If you had a simple lens made of a tube with one piece of optical glass at the front that focused the incoming light rays on a point at the back of the tube, the length of the tube would be the focal length of the lens. Modern lenses, however, use lots of different pieces of glass inside the casing to move light around before it hits the sensor and therefore focal length has nothing to do with the physical length of your lens. You can find two 85mm lenses that are completely different in size while, for example, the new NIKKOR Z 600mm f/6.3 VR S is less than 300mm in length.

Camera lenses are usually described by two main factors: one is the aperture or f-number (the maximum size of the hole where light gets through to the sensor, where the lower the number, the bigger the hole). The other is focal length, which is in millimetres. You will usually see lenses described by focal length first and then aperture, for example 85mm f/1.8.

Focal length

Usually between 70mm and 200mm, a telephoto lens is a popular choice for portraiture and weddings (especially an 85mm focal length) and at the longer end is great for wildlife where you can’t get too close to the subject. At the longer end, a telephoto lens gives you the freedom to shoot as an observer where the subject is unaware of the camera, and so is also great for fly-on-the-wall, reportage-style shooting. This is also the focal length range for many macro lenses.

Focaldistance vsfocal length

If you’ve ever seen a photo or a movie where the background is blurry while the target is still in focus (like the close-up of a yellow dandelion against a hazy field), you’ve encountered the practical effects of depth of field. The same is true for microscopy.

The more layers you have, the more detail you can include. It’s a fairly convenient way to overcome the limits of depth of field.

There are two types of lenses: primes, which have a fixed focal length, and zooms, where the focal length is variable. Zooms are super-handy as you often only have to carry one lens around that will be capable of shooting lots of different subjects, from landscapes to portraits, so it’s great for travel. Prime lenses, however, are usually lighter and are often available with larger apertures than zooms.

As angle of view goes down, magnification goes up. For example, a 24mm lens has a wide angle of view (around 84 degrees) and low magnification – perfect for sprawling landscapes. A 600mm lens has a very narrow angle of view and large magnification – great for taking close up shots of faraway wildlife (especially useful when you don’t want to get too close to a lion!).

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The focal length of a lens also affects the perspective of an image. With a long lens, perspective tends to be compressed, with objects in the background appearing closer to the subject in the foreground, whereas with a wide-angle lens the relative distance between two appears greater.

Lens choice can often be difficult, especially with so many options in the Nikon Z mount range (and access to another 300 or so Nikon F mount lenses with the FTZ II converter). So, here’s a quick guide to the different focal lengths and what they often get used for to help you.

The most important thing about focal length, however, is not what it is, but what it does. Focal length defines two main things about any lens: its magnification and its angle of view.

Camera lenses are usually described by two main factors: one is the aperture or f-number (the maximum size of the hole where light gets through to the sensor, where the lower the number, the bigger the hole). The other is focal length, which is in millimetres. You will usually see lenses described by focal length first and then aperture, for example 85mm f/1.8.

Any lens with a focal length of between 8mm and 24mm is usually described as an ultra-wide. You’ll be taking in a huge angle of view of what’s in front of the camera. These are lenses for getting in really close with your subject to create drama and are also used extensively for astrophotography. However, at really low focal lengths there will be significant distortion at the sides of the image where straight lines start to look curved. Ultra-wides are one the hardest lenses to master but, with effort, they can deliver incredible results.

Focal lengthcamera

Depth of field is a measure of how far your object can be away from the focal point while still remaining acceptably in-focus. It denotes the range of distance where objects are still sharp and detailed.

But there’s more. Depth of field determines what part of the image is in focus going from front to back. Lenses with longer focal length tend to have a shallower depth of field, meaning you can focus on and separate (or isolate) a particular object far away, whereas shorter lenses have a deeper depth of field, which means you can get more objects in focus throughout the image.

Try: NIKKOR Z DX 24mm f/1.7, NIKKOR Z 26mm f/2.8, NIKKOR Z 28mm f/2.8, NIKKOR Z DX 16-50mm f/3.5-6.3 VR, NIKKOR Z 35mm f/1.8 S

Some of the Dino-Lite digital handheld microscopes have the function Extended Depth Of Field EDOF this enables you to capture images that are fully in focus.

Focal lengthformula

From 24mm to 35mm, lenses are wide angle. These are beloved by landscape, interiors and architecture photographers, as well as being useful for street scenes and dramatic pictures of the night sky. Get close to your subject and you will accentuate the perspective in the scene. A wide angle is a great travel companion, allowing you to shoot landscapes, cityscapes, people and much more.

If you had a simple lens made of a tube with one piece of optical glass at the front that focused the incoming light rays on a point at the back of the tube, the length of the tube would be the focal length of the lens. Modern lenses, however, use lots of different pieces of glass inside the casing to move light around before it hits the sensor and therefore focal length has nothing to do with the physical length of your lens. You can find two 85mm lenses that are completely different in size while, for example, the new NIKKOR Z 600mm f/6.3 VR S is less than 300mm in length.

Also known as Z-stacking, this is a technique where you take a series of images of your sample at different focal depths, then use stacking software to compile the collection of layers into a single complete picture.

Try: NIKKOR Z 20mm f/1.8 S, NIKKOR Z 14-30mm f/4 S, NIKKOR Z 17-28mm f/2.8, NIKKOR Z DX 12-28mm f/3.5-5.6 PZ VR, NIKKOR Z 24mm f/1.8 S

Angle of view is how much of the scene your lens will capture from side to side (holding the camera horizontally). A wide angle of view takes in a lot, a narrow angle of view less. Magnification is how ‘close’ you get to the subject of an image with the lens, like a telescope.

35mm equivalentfocal length

From 35mm and 70mm, we have the ‘standard’ focal length, which is pretty close to what the human eye sees. Photographers talk about the ‘nifty fifty’ – a large aperture 50mm prime lens such as the NIKKOR Z 50mm f/1.8 S – because a 50mm lens is an ideal day-long companion, suitable for so many different types of shooting, especially in low light situations or indoors. This type of lens also creates a shallow depth of field and great bokeh blur.

Try: NIKKOR Z 180-600mm f/5.6-6.3 VR, NIKKOR Z 100-400mm f/4.5-5.6 VR S, NIKKOR Z 400mm f/4.5 VR S, NIKKOR Z 600mm f/6.3 VR S

focallength是什么

You should also bear in mind that focal length translates differently on a DX camera (such as the Nikon Z 30, Z 50 or Z fc) compared to an FX ‘full-frame’ camera because the sensor on a DX camera is 1.5 times smaller than the FX sensor. For example, if you put a 50mm lens on a DX camera, you will actually get the angle of view and magnification similar to an 75mm lens on an FX camera (because 50 x 1.5 =75).

Check out these images of the same scene shot from the same position but with focal lengths from wide angle 24mm to telephoto 180mm and you can see how the angle of view gets narrower as the magnification gets larger.

Depth of field (sometimes called depth of focus) dictates how much of your sample will be in sharp focus, in a vertical sense rather than horizontally.

A shallow depth of field will provide only a narrow band in which objects can be in-focus, while a deeper depth of field will allow you to see the details on objects much farther away from the focal point.

Moving closer or farther away from that focal distance will cause an object to become progressively blurrier as it moves out of focus.

FOV tofocal length

At 300mm and upwards, we have the super-telephoto range. This is most commonly used by sports and wildlife photographers, where it would be impossible to get close to the subject. At this range, and with such a narrow angle of view, it’s usually advisable to use a monopod or tripod to reduce camera movement (although Nikon’s in-camera vibration reduction (VR) and VR lenses can help with that), and also because lenses this size can be heavy to hold for long periods. Telephoto lenses can also be used with a teleconverter, which can double the focal length of the lens, giving you even more ‘reach’.

A larger depth of field will allow you to see more of your sample, or even allow you to view it at an angle due to the larger focal area. For this reason, it’s particularly useful for electronics inspection, repairs or soldering.

Try: NIKKOR Z 70-180mm f/2.8, NIKKOR Z 85mm f/1.8 S, NIKKOR Z 135mm f/1.8 S Plena, NIKKOR Z 70-200mm f/2.8 S, NIKKOR Z DX 50-250mm f/4.5-6.3 VR

Every lens, whether in a camera or a microscope, has a particular focal point – a set distance from the lens where everything is in perfect focus.

You can increase the depth of field by switching to a lower magnification or numerical aperture (NA), but there are the obvious drawbacks of lower resolution and reduced magnification.