Lens Optics and Selection Flashcards

What is the 'hyperfocal distance' of a lens?

Answer: The focus distance that maximizes depth of field from half that distance to infinity

The hyperfocal distance is the closest point at which a lens can be focused while keeping objects at infinity acceptably sharp, maximizing overall depth of field.

A macro lens with a 1:1 magnification ratio means:

Answer: The image on the sensor is the same size as the real subject

A 1:1 magnification ratio means the subject is reproduced at life-size on the camera sensor—a 10mm insect will appear 10mm on the sensor.

Which type of lens distortion causes straight lines to bow outward from the center?

Answer: Barrel distortion

Barrel distortion causes straight lines to bow outward, and is most common in wide-angle and zoom lenses at their widest focal lengths.

What advantage does an ED (Extra-low Dispersion) glass element provide?

Answer: Reduced chromatic aberration

ED glass bends different wavelengths of light more uniformly, significantly reducing chromatic aberration and producing sharper, more color-accurate images.

What does 'T-stop' measure, and how does it differ from f-stop?

Answer: T-stop measures actual light transmission; f-stop measures the geometric aperture ratio

T-stop accounts for actual light lost to glass absorption and reflection inside the lens, while f-stop is purely a geometric ratio of focal length to aperture diameter.

When shooting architecture, which lens type is used to correct converging vertical lines?

Answer: Tilt-shift lens

A tilt-shift lens allows the lens to shift perpendicular to the optical axis, keeping the sensor parallel to the building and preventing keystoning (converging verticals).

What is 'vignetting' in the context of lens optics?

Answer: Darkening of the image edges and corners compared to the center

Vignetting is a reduction of image brightness toward the periphery compared to the center, caused by the lens's optical design or by using an incompatible lens hood or filter.