04/11/2013. Sluitersnelheid: 1/50 sec = 0.02 sec. Frameduur= 2 x sluitersnelheid= 2/50 = 1/25 = 0.04 sec. Framerate= 1/0.

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1 Onderwerpen: Scherpstelling - Focusering Sluitersnelheid en framerate Sluitersnelheid en belichting Driedimensionale Arthrokinematische Mobilisatie Cursus Klinische Video/Foto-Analyse Avond 3: Scherpte en Scherptediepte Sluitersnelheid en bewegingsonscherpte Lensopening Diafragma - en belichting Lensopening Diafragma - en scherptediepte Chris Riezebos Aad Lagerberg Scherpstelling- Focusering Scherpstelling- Focusering Object dichtbij. Scherpstellen(focuseren) is het instellenvan de afstandvan de lens tot aande film c.q. de chip. Object ver af Scherpstelling- Focusering Sluitertijd Bijonjuistefocus wordthet beeld onscherp. 1

2 Sluitertijd en framerate Foto 1 1/ 1/4 1/8 1/15 1/30 1/60 1/15 1/50 1/500 1/1000 sec Video Beschikbaresluitertijden afhankelijk van de frame rate. Sluitertijd altijd korter dan de frame duur. Sli de 34 Sluitersnelheid: 1/50 sec = 0.0 sec Frameduur= x sluitersnelheid= /50 = 1/5 = 0.04 sec Framerate= 1/0.04 = 5 fps Voorbeeld: Frame rate = 5 fps Duur1 frame: 0.04 sec = 1/5 sec Langstesluitertijd: 1/5 sec, c.q. 1/30 sec Voorbeeld: Framerate= 10 fps Duur1 frame: sec = 1/10 sec Langstesluitertijd: 1/50 sec) Bij hoge framerates wordt de sluitertijd dus automatisch korter. Daarom meer licht nodig. Meestal: sluitertijd = ½ frameduur 1/50 sec 5 fps Sluitersnelheid: 1/100 sec = 0.01 sec Frameduur= x sluitersnelheid= /100 = 1/50= 0.0 sec Framerate= 1/0.0 = 50 fps 1/100 sec 50 fps Sluitersnelheid: 1/300 sec = sec Frameduur= x sluitersnelheid= /300 = 1/150= sec Framerate = 1/ = 150 fps

3 1/300 sec 150 fps Sluitersnelheid: 1/600 sec = sec Frameduur= x sluitersnelheid= /600 = 1/300= sec Framerate = 1/ = 300 fps 1/600 sec 300 fps Sluitersnelheid: 1/1000 sec = sec Frameduur= x sluitersnelheid= /1000 = 1/500= 0.00 sec Framerate= 1/0.00 = 500 fps 1/1000 sec 500 fps Sluitersnelheid: 1/50 sec = 0.0 sec 3

4 1/50 sec 1/100 sec 1/100 sec 1/15 sec 1/15 sec Je kuntin principekiezen voorb.v. 5 fps, maar een sluitersnelheid van 1/500 sec. De sluitersnelheid mag immerswel korterzijn dande frameduur, maar niet langer. Hoe meer lichtwordtgebruikt, des tekorterde sluitersnelheid welke de camera gebruikt. Klein: hooggetal, b.v. f/16 Diafragma Groot: laaggetal, b.v. f/4 4

5 f = brandpuntsafstandvan de lens (mm) D = diameter van de diafragmaopening (mm) f/stop of f-getal = f D Iederestop is een factor in hoeveelheid oppervlak = hoeveelheid licht (s) 0 (s) 1 (s) (s) 3 (s) Per stap halvering van de hoeveelheid licht. 1/4 1/8 1/15 1/30 1/60 1/15 1/50 1/500 1/1000 (s) = Diafragma opening Sluiter tijd a b r 1 r A = π r Hoe groot moet r zijn om oppervlak b twee keer zo groot te laten zijn als oppervlak A? π r = π r 1 r r = r = π r 1 π 1 r = s r 1 r = s s r 1 r = s r 1 f/stops are a bit more confusing because the numbers appear so arbitrary. This is the standard sequence of f/stops from f/1.4 to f/. Although it may not seem intuitive at first, in this sequence the f/1.4 setting lets in the most light while the f/ setting lets in the least. Also, each of these f/stops has precisely the same halving/doubling relationship as the shutter speed sequence On the face of it, going from f/4 to f/5.6 doesn't sound like halving the amount of light. What's more, 5.6 is a larger number and sounds like it ought to be more light, not less. Neither does f/4 to f/.8 sound like doubling the amount of light. In fact, each of the numbers in this sequence is a halving/doubling of the amount of light from its immediate neighbours, just like the shutter speed settings are. Not only that, but it makes sense, as I shall show below. The reason that both the halving and doubling and the smaller numbers mean more light things make sense is that the f/stop is a ratio. The ratio is between the diameter of the aperture in the lens and the focal length of the lens. The focal length is generally measured in millimeters, so we'll stick with those as our unit of measure. On a 50mm lens, f/ is saying that the diameter of the aperture is 5mm. The ratio is: 50/5 =. That seems pretty straightforward. A good question might be, what is the area of that aperture? Well, the aperture is usually a set of five to fifteen blades which form a roughly circular hole, so we'll use the formula for the area of a circle, which as I'm sure you'll recall is π * radius. For π I'll use On our 50mm lens, the aperture at f/ has a diameter of 5mm which is a radius of 1.5mm. The area of the aperture is thus π X 1.5, or X 156.5, or square millimetres. This fact by itself isn't all that useful. It is useful in relation to the adjacent f/stops. What is the area of the aperture at f/.8? Well, because the f/stop is a ratio of the focal length to diameter, our 50mm lens at f/.8 would have a diameter of 50/.8 = 17.86mm. Remember, we have to divide that by to get the radius of 8.93mm, so the area of the circle thus formed would be π X 8.93, or 50.5 square mm. Rounding off a bit, that's about 50 sq. mm at f/.8 and 500 sq. mm at f/, a double/half relationship. Aha! So that's it! The area of the hole doubles and halves, it's just represented by a ratio on the lens! No wonder it's so darn confusing. f/stop Diameter of aperture (mm) Radius of aperture (mm) Area of Aperture (sq. mm) f/ f/ f/ f/ f/ f/ f/ f/ f/ f/ (As shown on lens) f lens = 50 mm (50mm divided by f/stop) (1/ the diameter) (pi X the radius squared) Lensopening Diafragma- en scherptediepte Diafragmagroter: Diafragmakleiner:

6 Lensopening Diafragma- en scherptediepte Lensopening Diafragma- en scherptediepte Invloed op de scherptediepte: Diafragma: Groot diafragma(laag getal) : kleine scherptediepte Klein diafragma:(hoog getal): grotescherptediepte Brandpuntsafstand: Grote brandpunts-afstand(tele): kleinescherptediepte Kleinebrandpunts-afstand(groothoek): grotescherptediepte Afstand Kleine afstand: kleine scherptediepte cameraobject Grote afstand: grotescherptediepte B.v.:.: scherpstelpunt op 6 m. Scherpte diepte van 10 m Dit is geen kleine scherptediepte, maar bewegingsonscherpte (van zowel voor- als achtergrond) door het meetrekken van de camera. 6

7 5 frames per second (fps) 1 1 sec 5 Frameduur = 0.04 s = 1/5 s Sluitersnelheid: b.v = 1/100 s 7