There are two main types of lenses used in photography: concave and convex. Each has a different effect on incoming light rays.

Figuring out the equivalent crop factor for different camera formats is a handy way to quickly convert the size of media you can work with.

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In addition to the focal length calculator, I’ll also cover how to convert your lens’s focal length into its x-times optical zoom.

Fortunately, there’s a straightforward way this can be achieved, using a quick formula based on the full-frame diagonal size compared to the smaller sensor’s diagonal size.

Master the technique of calculating the focal length of a lens with our easy-to-follow guide, essential for choosing the right lens for your photography needs.

On the other hand, convex lenses are thicker in the middle and bring light to a point to create a positive object distance and an inverted image.

For example, if an object is 50cm away from a lens and produces an image of 100cm, the focal length of the lens will be 33.3cm.

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Whether using a converging lens or diverging lens, the focal lengths represent the distance from the optical center to the image plane in the camera.

The more you experiment with different focal lengths, the easier it will be to spot images taken with a longer or shorter focal length.

By developing the ability to guess what focal length has been used for an image, you can further understand how lenses control depth and perspective.

To do so, you’ll need to factor in the minimum and maximum focal length of the lens’s zoom capabilities in this simple equation:

Unless you’re using a fixed focal length prime lens, you may wish to figure out how to convert your lens’s focal length to its optical zoom.

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Andy Dilks is an experienced landscape photographer and former games industry veteran. When he isn’t taking photos or reviewing the latest tech gadgets, you can find him hiking and wild camping in the Peak District.

Finding the focal length of a specific camera lens is easy, and is typically printed directly on the barrel of the lens for ease of access.

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At the same time, bear in mind that crop factor may be something to consider when working out the optical zoom capabilities of a given lens and sensor combination.

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Some of the more common crop factors to be aware of that relate to specific camera manufacturer sensors include the following:

Knowing the focal length of a given lens is essential for selecting the right lens and image distance for a particular shot.

Ultra-wide-angle lenses, as well as fish-eye lenses, create a sense of distortion in horizon lines and other straight lines that other lenses won’t produce.

For example, wide-angle lenses create a sense of space and immersion, while telephoto lenses work well to flatten perspective.

If you don’t have the mathematical know-how or time to calculate focal length, these statistics can help you save time and cut to the information you need.

Most lenses include information about their focal length on the outside of the lens barrel, as well as being listed on the product’s specifications.

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Typically, this is indicated by a Φ symbol located on the top plate of the camera’s body, with different focal lengths used to accomplish different shots.

The equivalence of a 10x zoom in millimeters is dependent on the initial starting point and whether you’re using a crop or full-frame camera.

It’s important to bear in mind that different brands sometimes have different crop factors for their various camera sensors.

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Another way to calculate focal length is by using the lens equation technique, for which you’ll need to know the distance an object is away from the lens and the image distance.

Most photographers who are dedicated to improving their skills will spend a lot of time checking out work from professionals and their photography peers.

Concave lenses are thicker on their edges and cause light to diverge away from the focal point while having a negative focal length.

Master the technique of calculating the focal length of a lens with our easy-to-follow guide, essential for choosing the right lens for your photography needs.

If you’re using a prime lens, the focal length will be fixed to the lens’s native setting, with no adjustable scale to work with.

Conversely, super telephoto lenses bring the foreground and background elements together and can be used to create interesting patterns and textures.

If you’re using a zoom lens, the minimum and maximum focal distance should be printed on the barrel’s zoom ring, indicating your position between these focal lengths.

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This allows you to accurately adjust the focal length while framing your shot, while also understanding how much zoom leeway you have either way.

If you’re using a zoom lens, you can also find the range of your lens’s focal length on the zoom ring located in the middle of the barrel.

A larger zoom lens with a coverage of 18 – 200mm would have a larger optical zoom coverage, with the equation revealing this as an 11x optical zoom.

It’s a great way to gain inspiration and come up with new insights into the shooting process, composition, and technical considerations.

This information can be useful when shooting wildlife or sports photography to give a clearer idea of which lens is needed to reach the action.

At 35mm equivalent, a 20x optical zoom will provide a focal length of 26.8mm to 576mm, giving plenty of scope for long-distance shots.