Unit 3 Focus, Depth of Field and

Lenses

Tim Clouse

Resolution

• Ability of the camera system, which includes the lens optics, camera sensor (film or a digital sensor), image processing software, to distinguish, or “resolve” groups of alternating line pairs as the lines become increasingly thinner and they become increasingly closer together.

35mm Compared to Digital • Standard 35mm frame is 24mm x 36mm

• Standard 35mm frame has a resolution of 100 lp(line pairs)/mm or

• 24 (100) x 36 (100)=2400 x3600= 8,640,000 line pairs.

• Digital photos have roughly 3 to 4 pixels to adequately resolve the same photo

• This would be measured as 24 (200) x 36 (200)=4800 x 7200= 34,560,000 pixels or a 35 megapixel camera.

The Standard for Now

• The use of an 8 megapixel camera is acceptable at this time.

• Could this change in the future? Of course.

Acutance

Refers to the camera’s ability to render a sharp edge of the subject as a sharp edge in the photograph.

Focus

Manual

Automatic

Focus

• Pre-Focus

• Hyperfocal Focusing

• Zone Focusing

• Rule of Thirds

• Infrared and Ultraviolet Focus

Pre-Focus

• Setting the camera focus and moving back and forth until the image comes into focus.

• Too far way less detail

• Too close subject may run out of the frame

Hyperfocal

• A Technique to maximize the depth of field when infinity is composed in the background.

• This technique is used for getting maximum focus or DOF when shooting larger scenes.

• Use to get everything in focus from the foreground to the background.

Zone Focusing

• A technique used to maximize the DOF for an area when infinity is not in the background.

• Manually focusing is recommended for this technique due to determining your backgrounds distance.

• Determine the exposure then scale

Rule of Thirds

This rule indicates that one-third of the DOF range is in front of the object, with two-thirds of the DOF behind the object.

IR and UV Lighting

• When it is necessary to focus on an IR light you must first determine the correct focus under normal light.

• Whatever distance has been focused on is then rotated to the IR red focus dot.

• UV is the same you only focus to the left instead of the right.

Page 153-155

Depth of Field (DOF)

• f/stop

• Lens Choice

• Camera to subject distance

f/stop and DOF

• The larger the opening the less DOF ex. f/2

• The larger the number on the camera the smaller the opening or the more DOF ex. f/22

Tips to Max. DOF

1. Hyperfocal focus when taking photo’s of large outdoor crime scenes when infinity is in the background.

2. Zone focus when taking photo’s of large crime scenes but infinity is not in the background, which will require having a DOF scale.

3. Focus by the rule of thirds when taking photos of large crime scenes when infinity is not in the background, and when you do not have a DOF scale

One other thought

• On bright sunny days consider using 100 ISO film for a small f/stops

• For cloudy or dark days, indoor, night time, and flash photography consider 400 ISO film for smaller f/stops

Lenes

• Focal Length—some smaller than others

• Fast and Slow refers to the aperture opening

• Normal—50mm lens

• Telephoto Lenses—Focal length longer than 50mm

• Wide Angle—shorter focal length than 50mm

Lenses

• Macro—Use for magnification of objects

• Options to Macro

a. Use of a true macro lens

b. Use of close-up filters

c. Use of extension tubes

Diffraction• Loss of resolution • Reduction in the clarity of sharp edges • The cause of diffraction is the bending of light

from the diaphragm blades when small apertures are used to capture an image.

• The cure is to open up the aperture by 2 or 3 f/stops.

• Most the time f/8 or f/11 will help solve diffraction

Distortion

• The use of wide angel lenses will cause BARREL distortion. This will give the appearance of an image rounding.

• Pincushion distortion is an effect of telephoto lens. This gives the appearance that lines bend inward.

Summary

• Resolution

• 35mm compared to Digital

• Focus

• DOF

• f/stop

• Lenses

• Diffraction

• Distortion

Next week—Unit 4 Low Light • Read Chapter 5 of your text Crime Scene Photography

and Chapter 9, pages 457-459 concerning Nighttime Accident Photography.

• Review key terms • Complete the discussion questions regarding the basics

of camera operation with various lenses. • Participate in Web Field Trip • Complete and submit Project 1 • Complete Essay • Attend the weekly seminar • Respond to the discussion board (Main post and two

other classmates)