The Nikon AF-S 500mm f/5.6E PF ED VR lens is the lightest 500mm full-frame telephoto prime lens; weighing just 1.46kg, it is lighter than most 150-600mm zoom lenses – light enough to shoot with handheld. The Vibration Reduction system gives 4-stops of stabilisation.

Large-aperture prime lenses allow you to shoot indoors without flash, or blur backgrounds for creative effect. Not only is this small 35mm prime one of the best Nikon lenses of its type for APS-C DSLR users, it’s also very sharp. With a view roughly equivalent to a 50mm prime on full-frame, it’s suitable for subjects from street photography to portraits.

To take portraits to a higher level, then a large-aperture, short-telephoto prime is the way to go. Nikon’s AF-S 85mm f/1.8 is a good quality yet reasonably affordable choice, with fast autofocus and sharp optics. With a nine-bladed circular aperture, it can also provide very attractively blurred backgrounds. The lens is also nice and light, weighing less than the previous version despite having a more complex optical interior with more glass elements. The front of the lens doesn’t rotate when focusing, meaning you can freely use circular filters.

The lens gives impressive image quality, as well as rapid focus performance, making it ideal for when a telephoto prime lens is required. When we took the lens to Lords Cricket Ground for a sporting field test, we discovered just how well it delivers the goods: ‘If I were a Nikon user planning to go on safari, I’d put my name down to hire this lens…’ noted our reviewer at the time.

An upmarket version of Nikon’s standard zoom, the AF-S DX Nikkor 16-80mm f/2.8-4E ED VR commands a premium in price. However, for the money, you do get a more generous maximum aperture of f/2.8-4. What’s more, the price gap between the 16-80mm f/2.8-4E and the 16-85mm f/3.5-5.6 has narrowed now that both are on the second-hand market. New, there would have been about $300/£300 between them; now it’s more like $100/£100.

The maximum aperture is relatively slow, running from f/3.5 to f/5.6 once you’ve zoomed in. This will be fine for most day-to-day shooting, but you may start to struggle once light levels start to get low – though the aforementioned stabilisation will help by letting you get away with slower shutter speeds to let in more light.

Thermal lensingapplications

Often the first lens DSLR users buy after the 18-55mm that came with their camera is a telephoto zoom. But there’s a huge number to choose from, with Nikon alone offering six for its DX-format SLRs, distinguished only by opaque combinations of letters in their names.

The photothermal effect can be produced when a laser beam impinges on a sample and due to optical absorption, results in an increase of the localized temperature distribution in the sample around the propagating laser beam axis. For a Gaussian laser beam the temperature distribution [11] is then given by:

A discontinued lens that can still be acquired at a good price second-hand, the Nikon 28-300mm f/3.5-5.6G VR delivers unparalleled versatility for a Nikon DSLR user. It’s one of the few superzoom lenses that’s compatible with full-frame. Does it deliver the kind of optical quality you get from Nikon’s prime lenses? No, of course not – but it does pretty well across the entire zoom range, and you won’t have any problem shooting dynamic, striking images with it.

Where φ has been replaced by φ(r,t). As it can be seen in Eq. (11), amplitudes and linear phases have been eliminated, remaining only the photothermal phase shifting.

It certainly delivers impressive image quality though, with Vibration Reduction helping to keep shots steady, for which it is to be commended.

Yes. Nikon F-mount lenses can be used with Nikon mirrorless cameras, thanks to the FTZ or FTZ II mount adapters. In most cases, the adapter will give you full functionality of autofocus and stabilisation.

The lenses on this list aren’t just for DSLRs, however. The best Nikon mirrorless cameras in the Z system have taken centre-stage in recent years, but thanks to Nikon’s FTZ mount adapters, Nikon F lenses can be used on these cameras, too. In most cases, they’ll work with full functionality of autofocus and stabilisation, so owners of mirrorless cameras will also find bargains from our list. It includes a mix of new available lenses and some only available second-hand for bigger savings.

For more have a look at the latest news, lens reviews, and buying guides, or have a look at the best Nikon DSLRs, and the best Nikon mirrorless cameras.

An f/2.8 lens has a maximum aperture setting of f/2.8. The lower the number (eg f/1.4), the larger the aperture, and the more light a lens will let in. This also allows for shallow depth of field, which is handy for portraits. Some zoom lenses have a variable maximum aperture like f/3.5-5.6 – this means the maximum aperture changes depending on how far the lens is zoomed in.

Read on to find out which lenses we’ve picked. For newer options in Nikon’s mirrorless system, check out our guide to the best Nikon Z-mount lenses. If you’re new to buying lenses and need a primer, scroll to the bottom of the page where we’ve included an explainer section of key specs with answers to some frequently asked questions.

While it can be hard to find new, especially in the UK, the Nikkor AF-S 14-24mm f/2.8G ED can be picked up used for less than $749 / £689, and is a steal at that price.

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This lens is legendary in landscape photography circles. If you’ve seen any competition shortlists for landscape photography in the past 10 years, then you’ve seen an image taken with it.

In this work, we propose an experiment that combines the sensitivity of both thermal lensing and interferometric techniques, for a simple and quick thermal lensing approach based on the parabolic approximation and the Mach Zehnder interferometer. We use this approach to estimate optical absorption and thermal diffusivity coefficients of pure solvents such as ethanol, methanol, and carbon disulfide, verifying experimentally the validity of the approach. The advantages of this approach are mainly related with the simple and quick implementation of the experimental setup, absence of mechanical movements of the sample during the experiment, few parameters for data fitting and good sensitivity for the measurement of the phase shifting difference, which is around λ/4800.

where P, α, c, ρ and w are the optical power, absorption coefficient, specific heat, density, and waist laser beam, respectively. The radial coordinate is r and the characteristic time constant for the photothermal effect is given by tc=w2/4D, where D=κ/cρ is the thermal diffusivity of the sample, being κ the thermal conductivity. Eq. (1) is deduced by the assumption that all the absorbed energy of a laser beam passing through the sample is fully converted into heat. Also, the model assumes that heat only flows in the radial direction and that thermal convection and radiative effects are both negligible. Considering only the region around the center of the spot of the laser beam, Eq. (1) is reduced to the parabolic approximation of the temperature distribution [6]:

The brighter f/1.8 aperture will be of benefit to those shooting in low-light conditions, and we expect those interested in astrophotography would be well served by this lens.

Kerrlensing

We’ve reported previously on 35 F-mount lenses being discontinued in recent years. Despite this, there are still a vast number of lenses available new, and in the used camera market. A discontinued lens may still be a very good, or indeed a great performing lens. The most recent Nikon DSLRs released were the Nikon D780 and Nikon D6 – both in 2020.

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Welcome to our guide to the best lenses for Nikon F-mount. Here we pick out the best of the best lenses for full-frame Nikon DSLRs based on the many that we’ve tested and reviewed over the years.

Amy is a highly experienced photography and technology journalist who has been working on AP since 2018, having been working in the industry since 2009. She is a graduate of the magazine journalism course at Cardiff University and has written for a wide range of publications and websites. As Features Editor, she is responsible for commissioning an eclectic mix of features connected to general photography, along with interviews. She is also a very experienced reviewer of cameras and associated technology, with her reviews featured on multiple sites including TechRadar, Digital Camera World, Trusted Reviews, ePhotozine, Stuff, Expert Reviews, T3, Photography Blog and more. She is also an expert on smartphone photography and smartphones generally.

The Nikon AF-S Nikkor 20mm f/1.8G ED is a high-quality wide-angle prime lens, giving high-quality images, particularly at f/5.6-f/8 where we found it gave impressive resolution. It was only in the very corners of the image where we found slight blur. Distortion is also kept well controlled, with minimal vignetting and chromatic aberration. These are solved in-camera if you shoot JPEG images, or alternatively can be quickly fixed in photo editing software.

Again, though, its AF-P designation means that it only works on relatively recent APS-C DSLRs, so check compatibility before you buy. Otherwise, this is a great complement to a standard zoom for subjects such as landscapes, interiors, real estate and architecture, where you’d like to squeeze as much as possible in the frame.

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One downside is the rather uninspiring maximum aperture of f/3.5-5.6. This is part and parcel of keeping the lens to a sensible weight and cost, but all the same, those who want to create striking shallow depth of field or beautiful bokeh will want to look elsewhere.

By substituting Eq. (2) and Eq. (3) in Eq. (4), and then using this result in Eq. (5), we obtain a simplified expression for the phase difference based on the parabolic approximation:

To directly measure the photothermal phase shifting, we use a pump-probe experimental configuration based on Mach-Zehnder interferometer and the respective post-processing numerical analysis of their interferograms [17]. At the exit of the interferometer, the intensity distribution of a typical interference pattern can be written by the following equation:

Nikon’s AF-S 50mm f/1.8G is a classic example of the type, and will also work on full-frame cameras. We found it performed well across the board. Overall, Nikon has succeeded in taking a classic design and making it even better.

For many years, 50mm primes (or ‘nifty fifties’) were sold as general-purpose lenses with 35mm film cameras, but they fell out of favour for a few decades. Recently, however, there has been a resurgence in their popularity for use with APS-C format DSLRs. They tend to be small, light and relatively cheap, yet very sharp, and perfect for shooting portraits.

Fig. 2 shows a schematic diagram of the experimental set-up, based on thermal lensing and a Mach-Zehnder interferometer, used to validate the approach. The interferometer is formed by two beam splitters and two mirrors which divide and recombine a low power laser beam. With this set-up two separated beam paths are obtained, probe and reference beams, having the advantage that the fringe tilt and fringe spacing of the interferogram can be adjusted by varying the angle between the two beams at the exit of the interferometer. By placing the sample in the path of the probe beam, the optical phase shifting between wavefronts of both beams can be measured. As shown in Fig. 2, a CW Helium–Neon (He–Ne 05-UR-111, Melles Griot) laser beam of 1 mW of optical power and 632.8 nm of wavelength is first collimated to a 6 mm diameter by using a beam expander BE, and split on two beams by means of a fifty-fifty beam splitter BS (BS016, Thorlabs), after reflecting on the mirrors M (Thorlabs PF10-03-G01) both beams are recombined again by means of the second beam splitter, forming in this way the Mach-Zehnder interferometer. One of these beams passes through the sample S and it is used as a probe beam, as was previously mentioned. Due to the low power of this beam (∼1 mW), it is collimation in wide diameter and the thermal and optical properties of the tested sample, the induced photothermal effect is negligible, then, the effect of the probe beam in the induced photothermal phase can be neglected. The sample consists of a pure solvent placed in a quartz cuvette of 2 mm of optical path length (21-Q Quartz Cuvette 2 mm); for this experiment the selected solvents are ethanol, methanol, and carbon disulfide or CS2. A lens L is placed at the exit of the interferometer, in order to image the exit wall of the quartz cuvette on the sensor of the digital camera's CMOS (acA 2440-20gc, Basler). To avoid sensor saturation, reduce noise, and improve the interference contrast, neutral optical density (NEK01S, ND Filter Set) and band-pass optical filters F (FLH05633-5, Bandpass Filter) are placed in front of the camera. The pump beam is produced by a 405 nm laser diode at an optical power of 300 mW (M-33A405-300-G, S-Laser). Due to the high power of the pump beam, it is focused in the sample; its radius at the position of the sample remains approximately constant and our estimations indicate that w≅0.49±0.01mm. This experimental configuration satisfies the assumptions imposed on the theoretical model and any uncertainty in measuring the radius affects the measuring accuracy of the thermal diffusion coefficient. There is a small angle (∼4°) between the probe and pump beams due to the arrangement of the optical components used in the experimental setup, we can use the small-angle approximation. Also, because of the thermal diffusive nature of the photothermal effect, the influence of this small angle on the temperature profile can be neglected, especially when the exposure time are larger enough and the thermal diffusive process become Gaussian.

With an array of exotic glasses and coatings, it’s designed for use on the latest high-resolution DSLRs such as the 45.7MP Nikon D850. It can also be used with DX-format cameras, giving a 36-105mm equivalent range.

The most up-to-date is the AF-P 70- 300mm f/4.5-6.3 VR: a compact, image-stabilised optic with a usefully long zoom range and the latest fast, silent AF-P motor for autofocus that’s also suitable for video work.

where λ is the wavelength and L the optical path length of the sample. We define the phase difference as the radial variation of the photothermal phase shifting around the laser beam axis. Specifically, the phase difference between points r=0 and r≪w is given by:

From Eq. (9a) and Eq. (9b), one of the Dirac delta distributions is selected, for example B(u)(u+Δu) and {FFT[e−iφ]⨂B(u)}(u+Δu), and spatially shifted to the center of the inverse space; by applying the inverse 2D-FFT on these selected distributions the algorithm generates:

The Nikkor AF-S 14-24mm f/2.8G ED was introduced in 2007, and is quite simply a beautiful feat of optical engineering. It delivers images of outstanding sharpness thanks to its extra-low dispersion elements and the Nano Crystal Coating and Super Integrated Coating that have been added. It’s also weather-sealed, and the constant aperture of f/2.8 enables real creative freedom.

Once part of the laser energy is absorbed by the sample and the temperature rise is generated, the localized refractive index of the sample close to the laser beam axis varies producing a lens-like medium known as thermal lensing effect [6]. Correspondingly, the refractive index of the sample is not constant and is dependent of the radial coordinate and the time: n(r,t)=n0+(dn/dT)T(r,t), where n0 is the constant refractive index value in absence of the localized temperature increase, and (dn/dT) is the temperature dependence of the refractive index. The absolute refractive index change can be written as:

We should also mention the Vibration Reduction (VR) functionality, which really does work well in low light. Much slower shutter speeds than normal still produce sharp pictures, which makes this lens an ideal all-in-one, carry-everywhere choice.

The F-mount underpins Nikon’s legendary system of DSLRs. A list of the best Nikon DSLRs includes some of the greatest cameras ever made: the fast-shooting Nikon D850, for example, was regarded for years as the best wildlife camera money could buy.

Schematic diagram of the experiment used to validate Eq. (6). The setup is a pump-probe experimental configuration based on the Mach-Zehnder interferometer, where one of their arms is used as a probe beam, while the other is a reference beam. The pump beam is a 405 nm laser diode.

Prime lenses have a fixed focal length, while zoom lenses have a focal range that let you get closer to or further from your subject. Prime lenses produce superior optical quality, so picking between the two types is generally a choice between sharpness vs versatility.

Sometimes only the very best will do, and when it comes to standard zooms on a full-frame Nikon body, this is it. The latest version of Nikon’s pro workhorse lens adds optical image stabilisation and uses an electromagnetic diaphragm, which provides much-improved functionality when shooting in live view, and for video work.

Authors would like to thank “The Abdus Salam International Centre for Theoretical Physics (ICTP)” for the financial support and in particular the ICTP-SPIE Anchor Research Program.

Thermal lensingexamples

Once the experimental data are generated, two separate results are obtained. First, the numerical code described above is used to process the photothermal phase shifting and calculate the phase difference as a function of time for different relative radial positions. This results in a numerical surface such as shown in Fig. 4 for an ethanol sample. As can be seen, the surface shows the typical characteristics of a thermal lensing signal, i.e., the parabolic and inverse dependence of the phase difference on space and time, respectively. At the bottom of Fig. 4, on the r/w-time plane, is possible to observe the experimental level curves which agree well with the ones obtained by numerical simulation of Eq. (6) and shown previously in Fig. 1. The shape of the surface can be understood as a steady state regime for the phase difference after tc is reached. The direct relationship between phase difference and temperature change indicates that the phase difference is almost constant because the heat around the region delimited by w remains unchanged for times greater than tc.

Wide-angle lenses (around 8-35mm) are good for capturing expansive scenes like landscapes, and conveying scale in architecture. Standard lenses (40-75mm) provide a natural perspective, useful for street photography and documentary photography. Telephoto lenses (80mm and higher) are good for bringing distant subjects like wildlife into sharp focus, or flattering facial features for portraits.

A thermal lensing approach based on parabolic approximation and Mach-Zehnder interferometer for measuring optical absorption and thermal diffusivity coefficients in pure solvents is described in this work. The approach combines the sensitivity of both thermal lensing methods and interferometry techniques. The photothermal effect is induced by a pump laser beam generating localized changes in the refractive index of the sample, which are observed as a shift in phase of the interference pattern. Each interference pattern is recorded by means of a digital camera and stored as digital images as a function of time. The images are then numerically processed to calculate the phase shifting map for a specific time. From each phase shifting map, the experimental phase difference as a function of time is calculated giving a phase-time transient, which is fitted to a mathematical model to estimate the optical absorption and thermal diffusivity of the sample. The experimental results show that the sensitivity is approximately λ/4800 for the minimum phase difference measured.

In Fig. 3 the interferogram and the photothermal phase shift map are represented in false colors as an aid to visualization. In the photothermal phase shifting map, each color-pixel value has its correspondent radian value, for example, the lightest color corresponds to 0.7 rad while the darkest one approximately represents 0 rad. The white circle in the phase map encloses the region delimited by the spot of the pump beam laser at radius of 0.49mm. The red squares represent the areas around r=0 and r≠0 where the photothermal phase shifting is individually estimated by calculating the phase-mean-value of the radian pixel values enclosed inside each square. Subsequently, the phase difference is calculated for a specific time interval. The procedure is repeated for the other interferograms in order to obtain experimental data from Eq. (6).

ThermalLens paintball mask

Thermal lens spectrometry is an analytical method based on the photothermal effect, and it is used for measurements requiring high sensitivity and good accuracy of both thermal and optical properties of solvents and solutions [[1], [2], [3], [4]]. To achieve this goal, several theoretical and experimental methods have been proposed [[5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]], among them the thermal lens Z-scan (TLZ-scan), which is a method widely used and versatile [13]. Here a pump-probe experiment is performed, where the pump beam is a continuous wave laser (CW) focused by a lens and modulated in time by a mechanical chopper. The probe beam is also CW but without modulation. Because the sample absorbs part of the energy of the pump laser beam, its temperature is locally raised; therefore, a change in refractive index is produced. After passing through the excited sample, the wavefront phase of the probe laser beam is shifted. Detecting these wavefront changes in the far field, as the sample is scanned through the focal plane of the pump beam, the thermal lens signal is detected as a function of the sample position. Thermal and/or optical properties of the sample can be estimated using a mathematical model [13,14]. Despite its intrinsic sensitivity and experimental simplicity, TLZ-scan, normally making use of the aberrant thermal lens model [6,9,11], would require accurate data about a number of parameters, including the position of the sample, the Rayleigh range, the degree of the mode-mismatching between the probe-pump beams, the characteristic thermal time, etc. On the other hand, the interferometric methods used here provide a direct measurement of the phase shifting of the probe wavefronts and therefore the estimations of both thermal and optical properties of the sample [3,7,16,17] without the additional specification of the parameters previously described.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

In Fig. 5 we also plot a measure of the fluctuations or noise observed during the experiment, in this case, dots represent the root mean square value of the noise which is about 0.6mrad, averaged over the three sets of the experimental data. From this result and using the minimum phase difference of 1.3mrad measured with our experiment, we obtain a sensitivity of λ/4800 for a minimum SNR of approximately 2. It is important to point out that during the experiment current amplifier or photodiode gain are not used to increase the sensitivity of the measurements [26], which means the results are purely optical measurements performed from the induced photothermal phase shifting in the interference pattern. Therefore, the sensitivity of the method favorably compares with the sensitivity achieved by photothermal lens spectroscopy in which loc-kin amplifiers or current amplifiers are used for sensitive measurements.

Super-fast autofocus and top-notch build quality round off a truly excellent package. Overall, it’s a superb, fast standard zoom that is perfect for a range of shooting environments.

Nikon DSLR users had long been crying out for a lightweight, inexpensive wide-angle zoom, and finally it arrived in the shape of this 10-20mm lens for APS-C (its focal range works out to an equivalent of 15-30mm when mounted on DX cameras). Optically it’s OK, if not outstanding, but the short minimum focus distance provides plenty of versatility, making it a solid jack-of-many-trades for a reasonable price. The built-in optical stabilisation (VR) is excellent, providing compensation equivalent to 3.5 stops. Arguably, it’s less useful on a wide-angle like this than it would be on a telephoto, but there’s no harm in having it, particularly if you plan to do a lot of low-light shooting.

Second, the numerical code also selects experimental points of the phase difference as a function of time for a specific r/w position in a region close to the center of the pump beam spot. These experimental points are represented for the open symbols in Fig. 5, where the curves show the classical thermal lensing transients. In this figure, the continuous lines are the best fits to the data obtained using Eq. (6), where Δφ0 and tc parameters are left freely running during the fitting procedure. As is shown by Eq. (6) these parameters are independent from each other and therefore we can use them to estimate the optical absorption α or the thermal diffusivity D of the sample under study. From the experiment, we measured P and λ for the lasers, and L, κ and (dn/dT) are constants for each sample; by using the value of Δφ0 obtained by the fitting, the optical absorption coefficient α is calculated. On the other hand, if we use the experimentally measured value of w and the fitting value of tc, the thermal diffusivity D of the sample is then estimated, even if the other experimental parameters are unknown. This is possible because in Eq. (6), the first term related to α affects the amplitude and is independent of the second term which is related to the temporal evolution of the phase (tc and D). Table 1 summarizes the thermal constants of the samples used in the experiment, the fitting parameters and the estimations of optical absorption and thermal diffusivity calculated from the experimental results shown in Fig. 5. The estimated values of α and D, given in Table 1, agree well with values reported previously in literature [[20], [21], [22], [23], [24], [25]], also shown in Table 1. Note that, for measurements of the α at a laser wavelength of 405 nm there are no reported values so far. Therefore, our results were only comparable with the nearest measurement value at 460 nm and 532.8 nm [24,25].

If you want to get started with video, check out our top picks for budget-friendly used video cameras and accessories. Richard Sibley guides us through what you need

where i=−1, a(r) and b(r) are respectively intensity distributions related with the background and the fringe visibility of the interferogram, and φ1 and φ2 are the linear phases of each laser beam arm that forms part of the interferometer.

Finally, the photothermal phase shift can be calculated from the argument of the complex function resulting from the ratio between Eq. (10b) and Eq. (10a):

Thermallens spectroscopy

On Nikon F-mount lenses this stands for Vibration Reduction; Nikon’s name for its optical image stabilisation system. Image stabilisation keeps a lens steady when it’s being hand-held, allowing for the use of slower shutter speeds without the need for a tripod.

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The lens is equally suitable for use on full-frame and DX format DSLRs, giving a 135mm view on the latter. To get even better results, you’d need to invest in an 85mm f/1.4, with Sigma’s 85mm f/1.4 Art DG HSM ($ 1,199 / £929) being a fine example. If you don’t have that kind of budget, this is a very tempting alternative.

where φ is given by Eq. (4). The photothermal phase shifting is obtained by using an adaptation of the Takeda's method [19]. The adapted algorithm numerically calculates the two-dimensional Fast Fourier Transform (2D-FFT) of two interferograms that are the digital representation of Eq. (7) and Eq. (8). These 2D-FFT calculations generate three Dirac distributions in the inverse space for each interferogram, which are represented by the following equations:

Eq. (6) is only valid inside the region delimited by w, specifically when r/w≪1, and shows a way to experimentally estimate thermal and/or optical parameters of the sample. To analyze the approximation given by Eq. (6), we performed a simple numerical simulation using GNU Octave [18] and taking Δφ0=0.02rad, w=0.5mm, −1

Theoretical and experimental values of the parameters used and estimated in the experiment. The pump wavelength is λe=405nm, and the probe wavelength is λp=633nm. The pump beam radius is w≅0.49m.

For those blessed with the budget, Nikon’s AF-S Nikkor 180-400mm f/4E TC1.4 FL ED VR lens offers not only a 180-400mm telephoto zoom, but also features a built-in 1.4x teleconverter. With the new price of $12,396 / £10,999, it might be a lens to consider hiring for special shoots.

Thermallens Camera

Being an AF-P lens, though, it’s not compatible with Nikon DSLRs that were released five years or more ago – if you use an older model, you’ll need to buy the Nikon AF-S DX Nikkor 55-300mm f/4.5-5.6G ED VR.

The approach developed in this work allows for a fast analysis of both optical absorption and thermal diffusivity coefficients of pure solvents by measuring typical experimental variables and fitting a few theoretical parameters. The approach relies on the measurement of the de-phasing occurring in an interference pattern when a photothermal effect is induced by a pump laser beam. We have shown the validity of the approximation and the approach by estimating the optical absorption and thermal diffusion coefficients of pure solvents and comparing them with the values reported in literature. We also show that the approach has an experimental sensitivity of λ/4800, indicating that this approach can be an attractive alternative for the thermo-optical characterization of pure solvents and may be other materials.

where A(u) and B(u) are the 2D-FFT of functions a(r) and b(r), respectively. The symbol ⨂ is the convolution product in two dimensions, while u is the inverse space variable, and Δu is the displacement around the center of the inverse space depending on the linear phases.

Sure, you don’t get more modern features like lightning-fast autofocus and optical stabilisation, but landscape photographers don’t really need them. The main thing that’s likely to annoy landscape shooters is the fact that you can’t attach filters to the bulbous front element. Workarounds exist, such as the Lee Filters SW150 system, but they will add to the cost of the lens, so bear that in mind.

If you’ve outgrown the 18-55mm kit zoom that came when you bought your camera, this might just be the perfect upgrade. It offers a usefully extended zoom range, from 24mm equivalent wide-angle to 128mm telephoto, while providing a respectable optical performance that’s aided by a fast ultrasonic-type autofocus motor and built-in image stabilisation.

Digital images showing an experimental interferogram (a) captured with the digital camera and its corresponding numerical photothermal phase shifting map (b). The white circle approximately represents the area delimited by the spot of the pump laser, showing that the photothermal phase shifting extends beyond the area delimited by the laser spot. The experimental space scale is given by white line, ∼1 mm.

The optical power of the pump beam is adjusted by linear neutral density filters placed at the exit of the laser diode and, this allows us to control the intensity level on the sample and to avoid thermal convection effects as well. Due to the large value of w and considering the thermal diffusivity values of the solvents used here, the characteristic relaxation thermal time is expected to be around a half-second. Therefore, the samples are exposed to the radiation of the pump beam for times greater than 1 s. The exposure time is achieved by means of a homemade electronic shutter connected to the diode laser. During the exposure time, a set of thirty photographs per second are taken by the digital camera and recorded in a personal computer where they are post-processed once the experiment is done. During the post-processing, the first photograph of the sequence is the reference interferogram at t=0s, i.e., without any photothermal perturbation. This interferogram is numerically processed by following the method described in the previous section. The next interferogram is also processed with the same algorithm. By using Eq. (11) the photothermal phase shifting for a time interval of 0.033 s is then calculated. The same procedure is performed for the remainder of the interferograms, t>0s. The algorithm to process the interferograms and do the calculations is based on a Takeda's methods [18] and was also implemented on GNU Octave [17]. The results are shown in Fig. 3(a) and (b), plotting respectively, an example of an experimental interferogram and the corresponding photothermal phase shifting map, for 1 s of exposition time.

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The thermal lensing acts as a lens affecting the propagation of the laser beam, i.e., it generates a localized phase shifting of the laser beam wavefronts at the exit of the sample [6]. This photothermal phase shifting can be given by:

When the photothermal effect is induced in the sample, the interference fringes are locally shifted, and the intensity distribution given by Eq. (7) is rewritten as:

For a lens that will also work on full-frame, you’ll need the similarly-named Nikon AF-S Nikkor 35mm f/1.8G, but this costs almost three times as much. Other important things to know about this lens are its 30cm minimum focus distance, it accepts filters and adapters via a 52mm thread and accepts Nikon’s HB-46 lens hood.

Thermalblooming

Notice that, the theoretical model given by Eq. (6) is based on the assumptions that the thermal lensing is a perfect thin lens with no aberration, that the temperature distribution is approximately parabolic and that there is no radiative process. However, the theoretical-experimental approach is simpler to use and to implement than other models because fewer experimental parameters are needed to be accurately specified during the experimental data fitting. Additionally, the estimation of optical absorption and/or thermal diffusivity of the sample is almost immediate and direct. Moreover, the experimental variables such as reflections of the cell walls, mode-mismatches of the pump-probe waists, optimal sample z-position, critical sample-detector distance, optimal pinhole size, experimental set-up geometry and the Rayleigh parameter are not required by Eq. (6) and the procedure given in this work. This approach can be also an interesting alternative for measuring two-photon absorption coefficients and nonlinear refractive index, a work is progressing in this direction.

Phase difference as a function of the exposition time for the solvents used in the experiment. Open symbols represent experimental data while continuous lines are the best fittings obtained by means of Eq. (6). The coefficient of determination for the whole set of curves is approximately R2 = 0.99883. Dots indicate the root mean square value of noise (fluctuations) phase differences as a function of time.

You’ll see these letters in the names of all Nikon F-mount lenses, and they refer to the sensor size of the camera they pair with. Nikon DSLRs come in two varieties – APS-C sensor (DX) and full-frame sensor (FX). A DX lens will create a smaller image circle, designed to fit a smaller APS-C sensor found on Nikon’s DX series DSLRs, such as the Nikon D5600.

The lens has a 58mm filter thread and a construction of seven elements in six groups. Don’t confuse it with the cheaper AF 50mm f/1.8D, which won’t autofocus on Nikon’s entry-level D3000-series or D5000-series DSLRs.

It’s worth noting that, due to its 3.5kg weight, you might not want to carry it around for too long. A monopod can help out here, as we discovered when we took it for a review at a bird-in-flight workshop. Nikon has created an absolutely sensational lens, but the high price will have the final say over the number of photographers who get to use it.

This makes the AF-S DX Nikkor 16-80mm f/2.8-4E ED VR highly attractive, and as we noted in our review, it’s an excellent lens all-around. Vibration Reduction (optical image stabilisation), an electromagnetic diaphragm, a 5x zoom and the aforementioned generous maximum aperture, all wrapped up in a lightweight body make it impressive. Our AF-S DX Nikkor 16-80mm f/2.8-4E ED VR test results showed good centre sharpness, with some expected drop-off in the corners, especially at large apertures.

Thermalcamera

Luis G. Rodriguez: Writing – original draft, Visualization, Validation, Software, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Joseph Niemela: Writing – review & editing, Project administration, Funding acquisition. Humberto Cabrera: Writing – review & editing, Project administration, Investigation, Formal analysis.

If you want to get started with video, check out our top picks for budget-friendly used video cameras and accessories. Richard Sibley guides us through what you need

Simulations performed with Eq. (6) in order to show the behavior of the phase difference as a function of space and time variables.

Experimental phase difference surface obtained for ethanol after the numerical processing is performed on the digital interferograms.

At the other end of the scale, cameras in the Nikon D3000 series like the Nikon D3500 were such popular beginners’ cameras (and to an extent still are) as to be used as standard on introductory photography college courses everywhere.

Which is the best Nikon F lens for your DSLR setup? As different lenses suit different kinds of subject, the choice depends largely on what you plan to photograph. Here is a quick guide to the main considerations when picking a Nikon F lens.

This lens has been on the market for almost a decade now, meaning good prices can often be had if you’re prepared to shop around.