Tag Archives: ambient light

Underwater Video Tips: Panasonic LX7 Settings and Features

My previous testing of underwater video with the Sony RX100 has been quite successful I was initially pretty hard on myself but I would say the performance was as good as it could have been taking into account the conditions

Most of my videos considering the conditions look better than dedicated single chip camcorders on the market and as good as some badly shot 3-chip camcorders

It is worth noting that a decent camera in a good housing like Gates or Light and Motion costs in excess of $3,000 without any lenses or lights, whilst with the same amount of money you can get a complete set up for a high end compact camera with included two sola 1200 and various lenses.

The restrictions of a still camera though still apply at least to the Sony RX100 and those are:

  • No use of zoom at wide angle with wet lenses (problem of set up not specific to RX100)
  • Clumsy operation of functions like white balance
  • having to change wet lenses multiple times in the same dive because close up performance is average

So is there something else out there that at similar or lower price point can get us high quality underwater video?

I believe there is and it is the Panasonic Lumix DMC-LX7, this camera has a bright f/1.4 lens with good sharpness, a 24mm lens and more effective ergonomics than the Sony.

Obviously I am talking about video here as I do believe the RX100 is the camera to beat in terms of compact for still pictures. For video especially at wide angle we are shooting mostly with ambient light and the corner softness of the RX100 does show with wide apertures. So whilst for your photos at close focus wide angle with a strobe the camera does an outstanding job for an HD video at 1080p the image does not look that crisp.

I am glad I got the RX100 as this is going to be the next camera for stills once I abandon the Canon S95.

Ok moving on to the Panasonic LX7 I did a little stress test pointing at the fireplace in low light to see how the two cameras respond, the clips are done 1 minute after the other so have similar ambient light available. It is clear that the LX7 is a winner in virtue of the brighter lens not only that the wider 24mm lens against the 28mm of the Sony shows a clear advantage.

Now what else is good about the LX7 the major feature are definitely the ergonomics, let’s have a look at the rear controls.

Panasonic LX7 rear buttons
Panasonic LX7 rear buttons

The first button of interest is the AF/AEL lock that you can configure to lock focus, exposure or both. Now having this with one touch means that any shot of moving fish in front of the camera or a dive into a cave will resist the camera hunting for focus or trying to change the exposure.

The other button of interest is the WB you can recall and set white balance in any non automatic mode including video, in addition there are two custom settings for white balance and you can alter the tint after setting that is great.

The ISO button is also very useful but mostly for picture and a half press will tell you what combination of aperture, shutter and ISO the camera would shoot at.

This also brings one of the weaknesses of the camera and is the camera’s video Program submode. For some reason this behaves like the still camera program mode so does not take into any account the 180 shutter rule, so be careful and never use the camera in Creative Video mode with the Program submode as results will not be good.

So how should you shoot video with your Panasonic LX7? Simple you should shoot in shutter speed priority or in specific cases in manual.

I think the shutter speed priority is the simplest starting point, so let’ assume you are in the PAL system where video is 25 frames per second you should set shutter priority and speed of 1/50 for wide angle with ISO in Auto. Depending on available light the LX7 will keep the lens at widest aperture and ISO until needed and then start closing the lens, this is fine for us as it is better to have lower noise image than huge depth of field.

If you want to influence depth of field for example in a macro situation when you are zooming in a lot you can take a half press and set the ISO manually until you have the aperture you like. The LX7 sets ISO in 1/3 of f-stop so the fine-tuning possible is incredible.

I would not trust the camera aperture priority mode as the LX7 will quite happily reduce the shutter speed all the way to 1/30 of a second before increasing the ISO and this would give blurred footage.

Shooting macro with the LX7 may require you to operate at double frame rate modes of 50 or 60 fps in that case again in shutter priority mode or manual start with a shutter of 1/100 or 1/125 and pump up your lights until you see the aperture closing. If the image is still soft increase the ISO manually to get where you want to be take into account that this camera has really a lot of corner sharpness so in general it is not needed to get to small aperture as much as it is with other cameras.

So which housing for the LX7? I have done a quick review of the Nauticam in the unboxing video here

This housing is really impressive and makes the camera actually even easier to operate when outside the housing!

Now with all those good things why is the LX7 not as good as the RX100 for still pictures:

  1. Too wide lens: 24mm makes it difficult to get wide angle lenses and impossible to use a fisheye
  2. Resolution is only 10MP in RAW pictures this shows, not in video though
  3. Smaller sensor again the performance at the same ISO is better with the RX100 when you have a strobe

For video some of those drawbacks become actually plus points:

  1. The 24mm lens when coupled with the Nauticam wet mate dome has 84° field of view in water that is good for most situations
  2. Smaller sensor means more depth of field at same aperture

Another factor to consider with regards to the LX7 is the 1cm minimum focus distance, this means that diopters are only needed for super macro very small subjects as the capture area of the camera is incredibly small less than half the RX100.

Other plus points of the LX7

  1. Neutral density filter, -3 f-stops means the camera will not jump to shutter speeds of 1/1000 in bright sunlight but stay at the normal speed with the lens wide open
  2. Stabiliser: the LX7 optical stabiliser is rock solid and gives the same performance of the RX100 active stabiliser without any cropping of reduction of the field of view
  3. A normal Mp4 1080p video mode at 20 Mb/s bitrate that is great for general purpose wide angle

In the next post we will have a look at the Nauticam Wet Mate and the diopter that I have chosen for the LX7

Underwater Video Tips: Using filters with your GoPro or Compact Camera

Filters Test

Following a number of posts about filters in various GoPro forums I decided to check in detail the behavior of the UR/PRO filters and see what is that they really do.

I guess the reason is that people do not really know or want to know the physics behind it and prefer to entertain many discussion that involve trial and error.

One of the most interesting one is this clip here that generated some ferocious comments by some users of other products that of course were not pleased having spent money that their choice seemed not to be the best.

To understand a bit more about what filters do we need to look at light temperature graphs like the one below.

techcolour-temp-chart

Light colour is measured in K and high value means cold blue light and low values represent warm red light.

As we know underwater red gets absorbed approximately at a rate of 1 f-stop every 2.5 meters we go deeper compared to blue light with the result that red colour disappears pretty quick followed by green to become completely blue at depth.

Some time ago cameras were shooting film not digital and there was no way to correct colours when the film itself got developed. So to perform some decent underwater photography people used strobes and fisheye lenses to get really near and blast the reef with light in order to restore the real colors.

This worked very well for close shots but was useless for wide angle at distance, so color correcting filters that could go underwater were developed for ambient light photography.

So what is a CC filter? A common misconception is that filters add colours to the picture, whilst this is practically true this is technically incorrect.

So what does a CC filter really do? As the word says it filters light, more specifically filters selected part of the color spectrum. This is done at expense of available light so if we use a filter we will have less total light or for our purposes exposure. This is well explained on the URPRO website where they talk about film sensitivity, if you use a filter you will loose 1 f-stop so use a higher ISO film.

http://www.urprofilters.com/content.do?region=FilterInstructions

The filter can be designed for different purposes and depending on its color and opacity will be more or less aggressive. If you read very carefully the urpro website says that there is a maximum distance that the filter will be effective at.

UNDERWATER FILTER DISTANCE

Photographically and visually reds, oranges and other warm colors become dominated by the natural blue-green (cyan) effects of the water when it is more than 8-10 feet deep.

Because all water is a continuous filter, the deeper a subsea photographer goes beneath the surface, the more colors are naturally “filtered out” of the spectrum.

As a result, the depth of the water must be added to the distance between the camera (or flash) and the subject to give the underwater filter distance. Use the following formula to determine the correct underwater filter distance:

+ Depth of water above the photographer
+ Distance from camera (or flash) to subject


= Underwater filter distance

Scuba divers using a still camera or a movie camera must combine the depth of the water plus the distance of the camera from the subject. This sum should not exceed 80 feet for color negative films and video, and should not exceed 30 feet for color slides. In all cases, the best color is achieved when the camera is close to the subject!

What that means is that the working distance of the distance is not the same as depth so you can push a filter say down to 24 meters but then the distance to subject needs to be zero. So if you are shooting something 3 meters or 10 feet away in 21 meters of 70 feet that as much as you can get.

When it comes to underwater use we are mostly interested in eliminating blue in tropical waters or green in cold algae waters.

In order to eliminate blue that has a high colour temperature we need warm colors typically something around orange. This will some of the blue beams and also part of the green beams and will produce filter light that is of a warmer color and will look ‘more red’.

But how much does for example a URPRO orange filter for blue water really warm up the light?

I have done some empirical tests with my Sony RX100 in a day where the Sony would measure a temperature of 6500K which pretty much correspond to cloudy day indoor.

Filter

The URPRO orange filter which is the same that is on the SRP filter for GOPRO measured 2800K with a tint of 5 Magenta. It also measured an overall absorption of 1 and 1/3 fstop of total light. I measure this filter instead of the one I have (which is not SRP and we can cover why in another place) because I think the SRP is the market lead at this time and it uses UR/PRO filters.

So the URPRO orange filter has approximately a 3700K warming effect with a strong magenta tint. This means that a camera with auto white balance and an average lens like a GoPro can restore some color in the image until the overall color of the light is around 10,000K in water. After that the filter essentially stops working and the light absorption is so much that it just becomes plain noise. I think this website gives a good idea

http://www.seos-project.eu/modules/oceancolour/oceancolour-c01-p07.html

So the reason why the picture stops having any red and starts looking green is that there is no red left in the light!

The breaking point seems to be around 18-21 meters or 60-70 feet and corresponds to our personal experiences I would say.

So what about custom white balance? We are pretty much in the same situation we can re-balance the camera up to 10,000K and add magenta or orange tint to the picture but you reach a point where there is too much red color noise.

The other advantage of custom white balance is that there is no light absorption so the picture ends up being less noisy as at the same aperture a loss of 1 and 1/3 fstop is like saying doubling the ISO from 800 to 1600 to capture the same scene. This is the reason a camera with custom white balance will always outperform the same camera with a filter at depth in terms of picture noise.

And what about Magenta filters? This is an interesting one as magenta filter absorb little light around 1/3 of fstops for URPRO and warm up the colour very little around 700-800K with a magenta tinge more prominent. A magenta filter will therefore absorb less light in total and introduce just a tint to the image.

From my tests a magenta filter is totally worthless on a camera that can white balance and frankly not that good at depth on camera with auto mode only. The reason is that light will get cold very soon at depth and the camera will be outside the AUTO white balance operating range (2700-7000  on average) pretty soon.

So what it means for users of GoPro cameras? The summary is pretty much like this:

  • In blue water filters are worth down to around 18 meters or 60 feet
  • In green water filters are worth even less as the color temperature very soon reaches a temperature where the auto white balance of the gopro is out of range

Although I have not yet measured I would think probably max 10 meters and that is it as I had similar results with my Sanyo that has same sensor size of the gopro and actually a faster lens.

Hope gopro users find this post useful as well as other users of compact camera to shoot video in ambient light.

In the next post I will compare the optical quality of the SRP dome port with the PolarPro snap on filter that generated such a debate on youtube and we will see why this filter could perform better than the SRP dome.