again, I think the factor there is 1.5x. So add them up, 50mm x 1.5 = 75mm, then 75mm x 1.3 = 97.5mm. So the lens you started out with is now essentially almost a mild telephoto lens. And then a prime lens like a 50 isn't capable of very close focus, at least not in the macro range, so you'd end up with a narrow field of view, and no ability to focus very close.

One of the reasons for using wide angle underwater is because as light travels through water you lose color. So if you can get closer to the subject (wide angle) then you have less color loss, as well as it more often means your within flash range. So wide angle is very useful underwater, which is probably why you don't see much about using prime lenses. I've seen a few write ups for lower end zooms, usually kit lenses that come with cameras, say the 18-55 zooms and such, but then you have the lower end to work with, which by the time you factor everything in may end up being nearly 50mm effective FOV even at the 18mm range.

I have an older D50, and the 18-55 zoom, which wouldn't be terrible underwater, but when I looked at the cost of a housing, port, and all the other associated items I'd need, I found that in the end the price of the camera and lens was way less than the housing/port. And ports aren't universal. You might want a flat port for macro, and a dome port for wide angle. $$$ start adding up. I also hated to think of my DSLR getting flooded, so I ended up with a Canon G11 and housing, which camera is about $440 and housings for it range from $180 to $1100 depending on the feature you want. A very popular and capable P&S is the Canon S90 with Ikelite housing, which you can get in the $700 range, which is a far cry less than a housing/port for a DSLR. And you can get even higher end housing for the S90 that can take wide angle wet lenses, so you change them out underwater and not be stuck with one lens for an entire dive. And while the smaller P&S have their own challenges (smaller sensor, slower focusing, possibly less flexibility) they can still do some amazing things. Just something to consider.

04-09-2010, 15:20
Prime lenses are actually extremely common for underwater use.

Most common, off the top of my head, are the 60mm's and the 105's (most prime lenses are best only for macro work, except for the really wide ones).

There is an extensive discussion of this here:
best underwater lenses|Underwater Photography Guide (http://www.uwphotographyguide.com/underwater-photography-lenses)

04-14-2010, 13:45
You can use whatever lens you want but the effective focal length through a flat port is increased by a factor of 1.33. If using a dome port the lens native focal length is preserved underwater. N