focus lock

Some Words on Focus Lights

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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

The Whys of Back-Button Focus and Focus Lock

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Back-button focus is a technique where you change the focus button to on of the programmable function buttons (F1, F2, F3, etc) on the camera so that it makes the camera focus instead of the usual half-press on the shutter button.  This will let you lock the focus at the same distance from the end of the lens until you use the function button to refocus.

You then:

  • Choose a subject.
  • Push the focus button to get a focus lock.
  • Move the camera back and forth until the subject is focused the way you want it.
  • Push the shutter button for an instant picture.
  • Keep taking pictures with the same focus.

“That sounds complicated just to take a picture.  Why would you do this?”

For starters, autofocus is slow.  You half-press on the shutter button, the camera picks a piece of the picture, moves the lens in and out until the blur disappears or is the smallest that it will get, then signals that it has focus.  You then push the shutter button the rest of the way.  If you lock the focus, then for the cost of a little bit of time setting up the shot, you can take all of your pictures after that very quickly.

You get more control.  You can think of focal plane as a sheet of glass perpendicular to the lens and at a fixed distance away from the end of the lens.  As long as something is inside that sheet of glass, it’s in focus.  Now you can do like I did with the skeleton shrimp below and put eyes and “hands” in focus by angling the camera so that the those pieces of the picture are inside the focal plane.

You can focus on something that’s not the subject and then reframe.  I do this a lot with subjects that are hard to focus on.  Moving things.  Things inside holes.  Things not in the center.  Point your camera at something the same distance away from the camera lens as the subject and then focus lock on it.  You can then move your camera back to the subject and move it towards and away from the subject to get it in focus.

Macro photography is almost impossible without focus lock.  You have too many variables to consider to make a shot.  Simplify your shooting by reducing the effort of using autofocus by locking your focus.

Shooting in low-light situations is hard, even if you’re using strobes.  You can’t always use a focus light.  Crabs and shrimps look the other way when you shine white light in their eyes.  Nudibranchs feel the heat and change direction.  When you turn off the focus light, you’ll see the camera “hunt” when you try to focus: the lens moves in and out trying to find the right focus but because it’s too dark it can’t see the difference in focus distances.  So turn on the focus light, focus on the sand or coral, turn the focus light off, reframe on the subject, and keep shooting.

Most compact cameras don’t have a moveable focus point.  On most DSLRs and mirrorless, you can use the direction arrows or joystick to move the focus point around inside of the frame.  With compact cameras, you can get focus in the center of the frame, lock the focus, then reframe the subject.

“Wow, Mike, that sounds like an awesome idea that I’m really sold on, how do you set it up?”

It depends on the camera, they all do it differently across brands.  For a howto specific to your camera, try google for “<model> back button focus”.  I’ll post later on how to do this for the Olympus OMD mirrorless.

On compact cameras, programmable buttons are fairly rare.  However, they sometimes have a “focus lock” feature where you can focus on an object and then lock the focus point.  I’ll post later on how to do this for the Olympus TG4 and TG5.

Sample times when I’ve used back-button focus:

  • Fast Little Blue Fish.  They move in and around the coral too fast for you to get a good focus.  So lock your focus and take a picture when they appear in the gap between coral.  I talked about this in Little Fast Blue Fish.
  • Skeleton Shrimp.  They live usually on hydroids: cousins to coral that look like little white-brown shrubberies.  These hydroids sway gently in the current.  Back and forth, back and forth.  Too fast for your auto focus.  Next time they swing by, focus on them and lock your focus then snap each time they swing by after that.
  • “Fast-Moving” Nudibranchs.  Focus on a spot in front of their direction of movement where they crest a micro-hill and lock your focus.  When they move up on top of the terrain, get a picture when they’re more silhouetted. I describe this in this post about Bornella.
  • Critters in Tunicates. You’re taking a picture where the subject is inside a tube.  The autofocus on the camera sometimes will lock on the top of the tube.  Lock focus then move the camera forward to move the focus into the middle of the tube.
  • Hairy Shrimp and Other Teeny-Tiny Things.  When using supermacro gear and taking pictures of things smaller than 3mm across, your focal plane is extremely small.  Use focus lock to lock your focus then move the camera slightly to give you the focus that you want.

 

 

See you underwater!!

–Mike