Objectives Know the story you are trying to tell
Resources From this knowledge will come your kit, crew, location, etc.
What is the most important part of creating a picture? • Focal length – to give you shape, size and content. • F number – aperture to give you picture quality and depth of field. • Focus to give you definition and selection.
What is the most important part of creating a picture? • Get these right every time and you are a long way down the road to success.
Knowledge = CreativePower • You get what you pay for and this shows in the quality of the glass, and the build - through to the resolving power of the lens. • Always buy the best you can afford.
Knowledge = CreativePower • With semi-professional and consumer camcorders they don’t have the option of changing lenses.
Knowledge = CreativePower • Modem technology gives you automatic focus, automatic aperture, motorised zoom; all you have to do is point and press the button.
Knowledge = CreativePower • Are you in control, do you understand what is happening? • If not, its a pity because you will be losing out on one of the most creative skills in film making. • The lens is far more than a piece of glass through which a picture is taken. It is the tool you use to tell the story as you see it and, more importantly, how you want it to be seen.
“The camera never lies?” • If that is the case you and I will be out of a job. • There are occasions when accurate recordings have to be made. • In storytelling the camera, if not exactly lying, is often economical with the truth.
“The camera never lies?” • It needs to be because we live in a three dimensional world and film gives two dimensional pictures. • Perspective, depth, the impression of a three dimensional image telling your story is all down to the use of a lens of the correct focal length placed in the right position.
Focal length • Determines image size and extent of view. • It is the physical distance measured from the rear node of the lens (the bit at the back of the lens that bends the light rays coming in) to the point of focus (focal plane) when the lens is focused at infinity.
Focal length • This distance produces a figure in millimetres. The larger the figure the greater the distance from the rear node of the lens to the focal plane. The longer the focal length, the narrower the angle, the bigger the picture. The smaller the focal length, the shorter the distance from the rear node of the lens to focal plane, the wider the angle of view.
Pre-focusing • When the production requirement is for a zoom-in to a subject, the lens must first be fully zoomed in on the subject and focused, then zoomed out to the required starting shot. The zoom will now stay in focus for the whole range of its travel. If possible, always pre-focus before zooming in.
Zoom Lenses • The zoom lens gives you an infinite variety of focal lengths, but there can be a price to pay. • The lens’ resolving power, speed (the amount of light it transmits). • The ability to focus on small subject-to-camera distances. Although there are various lens attachments, such as diopters.
Zoom Lenses • Zoom lenses are identified by the range of variation in their focal length. • 6-1 would have a ratio of say from 9mm - 54mm • 10-1 say 12mm - 120mm, and so on. • Standard kit would include two zoom lenses like the above - these being the most practical.
Zoom Lenses • A lens manufacturer will state zoom ratio and the wide-angle focal length in one figure. A ‘14 x 8.5’ zoom lens for a 2/3 inch CCD camera can therefore be decoded as a zoom with a 14:1 ratio starting at 8.5 mm focal length (angle of view = 56º) with the longest focal length of 14 x 8.5 mm = 119 mm (angle of view 4º). • The zoom ratio thus (approximately) equates to ‘14 x ’ i.e. 14 x 4º = 56º.
Zoom Lenses • Lenses with ratios as high as 70:1 can be obtained but the exact choice of ratio and the focal length at the wide end of the zoom will depend very much on what is required from the lens.
Rangeextender A zoom lens can be fitted with an internal range-extender lens system which allows the zoom to be used on a different set of focal lengths. A 2x extender on the 14 x 8.5 zoom would transform the range from 8.5 - 119 mm to 17 - 238 mm but it may also lose 2 stops approaching maximum focal length of (238 mm).
Zoom Lenses • A zoom lens, is made up of lots of glass, some of which moves and all of which absorbs and scatters light. • The quality and range of the modem zoom lens is second to none, reducing the need to change lenses unless for a specific need.
Prime Lenses • Prime lenses (lenses of fixed focal length) from wide angle to tele photo. • Have the advantages of greater speed. • Allow more light to be transmitted through the body of the lens. • Greater resolving power. • Minimum subject-to-lens focussing distances improved.
Macro Photography • Ranges of special lenses that can be hired and some zooms have this facility built in. • The extended focusing needed to achieve a sharp image alters the light transmissions and depth of field, etc. but shouldn’t worry those working with decent viewing facilities. • It goes without saying a decent tripod is a must.
The ‘speed’ of a lens • This relates to the ability of a given lens to transmit a large amount of light. • Prime lenses normally have the edge over a zoom. There are also other advantages such as quality and resolution of the image, but with the onset of modern zoom lenses some of these can be argued.
The ‘speed’ of a lens • Speed is important in low key or very low light conditions where you want maximum aperture and still retain quality. • Prime lenses often have wide diameters giving minimum F-number and yet are still compact and manageable. • They are in the main faster.
f-number • The f-number of a lens is a method of indicating how much light passes through the lens. It is proportional to lens diameter and inversely proportional to focal length. For a given focal length, the larger the aperture of the lens, the smaller its f-number and the brighter the image it produces.
f-number • 1.4 2 2.8 4 5.6 8 11 16 22
f-number • Each division on this scale is called a ‘stop’. Half a division would be a ‘half stop’. The effective aperture of a zoom is not its actual diameter, but the diameter of the image of the diaphragm seen from in front of the lens. This is called the entrance pupil of the lens.
Story-tellingwithFocal Length • Director use a viewfinder. Assuming he, or she, is not posing (although many do!), what they are actually doing is looking to find the right focal length lenses and subject distance to tell their story.
Story-tellingwithFocal Length • Once you have settled on a lens size and subject distance you have to be careful to follow this as any changes can alter perspective.
Story-tellingwithFocal Length • To the extremes, we have all seen the interviewee whose nose seems twice the size of her face, caused by the short focus wide angle lens on the camera being held too close to subject. Or the long focal length lens shot of the train approaching the station all crunched up when the doors open.
Story-tellingwithFocal Length • Perspective plays a significant role in story telling and is part of the director/cameraman's creative skill - but it needs to be understood.
Story-tellingwithFocal Length • This applies to documentary as much as to drama, although clearly in documentary work you may not have much time to consider such niceties. • Mismatching of shots, changes of subject-to-lens distances and lens sizes (and thus perspective) are all there ready to catch the unwary. People do notice.
Story-tellingwithFocal Length • It is not for nothing a major part of set design is to ensure the camera can get in the right place to give the correct perspective.
Story-tellingwithFocal Length • The type of shot created by a certain focal length is not difficult to learn, neither are its limitations and benefits. • Once you have this knowledge you can apply it with confidence
Angleofview • The approximate horizontal angle of view of a fixed focal length lens can be calculated by using its focal length and the size of the pick-up sensors of the camera. • For most broadcast cameras (2/3 inch CCDs) the formula would be: angle of view = 2 tan-1 8.8 mm (width of CD) 2 x focal length (mm)
Ramping • When zooming in, entrance pupil becomes larger until it equals diameter of focusing lens group and cannot increase in size, f-drop or ramping may cause underexposure at low light levels. • Increasing the diameter of the focusing lens group to avoid ramping increases the weight and the cost of the lens.
Ramping F drop of a zoom lens
Entrancepupil • In low light conditions (e.g. twilight evening sports events) when the lens aperture may be at its widest at the start of a zoom-in, the picture may be underexposed when the zoom reaches its longest focal length.
Adjusting flange-back(back focus) 1. Set the IRIS selector to Manual. 2. Place star burst lens chart at approx. 3 m or more and open aperture to maximum. Adjust for correct exposure by using either ND filters or adjusting light on the chart. 3. Zoom in on star burst chart. 4. Adjust for sharp focus on chart with front focus ring.
Adjusting flange-back(back focus) 5. Zoom out to widest angle. 6. Loosen the flange-back (fF) adjustment ring lock screw. 7. Adjust fF for optimum definition on chart. Do not touch zoom focus ring. (NB FLANGE-BACK position should be close to standard marked position on lens)
Adjusting flange-back(back focus) 8. Repeat steps 4 through to 7 until focus is correct at telephoto and wide angle positions. 9. Tighten the fF adjustment ring lock screw. Switch in RANGE EXTENDER. Zoom in and focus. Zoom out and check that zoom holds focus over complete range.
Camera Line-upColour Temperature • Colour television transmission relies on an additive colour system of green, red and blue combining in different ratios to produce all the colours in the spectrum.
Camera Line-upColour Temperature • A combination of • 30% of red + • 59% of green + • 11% of blue will produce one unit of white and it is white that requires the greatest attention in camcorder line-up.