Parrotfish and Deep Focus

Posted in Under the Sea on May 30th, 2010 by MadDog
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Saturday dawned brilliant and promising. I was looking forward to going back to The Eel Garden near Pig Island  to find the Leafy Sea Dragon which has been reported to be on the old catamaran. I looked in vain for it last week, but a fellow diver, Hendirck, told me that he had found something promising. In return for the information, I dragged out my old Canon G10 and its underwater housing for him to try out.

Unfortunately, with all of the juggling around of cameras, housings and memory cards, I managed to show up at Magic Passage for our first dive with my G11 showing “NO MEMORY CARD”. Ai ya yai ya yai!  Stupido!  So, I did a very nice dive on which some very interesting critters were spotted, but I had no camera.

Never mind. I pretended to enjoy it, playing Divemaster and pointing out all sorts of fascinating items which I determined to burn into my brain memory cells instead of my usual memory contained in my camera. The camera is much  more reliable.

On the second dive at The Eel Garden, Rich Jones was not diving, so I used his new G11 which was out on its virgin underwater experience.

There were many very colourful parrotfish about. This is simultaneously exciting, euphoric and frustrating. If you are a snorkeller or diver you understand the first two. If you are an underwater photographer you get the latter. Google parrotfish and look at the sad offering of images. It is nearly impossible to get close to them. You must depend on the occasional quick shot when one darts past:

I don’t know the species of the one above. My fish book is at the office and I have photographed so few that I can’t remember most of the names.

This one, I do know, but I would call it a “failed” image:

It is a Hump Head Parrotfish (Bulbometopon muricatum).  They are huge. This one was at least 1.5 metres long. Unfortunately, they are delicious and easy to spear. In some areas of the South Pacific they have disappeared completely. This was a quick snap shot at the end of a long tiring chase during which I managed to corner it long enough for a very poorly framed image. The closer you get to them the bluer they look. I was about two metres away from this one in fairly dirty water.

I’ve been playing around with a photographer’s technique called “deep focus”. It sounds exotic, but it is easy to understand. The smaller the hole you are looking through, the more “depth of field” you will get. In other words, objects from near to far will be in focus if the hole is small enough.

Theoretically, a pinhole will have a focal range from very close to infinity. So, the larger the number of the f-stop you use on your camera (the size of the hole through which the light passes) the smaller the hole will be. I know it sounds backwards, but never mind. Big number – small hole  – more depth of field. That’s the way it goes. If you can get f 16 on your camera, you will get lots of stuff in focus from near to far. At f 2.8 you will get only near or far, but not both.

It works better for non close-up stuff. For instance this shot of the Nudibranch Phyllidia varicosa  doesn’t show much effect:

Sure, most of it is in focus, but there is not much to show the depth of the image. There are no obvious visual clues to indicate depth.

It this shot of coral with an anemone in the background, however, there are many clues to indicate distance:

It requires a lot of light to use the small lens opening, because not much can get through. If you don’t have enough light, you will be forced to use shutter speeds that are too slow to give sharp images. There’s no free lunch. You can have it one way or another, but not both. I manually blurred and darkened the very distant objects at the top to enhance the effect.

In both of these images I failed to note that when I changed the mode of my camera to Aperture Priority (meaning I get to set the aperture and the camera automatically sets the shutter speed) I lost my format setting and it reverted to JPG. I always shoot underwater in the RAW format mode because it allows me much more colour control. Sorry to bore you with these arcane details, but there are a few photographers out there who are constipated enough to care about these things.

Here is a pretty scene, never mind the colours are off, of some coral with Purple Antheas swimming around:

It nicely illustrates the reality which you can get with the deep focus technique.

Okay, that’s it for me. It’s Sunday evening. The sun is below the yardarm. I’m going for a wee dram and lay on the bed to watch some mind-numbing TV for a while. Then maybe I’ll rest my eyes for a bit.

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