Many digital camera sensors— especially older cameras with interchangeable lenses— have anti-aliasing or optical lowpass filters (OLPFs) to reduce response above Nyquist. Anti-aliasing filters blur the image slightly, i.e., they reduce resolution. Sharp cutoff filters don’t exist in optics as they do in electronics, so some residual aliasing remains, especially with very sharp lenses. The design of anti-aliasing filters involves a tradeoff between sharpness and aliasing (with cost thrown in).

If you want to know more about why you might choose a telephoto lens, scroll to the bottom of this article where I've put together a beginner's guide on the different types of telephoto and what they're used for. I've covered telephoto lenses for all mainstream systems, so I hope you find what you're looking for. Let's take a closer look

A full frame lens is ideal for both camera sizes, but getting an APS-C lens for an APS-C camera can save both weight and cash.

The stepping motor-based autofocus system is ultra-quiet compared with some Pentax lenses, but is still audible and not particularly fast. Pentax’s ‘Quick-Shift Focus System’ enables easy switching between autofocus and manual focus. There’s no optical stabilizer, the lens instead relying on the sensor-shift stabilization of Pentax camera bodies, which isn’t always ideal when shooting with telephoto lenses. Image quality is very good overall but sharpness drops off a bit at the long end of the zoom range.

The color aliasing metric is new in Imatest 5.1.12, released in October 2018. Prior to this release the color metrics did not correlate well with image appearance. The metric to display is selected in the Moiré dropdown menu, below Display.

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Although sharpness is an important image quality factor, a sharper lens is not always better. A lens can be too sharp for a sensor, resulting in disturbing visual artifacts.

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Segment of wedge (enlarged from above chroma-boosted image). Spatial frequency increases from left to right. Metric for each frequency is obtained by averaging the parameter (example: |R-B|) inside the wedge.

The graphs below show the comparative performance of the lenses in this guide, based on our in-house lab tests. Winners for sharpness are the Nikon Z 180-600mm and Sony FE 100-400mm lenses in this group. There’s some pincushion distortion on show, when uncorrected in-camera, along with a little color fringing.

To get the plot below, acquire an eSFR ISO chart image,then run eSFR ISO Setup, following the instructions here. eSFR ISO can also be run in batch-capable Auto mode. Under Display, select 18. Wedge moiré.

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If you're embarking on handheld telephoto shooting, image stabilization can be a huge help for getting consistently sharp shots. The optical stabilizers that built into telephoto lenses often come with auto panning detection, or give you the option of manually switchable static and panning modes. The latter means that when panning horizontally, stabilization is only applied in the vertical plane.

The image on the right is well beyond that. It has both extreme sharpening (standard sharpening with radius = 2 — stronger than any of the examples on the Sharpening page) as well as extreme aliasing. As a result, measured MTF summary metrics are quite meaningless. A few comments.

The original zone plate pattern consists only of concentric circles. Everything else is Moiré, resulting from sampling the original pattern without anti-aliasing (lowpass filtering).

By adjusting Frequency you can see how aliasing (output signal at a lower frequency than the input signal) starts at Frequency = 1x (0.5 cycles/pixel). Adjusting Phase with Frequency set to 1x illustrates the phase sensitivity of the output, which varies from maximum to zero amplitude.

Each wedge region is white-balanced prior to calculating the color aliasing metrics. The metrics are calculated inside the wedge. Smoothing (with a kernel of width 0.01 Cycles/Pixel) is recommended for consistent results. The color moiré metric is selected in the Moiré dropdown menu. Our primary recommended metric is Chroma (sqrt(a*^2 + b*^2)). This is the mean of the CIELAB chroma, C = sqrt(a*2 + b*2). Other useful color aliasing metrics are mean(|R-B|) and mean(|R-B|) / mean(R,B).  |R-B| is useful because Red and Blue are more sensitive to aliasing then Green.

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A reworking of Sigma's popular 'light bazooka' telephoto zoom for DSLRs, this newer mirrorless edition is available in both Leica L and Sony E mount versions.

On an Fujifilm X APS-C sensor, this powerful telephoto zoom can deliver a maximum effective focal length of 609mm. This coupled with its extensive weather-sealing makes it an excellent choice for outdoor sports and wildlife photography. It's also got fast, accurate autofocus that can handle moving subjects, as well as a 5-stop optical stabilisation system that lives up to its billing. In my review, I found sharpness to generally be very impressive in real-world situations, with some fall-off detected in lab tests, and distortion is controlled exceptionally well. This is a really powerful lens for Fujifilm users but be aware that at almost 1.4kg, it's no lightweight.

For users of APS-C K-mount DSLRs, this lightweight and versatile telephoto zoom is the natural choice. It's well made with Pentax's customary weather-sealing.

The MFT crop factor means this lens delivers an 'effective' 200-800mm range, which gives you serious reach, aided by effective optical Power OIS stabilization.

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The Nyquist sampling theorem states that if a signal is sampled at a rate dscan and is strictly band-limited at a cutoff frequency fC no higher than dscan / 2, the original analog signal can be exactly reconstructed. The frequency fNyq = dscan / 2 is called the Nyquist frequency. By definition fNyq is always 0.5 cycles/pixel.

The Foveon sensor used in Sigma DSLRs is sensitive to all three colors at each pixel site. It also has no anti-aliasing filter, so it can have high MTF at Nyquist, but aliasing is less visible because it is monochrome, not color.

With generous reach and superfast ultrasonic ring-type autofocus, this lens is a superb companion for Nikon DSLRs — it performed brilliantly in our lab tests.

Color aliasing (CIELAB Chroma) for an older iPhone with significant color aliasing. Chroma has been boosted in the image.

What is TelephotolensiPhone

Scores for sharpness and color fringing are averaged from data taken across the entire image frame, from the center to the edges and corners, throughout the aperture range. For zoom lenses, the scores are also averaged from data measured at all marked focal lengths, and the same applies to distortion. Bear in mind that these average values don't fully reflect specific areas of performance. For example, a zoom lens might have noticeable barrel and pincushion distortion at its shortest and longest focal lengths respectively, which tends to average out when looking at the data overall. For more detailed graphs of each lens's performance, which give the full picture, check out the graphs in our full standalone lens reviews.

“color_aliasing_max_mean_R_minus_B”: [0.1327,0.1088,0.07527,0.07033], “color_aliasing_max_mean_R_minus_B_normalized”: [0.391,0.2999,0.4362,0.3822], “color_aliasing_max_mean_R_minus_G”: [0.09607,0.02452,0.08199,0.07815], “color_aliasing_max_mean_R_minus_G_normalized”: [0.328,0.05977,0.4449,0.3945], “color_aliasing_max_mean_G_minus_B”: [0.1041,0.1088,0.06335,0.03999], “color_aliasing_max_mean_G_minus_B_normalized”: [0.2701,0.2991,0.2851,0.1786], “color_aliasing_max_mean_S_HSL”: [0.6033,0.9159,0.4902,0.5427], “color_aliasing_max_mean_S_HSV”: [0.3227,0.2781,0.4083,0.3311], “color_aliasing_max_mean_CIELAB_chroma”: [16.61,16.48,10.69,11.19],

Color moiré is the result of aliasing in image sensors that employ Bayer color filter arrays, as explained below. Key points:

A premium lens with a 150-600mm ‘effective’ zoom range, this fine Fujifilm zoom boasts a premium optical construction that delivers superb image quality.

Barely any larger and slightly lighter than Sony’s 70-200mm G Master 'trinity' telephoto zoom, this super-telephoto lens has a fundamentally different design, in that the inner barrel extends as you stretch through the zoom range. Even so, it’s very solid and well-built, with similar handling characteristics that include dual-mode optical stabilization for static and panning shots, an autofocus range limiter switch, and multiple autofocus hold buttons.

If you're using a camera that features sensor-shift stabilization, optical stabilization is less important and many manufacturers will omit it in the design of lenses compatible with these cameras. However, some will allow the optical and in-camera stabilization systems to work in tandem, delivering even more stabilization than either system would on its own.

Imatest includes a set of Educational apps that let you visualize the Sampling theorem as well as several other concepts such as MTF and sharpening.

Lenses with a 100-400mm focal range are hugely popular. It's a versatile focal range for telephoto shooting, making a broad range of subjects possible to capture, and the Panasonic Leica DG Vario-Elmar 100-400mm f/4-6.3 ASPH. POWER O.I.S. is a fine example. Naturally, the fact that it's a Micro Four Thirds lens means that it actually performs like a 200-800mm lens, making it all the more potent for telephoto shooting.

Because it is difficult to correlate MTF measurements with visible aliasing, strong MTF response above Nyquist should be regarded only as a warning that aliasing might be an issue and hence needs to be explored further. It is not a definite indicator of aliasing. Imatest techniques for directly measuring the effects of aliasing are listed below.

Wedges can be manually selected in the old ISO 12233:2000 chart with the Wedge module, which we don’t recommend because it’s inconvenient. (and the old chart is also not recommended by the current ISO 12233:2014+ standard). We strongly recommend using the eSFR ISO chart and module, which is compliant with the current standard and automatically detects wedges and other features. It measures a great many image quality factors (MTF, Lateral Chromatic Aberration, color, tonal response, noise, Signal-to-Noise Ratio, and more) in addition to color aliasing. Wedge moiré plots are identical in the Wedge and eSFR ISO modules. We illustrate eSFR ISO results below.

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For full-frame cameras, the most budget-friendly telephoto lens is usually a 70-300mm telephoto zoom with a variable aperture rating, typically going from f/4 to f/5.6 throughout the zoom range. This type of lens can generally be squeezed into a very compact body, making them more portable than similar optics,

You can use full-frame telephoto zooms on APS-C format Canon, Nikon and Sony cameras. The 1.5x or 1.6x crop factor boosts the ‘effective’ telephoto zoom range giving you much more powerful reach. Another bonus is that you’ll only be using a relatively small, central area of the image circle produced by the lens, where image quality is at its best.

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The curve in the plot is the mean of the selected metric (\(C^* = \sqrt{a^{*2} + b^{*2}}  \) in this case), taken inside the wedge as illustrated below.

Nicknamed the ‘light bazooka’, Sigma launched a relatively compact and lightweight 100-400mm zoom for Canon and Nikon DSLRs back in 2017. Three years down the line, this newer ‘DN’ edition is now available for Leica L and Sony E mount mirrorless cameras. The optical path is upgraded and includes a top-grade FLD (‘Fluorite’ Low Dispersion) element, in addition to four SLD (Special Low Dispersion) elements. Other enhancements include a customizable Focus-lock button and a TS-111 tripod mounting ring, which is available as an optional extra. I found the new DN lens to be sharper than the original design, throughout the entire zoom range. Overall, it’s an excellent performer at a very attractive price.

In digital cameras with Bayer color filter arrays— sensors covered with alternating rows of RGRGRG and GBGBGB filters— the problem is compounded because the spacing between pixels of like color is significantly larger than the spacing between pixels in the final image, especially for the Red and Blue channels, where the Nyquist frequency is half that of the total image. This can result in color moiré, which can be highly visible in repetitive patterns such as fabrics. Demosaicing programs (programs that fill in the missing colors in the raw image) use sophisticated algorithms to infer missing detail in each color from detail in the other colors. These algorithms can have a significant effect on color moiré.

The Power OIS stabilization system is hugely impressive, though the lens does lack the switchable stabilization modes that some comparable optics have. Image quality is generally very good, especially at the short end of the zoom range, with a customary slight drop-off in sharpness towards the long end. The relative lightness of the lens is welcome too, especially for MFT users who are working with smaller, lighter camera bodies.

Thanks to the ISO 12233 binning algorithm, slanted-edges can measure system response above the Nyquist frequency (fNyq = 0.5 cycles per pixel). As we have shown, response above the fNyq can lead to aliasing artifacts such as moiré, but there are some limitations to MTF measurements— especially with the slanted-edge MTF measurement, which is Imatest’s preferred method (in most instances) because of its speed and efficient use of space.

But you can also get lenses that are specifically designed for APS-C sensors. The advantage is that they are smaller, lighter and less expensive than full frame lenses. However, you can't use these APS-C lenses on full frame cameras (not without using 'crop modes' which you will want to avoid.

Sampling – Nyquist – Aliasing – Color Moiré – The Imatest Educational App – Effects of aliasing on MTF  Slanted-edge limitations – Wedges

His expertise with equipment doesn’t end there, though. He is also an encyclopedia  when it comes to all manner of cameras, camera holsters and bags, flashguns, tripods and heads, printers, papers and inks, and just about anything imaging-related.

It's undeniably a heavy lens, but that's typical of super-telephoto zooms. This lens hugely delivered in a range of shooting situations when I put it to the test in my full review, and anyone looking for a do-it-all sports or wildlife lens will not be disappointed.

Lightweight and relatively affordable, this telephoto zoom in the popular 100-400mm configuration is a great addition to any Canon EOS R system kit bag.

The first sensor null (the frequency where a complete cycle of the signal covers one sample, hence must be zero regardless of phase) is twice the Nyquist frequency. This means that image sensors can have large average sensitivity (the average of all sampling phases) at and above the Nyquist frequency, which can cause significant visible artifacts.

The 100-400mm lens also adds an adjustable friction damper for the zoom ring, due to the telescoping nature of the design. The optical path includes two ED (Extra-low Dispersion) elements and one Super ED element, while autofocus is driven by the speedy combination of a double linear motor plus a DDSSM (Direct Drive Super Sonic Motor). Sharpness and contrast are excellent, as is the creamy quality of bokeh, but the optical stabilizer has lackluster performance unless combined with in-body stabilization on later Sony camera bodies.

Matthew Richards is a photographer and journalist who has spent years using and reviewing all manner of photo gear. He is Digital Camera World's principal lens reviewer – and has tested telephoto lenses for every major camera system.

While it's not one of the premium 'S-Line' lenses for Z-mount, this wide-ranging zoom still delivers brilliant reach and quality for wildlife and sports photography.

Compact and lightweight for a super-telephoto zoom, the Canon RF 100-400mm f/5.6-8 IS USM looks and feels very much like shooting with a classic 70-300mm lens on DSLR cameras. Naturally though, it’s designed for EOS R-series bodies, on which it’s an excellent fit, making for a slimline and easily manageable overall package. Autofocus is super-fast, image stabilization is highly effective and image quality is highly impressive in all respects, with the caveat that sharpness drops off noticeably when combining close focusing distances with the longest zoom setting. The aperture rating of f/8 at the long end of the zoom range might be a bit slower than some might like, but that’s the price you pay for the conveniently downsized design.

Moiré is exceptionally visible on zone plate patterns (a kind of worst case pattern that can be created with the Imatest Test Charts module), but the zone plate is not suited for quantitative measurements.

The next step up for full-frame cameras is a 70-200mm lens. It might seem strange that a more expensive class of lens has less powerful telephoto reach, but the main advantage here is that these lenses will generally have a faster aperture rating of f/2.8 or f/4, and it will remain constant throughout the entire zoom range. These lenses are favoured by professionals, and so unsurprisingly, 70-200mm f/2.8 telephoto zooms can be much pricier. They're often heavier too, as the diameter of optical elements towards the front of the lens needs to be a lot bigger. You don't get the zoom range of a cheaper telephoto lens, but you do get a big jump in image quality and low-light performance, and better separation between your subject and its background, thanks to the wider lens apertures.

A 70-300mm lens is all very well, as is a 100-400mm lens, but this Nikon optic has an edge over both. The Nikon AF-S 80-400mm f/4.5-5.6G ED VR is a revitalised version of an original lens that was something of a misfire, but a lot of those problems have no been corrected – the most glaring one being the first lens's dreadfully slow autofocus, which is now rectified with a super-fast ultrasonic ring-type autofocus motor. I'm also impressed with the sharpness of the Nikon AF-S 80-400mm f/4.5-5.6G ED VR, especially in the centre, as confirmed in our lab tests. It's an all-around excellent lens, especially for one with such a generous zoom range.

For Canon DSLR users, this telephoto zoom lens delivers generous reach and fast autofocusing, and is light enough to use with APS-C as well as full-frame cameras.

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With a huge zoom range, the Nikon Z 180-600mm f/5.6-6.3 VR is one of the most versatile lenses in the Z-mount line-up. For wildlife, sports, aviation and similar pursuits, it's absolutely superb, delivering crystal-clear sharpness right the way through that zoom range. With a viewing angle of just 13.7 degrees at the short end through to just 4.1 degrees at the long end, it's a lens that can provide a real range of perspectives. You also get an effective 5.5-stop stabilization system that helps you keep things under control when working at long focal lengths.

In this simplified example, sensor pixels are shown as alternating pink and cyan zones in the middle row. By definition the Nyquist frequency is 1 cycle in 2 pixels = 0.5 cycles/pixel. The signal (top row; 3 cycles in 4 pixels) is 3/2 the Nyquist frequency, but the sensor response (bottom row) is half the Nyquist frequency (1 cycle in 4 pixels)— the wrong frequency. It is aliased.

Reasonably lightweight and portable, this workhorse 100-400mm lens for Sony E-mount boasts exotic handling characteristics and excellent all-round performance.

Clicking Save data (or running eSFR ISO setup with the appropriate boxes checked) saves data to CSV and JSON files. Here is a sample of JSON output for the color aliasing summary metrics (the maximum value for each metric shown in the above table). Recommended metrics are shown in boldface.

The (geeky) math for reconstructing the original signal is in Wikipedia. It involves a sinc (sin(x)/x) function, which is generally not used in digital imaging.

The original zone plate pattern consists only of concentric circles. Everything else is Moiré, resulting from sampling the original pattern without anti-aliasing (lowpass filtering).

Color moiré is artificial color banding that can appear in images with repetitive patterns of high spatial frequencies, like fabrics or picket fences. The example on the right is a detail of a shirt captured by the Canon Rebel XT (an older APS-C DSLR with relatively large pixels) with its excellent kit lens.

The long focal length of a telephoto lets you fill the frame with distant subjects, meaning its most common applications are wildlife and sports photography. However, telephotos have plenty of other uses, as a narrow perspective can be handy in all sorts of fields. They're great for portraiture, flattering subjects and separating them nicely from the background. They even have a place in landscapes and architecture, providing a very different perspective than the wide-angle lenses more commonly used in these scenarios.

Extreme aliasing. The long-discontinued 14-megapixel Kodak DCS 14n (the first full-frame 24x36mm DSLR), had no anti-aliasing filter. With sharp lenses, MTF response extended well beyond the Nyquist frequency. The 14n behaved very badly in the vicinity of Nyquist (63 lp/mm), as shown in this MTF test chart image, supplied by Sergio Lovisolo. This color moiré is about as bad as it gets. This camera was sold into the wedding photography market, where moiré on wedding gowns made for some very unhappy customers: bad for the photographer and bad for Kodak.

Recent DSLRs with 30+ megapixels (for full-frame sensors) have pixels that are small enough do that moiré is rarely troublesome (at least on non-repetitive patterns). These cameras don’t have anti-aliasing filters, resulting in a larger image quality improvement than might be expected from the increased pixel count alone.

The table below lists the available metrics, which are selected in the Moiré dropdown menu on the right side of the image below Display. Only three of the metrics are recommended: the others are informative or experimental. The maximum value of each metric is displayed in the upper left of the plot (shown above). The maximum values for all the metrics can be saved in JSON and CSV results files. Here is a list of the metrics, emphasizing the recommended metrics.

These artifacts, which include “stair-stepping” and moiré patterns (low frequency patterns that can be strongly colored), can appear because digital cameras— and all digitally sampled systems— have a maximum spatial frequency, called the Nyquist frequency, beyond which scene information cannot be correctly reproduced. Any information above the Nyquist frequency that reaches the sensor will be “aliased” to a lower spatial frequency, which can result in the artifacts described below.

As a handling highlight, it also has an in-barrel information screen with an adjacent button for cycling through multiple modes. It’s my favorite telephoto zoom for APS-C format SLRs and also makes a great compact, budget telephoto for full-frame Canon cameras, including EOS R-series mirrorless models via a mount adapter.

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Signal energy above fN is aliased— it appears as artificially low frequency signals in repetitive patterns, typically visible as moiré patterns. In non-repetitive patterns aliasing appears as jagged diagonal lines— “jaggies” or “stair-stepping” (a less severe form of image degradation). The figure below illustrates how response above the Nyquist frequency leads to aliasing.

Strong aliasing means that the lens has significant response well beyond maximum frequency where data can be reconstructed— the Nyquist frequency (fNyq = 0.5 C/P). It causes artifacts such as stair-stepping and moiré fringing, which corresponds to the boosted MTF at f > fNyq. The extreme artifacts caused by extreme aliasing can make measured results invalid — they have no real meaning. Aliasing can have significant effects on performance when MTF at fNyq is larger than about 0.20 or 0.25.

Matthew Richards is a photographer and journalist who has spent years using and reviewing all manner of photo gear. He is Digital Camera World's principal lens reviewer – and has tested more primes and zooms than most people have had hot dinners!

If you're looking for the best telephoto lenses for your camera, look no further. I've drawn on experience of testing and reviewing lenses to bring you this indispensable guide to the most capable long lenses for all major camera systems, while keeping an eye firmly on the budget. I'm after the most bang per buck, so I've bypassed really exotic glassware that costs a fortune.

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The Wedge moiré plot below shows the mean CIELAB chroma (\(C^* = \sqrt{a^{*2} + b^{*2}}  \) ) measured inside the wedge as a function of spatial frequency. Several other color aliasing-related metrics are listed in the table below.

Wedges, which are analyzed by Imatest’s Wedge and eSFR ISO modules, provide the best visual indication as well as measurement of aliasing. Wedges can be used to calculate

Canon makes a pretty good EF-S 55-250mm f/4-5.6 IS STM telephoto zoom for its APS-C format SLRs. It’s compact and lightweight at 70x111mm and 375g. Measuring 80x146mm and weighing 710g, this full-frame compatible lens is naturally larger and nearly twice the weight but, for my money, it’s more than twice as good. As well as having more powerful telephoto reach, equivalent to 480mm in full-terms, it boasts a super-fast Nano USM autofocus system, a more effective image stabilizer, and delivers sharper image quality.

We test lenses using both real world sample images and lab tests. Our lab tests are carried out scientifically in controlled conditions using the Imatest testing suite, which consists of custom charts and analysis software that measures resolution in line widths/picture height, a measurement widely used in lens and camera testing. We find the combination of lab and real-word testing works best, as each reveals different qualities and characteristics.

This Pentax lens is remarkably small for a 55-300mm zoom, partly because it’s designed exclusively for APS-C format cameras but mostly because it has a retractable design for compact storage. There’s nothing small about the zoom range, however, which is equivalent to 82.5-450mm on a full-frame camera. Build quality is very good, featuring weather-seals and a fluorine coating on the front element, while optical highlights include ED elements and Pentax’s HD coating to reduce ghosting and flare.