Pacific Octopus hatching

Back in March I posted a video of an octopus tending to eggs.  She laid those eggs around Dec 25, 2014.  Merry Christmas, octomom.   Last night, the eggs started to emerge from their sacks.   As each egg emerges, octomom pushes them out of the den and out into the world.
They initially live their lives as plankton, and a majority of the 100,000 hatchlings will not make it.   This was even true during the hatching – - fish lined up to feast on the fresh octo.  I was lucky enough to be there to watch many of these very very tiny octopus emerge and start their lives.
Many of the proto octopus bring a food nugget with them – - extra material from the egg, so they can start their day with a solid meal. You can see that breakfast nugget in the below photo.
These tiny creatures get launched out of the den by mom who is pushing them out at an alarming rate and speed.   I can only assume she is trying to saturate the waters such not all of her precious babies get eaten.  Photographing these creatures in the water is nearly impossible, so we collected a tiny sample for a few photographs (and then later released it).  Even at this age, you can see the complexity of the octopus eye, the amazing pigments on their bodies, and their siphon.  The octopus brain is located just below and behind the eye.

Optical Spectrum of Dive Lights

There are lots of attributes of dive lights which folks spend large amounts of time discussing and reviewing.  These include:  beam pattern, run time, battery technology, sealed vs exchangeable batteries, “twist to flood” vs “magnetic switch”, pistol grip/goodman handle/etc, rated depth, etc.  That stuff is important. It’s so important I won’t mention it here and ya’ll should read about it elsewhere.  

I’m going to discuss a geeky niche: optical spectrum.  Before we submerge into the data we’ve collected, let’s review some of the basics.  

Sunlight transmits light from about 200nm to over 3,000nm.  Our eyes can generally see stuff in the 400nm (blue) to the 530nm (green) and all the way out to about 700nm in the deepest of reds.  On each end of the visible spectrum we have Ultraviolet and Infrared.  

As I’m sure most of you pacnw divers know, not all water is the same color. This topic has been turned into an excellent book (Light Absorption in Sea Water By Bogdan Woźniak, Jerzy Dera), which dives into great detail. The graph below shows the optical absorption several different oceans. The northern pacific is #2 on the graph.

This absorption causes the light to change color the deeper we go. This is what wreaks havoc on our white balance on our cameras – -as the color of the light which is lighting up our subjects changes based on season, ocean, depth, and whatever buggers are in the water column above us. This ALSO impacts light transmission of our dive lights, and thus, helped motivate the collection of these data.

Dive lighting technology really comes in about three different flavors: Halogen, HID and LED. Halogen lights are pretty much end of life, as LEDs provide such clear advantages. You may have noticed that different dive lights are “warmer” or “cooler” colors. This is due to the composite nature of white light – -when you sum the amplitude of the various wavelengths of light (also called spectral power distribution) you can end up with a tinting which looks more yellow or bluer. Metamerism is the matching of apparent color of objects with different spectral power distributions. This means you can have different spectral readings, which have the appearance of the same color.

LEDs are interesting because they emit one core wavelength (typically around 465nm) and use a phosphor to shift the light so parts of it emit between 500 and 700nm. Depending on the phosphor used, it impacts the ratio of the two peak emission spectrums. They can change tint based on thermal properties and the power levels they are driven at. A light on “low” may exhibit different color tinting.

HID lights use high voltage to make a small continuous spark in a small fragile glass bulb. HID lights generally have lots of “spikes” which sum into some value of white. The different technology and specifics of the HID light impacts where the spikes are located and how strong they are. Different voltages, heat, gas in use, pressure of the bulb, temperature and gap size can also impact the color of a HID light. HID lights have a limited future – it used to be the only way to get MAJOR light underwater, but LEDs have recently surpassed them in light output.

During our dive planning meeting on October 19th, 2013, we measured the optical spectrum of several different dive lights. The results are below.

When reading the above chart, it’s important to understand that “counts” is only relative to each light reading. This makes it useful to compare the relative optical spectrum of each light, but can’t be used to compare overall brightness. Irradiance measurements have not been conducted.

It’s Interesting the note that the $30 import special light has a similar (but not identical) spectrum to much more expensive Sola light. It does show less green/red, which would make this light have a much more blue appearance. Of specific interest to photographers, the “red focus light” feature on the sola lights seem to peak at about 635nm. It has been reported that Cephalopods (as well as many sea creatures) have very poor optical sensitivity at these wavelengths. It is possible that this is because these creatures are rarely exposed to much light at these wavelengths as it’s absorbed so quickly by salt water. However, as the light is so readily absorbed it requires much power in order to penetrate the depths of our waters.

In conclusion, dive lights emit different colors of light. What purpose this serves is left as an exercise to the reader.

Dome calculations – how to increase your near focus behind a dome

My new dome came in for my 35mm F2.8 lens. My first dive with this system resulted in very poor performance; specifically, I couldn’t focus very close on most things – - I had to swim away at least 6 feet from the subject in order to get anything into focus.   This won’t work at all – -as I’d like to be able to get closer to my subjects: Ideally under a foot.  It would be really nice if I could still focus on things far away. Can I have the best of both worlds?

A dome port underwater creates a “secondary focal point” or “virtual image”.   This means the hyperfocal distance (frequently referred to as focusing at infinity)  is in fact much CLOSER than normal. If you take a normal lens and put it behind a dome, quite a bit of it’s focus range is simply of no use as it is focusing “to infinity and beyond!”.

According to Sony, my lens has a minimum focus distance of 0.35 meters (13.75 inches) and a magnification of x0.12 (8.3:1 Reproduction Ratio)  This is the distance from the sensor to the subject.  Anything closer it will not be able to focus on.

The dome port I have from nauticam is a 4″ diameter dome with a 0.125″ thickness. The material is acrylic with an index of refraction of about 1.5.   The exterior apex of the dome is approximately 5″ from the sensor.   Using a calculator over on scubageek we can then determine that the virtual image is 11.3 inches (287mm) from the dome.   Once you add the distance from the sensor to the dome you end up with 16.3″.   This virtual image is the hyperfocal distance – - meaning, that focusing at infinity when using this dome underwater the lens is required to focus on an object which it “thinks” is 16.3″ (414mm) away.

Remember this lens has a minimum focus distance of 13.75 inches.  Ah ha!  The reason why I can’t focus very close on my subjects is because my lens can barely focus closer than the hyperfocal distance of 16.3″.  I got lucky – -if my lens had a minimum focus distance of GREATER than 16.3″ then it wouldn’t have been able to focus on anything at all.  Whoops.

So now the question is:  How do we fix this?   In order to focus closer with a lens system you have three options:

  • Get a macro lens designed to focus closer.  This is really the ideal option, but as such a lens doesn’t exist for this camera yet…
  • Use an extension tube.  An extension tube increases lens magnification by an amount equal to the extension distance divided by the lens focal length.
  • Use a close up filter. A close up filter (aka Diopters) decreases the effective focal length of the lens system.

As stated above, my goals include being able to maintain focusing at the hyperfocal distance under water — I’d like to be able to get stuff far away in focus in addition to close up.     So that means whatever changes I made to the lens system I should try and ensure that the “Maximal working distance” of the combined system includes virtual image hyperfocal distance of  16.3″ (414mm), and I’d like to be able to estimate how close I will be able to get to the subject.

Close up filters are measured in terms of optical power (“diopter value”), which is the reciprocal of the focal length in meters.  We can estimate the max working distance by dividing 1 by the diopter value. Our target max hyperfocal distance is 414mm, 1/0.414m = 2.4 diopters.   Based on the diopters we have available (+1,+2,+4, +10), the +2 diopter close-up filter gives us a max working distance of about 500mm and looks like it would be a good option.    But how close can we focus?  I’ll spare you the nitty gritty, but provided you know your Magnification, focal length, minimal focus distance you can calculate it.   In our case this works out to be 230mm or about 9 inches; but bear in mind that’s 9 inches BEFORE you account for the dome lens – - it is in fact further away.

Extension Tubes are measured distances they increase between the objective lens and the sensor.   For this FE-mount camera I have both a 10mm and a 16mm extension tube.  Even using the shortest extension this works out to a ~200mm infinity distance, which is half of what we need in order to operate inside of a dome and hit the hyperfocal distance of 414mm.

Here’s a nice calculator which can help do these calculations for you.  One important think to keep in mind that wither either an extension tube or a close up filter installed, you won’t be able to reach hyperfocal distances above water, but you may be able to while UNDER water.

In summary, we looked at what impacts the focal range of lenses under water, and figured out a method for how to increase a method for close-focus without compromising the ability to shoot at objects far away.   Of course, I’ve just calculated this but I’ll give this a shot in the near future and report back in the comments.

There are lots of things I don’t yet understand.  Maybe someone reading this will help shed some light:

  1. How does one account for the near-focus plan changes inside of a dome port?
  2. What is the difference in Close-up filter calculations when it’s a wet vs dry diopter? As the index of refraction is different in water than on land between the interfaces, there should be a change?  Does this mean a +2 wet diopter is only a +2 diopter when wet, but is some other value when dry?

First light from a new camera

First shots from a new underwater camera. This has been a long time coming… I flooded my canon camera back in December and it took a long time for them to manufacture a housing for my new camera. The first shots wasn’t much to write home about as far as content goes, but I’m pleased with the overall image quality. This system is a bit odd in a few ways: For starters, it’s a compact/mirrorless full frame camera (Sony A7r) which sports a whopping 36 megapixels. This is a full generation or two newer than what I used to shoot on (Canon 5dmk2). This might be the death of the mirror, but people have been saying this for years.

The other strange part of this system is the lens I’m using: A nikonos 15mm F2.8 WET lens. Most dive lenses are really just normal photography lenses housed in “ports”.   The ports are generally either acrylic or glass, but are also designed to meet the broadest number of lenses possible – - thus, they end up not working perfectly on any lens.  Also, as these large ports tend to be imperfect optically, they make them very large in order to reduce the impact on the resulting image.    These nikonos lenses have a completely different approach:  They design the entire lens system including the “port” into one optical system.  This enables a very small port (2″ diameter vs 8-12″ diameter) while retaining EXCELLENT image quality.   I had a chance to dive this setup a few weeks ago – -and while I was let down with the overall wildlife available to photograph, I was completely BLOWN AWAY with the image quality.  Specifically, I could not see any chromatic aberration or distortion on the image, even all the way out to the edges.   One odd part of this setup is that it’s so optimized for water use that it won’t get focus on land.  It’s a highly specialized lens.   There isn’t a ton of technical information about this lens due to it’s age, but folks are mounting these lenses on cameras like the EPIC RED.

There are challenges with this system  - – besides being a new camera with lots of new stuff to learn, it’s also manual focus and f-stop, which adds even more complexity to this.    THe A7r does have many nice features to help ensure crisp focus, but I’m still playing around with the settings.  The good news is that you really don’t have to muck with the focus much on such a wide lens – the depth of focus is huge.

The above image has not been retouched at all.  It’s import into lightroom, export to flickr.  You can see the full photoset here:


Strobe signaling

Underwater cameras generally use one of three methods for firing strobes:

  1. A photodiode which detects the onboard camera strobe (or any neighboring strobe)
  2. That same thing coupled via a fiber optic cable
  3. An electrical connection
Roughly speaking, this really just boils down to “electrical or optical”.
There are advantages and disadvantages of all of these systems; the electrical sync systems can flood but can provide advanced signaling.    The optical systems tend to be robust to water (swap around cables mid-dive!) but are limited in communication methods as most of them just use a single pulse of light to trigger. Optical systems are also dependent on the main camera strobe, which frequently limits the rate at which you can fire and can consume your battery quickly.
Electrically controlled strobes have been around for a very long time.   As technology has evolved, so have the interfaces.  Early strobe interfaces had very high voltages present on the pins, but these days it’s a nice civilized 5 volt signal most of the time.   A majority of underwater electrical connections use dedicated pins for specific signaling which mimic their land-bound siblings:
  • Ground
  • Rdy pin: Strobe Ready
  • X pin: Trigger or sync
  • Q pin: Quench or TTL stop
These signals are available in nearly every hotshoe in a modern camera.  This enables cross vendor compatibility (A canon strobe works on a nikon camera!), but may not be able to access some advanced features.  When we get outside of the land of underwater cameras, we find there are additional signals going on such as digital serial data which set things like focal length, multi-strobe coordination, battery charge state, model, strobe position, etc.  This is an area where we’ve seen great advancements in strobe communications on the high-end DSLRs (Example:  the canon 580EXII has a focus motor so it matches the focal distance of a lens in real time as I zoom.. Magic!)    I have yet to see any of these advanced features show up in underwater strobes – -in many ways these are very primal creatures which change very slowly.   There are several competing standards in underwater electrical “sync cords”.  NIKONOS and IKELITE are two of the common ones.  They are physically very different but are electrically identical.  This allows pretty much any underwater strobe work with nearly any underwater camera.
Ikelite PlugNikonos Plug[1]
But things are even more simple:  A large number of housings and hotshoe fittings only connect up ground a one pin — you guessed it pin X.  We really only need a single, well timed pulse from the camera in order to get the strobe to fire are the right time.  Most underwater strobes have manual settings which control the total output.
Some underwater strobe systems use TTL – - and thus, take advantage of the extra pins to some degree.   TTL is this vague TLA which means “Through The Lens”.  All this means is that the camera uses light from the lens and a whole bunch of sensors, processing and patent violations[2] in order to guess what amount of light is needed.  The TTL system will sometimes trigger a “preflash” in order to better measure the return light.  Under water, these systems generally work best when there isn’t open water in the background, the distance to the subject is mostly flat and that there is minimal backscatter.   This is because the camera has to make judgement calls about how much light is needed where, and it surely can’t light up that ship 200′ away but they might try sometimes – - thus completely over-exposing the tiny critter floating in the water.
From a physical perspective, both nikonos and ikelite connectors all suffer the same list of features:
  • Have o-rings which must be maintained and serviced
  • Are poorly keyed – meaning, there is only one rotational position they can be installed in, it’s not clearly marked during the insertion, and it’s prone to bending pins.
  • Use external threads which are generally metal-on-metal connections, thus highly prone to oxidation.
  • Are not based on published standards (so when other vendors make “compatible” products, they frequently fit poorly or fail frequently.  No really, 50% of the cables I tried at a vendors shop recently just simply didn’t mechanically fit)
Optical sync cables also suffer:
  • Most “fiber optic” (which is really just a plastic lightpipe, not *glass*) is designed around being fed from a strobe, so energy loss doesn’t really matter to them much. This poses problems for LED based trigger systems as they need to hit a VERY high peak power in order to overcome all of the optical losses in the cables.
  • The cables are very fragile with thin jackets and most of the connectors do not offer very good strain relief.
  • Most of the connectors are not… very mature.  Think set screws digging into the fiber, or clamps that force the fiber into small radius bends until it’s “stuck”.
Is there room in this world for a new standard?  Not sure.  But if I was a kingfish for a day, here’s what requirements I would start with:
  1. Create and use a free, published, clear standard.
  2. Optical cable based digital communication, bidirectional.
  3. Use real large core diameter fiber optic cable with a strong jacket.
  4. Create a connector which is either designed to be operated in water, or at a minimum has internal threads/locking assemblies and is not prone to collecting sand/salt/rust
  5. Optimize for either laser or LED driven communication (not strobes).  Maintain old optical sync standard “light pipes” for triggering off existing strobes.
  6. Have ample signal margin in the optical path.
Will this happen?   My guess is no, but we can all dream.
[2] By patent violations, I mean innovation. There is much active development in the land of image processing real-time on camera – - from face tracking, real-time HDR, and all sorts of funky ways of trying to get exposure set right, while minimization of motion blur.   Many of the camera manufactures are quietly stomping on each others patents, but my guess is that sometime in the next 5 years we’ll see the heavyweights knock each other around in court over this stuff.  We are already purchasing “app upgrades” to our cameras, it’s only a matter of time.

Why we are here.

This is my first post here on this blog where I intend to write about underwater photography.  For starters, let’s discuss the name of this blog:   A substrobe is a industry pun which has been around for a very long time (pre-1997?)- – the prefix “sub” has origins in latin, meaning things like “under/below/beneath” while also also meaning “at a lower point in the hierarchy” aka “submissive strobe”.    First underwater strobes aka “strobe slaves” triggered based on the presence of an existing strobe going off.    There is also an unrelated term “strobist” this site is no affiliation or relation to that at all.

My goal in this blog is to make this a resource for folks interested in underwater photography and related technology.