Duyuru

Çökü?
Henüz duyuru yok

UNDERWATER VIDEO TECHNIQUES

Çökü?
Bu konu sabit bir konudur.
X
X
 
  • Filtrele
  • Zaman
  • Göster
Hepsini Sil
yeni mesajlar

  • UNDERWATER VIDEO TECHNIQUES

    Underwater Video Techniques

    There are many Underwater Video techniques to master. It is valid to use smooth camcorder movements in certain circumstances.

    Such instances include keeping a moving subject correctly composed, or when you wish to reveal a panorama too wide for your lens, or to relate two subjects together.

    Horizontal movement is called panning and vertical movement tilting.

    The Lead-in pan is often used to begin a scene and involves panning with a moving subject; coming to rest on a second subject (which is the important one) and allowing the first subject to disappear from shot. An example of this may be following a diver from mid water to a wreck and then allowing the diver to enter.

    Tilting is used less often than panning. Tilts can emphasise the relationship between the bottom and surface, but are usually pretty o-ring unless you are following a moving subject.
    Whatever you do (with your pans and tilts) you should try to end on something interesting. It is advisable to not follow a pan with a reverse pan (or tilt with reverse tilt) in the opposite direction.

    Underwater Filming Techniques

    The next underwater filming techniques we will look at concern when we can introduce movement

    Zoom lens are fun. Too much fun! After poor image stability the most common fault to afflict underwater video is over-use of this facility.

    Zooms should only be used as a tool to crop your subject whilst the camcorder is not recording. Excessive use of the zoom is called tromboning.

    Used sparingly a zoom can add emphasis to the subject. So can moving closer to your subject. This is called trucking. It can be effective providing there is a defined starting and finishing point, and it is done smoothly. Never track a subject from behind, there is nothing more boring than the back end of a fish. The only justification to shoot the back of a subject is when you want a shot to establish the end of the action; and then it is better you allow the subject to swim out of shot rather than follow it.

    Achieving smooth camcorder movement through the water requires conscious effort and expert scuba diving. Drifting with a current is smoother than finning. Diver propulsion vehicles can also provide a smooth movement.

    Whether you choose to zoom or truck in gives different effects. When you zoom the perspective is constant whereas, when you truck, perspective changes and exaggerates how quickly subjects move out of frame.

    Tracking involves moving whilst filming at 90° to your direction of travel. This allows you to explore a scene or follow a subject better than a pan because the subject distance is constant (you hope). This is not an easy technique to master but then, neither was diving at first!

    If you track around a subject then it is called arcing and, in dramatic terms, increases the importance of the subject.


    Underwater Video for Beginners

    Beginners at underwater video make mistakes!

    The trouble is.... that if you are going to have a problem the odds are in favour of it happening on your first dive with a camcorder. It is therefore rather important that you avoid disasters at this most vulnerable time. Nothing puts you off more than poor results or, even worse, a flood.

    Floods are 99.9% always caused by user error. Your manual will tell you how to assemble your particular housing properly but the one thing that all housings have in common are the O-ring seals. These are rubber rings that compress under pressure to seal the mating surfaces. Always remember that it is not the housing that keeps out the water, it is the O-rings and you must therefore pay particular attention to them.

    The most commonly held fallacy about O-rings is that it is the silicon grease you smear on them that keeps out the water. All that silicon grease does is keep the O-ring supple.

    Many housings used by scuba divers are shipped with excess grease and you could therefore be forgiven for thinking that you need liberal amounts of the stuff. In fact, all that excess amounts of grease do is attract floating particles from the atmosphere. Once you have a hair or other debris particle draped over an O-ring you potentially destroy the integrity of the seal and end up with a flood. A properly greased O-ring should just appear shiny.

    Burn these rules about O-rings into your consciousness for all time. Before every dive:

    Check that O-rings are in!
    Check that O-rings are clean and not damaged
    Ideally, if you are not familiar with O-ring maintenance, find someone who is (to show you).

    A golden rule on your first dive with a camcorder housing is to leave the camcorder out. This will give you the confidence of knowing that you have successfully greased the O-rings and assembled it properly. If you cannot spare a whole dive then at least close the (empty) housing and dangle it over the side of the boat on a rope to check that you have a seal.

    However, don't be discouraged by talk of floods. Everything to do with skin diving is a calculated risk. By all means wait and read the rest of these lessons but, if you are like me (impatient), and you already have a camcorder then go and have a dive with it. Just follow this advice.

    Read the manual that came with the camcorder/housing.
    -Familiarize yourself with the controls
    -Get a friend who has experience of u/w photography to watch you and set it up
    -Dedicate the dive to photography. Treat it like a Novice dive i.e. stay shallow in good conditions.
    -Take the lens cap off before you put the camcorder in the housing!
    -Most problems on your first dive are not as dramatic as a flood. You will be naturally excited and prone to be trigger-happy.
    -Do not try to be too clever on your first dive. You will have a lot to think about and so let the camcorder technology take over most of the decision making for you.
    -Don't bother with experimenting.
    -Do not try all the controls just for the sake of it. Use the autofocus and auto exposure facilities. Concentrate on finding your subject matter and filling the frame with it. Above all, Enjoy!

    Main points
    -Aim to have your viewers notice the action - not the camcorder-work!
    -Let your subject move, not your camcorder
    -stop recording when you zoom

    Video Lighting Underwater

    Do I need a light? This is the question I am most commonly asked by potential underwater videographers. The answer is yes - and no!

    Few would argue that video lights are essential for filming on night dives, inside wrecks and caves. Most people accept that colourful close-ups benefit from taking your own light source with you. However, is there any other reason for laying out not inconsiderable amounts of money on specialised video lights? We shall see!

    It is true to say that modern camcorders operate in extremely low light. In fact, underwater, video excels in the same conditions that make stills photographers jump back on the dive boat! Most camcorder models boast they work in light as low as 3EV. By comparison, a scene lit by candlelight weighs in at 10EV. This is equivalent to stills photographers of F2.8 @ 30 sec's on 100 ASA film! Basically, if you can see an image then your camcorder can record it.

    However, as you go deeper with scuba, the light levels decrease: and in really dim conditions your video will appear very grainy. Long before that happens though you will lose foreground colour and contrast. The only way to combat this is by adding a video light.


    Color Underwater

    Learning about loss of color underwater as we go diving deeper is an integral part of diver training and I am sure that I don't need to cover that ground again except to remind you that objects underwater appear closer (and larger) than they actually are. Another important point is that red is the first wavelength of light to disappear (at relatively shallow depths).


    Filters Underwater

    There is a lot of colorful subject matter down there. Is there any other way to get at that color apart from lights?
    Filters can be employed - within limitations.
    The basic principle of filters underwater is that they allow the same wavelength of light as their own color to pass. They are only subtractive, they reduce the amount of light, and this is not a good thing! Unfortunately, filters also stop other wavelengths of light so; ultimately any color gain is traded against an overall loss of light. A standard 30 red color-correcting filter is pretty cheap and will alter your color bias. However, there is precious little red light to let through to begin with so such filters are counterproductive. Better results are gained by 'pumping' up the reds when editing.
    However, most manufacturers offer a 'blue water' filter for their housings which operates on slightly different technology to simple color correcting filters and can be used, with limitations, to enhance color reproduction. Virtually all manufacturers supply the UR pro filter, which screws onto the camcorder lens, or (better still because you can remove it during the dive) it is fitted externally to the housing port. A proper underwater filter can easily be identified - it more pink than red (and costs more!).

    Scuba diving at depths between 3M and 20M use the UR Pro CY filter and set the white balance to outdoors. However, in the shallower end of this range (5M upwards) you may find the image too red. Set the white balance to indoors to compensate.

    The UR pro VLF filter will make your images more colorful (with or without lights) down to 10M.

    Complimentary blue filters can be used on your lights to correct for the differences in light source but most videographers feel the loss in light output unacceptable and prefer to do without.

    Diving in temperate waters, which exhibit a green rather than red cast, requires a different colored (Magenta) filter.

    Colour Temperature Underwater

    Not all underwater video light sources are the same! Some are 'warm' and produce a redder light, others a 'colder', bluer light. We can measure the colour characteristic of a light source and express it as a colour temperature in degrees Kelvin.
    A compact 25-watt underwater light, perfect as a video and diving light Color temperature approximates sunlight at 4700°K 60-minute continuous burn time with fully-charged battery Attaches to Sea Arm, flexible light arm and LX grip Bulb: 25-watt high-color temperature halogen bulb Bea...
    The colour temperature of most underwater video lights is generally far redder than available light is underwater. Our brains have the capacity to compensate for light sources of different colour temperatures. We can ignore colour casts but our video does not.

    Light Underwater

    We get a lot of light 'free' for shooting underwater video i.e. sunlight (AKA available light). In reasonably clear water on a sunny day you can shoot video down to 30M with available light and be happy with your results. All you need to do is set the white balance control for outdoors (if the camcorder doesn't do this for you automatically).
    Complete system with lite head, mounting arm, battery pack, quick-release toggle mounting system, cable with in-line switch, and Smart Charger that operates on any input from 100-240 volts.
    If you plan to never scuba dive below 10M then you arguably need not bother with video lights. In shallow water available light can overpower even the strongest lights anyway. However, most of us are not content to remain so shallow. However, there are a lot of interesting subjects deeper than 10M.

    White Balance Underwater

    The camcorder's automatic white balance control operates in the same way as our brains. It assesses the dominant light source and boosts other colors in the video signal in order to compensate. Some underwater housings allow you to override the setting underwater and this is useful.
    It is therefore impossible to assess color temperature by eye. Fortunately the video manufacturers provide a feature called white balance to assist us.
    Some white balance systems allow you to read a color cast from a white card and compensate accordingly. Usually there are only the two options, indoors or outdoors. Set the white balance to outdoors if the lights are being used for fill, indoors if lights are the main source.

    Backscatter

    Taking our own light source with us underwater obviously extends the range of our videographic activities. It also creates some new problem areas.
    Two video lights with 35 watt Halogen bulbs and two flexible arms. Optional 50 watt bulb and 52mm 80A Daylight Conversion filter also available. To be used with accessory Mini Pro Power Pack (LAPS2550 & LAPG2550 not included) utilizing two SONY® NP 1B batteries or equivalent (charger & batteries ...
    We cannot easily introduce lighting underwater without some awareness of the phenomenon called Backscatter. Water holds minute particles in suspension (technically known as CRUD) which catch, and reflect, the light back at us, making our pictures look like they were taken in a snowstorm!

    Underwater Lights

    At subject distances of 1/2 M to 2M an underwater video light will fill in shadows and bring out colors. However, even the most powerful video light is only effective at subject distances less than 2 meters/6 feet away. Typically, a 50W light has little effect beyond one meter/3 feet
    Usually, lights are mounted on the housing, which simplifies aiming although you can handhold (with a lot of practice!). Alternatively, you can get someone else to hold the light. This requires good co-ordination and communication. The lighting man must anticipate the cameraman's needs. A lot of serious underwater videographers use comm's (radio communication equipment) to direct their models and assistants.
    The favourite position to mount the light (in relation to the lens) is above and to the side. This gives what is known as Top quarter light. This is the most natural position and least noticeable probably because we are used to natural top light. There is nothing to stop us lighting from below, or behind, but only occasionally.

    Complete system with lite head, mounting arm, battery pack, quick-release toggle mounting system, cable with in-line switch, and Smart Charger that operates on any input from 100-240 volts.
    single light source, side lighting
    We only use a single light as main source for low light and close-up photography. Most of the time we mix it with natural light, a technique called mixed light of course!

    Twin lights

    The quickest way to double your power output is to add another video light. This also can double your problems!
    The main argument in favour of twin lights is that you can kill the shadows. Exposure systems can have trouble coping with the difference between the light side of a subject and the dark side.
    However, twin underwater lights can accentuate backscatter. Some underwater videographers angle twin lights to intersect at the subject. When the edges of the two beams overlap you will have a hotspot and possibly increase backscatter. It is better to aim the lights so that they intersect behind the subject. In extremely lower Vis aim them to intersect well behind.
    NUR ?Ç?NDE YAT KARDE??M
Haz?rlan?yor...
X