Some Words on Focus Lights

To follow up on my camera setup, you will see that I have a focus light set up.  I don’t use it constantly for reasons that I’ll explain in a minute.  However, I think it’s a very important accessory to have and use and it will save your dive several times over.

Why use a Focus Light

In order to understand focus lights, you have to understand autofocus.  The camera has a focus zone that depends on the camera make, model, and configuration.  On compact cameras like an Olympus TG5, it’s a fairly large square in the middle of the picture.  On my Olympus OMD EM10MkII, it’s a square that can be configured for size, location, and how much of the surrounding area is included as secondary focus.  On high-end DSLRs like the D850, it’s a set of squares inside a larger zone that can be configured in several ways.

The way that autofocus works is that the camera zooms the lens in and out.  This is called “hunting” in photography slang.  As it zooms in and out, the computer in the camera looks at the lines, patterns, and individual pixels inside the focus zone.  It tries to find the zoom setting where the largest piece of the focus zone is sharp.  Even with a slow autofocus, it will zoom in and out once or twice and then set the focus.

However, when you’re in low-light situations such as underwater, there is not enough contrast between light and dark for the camera to see how sharp or unsharp the photo is when it zooms the lens.  As a result, the camera keeps hunting.  If you see the camera hunt over 2 times, then you need to add light to help it.  I think this is worse with supermacro where the focal plane is very thin, so as a side-note, you can use higher aperture settings and maybe get better focus.

Extreme Low Light

I’ll turn on my focus light when the light is so bad that I can’t tell–even with back-button focus–if the subject is in focus.  Just a little bit of light helps me see in the viewfinder.  I will also use the focus light on my strobes during times like this.

Shrimps and Crabs and Focus Lights

Shrimps and crabs hate white light.  I think it hurts their eyes.  They will always turn away from you if you use a white focus light.  However, there is a way!  If you use a red focus light and strobes, they can’t see it.  They’ll gladly sit there all day while you take your photos.

Protip: you can drop a white-light torch around the back of the shrimp and they will turn around and face you or come to your side of the coral whip.  Just a little bit of light–if you overdo it, it’s rather abusive to the creature and is animal manipulation.

Nudies and Flatworms and Focus Lights

Nudies and flatworms can feel the heat from torches, including your focus light.  That’s why when they get within focus range, they turn to the side and “ruin” your face-on shot that you set up so meticulously.  After a couple of times, it begins to feel like they can sense right before you push the shutter button.  After a couple of days of doing this, you’ll think that the nudies are psychic and are reading your mind.

To fix this, use the minimum amount of focus light to reduce the heat or lock your focus and turn the light off.

Strobes and Focus Light

Some strobes have a button on the back that turns on a small onboard focus light.  In some cases, this is preferred to the main focus light because it doesn’t shine down the port.  On some strobe diffusers, like the ones that come with the YS-D2s that I have, they have a piece of plastic that you pop into the diffuser to make a red focus light.  To be honest, I don’t use this much except for super low light conditions.

Colors!

Some focus lights can add other colors into the picture.  Most of them can add red.  Because shrimp.  Some of them also can add blue or ultraviolet.  A tiny amount of blue or UV will make the white in the subject glow slightly, like a white t-shirt under a black light at your favorite nightclub.  It’s a very nice effect to put into your photos.  Just try not to disco dance.

 

Focus Lights and Backscatter

It’s an inconvenient truth for an underwater macro photographer: your focus light causes backscatter.  It’s probably ruining most of the photos that you’re taking today.  Because the focus light is shining down the side of your lens port, it lights up sand and dirt between the end of the lens and the subject.  Or sometimes behind the subject, but your strobes were going to hit that anyway.  That dirt and sand shows up in your pictures as backscatter.

All this ugly sand in my photos blocking my rhinophores, what’s a macro photographer to do?

Well, there are 3 ways to reduce backscatter with a focus light.

  1. Reduce the brightness of your focus light.  That minimizes backscatter because there isn’t as much light to be reflected.  It took me a long time to get into the habit, but always use the minimum amount of focus light that you need to get a focus and if you don’t need a focus light, don’t use it.
  2. Turn on the focus light, use focus lock, and then turn the focus light off.  You would be amazed how infrequently I refocus on a dive: mostly I focus once and then take many photos with that same focus.  Having a zoom gear on the camera helps, too: you can manually focus if you need to refocus.
  3. Add an arm to the focus light to move it up so that it shines down on the subject instead of shining down the side of the lens port.  That moves the light away from the end of the lens.

 

 

See you underwater!!

–Mike

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