Buoyancy, Floats arms, Underwater Photography, UNDERWATER VIDEO

Increase the your rig’s buoyancy using floats or float arms

March 15, 2014 interceptor121 11 Comments

As you add up lenses and accessories to your underwater photography or compact video rig you start experiencing an increase in weight first on land and afterwards in water.

My current rig for photography weights in excess of 5 Kg (11 lbs) and in water this is very near to 2 Kg (4.4 lbs). The housing and the hardware are usually the main culprit but even strobes or lights can easily add weight. As you add more and more components the weight of your rig ramps up.

I use locline arms for video and this greatly helps reducing weight both in and outside water. My compact video rig is around 500 grams or 1.1 lbs in water but also very lights outside water. The Sola lights really help with their incredibly compact size. The heaviest items are the tray and handle and the lenses.

For my video rigs I use STIX jumbo floats on the tray and on the locline segments. Each one of those floats gives around 160 grams 5.6 Oz lift in water.

Stix floats are available as large and jumbo format more information directly on the 4th generation designs web site here

For stills I use aluminum arms as I find them more precise but also need longer arms and be able to sustain a heavier weight for a strobe outside water. Strobes frequently weight over half a kg with batteries, this is too much for a 1/2″ locline arm and stiffer 3/4″ segments are required. I don’t particularly like the 3/4″ segments and I prefer ball and clamp solutions. 3/4″ segment can hold easily a strobe but can’t be really too long.

This is my basic still set up I had for the Panasonic LX7

Even in this case I tried to use as many floats as possible to keep it light around the usual half Kg 1.1 lbs underwater weight.

For my RX100 I have two strobes and arms with 8″ and 5″ long segments.

As you can read this is 5.5 Kg on land and even with 6 Jumbo stix floats the underwater weight is over 680 grams or 1.5 lbs this for me is a bit too much to carry around so I started looking into alternative solutions.

Left Inon Mega M - Center ULCS 8" with 3 Jumbo Floats - Right ULCS 5" with 2 Large Floats — Left Inon Mega M – Center ULCS 8″ with 3 Jumbo Floats – Right ULCS 5″ with 2 Large Floats

The ultralight buoyancy arms provide too little lift in my opinion to be worth using so I looked at float arms in carbon or plastic material as an alternative. I came across Inon and Nauticam products and so I ran some comparison based on some metrics I have defined myself.

Update 16 March I also include Stix float arms now.

Those are:

Buoyancy per $: how much lift do you get per $ spent
Buoyancy per mm: how much lift do you get per mm effective length*
Buoyancy per gram: how much lift do you get in relation to the on land weight of the arm

*effective length is measured from the center of the arm balls

I refer to US $ prices just for convenience the same would apply even more in UK/Euro terms so here are some results

Standard Float Arms

You would use standard float arms if you have an acrylic dome on an SLR or mirror-less or a plastic housing that gives considerable lift as those solution give limited lift in water ranging from 75 to 333 grams.

Arm Type	Buoyancy	Cost Total	Weight	Depth Rating
ULCS S + 2 Stix L	154	$57.50	101	40m/130ft
Stix 6″ L	142	$43.00	101	40m/130ft
Inon S	75	$75.95	142	70m/230ft
ULCS M + 3 Stix L	237	$66.75	146	40m/130ft
Stix 9″ L	260	$48.00	146	40m/130ft
Nauticam M	240	$80.00	200	100m/330ft
Inon M	135	$89.95	181	70m/230ft

I have compared an ULCS 5″ and 8″ segment with Nauticam 60 mm diameter and Inon arms of the same diameter 52 mm or 2″. Those are the results. Update the new graph also includes Stix arms made of aluminum with plastic balls and their own floats.

In this category you can see that a STIX arm with large floats beats a carbon or plastic float arms on all metrics in fact on the shorter segment nauticam does not even produce a float arm solution.

An ULCS 5″ segment with 2 large floats give a lift of 154 grams or 5.4 Oz and an 8″ segment a good 237 grams or 8.5 Oz, Stix arms offer 142 and 260 grams respectively in the 6″ and 9″ lengths.

This solution gives more lift in water and is lighter on land I see no benefits investing in a float arm in this range of buoyancy and for this reason I have not even considered ULCS buoyancy arms. A pack of large stix floats costs $25 for 4 units of 99 grams or 3.5 Oz lift each and those can be moved on your arm segments making it a very flexible option.

Mega Floats

I define as mega floats anything that offers at least 2 grams lift for each mm effective length. I put the Stix arms in this category even if they fall short in this metric as they are comparable and cost effective.

Each one of those solutions will provide in excess of 274 grams or 9 Oz lift in water. In this category we have the ULCS arms with Stix jumbo floats as the most agile solution at 2.5″ or 63.5 mm diameter, this has the benefit of not requiring extra long clamps to fold two segments with floats fully. Nauticam and Inon both have segments with 90 mm and 97 mm diameter. Inon segments have an extra benefit compared to Nauticam for compact camera users using wet lenses as they can support up to 2 single lens holder for each segment as in the picture earlier in this post. Stix arms made of plastic are the cheapest in this category though can’t offer the same amount of buoyancy of carbon or ABS arms.

Arm Type	Buoyancy	Cost Total	Weight	Depth Rating
ULCS S + STIX J	274	$62.50	122	40m/130ft
STIX 6″	284	$43.00	122	40m/130ft
Inon S Mega	390	$82.95	219	70m/230ft
Nauticam S Mega	375	$90.00	240	100m/330ft
Inon M Mega	650	$93.95	295	70m/230ft
ULCS M + STIX J	416	$74.25	175	40m/130ft
STIX 9″	425	$51.00	178	40m/130ft
Nauticam M Mega	655	$120.00	275	100m/330ft

Those are the results:

Stix float arms score higher on a Buoyancy/$ metric and also lead the way in terms of buoyancy/weight ratio however the amount of lift offered is limited and this solution does score low on the buoyancy/mm metric. Especially in the medium segment around 8/9 inches you can see that there is not much difference on a buoyancy/$ between a 9″ stix arm and an Inon M mega.

You do get a problem with this big arms if you want to fold the segments on themselves. Currently ULCS provides the AC-CSB clamp for 2″ arm segments but even with that you can’t fold two mega arms.

Here a few example of the issue I mentioned a mega arm with a 5″ segment with float reaches maybe 30º and without the float around 20º

Mega float + 5" segment — Mega float + 5″ segment

Ultimately I do not think is a big issue as you can use the strobe adapter segment and still achieve all possible positions for your light anyway if you are concerned do get a couple of the longer clamps.

This is my rig with the float arms it does look neat compared to the version with STIX floats

Sony RX100 Mark II rig with Inon Mega float arms

Conclusion

Unless you have a plastic housing or a housing nearly neutral in water floats or float arms at 2″ diameter are not really effective, produce limited lift and are not a really cost effective way to add buoyancy to your rig. 2″ floats can be used to trim your rig in case larger floats are too buoyancy but are not a primary way to achieve the purpose. For example if I wanted to make my rig neutral I could add 2 large Stix floats on each arm.

Stix floats offer a lot of flexibility as you can take them off arm segments and put them elsewhere in a flexible way. Stix floats are also an option just within recreational limits 40m/130ft past this depth the floats loose buoyancy and eventually crush. Stix do offer custom materials float that resist greater depths on request.

Mega arms are a bit clumsy but do provide the lift needed and are cost effective even if a bit heavy on land. My preference if you use wet lenses is for the Inon arms, those are the most cost effective and provide the most lift and can also support lens holders. Inon arms are rated for 70 m/230 ft if you go deeper you need the Nauticam arms that ca go down to 100 m/330 ft. So for technical photographer float arms are really the only way forward in terms of off the shelf solutions. Obviously you can get bespoke solution using submarine grade divinycell but that is beyond the expertise and reach of a normal user.

How much lift do you need?

To calculate the buoyancy of your rig you can use manufacturers data sheets (Inon is brilliant, ULCS does provide some weights, housing manufacturers usually don’t). Failing that you can calculate this item by item using a graduated measuring container or last resort put your whole rig in water and use a luggage scale.

Caution

I balance my rig to have it neutral WITHOUT wet lenses this is for safety reasons. If you use a heavy wide angle wet lens and your rig is overall neutral the moment you take the lens off the port your rig will start to go up. Likewise if you had to loose your lens your rig would float and could escape to the surface. If you want to balance the overall rig you need to find a solution to balance the lenses themselves otherwise severe risks of runaway ascent chasing the rig could incur

close up lens, diopters, SONY RX100, SONY RX100M2, Stabilization, UNDERWATER VIDEO, Video Lights, wide angle

Sony RX100 – In depth into digital settings

March 12, 2014 interceptor121 1 Comment

Over a year ago I wrote a set of posts for the RX100 and some of the quirks of this wonderful little camera.

Steadyshot – aka Image Stabilizer

The RX100 has a specific Active mode for video not available when taking stills. I described the differences between those two modes in this post

Everyone is so obsessed of having the widest possible field of view that other more important considerations are completely missed out.

If you have ever shot a video with a GoPro underwater you know how bad is the quality of the image in the corners, this is because the flat port combined with the gopro lens create many optical aberrations.

Our RX100, especially the original Mark I, also has an issue in the corners, this is not just an underwater issue is also true on land. The lens on the camera has a lot of distortion and when corrections are applied to the image this effectively creates corner softness.

When we add a wide angle lens the image quality in the corners deteriorates further especially if the lens is flat creating a lot of chromatic aberrations that you can see in pictures with a blue or yellow halo around the edges.

Now the good news the Active steady shot mode crops the image of a factor of 1.15x getting rid of the majority of the corner softness.

There is of course a price to pay which is the loss of some of the angle of view. According to my calculation if you use an Inon UWL-H100 you start from more than the declared 100.8º more around 104º in fact. When the active mode is on this drops to around 95º. Remember all those values represent the largest incident angle that means the diagonal field of view.

A lens with 100º diagonal field of view means 90º horizontal. So after the active mode is engaged our horizontal field of view looks more like 84º which is equivalent to a 20mm lens. This is sufficient for most close wide angle shots and plenty for ambient light videos of large fish or wrecks. I generally suggest to keep the Active mode on, of course if you can be in a fixed position and hold the camera really steady you can also use the standard mode and obtain more field of view. There is a chance though that you will need to crop the extra field of view if you need to stabilize in the editing phase.

For macro shots without a tripod the steadyshot is a must and helps greatly. I do not even see a reason to take it off if you have a tripod as the RX100 does not have a particularly small capture area.

Digital Zoom

This brings the second subject: digital zoom, if you shoot pictures you avoid it as what you are doing is to crop the image, something you can do yourself in processing. In video though there is very little quality loss as we use just 2 megapixels of the 20 of the RX100 camera. In my test you can use digital zoom until the 2x multiplier is reached, this corresponds to 7.2x magnification and see no noticeable degradation in the image quality. The other benefit is that the depth of field is the same despite the magnification so you can save yourself stacking two diopters with all the difficulties that follow in terms of focus.

Digital zoom is always on in video mode and I recommend to use it with a single close up lens before embarking on dual diopters or a strong single diopter. Also take into account that with a single +6 diopter your working distance is around 4″ which is ideal for most critters except pygmy seahorse and bobtail squid or some shrimps.

Video Lights

In another post I have explained that getting hung up about light angle coverage is not really the only thing to consider, there is also luminous flux and quality of light. With my Sola 1200 I can cover something between 2 and 4 feet away with decent results further away is just back scatter. Generally this is ok for some close portrait work and close wide angle and of course not sufficient to cover part of a wreck or much larger subjects. You may decide not to bother at all with lights for wide angle and just render your deep wreck dives in black and white in this case consider that a pair of Sola Dive 800 at $399 are a high quality macro set up, function as dive light and provide some decent close wide angle portrait illumination. For macro shots you need much less than that, I set my fill light at minimum (300 lumens) and the main light at 2/3 which is 600 lumens, I can shoot at f/11 with this light intensity. You can see me shooting in the feature image.

housing, SONY RX100M2, Underwater Photography, UNDERWATER VIDEO

Leak Sentinel V3 for RX100 Mark II – Review and Stress Bench Test

March 9, 2014 interceptor121 5 Comments

Following the failed test on the Nauticam Electrical Sync Cord bulkhead I was out in the market to check what else could be done with the M16 port on the RX100 Mark II housing.

I bumped into the leak sentinel while at the London Dive Show. As you may know Nauticam provides now a vacuum system with temperature compensation on all new micro 4:3 and DSLR housings. Also older models can be retrofitted but not the RX100 because essentially the moisture sensor is much simpler.

So if the Nauticam housing has already a moisture sensor why bother adding a vacuum test. The advantages are numerous:

A moisture sensor still requires the housing to be put into water to be tested
A moisture sensor starts beeping when water has already made its way into the housing, if you are in a situation where you have a mandatory safety stop or a deco stop you don’t want really to have the additional stress of a camera flood.
With a leak sensor you can check the integrity of the housing before the dive and without putting it in water
You can rapidly change battery and the likes and not worry if you have compromised the seal of your housing

With all of this in mind I went off and contacted Vivid housings

After an email exchange about the design of the product I was convinced that it was worth getting it so I ordered one and after just 3 days it turned up in my post directly from Slovenia.

The system comes with an M16 adapter to screw on the housing bulkhead. The best way to remove the cap on the Mark II housing is using a CR2032 battery like the one of the moisture sensor.

I set up the system on the housing as in the featured image and started my preparation. It takes 3 pump strokes to get a green light and the instructions say to add between half and a full stroke to make sure it is not on the edge. I had 4 full strokes.

I prepared the housing and camera in a room at 21C and waited 20 minutes before putting it in water at 15C.

I then put the camera in video recording mode for one hour, the Rx100 has a limit at 30′ so I had to record two files. After one hour the system was still showing a green light I took it out of the water and follow the depressurization procedure and extracted the camera. Measuring the temperature inside the battery compartment the sensor indicated 28C.

Now this made me think to the fact that this solution, although equipped with a temperature sensor, does not actually manage temperature compensation. If you know anything about physics you know that the following is true for an gas also known as Gay Lussac law

the pressure of a gas of fixed mass and fixed volume is directly proportional to the gas’s absolute temperature

As our housing is rigid and not compressible this means that the ratio between temperature and pressure is constant.

This also means that if the temperature increases because the camera warms up with use the vacuum will drop (pressure increases), this could create a false positive.

I therefore performed the following steps

I immersed in water at 32C and started shooting a video clip.
After around 50 minutes the led started to alternate red and green. The camera has the temperature warning indicating a possible temperature close to 40 degrees
I kept the camera in water pretty sure there was no leak and then at 60 minutes took it out of the water
After few minutes outside water in a room at 21C the light went back to green
The camera temperature in the battery compartment was 36C

The ambient pressure was 1016 mpa so I estimate I created around 750mpa inside the housing with 4 full strokes, however as the camera sustained an increase of 19 degrees from 21 to 40 the pressure sustained an increase of 6.5% bringing it in the warning area of the leak sentinel and generated a false positive.

Now there are a few considerations to be done:

1. If you shoot pictures even firing the flash is unlikely to get the camera as hot as when you shoot video
2. The water in the dive will seldom be 30C anyway
3. It is preferable to prepare the camera in a temperature as close as possible to the diving temperature and in the driest environment available
4. It is possible to estimate the amount of vacuum each pump strokes gives and compensate for the temperature changes

The worst possible scenario is a video camera housing prepared in an air conditioned environment this is the only scenario where temperature compensation is useful.

Generally the suggestion of the user manual to give one or half pump strokes should be changed. Say that I have a large housing and it takes 10 strokes to create the vacuum, I would suggest another 3 strokes is diving in warm water otherwise the possibility of false positives is increased.

For what concerns the RX100 and only for very warm water shooting a lot of video there is a theoretical possibility that the camera overheats, and if the housing had been assembled in a much colder room, this gives a false positive.

To minimize this possibility prepare your housing at the normal ambient temperature of your dive site is generally the best practice for tropical diving. I also do not recommend practices like preparing your housing in a cold air conditioned cabin, some people think they avoid condensation not thinking that a 20+ degrees thermal shock does do any good to the camera.

Ultimately at €200 including worldwide shipping I can definitely recommend the leak sentinel to all RX100 users. Considering the cost of your investment even at the price of the RX100 Mark II of $750/£649/€699 this is a good tool and more than anything give you the extra reassurance of having a watertight housing, and also helps you in all your situations where you have a battery change or you have to open the housing before the end of your day.

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Monthly Archives: March 2014