\begin{align}\text{AFOV} & = 2 \times \tan^{-1} \left( {\frac{50 \text{mm}}{2 \times 200 \text{mm}}} \right)  \\ \text{AFOV} & = 14.25° \end{align}

Se usi una distanza focale di 30 mm, la velocità d’otturazione minima da impostare sarà 1/30; con una distanza focale di 100 mm, il tempo d’otturazione minimo per ottenere un’immagine nitida sarà di 1/100.

Knowledge Center/ Application Notes/ Imaging Application Notes/ Understanding Focal Length and Field of View

Example 2: For an application using a ½” sensor, which has a horizontal sensor size of 6.4mm, a horizontal FOV of 25mm is desired.

Punto focale

Note: Horizontal FOV is typically used in discussions of FOV as a matter of convenience, but the sensor aspect ratio (ratio of a sensor’s width to its height) must be taken into account to ensure that the entire object fits into the image where the aspect ratio is used as a fraction (e.g. 4:3 = 4/3), Equation 7.

Dai un’occhiata a questo articolo sugli 8 aspetti da tenere in conto per ottenere immagini nitide. Nei punti 2, 4, 5 e 7 troverai altri suggerimenti per evitare questo tipo di problema.

In general, however, the focal length is measured from the rear principal plane, rarely located at the mechanical back of an imaging lens; this is one of the reasons why WDs calculated using paraxial equations are only approximations and the mechanical design of a system should only be laid out using data produced by computer simulation or data taken from lens specification tables. Paraxial calculations, as from lens calculators, are a good starting point to speed the lens selection process, but the numerical values produced should be used with caution.

Se vuoi approfondire l’argomento dei sensori e del fattore di ritaglio dai un’occhiata a questo precedente articolo prima di continuare la lettura.

Focale sinonimo

If the required magnification is already known and the WD is constrained, Equation 3 can be rearranged (replacing $ \small{ \tfrac{H}{\text{FOV}}} $ with magnification) and used to determine an appropriate fixed focal length lens, as shown in Equation 6.

When using fixed focal length lenses, there are three ways to change the FOV of the system (camera and lens). The first and often easiest option is to change the WD from the lens to the object; moving the lens farther away from the object plane increases the FOV. The second option is to swap out the lens with one of a different focal length. The third option is to change the size of the sensor; a larger sensor will yield a larger FOV for the same WD, as defined in Equation 1.

Lunghezza focale e zoom

Note: Fixed focal length lenses should not be confused with fixed focus lenses. Fixed focal length lenses can be focused for different distances; fixed focus lenses are intended for use at a single, specific WD. Examples of fixed focus lenses are many telecentric lenses and microscope objectives.

Sempre. Vale per ogni situazione in cui non stiamo usando un treppiede, soprattutto al momento di usare larghe distanze focali.

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Focale significato

Jun 27, 2022 — Field of view (FOV) is defined as the maximum area that a device can capture. The larger the field of view, the more data can be captured at ...

A volte capita di ritrovarsi con fotografie non perfettamente nitide e spesso il problema si deve al “micromosso”, il movimento generato dalle vibrazioni della fotocamera.

Si deduce quindi che la velocità d’otturazione minima da impostare con sensori più piccoli del Full Frame sarà più alta (più veloce).

Secondo questa regola, al momento di scattare una foto, dovremmo usare una velocità d’otturazione minima equivalente alla lunghezza focale impostata, per evitare il rischio di “micromosso” e immagini poco nitide.

Field of view describes the viewable area that can be imaged by a lens system. This is the portion of the object that fills the camera’s sensor. This can be described by the physical area which can be imaged, such as a horizontal or vertical field of view in mm, or an angular field of view specified in degrees. The relationships between focal length and field of view are shown below.

noun something that gives a minutely faithful representation, image, or idea of something else: Gershwin's music was a mirror of its time.

Note: As the magnification increases, the size of the FOV will decrease; a magnification that is lower than what is calculated is usually desirable so that the full FOV can be visualized. In the case of Example 2, a 0.25X lens is the closest common option, which yields a 25.6mm FOV on the same sensor.

202473 — This article is merely a guideline for the purpose of each focal length, including some technical differences between the various offerings you see today.

Per applicare correttamente la regola del Reciproco della Lunghezza Focale dovrai tenere in conto le dimensioni del sensore, infatti quanto detto finora vale su sensori Full Frame. In caso di sensori più piccoli, come i diffusi APS-C, dovrai applicare alla formula il fattore di ritaglio.

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Nell’esempio qui sotto ho scattato due foto senza treppiede dalla stessa distanza e lunghezza focale (70mm) con un sensore Full Frame. Nella prima ho usato una velocità d’otturazione di 1/10 s e nella seconda un 1/80 di secondo.

Apertura focale obiettivo

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As previously stated, some amount of flexibility to the system’s WD should be factored in, as the above examples are only first-order approximations and they also do not take distortion into account.

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Generally, lenses that have fixed magnifications have fixed or limited WD ranges. While using a telecentric or other fixed magnification lens can be more constraining, as they do not allow for different FOVs by varying the WD, the calculations for them are very direct, as shown in Equation 4.

Per capire come risolverlo, in questo articolo andremo ad approfondire la Regola del Reciproco della Lunghezza Focale, una base fondamentale per lo studio e la pratica della fotografia, che risulta sempre utile in tutte le situazioni in cui non disponiamo di un treppiede.

Spero che l’articolo ti sia utile e che questa regola ti accompagni sempre nel tuo cammino in fotografia. Se hai qualche dubbio o commento a riguardo puoi scrivermi nel box qui sotto.

Another way to change the FOV of a system is to use either a varifocal lens or a zoom lens; these types of lenses allow for adjustment of their focal lengths and thus have variable AFOV. Varifocal and zoom lenses often have size and cost drawbacks compared to fixed focal length lenses, and often cannot offer the same level of performance as fixed focal length lenses.

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While it may be convenient to have a very wide AFOV, there are some negatives to consider. First, the level of distortion that is associated with some short focal length lenses can greatly influence the actual AFOV and can cause variations in the angle with respect to WD due to distortion. Next, short focal length lenses generally struggle to obtain the highest level of performance when compared against longer focal length options (see Best Practice #3 in Best Practices for Better Imaging). Additionally, short focal length lenses can have difficulties covering medium to large sensor sizes, which can limit their usability, as discussed in Relative Illumination, Roll-Off, and Vignetting.

Distanza focale fotocamera

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Lunghezza focale e distanza dal soggetto

While most sensors are 4:3, 5:4 and 1:1 are also quite common. This distinction in aspect ratio also leads to varying dimensions of sensors of the same sensor format. All of the equations used in this section can also be used for vertical FOV as long as the sensor’s vertical dimension is substituted in for the horizontal dimension specified in the equations.

The focal length of a lens defines the AFOV. For a given sensor size, the shorter the focal length, the wider the AFOV. Additionally, the shorter the focal length of the lens, the shorter the distance needed to obtain the same FOV compared to a longer focal length lens. For a simple, thin convex lens, the focal length is the distance from the back surface of the lens to the plane of the image formed of an object placed infinitely far in front of the lens. From this definition, it can be shown that the AFOV of a lens is related to the focal length (Equation 1), where $ \small{f} $ is the focal length and $ \small{H} $ is the sensor size (Figure 1).

Lunghezza focale telescopio

A fixed focal length lens, also known as a conventional or entocentric lens, is a lens with a fixed angular field of view (AFOV). By focusing the lens for different working distances (WDs), differently sized field of view (FOV) can be obtained, though the viewing angle is constant. AFOV is typically specified as the full angle (in degrees) associated with the horizontal dimension (width) of the sensor that the lens is to be used with.

Once the required AFOV has been determined, the focal length can be approximated using Equation 1 and the proper lens can be chosen from a lens specification table or datasheet by finding the closest available focal length with the necessary AFOV for the sensor being used.

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Applicando un fattore di ritaglio di 1.5 ad una distanza focale di 30mm, otterremo 1/45 (pari a 0,2222 secondi). Con 100 mm, otterremo 1/150 (circa 0,006666 secondi).

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The 14.25° derived in Example 1 (see white box below) can be used to determine the lens that is needed, but the sensor size must also be chosen. As the sensor size is increased or decreased it will change how much of the lens’s image is utilized; this will alter the AFOV of the system and thus the overall FOV. The larger the sensor, the larger the obtainable AFOV for the same focal length. For example, a 25mm lens could be used with a ½” (6.4mm horizontal) sensor or a 35mm lens could be used with a 2/3” (8.8mm horizontal) sensor as they would both approximately produce a 14.5° AFOV on their respective sensors. Alternatively, if the sensor has already been chosen, the focal length can be determined directly from the FOV and WD by substituting Equation 1 in Equation 2, as shown in Equation 3.

Come puoi vedere, la figura nella prima immagine è sfuocata rispetto alla seconda. Ciò è dovuto a una velocità d’otturazione non corretta. Applicando la Regola della Reciprocità, con 1/80 s, mi sono assicurato di ottenere un risultato nitido.

Se il tuo obiettivo o fotocamera dispone di questa tecnologia, potrai ridurre la velocità dell’otturatore a numeri al di sotto di quanto la “Regola del Reciproco della Lunghezza Focale” suggerisce. In ogni caso è sempre bene tenerla in conto.

In many applications, the required distance from an object and the desired FOV (typically the size of the object with additional buffer space) are known quantities. This information can be used to directly determine the required AFOV via Equation 2. Equation 2 is the equivalent of finding the vertex angle of a triangle with its height equal to the WD and its base equal to the horizontal FOV, or HFOV, as shown in Figure 2. Note: In practice, the vertex of this triangle is rarely located at the mechanical front of the lens, from which WD is measured, and is only to be used as an approximation unless the entrance pupil location is known.

The focal length of a lens is a fundamental parameter that describes how strongly it focuses or diverges light. A large focal length indicates that light is bent gradually while a short focal length indicates that the light is bent at sharp angles. In general, lenses with positive focal lengths converge light while lenses with negative focal lengths cause light to diverge, although there are some exceptions based on the distance from the lens to the object being imaged.

Be aware that Equation 6 is an approximation and will rapidly deteriorate for magnifications greater than 0.1 or for short WDs. For magnifications beyond 0.1, either a fixed magnification lens or computer simulations (e.g. Zemax) with the appropriate lens model should be used. For the same reasons, lens calculators commonly found on the internet should only be used for reference. When in doubt, consult a lens specification table.