Camera Lenses
Written by Abin Alex and Anu Joseph.
Abstract
A camera lens is a coordinated optical, mechanical and electronic system: glass elements bend light to form an image, the barrel and aperture position every part, and contacts and motors link the lens to the camera. This guide explains how a lens bends light, how lens design developed, why lenses carry many elements, and what coatings, filters and hoods do. It also covers focus motors and image stabilisation, lens mounts and flange distance, lens markings and care, and the features that matter in each kind of photography. It is written for photographers and cinematographers.
Keywords: camera lens; lens elements; lens coatings; image stabilisation; lens mount
- How does a lens bend light?
- How did photographic lens design develop?
- Why does a lens have so many elements?
- What do lens coatings, filters and hoods do?
- How do focus motors and image stabilisation work?
- What is a lens mount and why does flange distance matter?
- How do I read lens markings and look after a lens?
- Which lens features matter for each kind of photography?
How does a lens bend light?
Short answer. A lens bends light by refraction, the change of direction of a ray where it passes between air and glass. A convex surface tends to bring rays together and a concave surface tends to spread them apart. A camera lens combines both kinds to focus light and to cancel optical faults (Ray, 2002).
- Surface curvature decides the job. Biconvex, plano-convex and positive meniscus lenses converge light. Biconcave, plano-concave and negative meniscus lenses diverge it.
- Parallel rays from a distant subject meet at the focal point of a convex lens. The film or sensor sits on the focal plane.
- If the object is beyond the focal length, a convex lens forms a real, inverted image that can fall on a sensor. If the object is inside the focal length, the image is virtual and upright, like a magnifying glass.
- For a real object, a concave lens always gives a virtual, upright and smaller image.
- The key words are refraction, principal axis, optical centre, focal point, focal plane and focal length. The Focal Length guide explains the last one.
Cham tipRemember the pair: convex converges, concave diverges. A camera lens needs both.
Cham taskHold a magnifying glass between a window and a sheet of paper. Find the distance where a sharp, upside-down picture of the window appears.
Check yourself: A convex lens forms an image on a screen. Is the image real or virtual, and is it upright or inverted?
Real and inverted. The object is beyond the focal length.
How did photographic lens design develop?
Short answer. The word lens comes from the Latin for lentil, because of its shape. Curved glass was studied for centuries, but precise photographic lenses came after photography was announced in 1839. Each milestone improved speed, correction, control or size (Kingslake, 1989).
- The Nimrud lens, a polished rock-crystal object from the 7th century BCE, may have been a magnifier, a burning glass or an ornament. Scholars still debate it.
- Ibn al-Haytham, about 965 to 1040, advanced the experimental study of vision, reflection and refraction.
- The grinding and polishing skills of 13th-century Italian spectacle makers were later used for telescopes, microscopes and cameras.
- After 1839, lens makers used maths to design lenses. Petzval’s portrait lens of 1840 was computed rather than found by trial (Kingslake, 1989).
- Each lens family balances correction, speed, size and cost differently.
| Date | Milestone | What it improved |
|---|---|---|
| 1829 to 1839 | Chevalier achromat, a crown and flint doublet used on Daguerre’s camera, about f/15 | Reduced colour fringing |
| 1840 | Petzval portrait lens, about f/3.6 | A fast, computed lens for portraits |
| 1858 | Waterhouse stops | Change the aperture without taking the lens apart |
| 1866 | Rapid Rectilinear, a symmetric design | Straight lines stay straight |
| 1891 | Practical telephoto | A long focal length in a shorter barrel |
| 1902 | Early zoom patent | Variable focal length, practical zooms came later |
| 1950 | Retrofocus wide-angle | Clearance behind the lens for a mirror |
Table 1. Milestones in photographic lens design. Dates are from (Kingslake, 1989).
Cham tipWhen you read a lens name that includes a design word such as Planar or Tessar, you are reading its family tree.
Cham taskFind your oldest or simplest lens and count its glass elements. Compare it with your most modern one.
Check yourself: What did Waterhouse stops make possible?
Changing the aperture without taking the lens apart.
Why does a lens have so many elements?
Short answer. One piece of glass cannot focus light without faults. A single element leaves spherical aberration, colour fringing and a curved field. Opposing positive and negative elements share the correction, and extra groups flatten the field and control distortion. More elements are not automatically better.
- An element is one shaped piece of glass. A group is one element, or several cemented together, separated from the next group by air.
- A lens listed as 6 elements in 5 groups has one cemented pair, which counts as two elements and one group.
- In a zoom, moving groups change the spacing and so the focal length. Compensating groups keep the image in focus.
- An aspherical element has a non-spherical surface that controls spherical aberration and can cut the number of elements.
- ED, LD or UD glass has low dispersion and reduces colour fringing. Fluorite crystal controls dispersion very well but is fragile and costly.
- Apochromatic describes a design that brings three wavelengths to one focus. It is not a material.
- Performance depends on the design, the glass, the coatings, the tolerances and the alignment, not on the element count.
Cham tipDo not choose a lens by its element count. Read tests of its sharpness and colour fringing instead.
Cham taskLook up the element and group count of one of your lenses. Find which elements are special, such as ED or aspherical.
Check yourself: A lens has 6 elements in 5 groups. What does that tell you?
One pair of elements is cemented together, so that pair counts as one group.
What do lens coatings, filters and hoods do?
Short answer. Anti-reflective coatings cut surface reflections so more useful light reaches the sensor. Filters change the light on purpose, such as a polariser or a neutral density filter. A hood blocks stray light from outside the frame. All three protect contrast.
- An uncoated air-to-glass surface reflects roughly 4 to 5 per cent of the light. With many surfaces, this causes flare, haze and loss of contrast.
- Alexander Smakula developed a practical single-layer coating at Zeiss in 1935. Later multilayer coatings widened the range of colours they control.
- A circular polariser cuts non-metallic reflections and deepens skies. It loses about 1 to 2 stops.
- Solid ND filters cut light evenly. ND2 is 1 stop, ND4 is 2, ND8 is 3, ND64 is 6 and ND1000 is about 10 stops.
- A graduated ND balances a bright sky against a darker foreground. A variable ND is handy for video, but check for uneven darkening and colour shifts at the extremes.
- A hood must match the lens. A petal hood suits wide lenses, a cylindrical hood suits longer lenses and a rectangular hood suits cinema matte boxes. A hood that is too deep will vignette.
- A UV filter has little visible effect on most digital cameras. It works only as clear protection.
Cham tipBuy filters for optical quality and thread size. A cheap filter in front of a good lens wastes the lens.
Cham taskShoot a sky with and without a circular polariser. Rotate it while looking through the viewfinder and see how the effect changes.
Check yourself: An ND8 filter reduces the light by how many stops?
Three stops.
How do focus motors and image stabilisation work?
Short answer. A focus motor moves the focusing group, and the type of motor decides how fast, quiet and smooth autofocus feels. Stabilisation counters camera shake. Lens stabilisation moves a floating optical group. In-body stabilisation moves the sensor.
- Screw drive: the camera body’s motor turns the lens, mainly in older DSLR systems.
- Ultrasonic motors, called USM, SWM, HSM or SDM by different makers, are fast and quiet.
- Stepping motors, called STM or AF-P, move smoothly in small steps, which suits video autofocus.
- Linear or voice-coil motors drive the group directly. Sony calls its version XD Linear Motor.
- Lens stabilisation: gyro sensors detect pitch and yaw, a processor calculates the correction and a floating group shifts across the optical axis.
- In-body stabilisation, or IBIS, moves the sensor in five axes: X, Y, pitch, yaw and roll.
- Compatible lenses and bodies can work together. Stabilisation reduces camera-shake blur. It cannot freeze a moving subject.
| Name | Stands for | Used by |
|---|---|---|
| IS | Image Stabilizer | Canon |
| VR | Vibration Reduction | Nikon |
| OSS | Optical SteadyShot | Sony |
| OS | Optical Stabilizer | Sigma |
| OIS | Optical Image Stabilization | Fujifilm, Panasonic |
| VC | Vibration Compensation | Tamron |
Table 2. Names for lens stabilisation by maker.
Cham tipTurn stabilisation off on a tripod unless the lens manual says it is safe.
Cham taskTake the same handheld shot at a slow shutter speed with stabilisation on and off. Compare sharpness.
Check yourself: Does stabilisation freeze a running subject?
No. It reduces camera shake only. A fast shutter speed freezes motion.
What is a lens mount and why does flange distance matter?
Short answer. The mount is the lock and the electronic link between lens and body. The flange focal distance is the fixed distance from the mounting flange to the sensor. A shorter distance in mirrorless cameras leaves room for an adapter, so many DSLR lenses can be used on mirrorless bodies.
- The bayonet tabs carry the lens and form a twist lock. The alignment index marks where to start. A spring pin stops rotation and a release button retracts it.
- Gold contacts exchange autofocus, aperture, stabilisation and lens identity data. Canon’s RF mount has 12 contacts and the EF mount has 8 (Canon Europe, n.d.). The number alone does not decide image quality.
- A DSLR needs room for the mirror box. Removing the mirror allows a much shorter distance.
- Canon says EF and EF-S lenses work on EOS R cameras with an adapter. RF lenses do not fit EF DSLRs, and no adapter exists (Canon Europe, n.d.).
- In general a DSLR lens adapts to a mirrorless body. The reverse cannot reach infinity focus without extra optics.
- A wider mount opening with a shorter register gives designers more freedom for large rear elements and fast, well corrected lenses.
| Mount | Type | Flange focal distance |
|---|---|---|
| Canon EF | DSLR | 44.0 mm |
| Nikon F | DSLR | 46.5 mm |
| Canon RF | Mirrorless | 20.0 mm |
| Sony E | Mirrorless | 18.0 mm |
| Nikon Z | Mirrorless | 16.0 mm |
Table 3. Flange focal distances (Canon Europe, n.d.).
Cham tipBefore you buy an adapter, check that the lens, adapter and camera support autofocus and stabilisation together.
Cham taskFind the mount name and flange distance of your camera. Write which of your lenses fit it directly.
Check yourself: Why can a DSLR lens be adapted to a mirrorless body but not the other way round?
The DSLR needs a longer distance to the sensor, so an adapter can fill the extra space. The reverse has too little room and loses infinity focus.
How do I read lens markings and look after a lens?
Short answer. A lens name packs focal length, maximum aperture, mechanisms, stabilisation and filter size into a short code. Clean less, and clean correctly: blower first, brush second and a wipe last, then keep the lens dry.
- The code on a teaching example reads 24-70 mm 1:2.8 IF OIS II Ø82 mm. The markings are for teaching only. Check the maker’s specification for the real lens.
- 24-70 mm is the focal length. One number means a prime. A range means a zoom.
- 1:2.8 is the maximum aperture, equal to f/2.8. A range such as 1:3.5-5.6 means a variable-aperture zoom.
- IF means internal focusing. OIS is stabilisation, which may appear as IS, VR, OSS, OS or VC. II is a version number and not a promise of better quality.
- Ø82 mm is the filter thread, not the size of the front element.
- Cleaning: use a blower while holding the lens downward, then a soft brush, and only then a microfibre cloth with a little lens fluid on the cloth, never on the glass. Wipe gently from the centre outward.
- Store with both caps on at about 40 to 50 per cent relative humidity. Check for fungus, haze, oil and coating damage. Avoid compressed-air cans, household tissue, direct sunlight and sea-salt residue.
| Marking | Meaning |
|---|---|
| 24-70 mm | Focal length range, so a zoom |
| 1:2.8 | Maximum aperture, f/2.8 |
| IF | Internal focusing |
| OIS | Optical image stabilisation |
| II | Second version |
| Ø82 mm | Filter thread diameter |
Table 4. Decoding a lens inscription. This is a teaching example.
Cham tipUse a blower first and often. Most dust does not need a cloth.
Cham taskRead every marking on one of your lenses and write what each one means.
Check yourself: What does Ø82 mm on a lens tell you?
The filter thread size. It is not the diameter of the front glass.
Which lens features matter for each kind of photography?
Short answer. Choose features to match the job: a wide maximum aperture for low light and portraits, stabilisation for slow shutter speeds, a macro ratio for close work, a shift lens for buildings, and weather sealing for harsh places.
- Portraits and fashion: a wide maximum aperture, such as f/1.8 or f/2, and smooth, quiet autofocus.
- Weddings and events: fast zooms or primes, stabilisation and reliable autofocus in dim halls.
- Sports and photojournalism: fast, accurate autofocus and a wide aperture, with a robust, sealed barrel.
- Wildlife, birds and reptiles: long focal length, stabilisation and fast autofocus motors.
- Insects and macro: a macro lens with a high reproduction ratio, and a comfortable working distance.
- Product: a macro or tilt-shift lens with low distortion and even sharpness.
- Automotive: a good coating and a hood to control reflections, and a polariser for paint.
- Landscape and architecture: a wide, low-distortion lens, good coatings and a polariser. A shift lens corrects converging verticals.
- Cinematography: matched lens sets, smooth focus and iris rings, minimal focus breathing and T-stop marking.
Cham tipBuy the lens for the job you do most, then add one specialist lens when you need it.
Cham taskList your main kinds of work. Beside each, write the lens feature that would help most.
Check yourself: Which lens feature helps most for macro photography?
A high maximum reproduction ratio, such as 1:1, with a comfortable working distance.
Questions beginners ask
What is an element in a lens?
One shaped piece of glass. A group is one element, or several cemented together, separated from the next group by air.
Do more lens elements mean a better lens?
No. Performance depends on the design, the glass, the coatings and how well the parts are made and aligned.
What does ED glass do?
ED, LD and UD are low-dispersion glasses. They reduce colour fringing by bringing different wavelengths closer to the same focus.
Can I use a DSLR lens on a mirrorless camera?
Usually yes, with a correct adapter, because the mirrorless body is closer to the lens mount. The reverse generally does not work.
Do I need a UV filter?
No. UV light has little visible effect on most digital cameras. A UV filter works only as clear protection, so buy a good one or skip it.
References
- Canon Europe. (n.d.) The RF mount explained. www.canon-europe.com/pro/infobank/rf-mount/
- Kingslake, R. (1989) A History of the Photographic Lens. Boston: Academic Press.
- Ray, S. F. (2002) Applied Photographic Optics, 3rd edn. Oxford: Focal Press.
How to cite this guide. Alex, A., & Joseph, A. (2026). Camera lenses: A guide for photographers and cinematographers. Creative Hut Academy. https://creativehut.org/library/camera-lenses/
Make this your craft at Creative Hut Academy
Creative Hut Academy in Mattakkara, Kottayam, Kerala teaches photography, cinematography, editing, sound and AI filmmaking in one-year residential diplomas. Students come from across India.
Want to talk? Message us on WhatsApp, or ask Cham, our AI mentor, a study doubt.