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For example, if I use a short focal length in portrait photography, parts of the body that are closer to me can be unflatteringly emphasized. On the other hand, in genres like landscape photography, it’s more common to see images taken with a wide-angle view, not only to capture the entire scene in a single image but to emphasize elements in the foreground.

Microscope objective lenses are typically the most complex part of a microscope.  Most microscopes will have three or four objectives lenses, mounted on a turntable for ease of use. A scanning objective lens will provide 4x magnification,  a low power magnification lens will provide magnification of 10x, and a high power objective offers 40x magnification. For high magnification, you will need to use oil immersion objectives. These can provide up to 50x, 60x, or 100x magnification and increase the resolving power of the microscope, but they cannot be used on live specimens.

Understanding your camera’s zoom ability helps you know what sort of pictures you can reasonably expect to take. Just like with an interchangeable lens camera (ILC), the camera will have a focal length range that tells you about the properties of the lens.

Hi Anne, it totally depends on the sensor size of the camera. For example, if you’re using a Micro 4/3 sensor camera with the 60mm f2.8 lens, since the crop factor is 2x, it means that you’re cropping the image the double, so technically it’s like shooting at 120mm focal length. Hope it’s clear. 🙂

Understanding focal length in photography can feel a bit overwhelming when trying to account for all of the ways it changes the properties of an image. Below, I’ve outlined the focal length differences across the major fields of view.

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Apart from the definition of focal length in photography as the measurement in millimeters from the lens to the image sensor, focal length has a direct impact on the angle of view, which is a static property of the lens in question but is impacted by the sensor crop factor.

Most microscopes rely on background illumination such as daylight or a lightbulb rather than a dedicated light source. In brightfield illumination (also known as Koehler illumination), two convex lenses, a collector lens and a condenser lens,  are placed so as to saturate the specimen with external light admitted into the microscope from behind. This provides a bright, even, steady light throughout the system.

Focal length determines many of the characteristics of the photos you can take as well as the physical dimensions of the lens.

As we step into normal focal lengths, which are closer to our human vision (like 35mm), this effect is subtle to invisible. However, once we hit telephoto angles of view, the background appears to be closer to the subject. This effect increases as your lens mm does.

Focal length comparisons are incomplete without the infamous crop factor discussion. Nowadays, we have APS-C, Micro 4/3rds, medium format, and full-frame, all of which use a lens focal length description centered around 35mm film gear. While this made sense when the digital revolution began, it’s often simply confusing to parse nowadays.

CameraFOV calculator

Focal length in photography comes up far more often than focal distance, which is an entirely different property of a lens. Focal distance is related to focal length but is not dependent on it.

Historically microscopes were simple devices composed of two elements. Like a magnifying glass today, they produced a larger image of an object placed within the field of view. Today, microscopes are usually complex assemblies that include an array of lenses, filters, polarizers, and beamsplitters. Illumination is arranged to provide enough light for a clear image, and sensors are used to ‘see’ the object.

The field of view (FOV) of a microscope is simply the area of the object that can be imaged at any given time. For an infinity-corrected objective, this will be determined by the objective magnification and focal length of the tube lens. Where a camera is used the FOV  also depends on sensor size.

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By twisting the barrel of a zoom lens, you can adjust the focal length and field of view of your lens, which affects depth of field, distortion, and all other aspects of your image.

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How focal length works is by describing each lens in terms of millimeters (lens mm). This description is a hard-physical reality of the lens in question, no matter the brand, format, or aperture.

Photos taken with a long focal length look more “compressed” as compared to shorter focal lengths, and allow you to capture subjects from a farther distance without losing image quality.

One key to understanding focal length is recognizing how the look of the image changes using lenses with different focal lengths. Using a wide-angle lens, foreground elements are emphasized while background elements are pushed even further away, looking smaller than they really are.

The eyepiece or ocular lens is the part of the microscope closest to your eye when you bend over to look at a specimen. An eyepiece usually consists of two lenses: a field lens and an eye lens. If a larger field of view is required, a more complex eyepiece  that increases the field of view can be used instead.

Telephoto lenses are those beyond 50mm. These lenses are also physically longer than wide and normal lenses. The field of view is smaller but you gain significant reach.

The simplest focal length definition is a description of the distance between the center of a lens and the image sensor when the lens is focused at infinity.

Wide-angle lenses or short focal lengths offer a great opportunity for shooting landscapes, cityscapes, Milky Way photography, and Northern Lights photography.

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Focal length

Focal length and depth of field are different properties of both a lens and sensor but are somewhat related. Depth of field is how much of a scene is in sharp focus. How narrow or wide the depth of field is, is an interaction between focal length, sensor size, subject distance, and aperture value.

Focal length touches upon many elements of the photography basics; composition, aperture, depth of field, and other aspects all shift when taking focal length into account! Each twist of the zoom ring or swap of a prime lens is a shift in the interplay of focal length and your creative vision.

Focal length can feel a little abstract when looking at one lens versus another. One of the easiest ways to understand focal length is to look at images that use the lenses in question! To wrap up, here are some focal length examples for you to consider:

When you look at the focal length of the lens in question and you see a number below 35mm, you know you’re looking at a short focal length.

A lens focal length that’s greater than 50mm is considered a long focal length. This view is narrower than the normal view we’re accustomed to when paying bare attention. An image taken with a 100mm telephoto lens will have a much smaller section of coverage than a normal or wide-angle field of view.

Camera zoom lenses allows to change the angle of view without moving and are more versatile than prime lenses. The downside is that maximum apertures are not usually as fast as the fastest prime lenses. For example, an f/1.4 zoom would be ridiculously expensive and massive.

Focal length is one of the main considerations when buying and selecting a lens. And understanding how focal length works is essential to capturing the photos you want. Otherwise, you’ll be choosing lenses with random angles of view that only serve to confuse you with choices.

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Zoom lenses are what anyone who has ever picked up a camera in recent times is familiar with. In fact, they are so common that I often find non-photographers get baffled when I hand them a camera with a prime lens attached!

While a magnifying glass consists of just one lens element and can magnify any element placed within its focal length, a compound lens, by definition, contains multiple lens elements. A relay lens system is used to convey the image of the object to the eye or, in some cases, to camera and video sensors.

Photographs taken with short focal lengths show distortion in certain elements; those closer to the foreground are magnified whereas all the elements in the background will show a diminished perspective.

The optical performance of an objective is dependent largely on the optical aberration correction, and these corrections are also central to image quality and measurement accuracy. Objective lenses are classified as achromat, plan achromat, plan semi apochromat, plan apochromat, and super apochromat depending on the degree of correction.

Please note that lens compression is not related to the lens, but to the distance from the subject (Ex. You can achieve the same field of view and perspective shooting an element with a short focal length like 20 mm or cropping the same area from a 50 mm as long as both images are taken from the same distance).

Remember that if you tend to specialize in any type of photography, it’s crucial to understand how focal length affects your image so you can have a better idea of what sort of lenses you should be shopping with, as well as the impact they have on a subject and background. You can download my PDF photography guide to get more information about this.

In practical terms, angle of view and field of view are used interchangeably in photography to indicate the way our cameras “see” the scene, and using a short focal length or a long focal length will change drastically the field of view or the amount of the scene that is photographed.

Focal length is the physical measurement of distance between the lens and the imaging sensor when the subject is in focus.

Focal length differences are especially stark with wide-angle lenses. Each mm of width makes a visible difference, unlike telephoto lenses where it takes several mm to be easily noticeable.

A microscope is an optical device designed to magnify the image of an object, enabling details indiscernible to the human eye to be differentiated. A microscope may project the image onto the human eye or onto a camera or video device.

At Avantier we produce high quality microscope objectives lenses, ocular lenses, and other imaging systems. We are also able to provide custom designed optical lenses as needed. Chromatic focus shift, working distance, image quality, lens mount, field of view, and antireflective coatings are just a few of the parameters we can work with to create an ideal objective for your application. Contact us today to learn more about how we can help you meet your goals.

There are great apps and websites that allow you to calculate depth of field for a given focal length, aperture, subject distance, and sensor.

In the relation between focal length and depth of field, when all other values are equal, short focal lengths (or wide angles of view) have deeper depth of field relative to long focal lengths (narrow fields of view). Thus, the longer the focal length, the farther the hyperfocal distance will be.

The parfocal length of a microscope is defined as the distance between the object being studied and the objective mounting plane.

The working distance of a microscope is defined as the free distance between the objective lens and the object being studied. Low magnification objective lenses have a long working distance.

By taking the crop factor of a specific sensor and multiplying it by the field of view, we get the field of view as if it were viewed in the 35mm standard.

It’s important to consider that focal length is a static property of a lens that’s true regardless of crop factor; for example, a 16mm APS-C lens is a 16mm lens even if it has a 24mm equivalent field of view in a full-frame camera. We’ll see + in-depth info about this below.

Can you help me understand why a lens advertised as 60 mm f2.8 macro is described as 120mm and equivalent to 35mm focal length? I am completely bewildered.

The angle of view in photography is the area of the scene that is captured by the camera sensor. This area is described in degrees of coverage in front of the camera.

Focus distance

Both the objective lens and the eyepiece also contribute to the overall magnification of the system. If an objective lens magnifies the object by 10x and the eyepiece by 2x, the microscope will magnify the object by 20. If the microscope lens magnifies the object by 10x and the eyepiece by 10x, the microscope will magnify the object by 100x. This multiplicative relationship is the key to the power of microscopes, and the prime reason they perform so much better than simply magnifying glasses.

As you can see, the focal length we choose affects the final image. Also, the field of view and lens distortions fundamentally affect the type of photography you do.

Focal length also relates to field of view (also called angle of view) because changing the focal length changes the field of view – I’ll explain more about how the field of view and focal length of a lens interact with each other in greater detail below.

Lens focal length is a surprisingly nuanced topic! A simple physical measurement leads to so many considerations that go into how an image is composed. From the angle of view to depth of field, no aspect of a photograph goes untouched.

Normal or standard lenses have a focal length between 35mm and 50mm in full-frame terms. When comparing across formats, they have a field of view that’s also equivalent to a normal lens. These lenses best duplicate how we see the world.

I emphasize that we get the field of view because again, lens focal length is inherent to a lens. A 25mm Micro 4/3rds lens has a 50mm full-frame field of view. However, it remains a 24mm lens with the distortion properties of a 24mm lens; it’s not magically a 50mm lens.

This concept can be complicated when the crop factor and the field of view come into play since we began to ask what is the equivalence of the focal length of a lens using it in a camera with a different sensor format.

A prime lens can’t be adjusted and its focal length and field of view are fixed. The trade-off for flexibility in focal length is usually a wider aperture and better image quality because the prime lens can be optimized for its angle of view. Usually but not always; some top-quality zoom lenses nowadays are absolutely comparable to prime lenses in terms of quality for a given focal length.

A reflective objective works by reflecting light rather than bending it. Primary and secondary mirror systems both magnify and relay the image of the object being studied. While reflective objectives are not as widely used as refractive objectives, they offer many benefits. They can work deeper in the UV or IR spectral regions, and they are not plagued with the same aberrations as refractive objectives. As a result, they tend to offer better resolving power.

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Macro lenses have the highest magnification due to their unique construction, which reduces the focal distance they operate within and allow you to focus in very close subjects.

There are some important specifications and terminology you’ll want to be aware of when designing a microscope or ordering microscope objectives. Here is a list of key terminology.

Standard lenses or medium focal lengths are suitable for shooting many different genres like portrait, street photography, landscape, etc.

While most microscope objectives are designed to work with air between the objective and cover glass, objectives lenses designed for higher NA and greater magnification sometimes use an alternate immersion medium. For instance, a typical oil immersion object is meant to be used with an oil with refractive index of 1.51.

Super telephoto lenses have very different focal lengths, ranging from 300mm and beyond. When considering focal length and field of view, crop factor is incredibly important because you can gain significant amounts of reach using a crop sensor like Micro 4/3rds.

Depth of field

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An microscope objective  may be either reflective or refractive. It may also be either finite conjugate or infinite conjugate.

A basic achromatic objective is a refractive objective that consists of just an achromatic lens and a meniscus lens, mounted within appropriate housing. The design is meant to limit the effects of chromatic and spherical aberration  as they bring two wavelengths of light to focus in the same plane. Plan Apochromat objectives can be much more complex with up to fifteen elements. They can be quite expensive, as would be expected from their complexity.

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There are two major specifications for a microscope: the magnification power and the resolution. The magnification tells us how much larger the image is made to appear. The resolution tells us how far away two points must be to  be distinguishable. The smaller the resolution, the larger the resolving power of the microscope. The highest resolution you can get with a light microscope is 0.2 microns (0.2 microns), but this depends on the quality of both the objective and eyepiece.

Although today’s microscopes are usually far more powerful than the microscopes used historically, they are used for much the same purpose: viewing objects that would otherwise be indiscernible to the human eye.  Here we’ll start with a basic compound microscope and go on to explore the components and function of larger more complex microscopes. We’ll also take an in-depth look at one of the key parts of a microscope, the objective lens.

These lenses take on an expansive field of view that’s wider than what we normally pay attention to. An image taken with a 15mm lens will seem abnormally expansive, taking, for example, an entire landscape with ease.

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In modern microscopes, neither the eyepiece nor the microscope objective is a simple lens. Instead, a combination of carefully chosen optical components work together to create a high quality magnified image. A basic compound microscope can magnify up to about 1000x. If you need higher magnification, you may wish to use an electron microscope, which can magnify up to a million times.

Standard focal lengths range from 35mm to 50mm depending on the type of camera sensor. The field of view provided by standard focal lengths approximates the field of view of the human eye.

Focal distance is the distance between the subject you are focusing to the camera sensor. Lenses that can work at close focal distances have higher magnification (or reproduction ratios) relative to lenses that need you to stay far from the subject.

So what are the mm in lenses? The key is to understand that focal length is calculated by measuring the distance from the optical center of the lens to the image sensor, and this distance is measured in mm. The longer the focal length, the physically longer the lens will be. Lenses with a wider view will have a shorter focal length and are physically shorter by comparison.

Hello Dan! I’m Mariam from Mauritius. I wanted to thank you for this deep explanation on focal length! I just bought my first camera and your article helped me so much!

Numerical aperture NA denotes the light acceptance angle. Where θ is the maximum 1/2 acceptance ray angle of the objective and n is the index of refraction of the immersive medium, the NA can be denoted by

These super long focal lengths are usually more expensive but they allow to capture subjects from a very far distance like in sports and wildlife photography, and to shoot other genres like deep astrophotography.

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However, using a prime lens means that you have to physically move in order to create a given field of view. Which kind of lens is better is an age-old question and really comes down to your own personal preferences!

Refractive objectives are so-called because the elements bend or refract light as it passes through the system. They are well suited to machine vision applications, as they can provide high resolution imaging of very small objects or ultra fine details. Each element within a refractive element is typically coated with an anti-reflective coating.

While we do go into some depth here and there are some confusing elements surrounding the topic, I’m confident that by the end of this article, you’ll have a solid foundation on what is focal length and how it relates to digital photography.

A basic compound microscope could consist of just two elements acting in relay, the objective and the eyepiece. The objective relays a real image to the eyepiece, while magnifying that image anywhere from 4-100x.  The eyepiece magnifies the real image received typically by another 10x, and conveys a virtual image to the sensor.

2024520 — The darkfield microscope is a conventional microscope, in this microscope, the specimen appears as bright against a dark background.

Fixed lens camera focal lengths can also be multiplied by the crop factor of the sensor in order to compare it across formats. This is generally only important if you’re trying to replicate a look across focal lengths; i.e. you know you want a 135mm full-frame portrait style.

Hopefully, this article on explaining focal length has clarified some of the stickier aspects of the topic. Especially where they affect wide, normal, and telephoto fields of view.