Jump to content


davelew

Member Since 11 Jul 2007
Offline Last Active Dec 28 2012 01:20 PM
-----

Posts I've Made

In Topic: Underwater settings for the Olympus OM-D E-M5

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.

In Topic: Anemone ID

23 November 2012 - 11:11 AM

I would have guessed a branching anemone Lebrunia danae




Posted Image


Thanks-- that looks exactly like what I saw.

In Topic: Anemone ID

22 November 2012 - 07:28 PM

Beaded anemone (Epicystis crucifer)


Just out of curiosity, what makes you certain? I actually considered E. crucifer, but rejected it because of the lack of a prominent mouth (or whatever you call the center region of an anemone without any tentacles).

In Topic: Seacam 3D housing

15 November 2012 - 10:57 AM

Normally, as far as I know (i am sure someone will have a different view) a 3D rig can't have a dome or a single lens. A flat port allows separation of one camera to another to achieve the 3D illusion. Its flat so no variation through the port. A dome is different. Its curved. I don't know how this works. Maybe the camera is automatically toeing the other like an optical stabilizer but not in the C300 and even if possible only limited to minute distances inside the lens barrel. I suspect it is a fixed distance close wide angle 3D rig. I could be wrong until I see some footage. It would be a shame if 3d has to be correct in post.


I have no idea if this is how they are doing it, but here's a way to get 3D through a dome port: have the axis of both lenses pass through the theoretical center of the dome. The trick is that the two cameras can't be exactly parallel to each other (or, if using a beam splitter, they can't be exactly 90 degrees off from each other). If you want the cameras pointed at the same subject, and that subject moves to a different distance, you would have to move the cameras as though on a curved track (both rotating and translating them).

In Topic: Glass for Nex 7?

15 November 2012 - 06:23 AM

Hi all,

I will (most likely) buy a NEX-7, but the available lenses are of no interest to me for underwater use.
I'm getting a bit desperate, as I'm leaving on a (very) long journey of photo and diving soonish.

Looking at the Nauticam port chart (http://www.nauticam....t/pdf_143_1.pdf), there are some Nikonos to Nex adapter.

I've no experience in Nikonos, but would that be a viable option?
How does Nikonos lenses work, the aperture and focus knobs are directly on the lens IIUC, which is waterproof without a port? (forgive my ignorance, I was not in the water during the Nikonos era Posted Image.
Would they be alright for an APC-S sensor?

Any input on the combination NEX 7 with Nikonos glass most appreciated!

cheers,
Christian


I use some Nikonos lenses on a micro-four-thirds camera (Olympus EP1) in a one-of-a-kind experimental housing. The EP1 has a higher crop-factor than the NEX cameras, 2.0 instead of 1.6, but it's lower resolution so the pixel size is probably similar.

Here are my opinions:

The 80mm is REALLY hard to use. I usually try it with the Nikonos close-up adapter for supermacro, but the depth of field of a 160mm equivalent lens along with manual focus is problematic, at least for me. I believe that the lens is sharp, I just haven't gotten any supermacro images in focus yet. Here are the closest:


Posted Image
P5040991.jpg by davelewinn, on Flickr


Posted Image
P5040978-2 by davelewinn, on Flickr

The 28mm lens is OK, maybe a little better with the closeup adapter, but nothing great. This is my best shot with the 28mm:


Posted Image
P5030857.jpg by davelewinn, on Flickr

The 15mm Nikonos lens is the only one I regularly use. It is more than sharp enough for a 12 megapixel sensor on a 2.0 crop factor camera, which is pretty astounding for a lens that age. Here is an example of a shot I took to try to later identify the beaded anemone, which shows what the 15mm is capable of even on a crop sensor camera:

Posted Image
Turks and Caicos by davelewinn, on Flickr

Personally, I find myself using a modern fisheye lens with autofocus and a dome port more than the Nikonos lenses. As frustrating as autofocus sometimes can be, manual focus is even more frustrating.