A lens is an optical device usually made from transparent polished glass or plastic that focuses or disperses light depending on its shape. Light passing through the material of the lens is bent – that is, it changes direction depending on the shape and thickness of the lens. The word lens comes from the Latin for lentil because the biconvex (curving outwards on both sides) shape of a lens looks a lot like a lentil. However, not all lenses are biconvex, some are biconcave (curving inwards on both sides) or combinations of convex and concave. Biconvex lenses focus light, whereas biconcave lenses disperse or spread light (see Figure 2.6).

Some kaleidoscopes have bits of coloured glass, beads or shiny objects inside them, so when you look into the tube, you see interesting geometric patterns made from these colourful objects and the reflected light from the mirrors (Figure 2.9).  Other kaleidoscopes have lenses in them that bring light from outside objects into the kaleidoscope, and the patterns are made from the image you are viewing through the kaleidoscope tube.

Motion detection is reliable, and you can tweak the sensitivity and customize the notifications you receive. The video is crisp, but the frame rate maxes out at 20 fps, so fast-moving subjects sometimes appear blurry. You can set activity and privacy zones in the Tapo app, and there’s AI detection to recognize people, pets, vehicles, and the sound of a baby crying. Sadly, rich notifications, including a snapshot, are bundled with the optional Tapo Care subscription, along with 30 days of cloud storage for clips, and it’s expensive at $3.50 per month for a single camera or $12 per month for up to 10 cameras. There is no HomeKit or IFTTT support, but it works with Google Home and Amazon Alexa, though it was a little slow to load the stream on my Nest Hub. This camera also supports the open Real-Time Streaming Protocol (RTSP).

The most common lenses used in optical eyeglasses are meniscus lenses, which are convex-concave lenses that are customised to suit each individual’s vision requirements.

Cute ears are amazingly effective at adding personality to a device. This pan and tilt security camera doubles up as a smart home hub. It boasts wide compatibility, including Apple HomeKit, Google Home, Amazon Alexa, and IFTTT. It also acts as a Zigbee 3.0 hub, offering a way to bring all kinds of Aqara sensors and accessories into your smart home fold, and it even has an IR controller. A door or window sensor can trigger the camera to turn and start recording.

Along with physicist Charles M. Falco, Hockney claimed that many of the developments in realistic painting from the time of the early Renaissance (c.1430) were due to the technological development of optics devices. This is known as the Hockney-Falco Thesis. They didn’t consider using optical devices as ‘cheating’, rather they considered it part of the set of tools and devices artists could use in their work. Artists still require skill in painting techniques and visual style to create great masterpieces.

After years of rigorous testing, these are our favorite security cameras, and we’ve also got details on what to look for when shopping for one. Be sure to check out our many other guides, including the Best Outdoor Security Cameras, Best Pet Cameras, and Best Video Doorbell Cameras.

And this video will show you how kaleidoscopes are made – you can make your own using a cardboard roll, clear plastic and reflective cardboard instead of mirror glass.

Donkey plural

As a camera, you can expect crisp 2K footage (HomeKit is limited to 1080p). The camera has a 110-degree field of view. It rotates through 340 degrees, tilts up 30 degrees, and down 15 degrees to cover a large area. Sadly, recording at 20 fps means fast movement can cause blurring. Onboard AI enables person, pet, face, and gesture detection, a cruise mode has the camera cycle through positions, and it can track subjects (though it is a little slow to do so sometimes). Insert a microSD card (up to 128 GB) for local recordings. The sleep mode has the camera lens roll up and shows a pair of closed eyes. It’s a shame you can only connect Aqara accessories and must dig into the Aqara app to access certain features (including pan and tilt). But if you’re into automation, you will enjoy tinkering with this highly customizable security camera.

Some historians speculate that prehistoric cave paintings may have been inspired by accidental Camera Obscura effects from small holes in tents or animal hides. The Camera Obscura was most notably used as an artist’s device during the Renaissance and later periods of realism in painting to assist in the depiction of realistic scenes and accurate perspective in artworks.  There are records of its use in ancient Chinese, Arabic and European cultures as a means of telling the time of day and year by the position of the sun inside the camera. It was also used to safely view phenomena like solar eclipses, which can cause eye damage if viewed directly.

Some security camera manufacturers, like Wyze, offer their own branded microSD cards. They work just fine in my experience, but for maximum reliability, here are my favorites. Always remember to check the specs. Even different sizes of cards in the same range often have different capabilities.

This feature-packed camera from Eufy is likely overkill for most folks, but it’s an impressively versatile device. It combines a regular camera with a 130-degree field of view that can go up to 4K with a 2K telephoto lens that provides 3x optical zoom. It also has 360-degree pan and 75-degree tilt controls, AI tracking that works well, and support for up to four preset positions it can patrol through, including the default it returns to after tracking a subject out of frame. There’s also privacy mode, two-way audio, and onboard AI to detect people, pets, and sounds. You can record locally with a microSD card up to 128 GB (not included), hook it up to a HomeBase 3 (sold separately), or subscribe for cloud storage from $3 per month.

RealD 3D cinema technology is a polarised 3D system that uses circularly polarised light to create stereoscopic image projection. The principle for the polarising glasses we wear now for viewing 3D cinema is the same principle as the original stereoscope – the film we are viewing is actually two sets of moving images projected with a special projector that alternates right-eye frames and left-eye frames, switching between them 144 times per second.

Photo plural

I test every security camera for at least two weeks, but often far longer. I run through the installation process and note any issues. I check that alerts come through correctly to my phone when I am home, connected to Wi-Fi, or away connected to a cellular network. I usually place two or more cameras in the same spot to compare picture quality, motion detection, and other features. I consider the image resolution, frame rate, and audio quality of videos and the live feed. I also check for lag with the live feed. I test the performance during the day, see how it copes with the sun facing the lens, and how it performs in the dark at night (testing both spotlight and night vision). I check how long the live feed and recorded videos take to load at different times of the day.

With a compelling range of features, including video at up to 2K and 30 frames per second, 360 degrees of pan and 149 degrees of tilt, and local storage on a microSD card (up to 512 GB), this camera unseats the Wyze Cam Pan V3 as my favorite panning camera. The live feed is consistently quick to load, and image quality is excellent if you select the higher resolution and frame rate and toggle on HDR in the app. You can also set waypoints for the camera to patrol through on your chosen schedule, and the automatic subject tracking is top-notch. The onboard AI can categorize by motion, person, pet, or vehicle, and you can set an alert when a line is crossed. The two-way audio is relatively clear and lag-free, and there’s sound detection too (baby, pet, or glass breaking). There’s also a large image sensor (TP-Link calls it the Starlight Sensor) for clear image capture in low light. The privacy mode prompts the camera lens to rotate inside, so you know you aren’t being recorded.

Figure 2.9. Example of the view looking through a kaleidoscope with coloured glass beads. Image attribution: Albarubescens, Rotational symmetries in designs produced by a kaleidoscopeDSCN2440, on Wikimedia Commons, CC BY-SA 4.0

Binocular vision has also led to technological developments that try to replicate our 3D vision using different devices. The earliest experiments with this were with stereoscopic photography, where two photographic images were captured at a small distance from each other (similar to the distance between human eyes). These two photographs were placed in a viewer so that each eye views a different image (Figure 2.10). The brain interprets this information as a single image, and it appears that we are looking at a 3-dimensional scene.

The effect is the same as the stereoscope because the brain interprets these two images as one, which appears as a 3-dimensional scene.

If you rotate the kaleidoscope while looking through it, you can change the coloured pattern by shifting the coloured objects around or changing the light that the mirrors are reflecting.

The eye looking through the red filter only sees the cyan image (as a black image), and the eye looking through the cyan filter only sees the red image (as a black image). This is because these two colours are opposites and their light waves do not pass through the filter of the opposite colour.

The artist can then trace the superimposed image (which is an illusion created by the device) and create an accurate representation of the scene with correct proportions and perspective on the paper below. It was much easier to use than the Camera Obscura because it didn’t require a darkened space, and you could use it anywhere in any light conditions.  The technology of the Camera Lucida is similar to that used in microscopes that use mirrors to reflect the contents being viewed up into a lens that magnifies the image.

Mouse plural

We recommend formatting the card as soon as you insert it into the camera. You will usually be prompted to do this, but if not, there is generally an option in the settings. Just remember, formatting will wipe anything on the microSD card, so back up the contents first.

A similar principle is used with the Anaglyph 3D technique, which overlays two images of different colours that are slightly apart. Usually, one image is red, and the other is cyan (Figure 2.11). To view this kind of image in 3 dimensions, you need special glasses with different coloured transparent filters for each eye.

Hockney, David (2006). Secret Knowledge: Rediscovering the Lost Techniques of the Old Masters. Thames and Hudson. ISBN 9780500286388.

Note: After a security researcher identified cloud uploads from a “local” only device and a report warned of video streaming without encryption following a bug in May 2021 that exposed some camera feeds to other Eufy users, we stopped recommending the brand. After initial denials, parent company Anker acknowledged and fixed the issues, overhauled its policies, and instituted a bug bounty program. We spoke with third-party security researcher Ralph Echemendia, who was hired to conduct an audit, and have decided to start testing Eufy cameras again.

You can now install mobile device apps that simulate a kaleidoscope effect using your camera or coloured geometric patterns, and you can save these images to use in creative projects.  You can also get kaleidoscopic lenses that can be placed over a camera lens which add interesting patterns to a photographic image.

With a compact design, clear video, and two-way audio, this camera from Arlo matches our top pick on features and performs reliably well. It can sit on a shelf or be wall-mounted, has a privacy shutter that comes down when the camera is not in use, and stores video in the cloud. Footage is detailed, and there’s no blurring on motion (the frame rate is 24 fps). Arlo’s second-generation Essential Indoor cameras come in two varieties: the cheaper 1080p camera and a pricier 2K model. I’m a fan of the app for its ease of use, loading speeds, and two-factor authentication, enabling you to log in to the live feed with your fingerprint or face scan (phone permitting). There’s also a built-in siren and smart home integration for Amazon Alexa, Google Assistant, and IFTTT, but not Apple HomeKit.

These separate projections for each eye are made with a special polarising screen that switches the polarisation, so each eye only sees the frames that match the polarisation of the glasses. This is what gives us a realistic 3D effect (Figure 2.12).

Plural of butterfly

Other significant developments, such as Galileo’s refracting telescope (c.1609), also had a great impact on the fields of optics and astronomy. Since that time, many technological developments have expanded the field of optics to include both the visible and non-visible spectrum.

Updated September 2024: We changed our top pick, added cameras from Ring, Imilab, and Ezviz, a new slide on how we test, removed some older entries, and updated prices.

The footage is crisp and detailed enough to zoom in on, though bright areas like sun streaming in a window can appear blown out. Because the frame rate is 15, sometimes fast-moving subjects appear blurry. The motion detection is reliable, and you can set up privacy zones in the app. Notifications are swift and come with a thumbnail if you don’t mind uploading to the cloud (it is optional). I sometimes noticed a slight lag on the live feed, and sound quality could be better. There is no HomeKit support, but you get Alexa and Google Assistant, though the camera was very slow and sometimes failed to load for me via Google.

During the Middle Ages and Enlightenment periods, the significant work of scientists Ibn al-Haythem (Book of Optics c1011) and Sir Isaac Newton (Opticks, 1704) made contributions to the field of optics with their observations of the visible spectrum and how light moves through different substances, as mentioned in Chapter 1.1 History of colour theories.

We have evolved to have two eyes (binocular vision), perhaps partly because there is less risk of total blindness if one eye is damaged. But have you ever thought about how we have two eyes but only see one image?  The way our eyes work with our brains allows us to see in 3 dimensions (3D), and this is very useful for judging distances between objects and spatial navigation in the world.

Unfortunately, cloud storage for your videos and the best features, like person alerts and rich notifications, require a Ring Protect Plan ($5 per month for one camera or $10 per month for all your cameras and doorbells). I don’t recommend this camera without the plan, as you are limited to the live feed, motion alerts, and two-way audio. The perfect spot is vital for this camera because it has a relatively limited 115-degree horizontal and 59-degree vertical field of view, and there is no HDR, so bright areas can blow out.

Plural of television

Folks with Philips Hue smart lights will find the company’s security camera intriguing. The Philips Hue Secure (7/10, WIRED Recommends) is a wired security camera with an optional weighted base. It feels solid and durable (it has an IP65 rating). Video maxes out at 1080p but is crisp and deals with mixed lighting and moving subjects well. It offers a wide 140-degree field of view. Night vision is decent, there’s two-way audio, and it’s quick to send alerts or load the live feed in the Hue app. But, if you want more than that, you need to subscribe from $4 per month ($40/year) for a single camera, which gives you 30 days of cloud storage and unlocks smart detection features.

Artist David Hockney wrote a controversial book where he claimed that many famous Old Master artworks were, in fact, created with optical devices like these. Some art historians were upset by this claim – they thought that Hockney was accusing the Old Masters of ‘cheating’ because of the suggestion that the artists hadn’t recreated the scenes in the paintings by eye alone. This implied that these Old Masters were less technically skilled than previously thought.

The person and animal detection works well, helping to filter out false positives, and you can also set multiple activity and privacy zones. There’s vehicle and package detection, too, for outdoors use. There’s no local storage, but footage is end-to-end encrypted, so only you can access it. If you have a Hue bridge and lights, you can have the camera trigger them. I set it up in my office to turn the lights on and off automatically, with different brightness and color settings for different times of day. When you arm the system, it gives you a countdown, and when you get an alert, you can review and trigger flashing lights and a siren to try and scare away intruders, though the siren tops out at 80 decibels. While there are better cameras for this money, the impressively slick integration with the Hue ecosystem is the attraction. Trust is crucial with a camera inside your home, so it’s an easier sell for Hue fans.

Folks with a Ring doorbell should consider this affordable Ring camera if they need something inside the home, as it means you can keep everything in one app. The Ring Indoor Cam (2nd Gen) records crisp 1080p footage at 24 frames per second, has optional color night vision, and has a privacy shutter you can swivel around when you don’t want it recording. You can get motion alerts, pre-roll captures a few seconds before each event, two-way audio is decent, and the Ring Indoor Cam has a built-in siren. Customizable zones are handy if you need them. The Ring app is feature-packed but can be slow to load the live feed and somewhat confusing to navigate, though there are good in-app tutorials.

You only get three hours of history unless you sign up for a Nest Aware subscription, which now costs $8 per month ($80/year) for 30 days of event video history and familiar face alerts, but that covers all your Nest devices. (You can also use the camera in a Nest Hub Max as an indoor security camera.) Once you have tagged familiar faces, your notifications include their names, which is handy (and can be reassuring). It’s good to know when your kids get home versus when an unfamiliar face pops up. It’s not 100 percent accurate, but it’s closer than any other camera I have tested. Sadly, there’s no local storage option, and the thing that really sets it apart (familiar faces) requires a relatively expensive subscription. It also lacks a privacy shutter. Try not to buy it at full price, as it's frequently on sale.

Security cameras are great tools, but you also need to protect your security from those cameras. You don't want to find out that a stranger has been watching you sit in your bathrobe bingeing trash TV for the third day in a row, or worse. If you follow these tips, you can be a vigilant and conscious consumer and still feel like your home is protected while you're away.

With an understated style, Google’s indoor Nest Cam comes in a few elegant finishes (including one with a maple wood base) to help it blend in with your decor. It has HDR, the 1080p video quality is clear at 30 fps, and night vision kicks on automatically when the lights are out. There’s also two-way audio, enforced two-factor authentication, and accurate detection to alert you about people, animals, or vehicles. You can install and use the Nest Cam through the Google Home app, and it’s quick to load on Nest displays or a Chromecast with Google TV. (It's even now accessible via a web interface.)

A Camera Obscura (Latin for dark chamber) is a dark space used to create an image projection.  It works with a room, tent or box which has a very small hole or lens on one side that projects an image from the outside of the space to the opposite wall on the inside of the space (Figure 2.7). The projected image is upside-down and back-to-front because light bouncing off objects outside the Camera Obscura enters the internal space through the hole or lens at an angle. Light from an object at the top-left of a scene outside the camera, will project onto the bottom-right of the inner wall of the camera.

Lenses are in many devices we use every day, such as eyeglasses, magnifying glasses, cameras, telescopes, microscopes, etc.

The Blink Mini 2 (7/10, WIRED Recommends) brings a few crucial improvements over its predecessor that earn it a recommendation here: better image quality with a wider field of view (up from 110 to 143 degrees), enhanced low-light performance (with an optional spotlight), and on-device person detection (fewer false positives). Amazon’s Blink turns out some of the most compact security cameras available, and this rounded square comes with a circular base for easy mounting, or it can sit unobtrusively on a shelf. Footage is 1080p at up to 30 fps, and I found it clear, even in low light. You can also set activity and privacy zones, and the two-way audio is passable, though the sound quality isn’t great. I also appreciate the option to log in to the app with biometrics (phone permitting).

Colour Theory: Understanding and Working with Colour Copyright © 2023 by RMIT University is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

Optics is a branch of Physics – it’s the science that deals with light. Optics explains how light energy behaves and interacts with matter. Some of the earliest recorded experiments in optics were done by ancient Egyptians, Mesopotamians, and Greeks using glass lenses and reflective materials like obsidian.

Unfortunately, cloud storage, accurate subject detection, and smart animated alerts require an expensive Arlo Secure subscription at $8 per month for a single camera. It’s a bit more palatable if you have multiple Arlo devices, as it costs $13 per month for unlimited cameras. For folks with video doorbells or other cameras from Arlo, this camera is an obvious pick to keep things in a single app. But the lack of local storage might be a turnoff, and there are occasionally a few seconds of lag on the live feed.

I play around with the settings in the app to try every mode and feature. I test any smart detection features to see if they can correctly identify people. I test the two-way audio for a short conversation and try the siren where applicable. I also test local storage and cloud storage options for recording videos. If there are any smart home integrations, I set them up and check how quickly the feed loads on a smart display. I always ensure the cameras we recommend support 2FA and test any additional security or privacy features.

Kaleidoscopes were first invented as toys in 1816 by Scottish physicist Sir David Brewster, but they can also be useful devices for designers and artists because they create complex and colourful symmetrical patterns. A kaleidoscope is usually made from a tube with angled mirrors inside of it that reflect light waves. Light usually travels in straight lines, but if it hits a shiny surface like a mirror, the light waves bounce back at a similar angle – like a bouncing ball.

You don't need to spend money on a new security camera—an old smartphone will do as long as it can still connect to Wi-Fi. Just download a camera app (we like Alfred) to both your old phone and your new phone, then sign in with the same email address. Find a spot to mount your device and keep it charged, and you'll be able to view the camera feed through your current phone.

If your budget is tight, the Tapo C110 ($19) is even cheaper with only a few compromises (lower frame rate, no pet or vehicle detection, microSD limited to 256 GB).

what is the plural form of the word battery?

© 2024 Condé Nast. All rights reserved. WIRED may earn a portion of sales from products that are purchased through our site as part of our Affiliate Partnerships with retailers. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of Condé Nast. Ad Choices

The concept behind the Camera Obscura led to the development of the photographic camera – which is where the name comes from. Cameras we use today still work on the same principle as this device, which was created many hundreds of years ago.

Not quite ready to deck out your house with window, door, and motion sensors and hire an on-call monitoring service? Don’t fret! You can still keep your home secure without messing with your wiring by going with an indoor security camera or two. Knowing you can check in when you are away from home offers peace of mind, but these cameras aren’t perfect. There’s an obvious security benefit, but you expose yourself to privacy risks.

The microSD card you choose should have fast read and write speeds so that you can record high-quality video and play it back without delay. We recommend going for Class 10 microSD cards rated as U1 or U3. You can dive deeper into what that means in our SD card explainer. Before buying, check the card type, format, and maximum supported card size for your security camera. Consider how many hours of video each card capacity can store. For example, you might get a couple of days of HD video on a 32-GB card. If you want to record continuously, you likely want a higher-capacity card.

The C120 can stream and record video at up to 2K resolution, supports two-way audio (with a slight lag), and has a slot for up to 512-GB microSD cards to keep recordings local. This affordable security camera has a starlight sensor that offers impressive color night vision, smart detection (people, pets, and vehicles) without a subscription, and an IP66 rating, which means you can also use it outdoors (provided you can run the power cable). The handy base is easy to wall-mount, can sit on a shelf, and is magnetic. There is no need to spend more than this to keep an eye on an entrance or a specific room in your home.

Plural of foot

Learn more about kaleidoscopes from this text: The kaleidoscope, its history, theory and construction with its application to the fine and useful arts by Sir David Brewster, 1858 on the Internet Archive.

Many security cameras support local storage, enabling you to record videos on the camera or a linked hub. A few hubs have built-in storage, and some provide slots for hard drives, but most rely on microSD cards. Here are some details on what to look for (and a few recommendations).

Visit Optics 2: electronic technologies and spectral analysis to see more examples of technologies that use optics such as lasers, optical fibre, photovoltaic cells, and spectral analysis in astronomy.

The field of view won't be as wide, the battery won't last as long, and the mount will probably be a lot less secure. Still, if you're going on a weekend vacation, it's a quick and easy way to set up something essentially for free. Alfred is available for iOS and Android. It offers motion detection and can set off an alarm when it detects someone.

Artists used both of these technologies to assist in the depiction of realistic scenes in paintings and other art forms. Camera Lucida devices were also used by biologists and naturalists to create scientific illustrations.

Jump to Activities at the bottom of the page to learn how to create your own Camera Obscura Pinhole Camera box with a cardboard box, or turn your entire room into a Camera Obscura.

A Camera Lucida (Latin for light chamber) is a portable device that was developed after the Camera Obscura. The technology may have existed in the 17th century, but it wasn’t patented until 1806. A Camera Lucida creates an optical illusion, where the scene in front of the artist is superimposed onto paper, which is usually on a flat surface like a table. The artist is able to look down into the device, which uses glass, a one-way mirror, or a prism, and see both the image of the scene in front of them, and the drawing on the paper combined together. See Figure 2.8 which shows a diagram of how a Camera Lucida is used.

The catch is that you really need the subscription at $3 per month or $30 per year for a single camera, or $10 a month or $100 a year for unlimited cameras. You can technically record locally, if you purchase a Sync Module 2 ($50) and insert a USB flash drive, but without a subscription, your live feed is limited to five minutes with no record option, videos are much slower to load, you don’t get person detection, and you can’t share clips. If you subscribe, you get all that and a generous 60-day unlimited cloud video history (30-day in the UK and Europe).

Cameraplural possessive

Power up with unlimited access to WIRED. Get best-in-class reporting that's too important to ignore for just $2.50 $1 per month for 1 year. Includes unlimited digital access and exclusive subscriber-only content. Subscribe Today.

On the downside, a Tapo Care subscription (starting from $3.50 a month or $35 a year for one camera) is required for cloud storage, rich notifications with snapshots in them, and easy video filtering. Everything else is available without a subscription, making this an excellent local recording option, but it’s a real shame that the rich notifications are behind the paywall. This camera is usually cheaper on Amazon under the model name C225, but it also appears as TC73 sometimes.