Photography Lens Optics and Selection 3 — Questions and Answers
Question 1: What is the 'hyperfocal distance' of a lens?
- The maximum focus distance a lens can achieve
- The closest focus distance at a given aperture
- The focus distance that maximizes depth of field from half that distance to infinity (Correct answer)
- The optimal distance for portrait photography
Correct 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.
Question 2: A macro lens with a 1:1 magnification ratio means:
- The subject appears twice as large as in real life on the sensor
- The image on the sensor is the same size as the real subject (Correct answer)
- The lens can focus at twice its focal length
- The subject must be exactly one meter away
Correct 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.
Question 3: Which type of lens distortion causes straight lines to bow outward from the center?
- Pincushion distortion
- Barrel distortion (Correct answer)
- Mustache distortion
- Spherical aberration
Correct 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.
Question 4: What advantage does an ED (Extra-low Dispersion) glass element provide?
- Increased maximum aperture without added weight
- Reduced chromatic aberration (Correct answer)
- Better resistance to lens flare
- Improved close-focusing performance
Correct answer: Reduced chromatic aberration
ED glass bends different wavelengths of light more uniformly, significantly reducing chromatic aberration and producing sharper, more color-accurate images.
Question 5: What does 'T-stop' measure, and how does it differ from f-stop?
- T-stop measures telephoto reach; f-stop measures wide-angle reach
- T-stop measures actual light transmission; f-stop measures the geometric aperture ratio (Correct answer)
- T-stop is used only for video; f-stop is used only for still photography
- T-stop accounts for zoom range; f-stop does not
Correct 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.
Question 6: When shooting architecture, which lens type is used to correct converging vertical lines?
- Fisheye lens
- Tilt-shift lens (Correct answer)
- Telephoto lens
- Macro lens
Correct 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).
Question 7: What is 'vignetting' in the context of lens optics?
- A rainbow-like flare pattern caused by bright light sources
- Darkening of the image edges and corners compared to the center (Correct answer)
- Color shift that occurs when shooting in low light
- Softening of the subject at close focus distances
Correct 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.
Photography Lens Optics and Selection 3
What is the 'hyperfocal distance' of a lens?