What isfocal lengthof lens

As you can see, this Sigma lens has a 67mm diameter; therefore, if you are looking for filters or a new lens hood, you would need to make sure you are purchasing ones that fit a 67mm diameter lens.

What is thefocal lengthof a lens Physics

In some cases with zoom lenses, you will see two numbers following the "1:", as in the example below, which shows an aperture range of 1:3.5-4.5.  The aperture changes with the zoom's focal length between f/3.5 and f/4.5.

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In general, the letters on the lens are simply used to describe specific features, such as the type of technology the lens uses, the type of camera to which the lens can be mounted, or the grade of the lens.

FOV tofocal lengthcalculator

Anna Gay is a portrait photographer based in Athens, GA and the author of the dPS ebook The Art of Self-Portraiture. She also designs actions and textures for Photoshop. When she is not shooting or writing, she enjoys spending time with her husband, and their two cats, Elphie and Fat Cat.

Let's look at an 18-55mm lens as an example.  The pair of numbers refers to the focal length range or that particular lens.  You can use this lens at its widest angle (18mm), the most zoomed (55mm), or anywhere between 18mm and 55mm.

If you are new to photography, you might find yourself wondering what all of the different numbers, letters, and symbols on your camera lens mean.  They may seem complicated at first, but its really easy to understand once explained.

Do you have any questions or comments about Understanding Your Lens? Leave us a comment below - we would LOVE to hear from you!  And PLEASE SHARE our tutorial using the social sharing buttons (we really appreciate it)!

Focal length unitscomparison

Image Stabilization (IS - Canon) and Vibration Reduction (VR - Nikon) is a lens technology designed to reduce the effect of camera shake.  Not all lenses come equipped with this technology, but you will know if your lens does if you see the abbreviations "IS" or "VR" near the glass on the lens or you see "Image Stabilization" or "Vibration Reduction" on the body of the lens.

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Focal lengthof lens formula

Anna Gay is a portrait photographer based in Athens, GA and the author of the dPS ebook The Art of Self-Portraiture. She also designs actions and textures for Photoshop. When she is not shooting or writing, she enjoys spending time with her husband, and their two cats, Elphie and Fat Cat.

Focal length unitsnikon

Irradiance is the power received by a surface per unit area, W/cm2. Radiant exposure (fluence) is the energy received by a surface per unit area, J/cm2. We already know that energy is power multiplied with a unit time. Fluence is the most common adjustable treatment parameter you will encounter in photothermal laser therapy. The question now is how much fluence do I need to create a desired result? There is no short answer to this. It is not only the amount of energy that you put into the skin over a given area that is important. More important is what happens with the energy the moment it hits the skin. The fat and water content of the skin determine scattering for a large part. This means that the beam gets broken up in many smaller beams and various factors may cause it to increase or dilute the energy density in the area you need it. The same treatment will have a different result depending on the hydration level of the skin and the quantity of fat present in the treatment area. Apart from this, the density of target chromophores in the path of the laser beam also effects the fluence needed. The spot size has a great influence on penetration depth and it has been shown in various studies that the larger the spot size is, the deeper penetrations the beam has. This is because of the phenomenon that scatter away from the target area mainly appears on the outer edge of the beam. Thus, the larger the spot size the more energy remains within the target area and it leads to deeper penetration depth. Traditionally, high fluence laser for hair removal range up to 120 J/cm2. However, this has been challenged in various ways lately. Low fluence, high frequency diode lasers have become quite popular in the name of “pain-free” hair removal. This is where 10 J/cm2 to 20 J/cm2 are rapidly pulsed while the therapist constantly glides the hand piece over a larger area of 10 cm2 to 15cm2. It is believed that ‘staging’ of the heat will lead to destruction of the dermal papilla. From studies, it seems that the low fluence, high frequency motion technique has an advantage on areas with thick dark hair due to the reduction in pain. However, this seems not to be the same all over the body and in particular not the bikini area. The larger the area over which you spread the energy, the lower the energy will be at any specific point within that area. If you have thick dark hair, which is usually the case for at least the first two treatments, the higher chromophore content requires less energy to create sufficient heat to kill the dermal papilla. Therefore, it seems that it may be beneficial to start a hair removal treatment series with a low fluence, high frequency technique and switch midway over to more traditional high fluence technique. The depth of the target chromophore also determines the fluence require. If you treat a pigmented lesion on the epidermis, much less energy is required than treating a vein in the dermis. The deeper the target chromophore the more important a higher fluence become. The penetration depth of a laser beam is greatly determined on the machine side by the fluence in combination with the spot size. Capability to generate a high energy level over a large enough area, thus high fluence is one of the factors that is greatly reflected in the purchase price of a machine. The luxury of a large spot size with sufficient energy for hair removal comes at a high price. Most manufacturers of low-end equipment tries to disguise this by eliminating fluence (J/cm2) as a parameter from the user interface and instead goes with energy (J) only.

Focal length unitsexplained

The circle with a line through it is a diameter symbol.  So when you see this symbol followed by a number, it refers to the diameter of your lens.

If you are unsure what any of those other abbreviations mean, a quick Google search should tell you exactly what you have.

These letters tell you what type of Autofocus motor is in your lens. USM = Ultrasonic Motor and HSM = Hypersonic Motor.  They are the same thing, but each manufacturer uses different terminology.

Sometimes, you will see II at the end of the lens name/description.  This means it is the second generation of that particular lens.  Popular lenses are often improved with a newer version and updated features so they can be sold again to photographers who want to upgrade.

Focal length unitsin mm

Not all lenses have the same diameter, and knowing the diameter of YOUR lens is essential when purchasing lens filters and lens hoods.

On the side of your DSLR lens, you will see the letters AF/MF (Canon) or M+A/M (Nikon) with a small white line and switch beneath.  This switch will allow you to change your lens from Autofocus to Manual focus:

The number, letters, and symbols described above are the most common, but there are plenty of less common abbreviations used by different lens manufacturers.

When you see a 1: followed by a number, this represents the lens's maximum aperture or how wide the opening on your lens is when you take a photo.  The smaller the number, the wider the opening (which lets in more light).

So, for this lens, when zoomed out at 10mm, the widest aperture is f/3.5, but when zoomed in to 22mm, the widest possible aperture is f/4.5:

In this post, I will show you a few examples of standard lenses and explain some of the most important numbers and letters you have on your lens.

Millimeters, or "mm" for short, is the standard unit of measurement for the focal length of a lens.  So when you see "mm" following a number or a pair of numbers on a lens, you will know that the number refers to the focal length (single number) or focal range (pair of numbers).