Reducing Camera Focus Length: Tips For Better Photography

Photographers often want to decrease the focal length of their camera lens to achieve a wider angle of view and lower magnification. This is especially useful for close-up photography, where the minimum focus distance of longer lenses can become a problem. One way to achieve this is by using an extension tube, which is a hollow tube that increases the distance between the lens and the camera sensor, allowing the lens to focus closer. Another method is to use a focal reducer or speed booster, which makes the image circle of a lens wider. Additionally, certain techniques such as the hyperfocal-distance shortcut or the quick-and-dirty method can help photographers achieve the desired focus distance.

Use a focal reducer or speed booster

One way to decrease the focal length of your camera is to use a focal reducer or speed booster. This is a type of lens adapter that allows you to mount a full-frame lens onto a camera with a smaller sensor, such as an APS-C or micro four-thirds mirrorless camera.

Focal reducers or speed boosters contain optical elements that change the effective focal length of the lens. They achieve this by reducing the image magnification, resulting in a wider field of view. For example, a 0.7x focal reducer will increase the field of view of a 50mm lens, making it equivalent to a 35mm lens. This means that you can achieve a similar field of view to a full-frame camera, even with a smaller sensor.

In addition to changing the focal length, focal reducers or speed boosters also increase the maximum aperture of the lens. For instance, an F2.8 lens would become an F2.0 optic, allowing for better low-light performance and lower ISO sensitivity. This is because the speed booster concentrates the light from the lens onto the smaller sensor, resulting in a brighter image.

It's important to note that using a focal reducer or speed booster can affect image sharpness and introduce optical aberrations due to the additional optical elements between the subject and the sensor. However, the impact on image quality is generally minimal and may be worth the trade-off for the increased versatility and improved low-light performance.

When purchasing a focal reducer or speed booster, it's essential to ensure compatibility with your specific camera and lens setup. Different adapters are available for various lens mounts and camera systems, so make sure to select the correct model for your equipment.

Use an extension tube

An extension tube is a hollow cylinder that fits between your camera and lens, moving the lens further from the sensor. This allows your lens to focus more closely, increasing magnification. The thicker the extension tube, the higher the lens magnification as you can move the lens closer to the subject while still achieving focus.

Extension tubes are particularly useful for macro photography, as they can turn any lens into a macro lens. They are also relatively inexpensive, as they contain no optical elements.

When using extension tubes, you will no longer be able to focus to infinity. You will also experience a loss of light, requiring a longer exposure time. The effective f-stop of the lens will change, and you may experience vignetting at wide apertures and stack heights.

You can buy extension tubes from your camera manufacturer, or opt for cheaper third-party extension tubes. The latter are a good option if you are on a budget, but be aware that the cheapest extension tubes do not have electrical contacts, meaning you will not be able to autofocus or control your aperture electronically.

Use a wide-angle lens

Using a Wide-Angle Lens to Decrease Focal Length

A wide-angle lens is a lens with a focal length of 35mm or shorter, which gives you a wide field of view. The wider your field of view, the more of the scene you’ll be able to see in the frame.

When to Use a Wide-Angle Lens

Wide-angle lenses are a staple in most landscape photographers’ kits, popular for their ability to capture sweeping vistas and starry nights. They are also frequently used in architecture and real estate photography to make a space feel more expansive and impressive. The classic focal length that street photographers use is 35mm, as it approximates how you see the world with your naked eye. Wide-angle lenses are also well-suited for travel photography, as the short focal length gives you more versatility to capture a multitude of scenes.

Types of Wide-Angle Lenses

Any lens with a focal length under 35mm is considered a wide-angle lens, but a lens with a focal length under 16mm is an ultra-wide-angle lens. You can generally place wide-angle lenses into one of three subcategories:

• Ultrawide-angle lens: Focal lengths under 16mm fall into this category, and they’re generally considered specialist lenses, used only for certain circumstances, such as astrophotography scenes where you want to capture the whole Milky Way band. Fish-eye lenses are a type of ultrawide lens that has a full 180-degree field of view, and as a result, has a distinct, circular, distorted look.
• Wide-angle lens: Ranging from 16mm to 24mm, these lenses are wide without falling into fish-eye territory, where extreme stretching of the frame occurs. The sweet spot for most landscape photography lies between these focal lengths, but you can use this range for any number of everyday uses too.
• Standard wide-angle lenses: Focal lengths from 24mm to 35mm generally get labelled as “standard.” This is a great range for getting wide shots without too much distortion. But if you want a lens that really opens up tight spaces, such as cityscapes or small rooms, you might want to go wider.

Pros and Cons of Wide-Angle Lenses

Wide-angle lenses can bring with them the temptation to point and shoot at the entire scene, which can make your image lack a focal point or effective composition. With a larger field of view, you need to arrange more elements, which introduces more room for error in the details.

Another issue to watch out for when using a wide-angle lens is distortion. Barrel distortion, where straight lines appear to bow outward, will often show up in your photos the wider you go. Be especially mindful of this when you photograph people, and watch out for objects at the edges of your frame.

Despite these challenges, wide-angle lenses are powerful tools of expression, providing options that no other lens type is capable of.

Adjust the distance between the lens and the camera's sensor

Adjusting the distance between the lens and the camera's sensor is a viable method to decrease the focal length. This method is based on the relationship between the focal length, the distance from the lens to the object, and the distance from the lens to the image.

When focusing on distant objects, the rear principal plane of the lens is positioned at a distance equal to the focal length from the image sensor. However, to focus on closer objects, the lens must be adjusted to increase the distance between the rear principal plane and the sensor. As the distance from the lens to the object decreases, the distance from the lens to the image must increase to maintain focus.

For example, consider a lens with a focal length of 50 mm. To focus on a distant object, the rear principal plane of the lens should be positioned 50 mm away from the sensor. Now, if you want to focus on an object 1 metre away, the lens must be moved slightly farther from the sensor, resulting in a distance of approximately 52.6 mm.

It is important to note that this method of adjusting the distance between the lens and the sensor has limitations. The working distance, or the distance from the lens to the object, may be restricted in certain situations. Additionally, lenses with shorter focal lengths (less than 12 mm) tend to produce images with significant distortion. If image quality is a priority, it is advisable to use a longer focal length lens and adjust the working distance accordingly.

Use a teleconverter

A teleconverter is a magnifying secondary lens that is typically attached between a camera body and an existing (primary) compatible lens. The purpose of a teleconverter (TC) is to increase the effective focal length of the primary lens, which unfortunately comes at the cost of decreased sharpness and reduced maximum aperture (due to loss of light). The magnification effect of a teleconverter and its effect on maximum aperture depends on its multiplication factor, which varies from 1.2x all the way to 3.0x (the most common ones are typically 1.4x and 2.0x).

For example, if one uses a 300mm f/2.8 prime telephoto lens, a 2.0x teleconverter will double its focal length and decrease its maximum aperture by two full stops, which will make it a 600mm f/5.6 lens. Teleconverters also have the same effect on zoom lenses – the whole zoom range will get magnified and their maximum aperture decreased. For example, a 1.4x TC would make a 70-200mm f/2.8 into a 98-280mm f/4.0 lens.

Teleconverters are typically made in 1.4x, 1.7x, 2x and 3x variants, with 1.4x and 2x being the most common. A 2x teleconverter doubles the apparent focal length of a given lens. Teleconverters also decrease the intensity of the light that reaches the film plane (or sensor) by the square of its magnification. A 2x teleconverter reduces the light to 1/4, doubles the focal ratio and halves the resolution of the master lens it is connected to.

The obvious advantage of using teleconverters is extended reach at a relatively low cost. This becomes especially true when utilizing high-quality prime lenses with a variety of teleconverters. For example, the Nikon 300mm f/2.8G VR II is a phenomenal lens that works well with all three modern Nikon teleconverters, TC-14E III (1.4x), TC-17E II (1.7x) and TC-20E III (2.0x). With these teleconverters, the 300mm f/2.8G can transform into 420mm f/4, 510mm f/4.8, and 600mm f/5.6 lenses, which makes it a very versatile option for sports and wildlife photography. The 1.4x and 1.7x teleconverters have little impact on autofocus performance and sharpness because the lens was specifically optimized in its design to couple well with these teleconverters.

The 2.0x teleconverter certainly does degrade AF performance and especially sharpness, but stopping down the lens by a full stop still makes it quite a usable setup. In essence, this allows the 300mm lens to cover three additional focal lengths from 420mm all the way to 600mm!

Another advantage of teleconverters is that they do not affect the minimum focus distance of a lens. Teleconverters do not affect the optical characteristics of lenses – they only magnify the centre portion of the frame. This means that if one were to use a telephoto lens with a short minimum focus distance, it could be used as an excellent option for extreme close-up/macro photography as well.

However, teleconverters per se have some significant downsides. The biggest negative drawback of teleconverters is their impact on overall sharpness. The biggest negative drawback of teleconverters is their impact on overall sharpness. As you can already tell, some teleconverters have serious disadvantages that you have to keep in mind. Aside from lens compatibility and cross-brand compatibility issues, teleconverters decrease the overall sharpness of the primary lens, magnify its lens aberrations, and reduce autofocus speed and accuracy. This is especially true for 2.0x and longer teleconverters.

Frequently asked questions