LET S FOCUS ON FOCUSING

Transcription

1 LET S FOCUS ON FOCUSING

2 How A Lens Works The distance between the center of the lens and the focal point is called the FOCAL LENGTH.

3 Images are only sharp where the focal plane meets the focal point.

4 To understand circles of confusion, watch this video. Start at 2:55

5 To focus, we must move the lens back and forth until the focal point hits the focal plane. In Auto Focus, How does our camera know how far to move the lens? How does it know which direction to move the lens? How accurate is it? How fast is it?

6 Active, Passive, and Hybrid Focus Systems Active Requires the camera to send out a signal, then calculates the distance based on the amount of time it takes for the signal to return. (Ultrasonic sound waves, Infrared Light) Passive analysis image projected on sensors. (Phase or Contrast Detections) Hybrid Uses a combination of two or more methods of detection.

7 Light traveling through a SLR camera.

8 HOW PHASE DETECTION WORKS

9 Focusing Sensor The CCD s work in pairs. Every pair is associated with one auto focus point.

10 Focusing Sensor Vertical sensors read horizontal contrast. Horizontal sensors read vertical contrast. Some cameras have a cross type sensor.

11 Focusing Sensor The further apart the sensors, the more accurate the focus will be. If too far apart, they may be covered by the aperture. Available points are determined by the minimum aperture of the lens.

12 Canon s 61 focusing points

13 Phase Detection - Pros Very Fast! All available points can read, analyze, and respond instantly. Processor tells focus motor which direction to move and how much to move. Algorithms predict speed, acceleration, and direction of moving subject. Lens moves to focus on area before subject gets there. (AI Servo) Phase Detection - Cons Must have the mirror down. Can not use in Live View unless using Quick Mode Needs a lot of light to be quick and accurate. Need faster lenses in order to take advantage of the more accurate points. Points are closer to the middle of the screen and don t reach across the screen. Because of the aperture and because of lens vignetting. Not as accurate because camera and lenses have tolerances. Need to make micro adjustments for each lens.

14 Click on photo CONTRAST DETECTION

15 Contrast Detection Reads right from the sensor that captures the image. Used by phone cameras, point and shoots, Live View Mode, and Mirrorless Cameras. Reads image information using the Rolling Shutter. You can select points closer to edge of screen. Very accurate because you are focusing right on the focal plane. No micro adjustments needed. Slower process than phase detection. Lens has to move, but it doesn t know which direction. Then is has to compare contrast and move again. When it reaches sharp focus, it continues to move until it is out of focus. Then it moves back to where it was in focus.

16 Hybrid Focus Systems Mirrorless cameras use both phase and contrast from the sensor screen. Uses a rolling shutter (stores 14 photos at once) Phase tells which direction to move, contrast tells how much. Sensors leave holes in photo, which processor interpolates to add pixels. New cameras (Canon 5D IV) uses IR and Color to aid in tracking.

17 First Decision to Make Manual Focus or Auto Focus? My suggestion: On a Tripod use Manual Without Tripod..use Auto

18 Let s assume we are on a tripod and shooting Manual. Second decision. Are we going to use Live View or the View Finder? View Finder: Less accurate because you can t zoom and it s harder to see. Dioptric adjustment must be sharp. Uses phase detection, so focus confirmation does activate. Live View: Most accurate reads right from focal plane. You can zoom 10x Move your focus point anywhere on the screen. Can use exposure simulation to see your subject better. Uses more power and drains the battery. Heats up the sensor which produces noise and color shifts.

19 If we want to use View Finder: 1. Make sure your dioptric adjustment is correct for your eyes. 2. If you want confirmation, select your focus point. 3. Manually adjust focus until your subject is in focus. You should see and hear focus confirmation when in focus.

20 If we want to use Live View: 1. Make sure your exposure simulation is turned on. 2. Turn on your Live View. 3. Place your focus square over your subject. 4. Zoom in to 10x. 5. Manually adjust focus until subject is tack sharp. 6. Zoom out. 7. Adjust exposure. 8. Take picture Note: Use 2 or 10 second timer for sharper photos.

21 Now let s take it off the tripod and shoot in Automatic Focus Again. What s the first decision to make? View Finder or Live View? Live View: Set your Live View Shoot Mode to use either phase detection or contrast detection. Harder to keep steady. Harder to see in bright lights. Won t track (not on my camera anyway) Drains battery Slower to focus Overheats sensor digital noise.

22 Before we go any further. Calibrate your lenses!

23 Automatic Focus Mode in Live View: 1. Select your Live View Mode: 1. Live uses contrast detection 2. Quick mirror flips up, phase detection to focus, mirrow flips back down. 3. Face Uses contrast detection to find a face. 2. If you are using Quick Mode, then you can select your focus point, or points, or zone. 3. Turn on Live View 4. Move your focus point over your subject and press the focus button. 5. Camera will focus and lock regardless of your shooting mode. 6. Take picture. Note: Your exposure will be read from the area your square is in, not your focus area.

24 Automatic Focus - View Finder Second Decision in Automatic Mode to make is.. Which Auto Focus Mode to Shoot in? Single (One Shot) Automatic (AI Focus) Continuous (AI Servo)

25 Automatic Focus Modes Single One Shot: Locks focus and stays locked until you release the focus button. Automatic AI Focus: Locks focus but will come out of lock if the subject moves. Continuous AI Servo: Never locks, continues to focus all the time. How to choose which mode to use: If neither you nor your subject are moving, use Single. If either your or your subject is moving, then use Continuous. If neither you nor your subject care if your photo is in focus, use Automatic.

26 3 rd Decision to make: Do you want to use focus points or focus zones? Your camera may have a hundred or more points, but only ONE can tell the lens were to move at a time.

27 Points or Zones? Use the Points if: Subject isn t moving very fast or not at all. We want precise focus (eyes) We have a shallow depth of field. (want precision) Use Zones if: Subject is moving and would be hard to keep a point on it. Don t need precise focus. Using a larger depth of field.

28 Let s choose Points, now what s our next decision? Which type of point should we use? Our choices are: 1. Single AF Point 2. Spot AF Point 3. Expanded AF Point 4. Surround AF Point - Uses One point only - Uses an even smaller area for precision (cages, leaves) - Adds 4 helping points L,R, T, B - Adds 8 helping points surrounds single point Note: When more than one point is used, only the selected point will focus, the other s will help maintain that focus.

29 Now that we decided how many points to use, we have one more decision to make. Which one of our many points do we want to use? Most people just use the center point and re-compose. It s faster It s what we are taught. Less things to think about.

30 Do NOT focus and re-compose! Your Focal Plane Changes when you move your camera. Especially when: Close Up Wide Aperture Long Focal Length Instead.. Select a focus point closer to the subject. And do NOT more the camera before taking the shot.

31 Now let s assume our subject is moving too fast for us to follow so we decide to use the Zone method. Next question Which Zone Method? Our choices are: 1. Manual Area Selection 2. Auto Area Selection

32 Manual Zone Selection Uses several points for form a zone. All points have equal priority for being active. Will usually focus on closest subject. Does NOT track. You must follow with camera. If subject leaves zone, camera will re-focus on what s still in the zone.

33 Auto Zone Selection Uses every point available. In One Shot Mode, it will focus on the closes subject or closes to center. Then Locks Focus. In AI Servo, you must select the starting point and it will focus there to start. After focus is established, it will track the moving subject in accordance with your case settings. Case Settings??????

34 Auto Focus Cases One more decision to make: Tracking Sensitivity How long will it stay on a subject after losing focus before it selects another point. Accel/Decel Tracking Tracks subjects back and forth movement. AF Pt auto Switching Tracks subject left and right. How quickly it switches points.

35 AUTO FOCUS RELEASE PRIORITY

36 Automatic Orientation

37 For Precision Manual Focus through the View Finder when using very fast lenses. Focus Screens

38 Focus Trapping A method of pre-focusing where the subject is going to be. Then take the photo when the subject enters the field of focus. Manually use manual focus, have everything ready to go, and just take photo when subject enters the area in focus. Automatically Manual focus, turn auto focus release priority to in focus. Hold shutter button down, and then the subject enters the field of focus, you will get a focus confirmation and the photo will automatically be taken.

39 Focus Breathing When you focus a lens, you are moving the lens closer or further from the focal plane, which is increasing or decreasing the focal length. This causes the field of view to change. When the Nikon lens is focused on something close, the actual focal length is closer to 135mm.

40 Back Button Focus Method of taking the focus activation button away from the shutter button and placing it on the back AF on button. Customize the back button to activate the focus, and de-activate the shutter button from focusing. Now set your Focus Mode to Continuous or AI Servo and leave it there. Press and hold the back button and the camera will continuously focus using the focus point or zone you selected. This is good for anything moving. When you release the focus button, focus will be locked automatically. Now when you press the shutter button, the focus will not change. Use this method for fast moving subjects or anything still. You can use it for focus trapping also.

41 Any Questions?