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davelew

Member Since 11 Jul 2007
Offline Last Active May 19 2014 11:48 AM
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#321624 Underwater settings for the Olympus OM-D E-M5

Posted by davelew on 28 November 2012 - 08:06 PM

Thanks for the excellent suggestions. I have a couple questions/thoughts. Apologies for the long post, I'm doing research into what to buy for my next trip. First, I have to plead a bit of ignorance. I've only snorkeled, but my next trip to the Hawaiian islands I plan to get certified and go diving.


I'll repeat what MarkHerm said. Photography is an advanced diving skill, not something that most new divers can do safely or easily.

Question 5: I have seen filters built to compensate for underwater lighting conditions...But seems to me this could be accomplished in post-processing. Do folks have tips on white balance or post-processing to color correct?


The problem with fixing white balance in post-processing is that most cameras don't allow you to set the ISO to one value for red pixels and to another value for blue or green pixels. Water filters out most red light in a couple feet, so an exposure for proper reds is going to completely overexpose the greens and blues, while a proper exposure for blue is going to underexpose the reds. The E-M5 has a great dynamic range for such a small sensor, but most natural light seen when diving has hundreds of times more blue light than red light, and the E-M5 can't compensate for that (no camera can, to my knowledge).

Unfortunately, the human brain is wired to respond to reds, and most of the best underwater photos have red in them. Needing red in photos and not having much red light underwater is one of the big challenges of underwater photography. There are four main ways of dealing with this problem:

1. Bring your own light in the form of underwater strobes. Inon and Ikelite are two popular brands. Alex Mustard has done some work which, I believe, shows that Inons are slightly better for cold water and Ikelites are slightly better for warm water, but both are excellent choices. The main drawback to using strobes is the short range of strobes underwater, but since the water column degrades image quality, you generally need to get close to your subject anyway for a good photo, so this isn't much of a drawback.

2. Put a red filter on your camera. This cuts down on the green and blue light, letting proportionally more red light in, at the cost of reducing the total amount of light, which means higher ISOs (with more noise), slower shutter speeds (with more motion blur) or wider apertures (loss of sharpness and DOF) are required. Since this balances the red, green, and blue channels of the camera before the signals go the A2D converter, it gives pretty good quality as long as the photo is properly exposed to start with.

3. Using the white balance option on your camera. Some people will bring a white slate or wear white fins, and take a photo of the white reference underwater to set the white of the camera. This tends to cause problems with the red in photos. Think of a camera that normally assigns a value of 0 to 999 for the redness of every pixel. Now imagine that all the reds are 0 to 9, so the camera multiplies each red value by 100 to get the full range, but it ends up only having 10 shades of red instead of 1,000, so the reds end up looking really weird and banded, not smoothly varied like the other colors that use the full of numbers from 0 to 999.

4. White balance in post-processing. This is about the same as #3, with the same drawbacks. It helps to shoot RAW in order to do this, since JPEGs lose some of the image information.

In practice, most photographers use a combination of #1 and #4. Many photographers have dual strobe setups, with two strobes on arms in order to get the distribution of light they want.


#320493 Nikon D7000 or Olympus OM-D E-M5?

Posted by davelew on 13 November 2012 - 06:54 PM

I have a D90 (basically the previous generation of the D7000) and an OM-D E-M5. I find that, when running out the door, I tend to grab the OM-D. The Nikon has slightly better dynamic range, slightly faster focusing, and I'm more used to the Nikon shortcuts to adjust settings. My impression is that lenses of the same quality are cheaper for the Nikon, but smaller and more portable for the Olympus (for example looking at good-but-not-great fast normal primes, the Nikkor 35mm f/1.8 is US$200, while the Panasonic 20mm f/1.7 is US$300), but it's really hard to compare lenses of similar quality. The OM-D is smaller and easier to carry around for those times when I'm not photographing, and that single fact outweighs the minor performance advantages of the Nikon. The one area where the OM-D significantly outperforms Nikon is with the image stabilization, but that's not much of an issue underwater.

An added advantage is that, with either the 60mm macro or the 8mm Zuiko fisheye and MMF-3 adapter, the OM-D is splashproof so a minor housing leak won't be an issue. I don't know if there's another splashproof fisheye lens for the MFT mount, I own the four-thirds 8mm so I just use it with an adapter.

In the end, I'd get the OM-D. It's more fun, and image quality is similar. My only advice is to get it without the 12-50 kit zoom. I find that lens to be awful, even compared to other kit zooms. I never thought contrast would be an issue with a modern lens, but the 12-50 has such poor contrast that images often appear to be blurry.