Video Macro Breakthrough

I have been shooting UW video for 3 years after 30 years of UW stills. I have never had a huge interest in "small stuff" photography, until earlier this year when I started diving with a group of Thai divers. Not only are they fascinated by little critters but they are really great at finding it. So, now, after each trip, I have a bunch of sequences of nudibranchs, shrimps, pipefish, minute crabs, etc.

Some of the footage was great but I noticed that about 1/3rd of these close-up sequences had an out-of-focus problem, with the background sharply in focus and the critter blurry. (possible reason described below)

How to ensure consistent sharp focus for close-up video footage?

So, taking a technique from the world of still UW photography, I decided to make a focus wand. I use flexible "modular hose" for my two HID lights and I recently, following advice elsewhere in this forum, added a Y joint to add an arm with a WB card to the left housing handle. So, I simply added a second Y joint to the top of the right handle and added 6 segments of 1/4 inch modular hose. I figured 6 segments looked about the right distance for typical "small critter" images. This puts the focus distance about 8cm (3 in) from the front glass of the L&M standard lens.

Next, I needed to test it. I was not sure if the focusing would be the same in or out of water so ran the tests in my outdoor fish pond (my Thai neighbours already think I am crazy ). I used a steel ruler as the subject to be able to accurately judge focus and distances. I studied the focus on the finder and again by importing the HDV footage into FCP.

I found that, with the focus wand straight out forwards from the the right housing handle, perpendicular to the lens surface, anything within 1 cm of an imaginary plane in line with the end of the wand will be in focus if the camcorder's manual focus is set to 0.2cm. I found that it remains in focus if I zoom from W to half-way to T. A bit more than half-way to T and it blurs.

I also learned something very interesting: THE MOM / AUTO-FOCUS FUNCTION DOES NOT ALWAYS WORK AS EXPECTED IN UW CLOSE-UP SITUATIONS. This is what I think had been causing my focus problems in the past. My previous approach was to position the camcorder, placing the subject to fill 70% of the image area, then press the momentary-auto focus button and assume that the Sony would focus on the large central subject. But my tests today showed that, more often than not, it would find its focus in the background and lock in on that. I guess I should have been checking focus in the viewfinder but I assumed that the L&M/Sony MOM mechanism would work correctly ("you fool", I hear all you wiseheads chuckling). It works OK for other types of shots as long as there are clear lines or edges in the subjects.

I guess that, when you press MOM, the Sony auto-focus mechanism starts hunting inwards looking for sharp edges. When it finds some (in the background), it says OK and locks. In several of my tests, it locked at 0.7cm, even when there was a great big steel ruler taking up the middle 60% of the image that was not in focus until 0.2cm.

So, in summary, here is what I have learned from my afternoon's kneeling over my fish pond:

- don't rely on MOM or auto-focus for close-up subjects

- always check focus in the viewfinder

- with my focus wand in place, I can confidently

- manual focus to 0.2cm

- zoom anywhere from W to 50% of T

- position the subject within 1cm of the end of the focus wand.

Armed with my new focus wand and knowledge, I intend to get back into the sea next week and see how it works in reality.

I have attached here a photo of the focus wand. For the next couple of outings I'll keep it as decribed above. But, the beauty of "modular hose" is I can add and remove segments. So, I could adjust the length for different circumstances, as long as I know the correct manual focus length.

I'll post an update after some reality tests...

Regards

Peter

Good idea Peter.

The best way is to have a housing with a true mechanical focus wheel, not electronic.

I find let it focus itself then lock it and grab your shot for as long as it remains in focus. Moving the housing in and out a bit sometimes helps to keep the little moving critters in focus.

Good idea Peter.

The best way is to have a housing with a true mechanical focus wheel, not electronic.

 

I find let it focus itself then lock it and grab your shot for as long as it remains in focus.

The L&M housing for the Sony HC3 does have a mechanical focus wheel that runs through the housing to the control wheel on the left front side of the camera. It can be set to manually adjust either focus, exposure, or WB. But I find the "Far" and "Near" focus buttons on the L&M left handle to be just as precise, once you get used to how they react.

I prefer to keep the mechanical control wheel set to exposure adjustments. I like to drop the exposure down a stop or two at deeper, darker depths to prevent the camera from trying to over-compensate for the lack of light.

When you say "focus itself" you are referring to auto-focus? On the HC3 I find that auto-focus is a bit too unpredictable in close-up shots, sometimes focusing on the background rather than the subject.

Regards

Peter

O you have a manual focus wheel on it.

Is it smooth/sensitive or rough/clunky?

Yes put it on auto focus, move the housing around if needed till it's locked on your target and not the background etc and then lock it to manual.

O you have a manual focus wheel on it.

Is it smooth/sensitive or rough/clunky?

 

Yes put it on auto focus, move the housing around if needed till it's locked on your target and not the background etc and then lock it to manual.

The manual focus wheel on the HC3 is a bit too sensitive in my opinion. But, then, topside, I use Hasselblad lenses that have a long smooth focus movement. Also, the positioning of the focus wheel puts the housing's manual control front-side the left housing handle, an awkward position to reach. I have found it better to get used the LANC-based housing manual focus controls.

Regards

Peter