Forensic photography exam 2

F-stop (focal length,/diameter of lenses opening)

F-stop: Controls the amount of light entering the camera by adjusting the diameter of the lens opening. Smaller f-stop values (e.g., f/2.8) result in larger lens openings and more light, while larger f-stop values (e.g., f/16) reduce the lens opening and limit the amount of light.

The inverse square law

The inverse square law states that the intensity of a physical quantity decreases in proportion to the square of the distance from the source.

ISO setting

The sensitivity of a camera's image sensor to light. Higher ISO values make the sensor more sensitive, allowing for brighter images in low-light conditions, but with increased noise. Lower ISO values reduce sensitivity, resulting in darker images but with less noise.

Image quality settings (resolution)

The setting that determines the clarity and level of detail in an image. It refers to the number of pixels in an image, affecting its sharpness and size. Higher resolution means more pixels, resulting in better image quality. Lower resolution reduces file size but sacrifices image detail.

Camera filters (UV-haze, polarizing, ND, color contrast -wratten)

Camera filters are accessories used to modify the light entering the camera lens. UV-haze filters reduce haze and protect the lens. Polarizing filters minimize reflections and enhance colors. ND filters reduce the amount of light entering the lens, allowing for longer exposures. Color contrast filters, like Wratten filters, alter the color balance for creative effects.

Determining privilege direction of polarizer linear, circular, elliptical polarization

Determining the privilege direction of a polarizer:

1. Linear polarization: Use a polarizer and rotate it until maximum brightness is achieved.

2. Circular polarization: Use a polarizer and rotate it until the image appears unchanged.

3. Elliptical polarization: Use a polarizer and rotate it until the image appears partially darkened and partially brightened.

Linear vs circular polarization

Linear polarization: The orientation of the electric field of an electromagnetic wave is fixed in a single direction.

Circular polarization: The orientation of the electric field of an electromagnetic wave rotates in a circular pattern as it propagates.

Right-handed/left handed polarization

The direction in which an electromagnetic wave oscillates. Right-handed polarization occurs when the wave oscillates clockwise, while left-handed polarization occurs when it oscillates counterclockwise. It is determined by the orientation of the electric field vector.

Dynamic range (highlights and shadows)

The range of brightness in a photo, from the brightest highlights to the darkest shadows. It determines the level of detail and contrast in an image.

Focal length and perspective

Focal length: Distance between the lens and the image sensor. Longer focal length = more zoom, shorter focal length = wider view.

Perspective: How objects appear in relation to each other. Short focal length = exaggerated perspective, long focal length = compressed perspective.

NIST- minimum image resolution (1000ppi)

NIST- minimum image resolution (1000ppi): The minimum resolution recommended by the National Institute of Standards and Technology (NIST) for high-quality image reproduction. It stands for pixels per inch (ppi) and ensures sharp and detailed images.

F-stop (Aperture) and depth of field (DOF)

F-stop: Controls the size of the aperture, determining how much light enters the camera. Lower f-stop values result in larger apertures and shallower depth of field. Higher f-stop values create smaller apertures and wider depth of field.

Depth of Field (DOF): The range of sharpness in a photograph, from the nearest to the farthest point in focus. It is affected by the aperture size, focal length, and distance to the subject. A shallow DOF has a small area in focus, while a wide DOF has a larger area in focus.

Oblique lighting

Oblique lighting: Lighting technique where the light source is positioned at an angle to the subject. It creates shadows and highlights, enhancing texture and depth.

DOF and focal length

Flashcard: "DOF and focal length" DOF: Depth of Field is the range of distances in a photograph that appear acceptably sharp. It is influenced by aperture, distance to subject, and focal length. Focal Length: Focal length is the distance between the lens and the image sensor. It affects the angle of view and magnification of the image. Shorter focal lengths provide wider angles, while longer focal lengths offer narrower angles and magnification.

Shooting “thru” a fence (photography)

A technique where a photographer captures an image by shooting through the gaps or openings in a fence. This creates a visually interesting effect, adding depth and texture to the photograph while maintaining a sense of mystery or intrigue.

Attenuated lighting technique (scale with luminal)

Attenuated lighting technique: Adjusting the intensity of light to create a gradual decrease in brightness. It is used to control the overall lighting effect and create a sense of depth in a scene.

“Confident” magnification

2mm/foot of distance

Best practices in digital image enhancement

contrast stretch, density slicing, edge enhancement, and spatial filtering are the more commonly used techniques. Image enhancement is attempted after the image is corrected for geometric and radiometric distortions.

Histogram Analysis

Histograms show the shape of your data. The horizontal axis shows your data values, where each bar includes a range of values. The vertical axis shows how many points in your data have values in the specified range for the bar. In the histogram in Figure 1, the bars show the count of values in each range.

FFT plug-in or filter

Filters out large structures (shading correction) and small structures (smoothing) of the specified size by gaussian filtering in fourier space

Filters out large structures (shading correction) and small structures (smoothing) of the specified size by gaussian filtering in fourier space

Zone focusing

the act of turning your camera to manual focus and choosing a set distance away to be in focus.

Hyperfocal focusing

is a handy way of figuring out where to focus in a landscape to maximize the depth of field and to get as much of the scene as possible “acceptably sharp“

Rule of thirds

is a composition guideline that places your subject in the left or right third of an image, leaving the other two thirds more open.

Photographing impression evidence

a tripod and ruler (scale) must be used, and the ruler must be in the same plane as the impression. The camera needs to be directly over the impression, not taken from an angle. A level on the tripod is recommended.

Inversion effect

face-selective activity in the brain was delayed when the configural information of faces was disrupted (for example, when faces were inverted). This means that it took longer for the participants to recognise the faces they were viewing as faces and not other (non-facial) objects.

Examination quality photographs

A special set of close-up photographs that can be absolutely critical to an investigation is known as the Examination Quality Photographs. These images will be compared to real evidence to make an identification.

Flash photography (precautions to take)

blinding and too strong, leading to blown-out images. If you are using a DSLR, the problem can easily be rectified by investing in a camera-mounted flash accessory, which comes with the ability to be bounced in different directions.

Built-in vs external flash

a built-in flash does not need to be carried around separately, it also has disadvantages such as insufficient flash power and ability to cast light only in the front direction. To produce more professional results, the use of an external flash is recommended

Fill-flash

adds light to deep shadows cast harsh lighting.

Painting in light

expose image details in dark or near-‐dark conditions. In this technique, the shutter is held open for seconds or minutes and the photographer walks through the scene adding light from sources such as a flashlight or detached camera flash.

Bounce-flash

the use of an external flash unit (also known as hot shoe-mounted flash) to reflect the appropriate amount of light onto your subject so that your shot appears bright and sharp

Stroboscopic-flash

to stop the appearance of motion of rotating and other repetitively operating machinery and to measure, or adjust, the rotation speeds or cycle times

Second curtain sync-flash

the flash fires at the end of the exposure.

“Diffused” flash

soften or spread the harsh, concentrated light that bursts out of the flash. It also creates a more even and flattering light on the subject

“Bracketing” an image

Is a technique where a photographer takes shots of the same image using different camera settings. This gives the photographer multiple variations of the same image to choose from or combine to ensure that they get the perfect shot

Image histogram analysis

a type of histogram that acts as a graphical representation of the tonal distribution in a digital image. It plots the number of pixels for each tonal value. By looking at the histogram for a specific image a viewer will be able to judge the entire tonal distribution at a glance.

Perspective distortion (telephoto, wide angle)

This is because the field of view of wide-angle lenses is wider than the image sensor on a digital camera and therefore the image looks like it has been squeezed and constricted to fit in the edges of the frame.

often used to give the appearance of compressed distance between distant objects, such as buildings or automobiles in order to convey a feeling of congestion.

Telescopic effect of telephoto lens

makes near and distant objects seem closer together and more similar in size than they appear in real life

Magnification= focal length/50mm

Focal length/50mm

DOF asa function of focal length

The shorter the lens focal length, the longer the DOF

Stops of light (doubling and halving)

A “stop” means either doubling or halving the amount of light. Whether you are changing the amount of light let in to your sensor by changing the aperture, shutter speed or ISO, a stop means either doubling or halving the amount of light that reaches your sensor.

Reciprocity between f-stops, shutter speeds, and ISO settings

that one stop increase in aperture is equivalent to the shutter duration doubling. Both increase light by one stop.

Scale guidelines

a key compositional technique that is used in landscape photography to convey the size of a scene. When utilised appropriately, it can make the various components of your photo look their natural size again, without you having to reframe the entire composition.

Calculating angle of film plane (by “circle” on scale)

FOV = 2 arctan x2f, where x is the width of the film.

Calculating tread depth by shadow length

In the plane of the thread axis, the flanks of the V have an angle of 60° to each other. The thread depth is 0.54125 × pitch. The outermost 1⁄8 and the innermost 1⁄4 of the height H of the V-shape are cut off from the profile.

Cardinal rules of crime scene photography

fill the frame, maximize depth of field and keep the film plane parallel

Proper composition (filling the frame)

the technique of composing an image so that positive space takes up most or all of the frame

Maximizing DOF and parallel film plane

Normally, the lens and image (film or sensor) planes of a camera are parallel, and the plane of focus (PoF) is parallel to the lens and image planes. If a planar subject (such as the side of a building) is also parallel to the image plane, it can coincide with the PoF, and the entire subject can be rendered sharply.