Focus, Lenses, and Macro Photography in Crime Scene Analysis

What is the primary advantage of auto focus in photography?

Faster and easier to use, especially for moving subjects.

What is a key advantage of manual focus?

More precise and selective focusing, beneficial for macrophotography and low-light conditions.

What is a disadvantage of auto focus in low-light conditions?

It is less precise and selective.

What is the minimum focusing distance for the lens used in the course?

Approximately 18 inches.

What is the focal length multiplier for a full frame camera?

1.0x.

What is the formula for calculating crop factor?

Crop factor = Full frame diagonal / Crop sensor diagonal.

What is the difference between zoom and prime lenses?

Zoom lenses have many focal lengths, while prime lenses have one fixed focal length.

What is 'optical infinity' in photography?

The distance where light rays from a distant subject arrive at the lens as parallel rays.

What does AoV stand for in photography?

Angle of View.

What does FoV stand for in photography?

Field of View.

What is the definition of 'Circle of Confusion'?

The largest out-of-focus circle that appears to be in-focus, used to calculate depth of field.

What is the CoC value for the Nikon D7500?

0.02 mm.

What are the two types of autofocus systems mentioned?

Phase detection and contrast detection.

How does phase detection autofocus work?

It uses micro-sensors to divide incoming light into pairs of images, compares intensity patterns, and adjusts the lens.

What is the focus distance equation for near distance of acceptable sharpness?

Near distance = (Focus distance (HD - Focal Length)) / (HD + Focus distance - 2(Focal length)).

What is the focus distance equation for far distance of acceptable sharpness?

Far distance = (Focus distance (HD - Focal length)) / (HD - Focus distance).

What is the significance of the 'optical center' of a lens?

It is the point where all light rays converge to form an image on the sensor.

What is the difference between wide-angle and long lenses?

Wide-angle lenses have a focal length less than normal, while long lenses have a focal length greater than normal.

What is the typical focal length range for fisheye lenses?

Less than 10 mm.

What is the focal length range for long lenses?

Above 1000 mm.

What are the common dimensions for a full frame sensor?

36mm x 24mm.

What is the approximate normal lens focal length for an APS-C sensor?

Approximately 35mm.

What is the relationship between sensor size and focal length in crop sensors?

Crop sensors require shorter focal lengths to match the field of view of full frame sensors.

What is the relationship defined by magnification ratios?

The relationship between the size of the subject's projection on the digital sensor to the subject's size in real life.

What does a 1:2 magnification ratio indicate?

The subject is 2x larger in real life than its size projected on the sensor.

What does a 4:1 magnification ratio indicate?

The subject is projected onto the sensor 4x its real-life size.

What is the purpose of macro lenses?

To magnify small objects to fill the frame.

What is the minimum focusing distance of the Nikon 18-140mm zoom lens?

Approximately 18 inches.

What is the maximum reproduction ratio of the Nikon 18-140mm lens?

0.23x at minimum focusing distance (or ~1:4.3).

What is the minimum focusing distance for the Nikon Micro NIKKOR 60mm lens?

Approximately 7 inches.

What is the maximum reproduction ratio of the Nikon Micro NIKKOR 60mm lens?

1x (or 1:1), which means life-size on the sensor.

What is the significance of extension tubes in photography?

They decrease the minimum focusing distance and increase magnification.

How do extension tubes affect optical distance?

They move the optics further from the camera.

What is the formula for calculating magnification using extension distance?

Magnification = Extension Distance / Focal length.

What do close-up lenses do?

They change the path of light rays by bending light prior to entering the main lens.

How is magnification measured for close-up lenses?

Measured in diopters; the higher the number, the more magnification.

What is the formula for calculating magnification with close-up lenses?

Magnification = Focal Length of Main Lens / Focal Length of Close-up Lens.

How is magnification defined in terms of focal length?

It refers to how close a subject appears through the lens compared to the naked eye.

How can you approximate magnification at longer distances?

Divide the current focal length by the normal focal length.

What focal length is suggested for recognizing a subject at a distance?

Use a lens that has a focal length of 2 mm of lens per foot of subject-to-camera distance.

What is a consideration when using longer focal lengths?

They may be needed to enlarge an individual element of the scene, especially in situations where caution is required.

What should be assessed when getting closer to a subject?

Consider safety and obstacles in the environment.

What is the maximum ratio for true macro lenses?

They can achieve a 1:1 ratio.

What is infinity focusing?

A method useful for scenes with distant components, focusing on a distant object to provide reasonable foreground sharpness.

What is hyperfocal focusing?

A technique that ensures objects near and far are acceptably sharp by focusing at the hyperfocal distance.

What is zone focusing?

A method used for scenes comprising a specific zone, focusing 1/3 into the scene to maximize depth of field (DOF).

What is pre-focusing?

A technique best for close-up photographs using a tripod, involving pre-focusing to the closest distance and then moving the camera toward the subject.

What are the steps for zone focusing in CSI?

1. Compose the scene 2. Estimate depth 3. Focus 1/3 into the scene 4. Utilize f/stop to achieve DOF.

How do you perform hyperfocal focusing for CSI?

1. Compose the scene 2. Estimate distance to the near object 3. Double that distance 4. Focus at this distance.

What happens as the f/number increases?

More in-focus area in front and behind the focus point approaches infinity.

What is field curvature?

An optical issue causing a flat object to appear sharp only in specific parts of the frame.

What is the difference between curved and flat lenses?

Curved lenses project images as curved, while flat lenses project images as flat, resulting in uniform sharpness.

What is perspective distortion?

A visual distortion based on the subject's positioning in relation to the camera.

What is radial distortion?

Occurs due to unequal refraction of light at the edges compared to the center of the lens.

What is barrel distortion?

A distortion that tends to occur with wide-angle lenses, where straight lines appear to curve outward.

What is pincushion distortion?

A distortion that tends to occur with long lenses, where straight lines appear to curve inward.

What factors influence sharpness in photography?

Camera system resolution, lens acutance, sensor size, and focus.

What is lens acutance?

The edge contrast within an image, affected by the lens quality and its ability to focus light.

What is the general rule for aperture usage in examination quality photographs?

Refrain from using the two smallest and two largest apertures of a lens due to optical issues.

Why are longer focal lengths beneficial for portraits?

They make faces appear more natural and proportionate by compressing perceived depth.

What is the 1/3 in front and 2/3 behind rule?

A guideline for depth of field distribution, though not very accurate.

What is the effect of increasing focus distance on in-focus area?

There will be more in-focus area in front and behind the focus point.

What is the recommended focusing technique for macrophotography?

Focusing down the side of a curve may be beneficial.

What is the effect of decreasing the field of view?

Achieved resolution is increased by moving the camera closer.

What is the significance of the sensor in photography?

Digital sensors are flat, affecting sharpness as light converges further out.

What is the ideal DOF percentage for close-up photographs?

Approach 50%/50% near/far depth of field.

What should be considered when determining where to focus?

The objective, size of the subject, depth, and important areas of the subject.

What is the importance of knowing your camera system?

Understanding your camera system is crucial for effective focusing and overall photographic process.