Many experienced photographers use manual exposure, but not many fully understand metering. Metering is the process by which your camera (or any light meter) decides what a “correct” exposure is. A light meter measures the actual light in a scene and tells you which combination(s) of shutter speed, aperture, and ISO will give you a correct exposure. It is important to understand the basics of metering. However, to fully master your camera, you really should learn about spot metering.

Our discussions of diffraction have used a slit as the aperture through which light is diffracted. However, all optical instruments have circular apertures, for example the pupil of an eye or the circular diaphragm and lenses of a microscope. Circular apertures produce diffraction patterns similar to those described above, except the pattern naturally exhibits a circular symmetry. Mathematical analysis of the diffraction patterns produced by a circular aperture is described by the equation:

This experiment was first explained by Augustin Fresnel who, along with Thomas Young, produced important evidence confirming that light travels in waves. From the figures above, we see how a coherent, monochromatic light (in this example, laser illumination) emitted from point L is diffracted by aperture d. Fresnel assumed that the amplitude of the first order maxima at point Q (defined as εQ) would be given by the equation:

The resolving power of optical microscopes is determined by a number of factors including those discussed, but in the most ideal circumstances, this number is about 0.2 micrometers. This number must take into account optical alignment of the microscope, quality of the lenses, as well as the predominant wavelengths of light used to image the specimen. While it is often not necessary to calculate the exact resolving power of each objective (and would be a waste of time in most instances), it is important to understand the capabilities of the microscope lenses as they apply to the real world.

That’s it! Your subject, because you metered it directly, will always be correctly exposed. What if your subject is very light or very dark in tone, and neutral is not actually the best exposure? Simply spot-meter it at +1 or -1, and see how that looks. This is a common technique when photographing various portrait subjects with different skin tones, and it’s really easy to learn. You’ll be surprised how quickly your brain learns how to expose all your favorite subjects.

When you combine this with a camera that has an electronic viewfinder (EVF) that provides visual confirmation of your exposure, you’ll find that your images look perfect in-camera!

Many experienced photographers use spot metering in conjunction with manual exposure in order to maintain total control over each exposure. In this article, you will learn how spot metering works and how to use it effectively with manual exposure mode. Also, we’ll describe how to use spot metering with Aperture priority or other modes to deal with extremely dynamic light.

Diffraction of light plays a paramount role in limiting the resolving power of any optical instrument (for example: cameras, binoculars, telescopes, microscopes, and the eye). The resolving power is the optical instrument's ability to produce separate images of two adjacent points. This is often determined by the quality of the lenses and mirrors in the instrument as well as the properties of the surrounding medium (usually air). The wave-like nature of light forces an ultimate limit to the resolving power of all optical instruments.

Thus, if two objects reside a distance D apart from each other and are at a distance L from an observer, the angle (expressed in radians) between them is:

where A is the amplitude of the incident wave, r is the distance between d and Q, and f(χ) is a function of χ, an inclination factor introduced by Fresnel.

This technique often becomes effortless and second nature to landscape photographers. Point your camera at your subject, and dial in your exposure. Then, point your spot meter at the brightest highlight and darkest shadow in your scene to see where they fall relative to that neutral point. Say, for example, your highlights register as +3 EV and your shadows register as -2 EV. That is a total of 5 EVs of dynamic range, and most cameras today can handle that with ease. You’re done!

The DL194 small dome light is available in a wide range of wavelengths, including a 3 channel, RGB configuration. Contact Advanced illumination today to ...

Unfortunately, all camera manufacturers, and even different models of the same make, have different spot metering options. I can’t even say, “oh, all Sony cameras work this way, and all Nikons work that way” …because you will have different options depending on whether you buy an entry-level camera or a flagship model.

We can often observe pastel shades of blue, pink, purple, and green in clouds that are generated when light is diffracted from water droplets in the clouds. The amount of diffraction depends on the wavelength of light, with shorter wavelengths being diffracted at a greater angle than longer ones (in effect, blue and violet light are diffracted at a higher angle than is red light). As a light wave traveling through the atmosphere encounters a droplet of water, as illustrated below, it is first refracted at the water:air interface, then it is reflected as it again encounters the interface. The beam, still traveling inside the water droplet, is once again refracted as it strikes the interface for a third time. This last interaction with the interface refracts the light back into the atmosphere, but it also diffracts a portion of the light as illustrated below. This diffraction element leads to a phenomenon known as Cellini's halo (also known as the Heiligenschein effect) where a bright ring of light surrounds the shadow of the observer's head.

Why would you want to use spot metering in aperture priority mode, though? This advanced technique can be useful when you are working in extremely dynamic lighting, where the light on your subject can vary by more than 2-3 stops in a matter of seconds. In other words, you probably can’t even manually turn your camera dials fast enough to correctly expose your subject.

We classically think of light as always traveling in straight lines, but when light waves pass near a barrier they tend to bend around that barrier and become spread out. Diffraction of light occurs when a light wave passes by a corner or through an opening or slit that is physically the approximate size of, or even smaller than that light's wavelength.

You can work around this challenge using two methods. First, as I mentioned earlier, many cameras now allow you to connect your spot meter to your focus point. If you do this, then as long as your focus point is perfectly over your subject, you’ll always expose them correctly. Alternately, you can use a dedicated button on your camera to perform AE-L, or Auto Exposure Lock. This allows you to temporarily lock in your exposure while you compose your image framing.

Illuminate your spaces with precision and efficiency using our advanced LED lighting Fixture. Designed to deliver uniform, homogeneous lighting with minimal ...

As shown in the left side of the figure, when the wavelength (λ) is much smaller than the aperture width (d), the wave simply travels onward in a straight line, just as it would if it were a particle or no aperture were present. However, when the wavelength exceeds the size of the aperture, we experience diffraction of the light according to the equation:

Basically, spot metering differs from other metering modes on your camera because it uses a simple concept. It meters one small spot in your image and totally disregards everything else. That’s it! Other metering modes try to balance your entire image. Sometimes they use an average of the entire frame, other times emphasizing the central part of your image. Some cameras can even meter off of human faces.

Most cameras, when switched to spot metering in a default setup, take meter readings from the center of the image. This center spot is a circle that is as small as 1-5% of the whole image frame. Some cameras have a visible circle in the center of the images. With others, you’ll just have to make sure your focus point is dead-center. As I mentioned before, this tiny little spot is the only part of the entire image being metered. So, if other parts of the image are extremely dark, or extremely bright, you may blow out your highlights or lose your shadows.

This is a very rare situation, of course, and you may never use it. It’s still exciting to try, though, if only just for practice.

Our solid rod light pipes provide highly uniform illumination of the microdisplay, even though the light source may be non-uniform, Key functional ...

Using spot metering may not be something you ever thought of, because at a glance it may seem intimidating. However, it really is a simple process. With this basic understanding of how spot metering works, you’ll be able to manually adjust your exposures with precision. You won’t ever have to just hope that everything turns out okay whether your subject is light or dark-toned, and/or your background is significantly different. You’ll always know exactly what your subjects’ tones are going to look like.

The act of illuminating, or supplying with light; the state of being illuminated. illuminationnoun. Festive decoration of houses or buildings with lights.

Explore a wide range of our Uv Safety Glasses selection. Find top brands, exclusive offers, and unbeatable prices on eBay. Shop now for fast shipping and ...

Here’s the simple version of how to use spot metering on most digital cameras. Simply look for that center dot in your viewfinder and point it right at your subject. In manual exposure, dial your camera settings until that center dot registers as “0” or neutral. Then, re-compose your shot if you don’t want your subject to be smack-dab in the middle of your frame.

A very simple demonstration of diffraction can be conducted by holding your hand in front of a light source and slowly closing two fingers while observing the light transmitted between them. As the fingers approach each other and come very close together, you begin to see a series of dark lines parallel to the fingers. The parallel lines are actually diffraction patterns. This phenomenon can also occur when light is "bent" around particles that are on the same order of magnitude as the wavelength of the light. A good example of this is the diffraction of sunlight by clouds that we often refer to as a silver lining, illustrated in Figure 1 with a beautiful sunset over the ocean.

So, here’s what you need to know: Some cameras only let you spot meter off the dead-center of your image frame, while other cameras let you link spot metering to your selected autofocus point. How convenient!

As I mentioned earlier, whether you do portrait photography, wedding/event photography, or wildlife or even landscape photography, you’ll quickly find yourself memorizing all of your common subjects, and whether they should spot meter at “0”, or +1, -1, etc. You will also learn how big the spot itself is, so that you can correctly meter both large and small subjects, near and far…

You might be asking, “what about my dark/bright background? Is there any hope of saving it?” The answer is, yes! In fact, the solution is just as easy as spot metering your subject. Simply point your camera’s spot meter at those highlights/shadows, and see what they are.

Therefore, practically speaking, spot metering is mostly useful in situations where there is, in fact, a lot of extreme contrast that could “mess up” your other metering modes. Some common examples of these types of situations include:

However, what if your brightest highlight registers totally off the scale? Let’s say that by dialing your exposure down, you calculate the highlight to be at +8 EV. If that’s a blown-out background in a portrait, it may be just fine being white. If you’re a landscape photographer shooting a sunset, though, you have a problem!

A 10x magnifier lamp combines a light source and a magnifying lens to provide exceptional detail viewing. It helps viewing minute details while working on ...

Fiber Optic LED Light Pipes are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for Fiber Optic LED Light Pipes.

Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

Since your spot meter will only meter those subjects, you’ll see your light meter jump to, say, +2 or -2. Again, when you’re in manual exposure mode, so your exposure isn’t changing — just the meter reading.

Where θ is the angle between the incident central propagation direction and the first minimum of the diffraction pattern. The experiment produces a bright central maximum which is flanked on both sides by secondary maxima, with the intensity of each succeeding secondary maximum decreasing as the distance from the center increases. Figure 4 illustrates this point with a plot of beam intensity versus diffraction radius. Note that the minima occurring between secondary maxima are located in multiples of π.

Start by simply getting in the habit of always spot metering off your subject, and dialing the exposure to be “0” or neutral. Of course, expose lighter subjects a bit brighter than zero, and darker toned subjects a bit under the “0.”

Also, remember that quickly pointing your spot meter at the highlights and shadows in your scene can give you some peace of mind, or warn you about potentially challenging light.

Also, some cameras allow you to vary the exact size of your metering spot. They may call it small, medium, and large, or they may actually tell you that you’re choosing from a 1%, 5%, or 10% in your viewfinder. Either way, this feature is usually reserved for the topmost flagship cameras such as the Sony A1, but we’re starting to see it in more affordable models now too.

Where D(0) is the minimum separation distance between the objects that will allow them to be resolved. Using this equation, the human eye can resolve objects separated by a distance of 0.056 millimeters, however the photoreceptors in the retina are not quite close enough together to permit this degree of resolution, and 0.1 millimeters is a more realistic number under normal circumstances.

Of course, if you know that your camera does not have enough shadow recovery to “dig” 3+ stops into your shadows, this means you will need to bracket and create an HDR landscape.

Chauvet Scorpion Dual FAT BEAM ... Laser Light Show Fixture. X-RAW-1-7-RGB.

Speaking of landscape photography, would you like to get even more advanced? Here is the classic technique that goes back to the days of film and Ansel Adams’ “Zone System.” Start by metering the brightest highlight in your scene first, and dial it to +2 or +3 EV. (Based on your personal testing of what your camera can handle before that highlight clips to white.) Next, meter the darkest part of your scene. As long as it is within, say, -3 EV, you know that a single raw exposure will capture detail in both your highlights and shadows. You have just used your spot meter to perfectly optimize your histogram.

The terms diffraction and scattering are often used interchangeably and are considered to be almost synonymous. Diffraction describes a specialized case of light scattering in which an object with regularly repeating features (such as a diffraction grating) produces an orderly diffraction of light in a diffraction pattern. In the real world most objects are very complex in shape and should be considered to be composed of many individual diffraction features that can collectively produce a random scattering of light.

Why would you want to do something this risky? Well, for starters, your subject better be very important, and any foreground/background better be a lot less important.

Explore how a beam of light is diffracted when it passes through a narrow slit or aperture. Adjust the wavelength and aperture size and observe how this affects the diffraction intensity pattern.

Pro Tip: If you’re using a wide-angle lens and your subject is small enough that your spot meter can’t accurately measure it without the background affecting the reading, try zooming in when you meter if you have a constant-aperture zoom lens. Alternatively, you’ll have to learn to compensate for lighter or darker backgrounds manually.

Until now, I have been describing how to use spot metering as part of a manual exposure technique. In other words, you’re still totally in charge of your exposure, and you glance at your exposure meter for input when you need to change your shutter speed or aperture, etc.

As long as your shadows aren’t too dark, all you have to do is under-expose your main subject by, say, 3-4 EVs, and then use raw processing in post-production to recover that shadowy subject.

As a general rule with all modern digital cameras and RAW image capture, as long as your meter doesn’t go completely off the scale when spot metering a highlight or shadow, you’ll be okay.

Since every camera make and model can be different, just familiarize yourself with your own camera’s menu; look for a tab or page dedicated to metering or exposure.

UsedPhotoPro is the premier way to buy, sell and trade your used camera gear. Shop our huge selection of quality used cameras, lenses, ...

Of course, if you mostly shoot in flat light with no significant highlights or shadows, then the risk is low. In fact, you don’t really need spot metering in these conditions. All metering modes will give you almost the same reading.

One of the classic and most fundamental concepts involving diffraction is the single-slit optical diffraction experiment, first conducted in the early nineteenth century. When a light wave propagates through a slit (or aperture) the result depends upon the physical size of the aperture with respect to the wavelength of the incident beam. This is illustrated in Figure 3 assuming a coherent, monochromatic wave emitted from point source S, similar to light that would be produced by a laser, passes through aperture d and is diffracted, with the primary incident light beam landing at point P and the first secondary maxima occurring at point Q.

If you learn how to use spot metering, you will feel like you’ve mastered manual exposure all over again. It enables you to consistently get perfect exposures in one click — especially when the lighting conditions are extremely challenging.

From these equations it becomes apparent that the central maximum is directly proportional to λ/d making this maximum more spread out for longer wavelengths and for smaller apertures. The secondary mimina of diffraction set a limit to the useful magnification of objective lenses in optical microscopy, due to inherent diffraction of light by these lenses. No matter how perfect the lens may be, the image of a point source of light produced by the lens is accompanied by secondary and higher order maxima. This could be eliminated only if the lens had an infinite diameter. Two objects separated by a distance less than θ(1) can not be resolved, no matter how high the power of magnification. While these equations were derived for the image of a point source of light an infinite distance from the aperture, it is a reasonable approximation of the resolving power of a microscope when d is substituted for the diameter of the objective lens.

So, what if you switch your camera to aperture oriority, though? What if you want to use Auto ISO? Be careful! In these modes, your camera is now constantly changing your exposure based on that precise spot meter reading. If you’re not actively metering your subject perfectly at the moment you click your shutter, you’ll likely ruin your exposure.

where θ(1) is the angular position of the first order diffraction minima (the first dark ring), λ is the wavelength of the incident light, d is the diameter of the aperture, and 1.22 is a constant. Under most circumstances, the angle θ(1) is very small so the approximation that the sin and tan of the angle are almost equal yields:

This is known as polarized light. When two orthogonal light waves are in-phase, the resulting light will be linearly polarized. The relative amplitudes ...