A common rule of thumb for estimating how fast the exposure needs to be for a given focal length is the one over focal length rule. This states that for a 35 mm camera, the exposure time needs to be at least as fast as one over the focal length in seconds. In other words, when using a 200 mm focal length on a 35 mm camera, the exposure time needs to be at least 1/200 seconds — otherwise blurring may be hard to avoid. See the tutorial on reducing camera shake with hand-held photos for more on this topic.

Keep in mind that this rule is just for rough guidance; some may be able to hand hold a shot for much longer or shorter times. For users of digital cameras with cropped sensors, one needs to convert into a 35 mm equivalent focal length.

The focal length of a lens determines its angle of view, and thus also how much the subject will be magnified for a given photographic position. Wide angle lenses have short focal lengths, while telephoto lenses have longer corresponding focal lengths.

Poi zooma all’indietro dimezzando la lunghezza focale originale, ma avvicinati anche al soggetto cercando di rimanere in linea con lo sfondo in modo che riempia ancora, in maniera approssimativa, la metà inferiore del mirino e fai un altro scatto.

Keep in mind that using a zoom lens does not necessarily mean that one no longer has to change their position; zooms just increase flexibility. In the example below, the original position is shown along with two alternatives using a zoom lens. If a prime lens were used, then a change of composition would not have been possible without cropping the image (if a tighter composition were desirable). Similar to the example in the previous section, the change of perspective was achieved by zooming out and getting closer to the subject. Alternatively, to achieve the opposite perspective effect, one could have zoomed in and moved farther from the subject.

The focal length of a lens may also have a significant impact on how easy it is to achieve a sharp handheld photograph. Longer focal lengths require shorter exposure times to minimize blurring caused by shaky hands. Think of this as if one were trying to hold a laser pointer steady; when shining this pointer at a nearby object its bright spot ordinarily jumps around less than for objects farther away.

An f-number of X may also be displayed as 1:X (instead of f/X), as shown below for the Canon 70-200 f/2.8 lens (whose box is also shown above and lists f/2.8).

Inizia scegliendo un oggetto che sia alto da 1m a 2m, l’ideale sarebbe un parente o un amico, a patto che non si muova troppo :).

Depth of field

Premessa: puoi replicare questo esercizio anche su un tavolo in interno, ma se vuoi proprio approfondire la cosa con risultati subito individuabili ti conviene farlo all’esterno.

Grazie alle 50 Schede di facile lettura che ti guideranno passo passo nel mondo della composizione otterrai scatti sempre perfetti, inoltre le schede sono fatte per essere stampate ed eventualmente plastificate o, ancora meglio potresti caricarle nel tuo smartphone in modo da averle sempre con te!

Camera Type Digital SLR with CF of 1.6X Digital SLR with CF of 1.5X Digital SLR with CF of 1.3X Digital compact with 1/3" sensor Digital compact with 1/2.5" sensor Digital compact with 1/2.3" sensor Digital compact with 1/1.8" sensor Digital compact with 1/1.7" sensor Digital compact with 2/3" sensor Digital compact with a 1" sensor Digital SLR with 4/3" sensor 35 mm (full frame) APS-C 6x4.5 cm 6x6 cm 6x7 cm 5x4 inch 10x8 inch

Imposta lo zoom sulla lunghezza focale più lunga e posizionati in modo che l’oggetto riempia la metà inferiore dell’inquadratura prima di scattare.

Focal length

Con le tre immagini che mostrano grossomodo la stessa scena, l’oggetto dietro dovrebbe essere interamente fuori fuoco nello scatto con lunghezza focale 170mm, più nitido nello scatto con lunghezza focale di 80-100mm e a fuoco, così come l’oggetto davanti, in quello preso con una lunghezza focale di 28-35mm.

*Note: Lens focal lengths are for 35 mm equivalent cameras. If you have a compact or digital SLR camera, then you likely have a different sensor size. To adjust the above numbers for your camera, please use the focal length converter in the tutorial on digital camera sensor sizes.

Minimum apertures for lenses are generally nowhere near as important as maximum apertures. This is primarily because the minimum apertures are rarely used due to photo blurring from lens diffraction, and because these may require prohibitively long exposure times. For cases where extreme depth of field is desired, then smaller minimum aperture (larger maximum f-number) lenses allow for a wider depth of field.

Ora, con lo zoom impostato sui 170mm circa, o in ogni caso alla massima focale a tua disposizione, inquadra l’oggetto che è davanti a te in modo che riempia almeno metà dell’altezza del mirino e mettilo fuoco assicurandoti che l’oggetto di dietro sia ancora visibile in maniera chiara.

Note: The location where light rays cross is not necessarily equal to the focal length,as shown above, but is instead roughly proportional to this distance.

Perspective control can be a powerful compositional tool in photography, and often determines one's choice in focal length (when one can photograph from any position). Move your mouse over the above image to view an exaggerated perspective due to a wider angle lens. Note how the subjects within the frame remain nearly identical — therefore requiring a closer position for the wider angle lens. The relative sizes of objects change such that the distant doorway becomes smaller relative to the nearby lamps.

Per il secondo esercizio avrai bisogno di un’area leggermente più grande in cui lavorare e più grande è la differenza tra l’obiettivo con la lunghezza focale più corta e quello con la lunghezza focale più lunga più sarà evidente il risultato.

Bene, dopo aver fatto questi interessanti esercizi, dovresti aver ben chiaro come funziona la profondità di campo, per cui ora esci a scattare.

CameraSize comparison withlens

Finally, some zoom lenses on digital SLR and compact digital cameras often list a range of maximum aperture, because this may depend on how far one has zoomed in or out. These aperture ranges therefore refer only to the range of maximum aperture, not overall range. A range of f/2.0-3.0 would mean that the maximum available aperture gradually changes from f/2.0 (fully zoomed out) to f/3.0 (at full zoom). The primary benefit of having a zoom lens with a constant maximum aperture is that exposure settings are more predictable, regardless of focal length.

When one is considering purchasing a lens, specifications ordinarily list the maximum (and maybe minimum) available apertures. Lenses with a greater range of aperture settings provide greater artistic flexibility, in terms of both exposure options and depth of field. The maximum aperture is perhaps the most important lens aperture specification, which is often listed on the box along with focal length(s).

CameraFOV calculator

Why would one intentionally restrict their options by using a prime lens?Prime lenses existed long before zoom lenses were available, and still offer many advantages over their more modern counterparts. When zoom lenses first arrived on the market, one often had to be willing to sacrifice a significant amount of optical quality. However, more recent high-end zoom lenses generally do not produce noticeably lower image quality, unless scrutinized by the trained eye (or in a very large print).

Le distanze non sono realmente importanti, ma quello che davvero importa è che con lunghezze focali che spaziano da 35 a 170mm tu riesca a vedere in maniera chiara entrambe gli oggetti.

Note: Calculator assumes that camera is oriented such that the maximum subject dimension given by "subject size" is in the camera's longest dimension. Calculator not intended for use in extreme macro photography.

Dovrebbe essere evidente come, nello scatto con la lunghezza focale più lunga, lo sfondo appaia compresso e l’angolo di campo ristretto.

Per vedere gli scatti al meglio, scaricali su un pc e prova a ritagliare il secondo ed il terzo scatto in modo tale che mostrino grossomodo la stessa scena del primo, ovvero quello con l’oggetto davanti che riempie il mirino per metà.

Portrait and indoor sports/theater photography often requires lenses with very large maximum apertures, in order to be capable of a narrower depth of field or a faster shutter speed, respectively. The narrow depth of field in a portrait helps isolate the subject from their background. For digital SLR cameras, lenses with larger maximum apertures provide significantly brighter viewfinder images — possibly critical for night and low-light photography. These also often give faster and more accurate auto-focusing in low-light. Manual focusing is also easier because the image in the viewfinder has a narrower depth of field (thus making it more visible when objects come into or out of focus).

focallength中文

For compact digital cameras, lenses listed with a 3X, 4X, etc. zoom designation refer to the ratio between the longest and shortest focal lengths. Therefore, a larger zoom designation does not necessarily mean that the image can be magnified any more (since that zoom may just have a wider angle of view when fully zoomed out). Additionally, digital zoom is not the same as optical zoom, as the former only enlarges the image through interpolation. Read the fine-print to ensure you are not misled.

The following table provides an overview of what focal lengths are required to be considered a wide angle or telephoto lens, in addition to their typical uses. Please note that focal lengths listed are just rough ranges, and actual uses may vary considerably; many use telephoto lenses in distant landscapes to compress perspective, for example.

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Many will say that focal length also determines the perspective of an image, but strictly speaking, perspective only changes with one's location relative to their subject. If one tries to fill the frame with the same subjects using both a wide angle and telephoto lens, then perspective does indeed change, because one is forced to move closer or farther from their subject. For these scenarios only, the wide angle lens exaggerates or stretches perspective, whereas the telephoto lens compresses or flattens perspective.

This is primarily because slight rotational vibrations are magnified greatly with distance, whereas if only up and down or side to side vibrations were present, the laser's bright spot would not change with distance.

Il primo esercizio mostra come la lunghezza focale influisca sulla profondità di campo, mentre il secondo mostra come la lunghezza focale possa essere utilizzata per modificare efficacemente i punti di vista dello sfondo.

Any of the above problems is present to some degree with any lens. In the rest of this tutorial, when a lens is referred to as having lower optical quality than another lens, this is manifested as some combination of the above artifacts. Some of these lens artifacts may not be as objectionable as others, depending on the subject matter.

Quando ritagli, non preoccuparti della qualità dell’immagine, in quanto quello che in questo momento ti interessa è solo ed esclusivamente la profondità di campo.

All but the simplest cameras contain lenses which are actually comprised of several "lens elements." Each of these elements directs the path of light rays to recreate the image as accurately as possible on the digital sensor. The goal is to minimize aberrations, while still utilizing the fewest and least expensive elements.

Note: For a more quantitative and technical discussion of the above topic, please see thetutorial on camera lens quality: MTF, resolution & contrast.

Il consiglio che sento di darti è quello di utilizzare un treppiede in modo che la fotocamera non si sposti tra uno scatto e l’altro.

Lenscalculator

Con il secondo ed il terzo scatto, sebbene le dimensioni del soggetto dovrebbero essere rimaste grossomodo le stesse, vedrai che lo sfondo sembra allungarsi lontano dal soggetto e lo spazio tra i vari oggetti dello sfondo dovrebbe essere sempre più delineato.

Optical aberrations occur when points in the image do not translate back onto single points after passing through the lens — causing image blurring, reduced contrast or misalignment of colors (chromatic aberration). Lenses may also suffer from uneven, radially decreasing image brightness (vignetting) or distortion. Move your mouse over each of the options below to see how these can impact image quality in extreme cases:

The aperture range of a lens refers to the amount that the lens can open up or close down to let in more or less light, respectively. Apertures are listed in terms of f-numbers, which quantitatively describe relative light-gathering area (depicted below).

Sarebbe d’aiuto posizionare la fotocamera su un treppiede, in modo da rendere più facile realizzare gli scatti e confrontare i risultati, e non preoccuparti del tempo di otturazione lento se stai fotografando in condizioni di luce scarsa.

Note that larger aperture openings are defined to have lower f-numbers (often very confusing). These two terms are often mistakenly interchanged; the rest of this tutorial refers to lenses in terms of their aperture size. Lenses with larger apertures are also described as being "faster," because for a given ISO speed, the shutter speed can be made faster for the same exposure. Additionally, a smaller aperture means that objects can be in focus over a wider range of distance, a concept also termed the depth of field.

The primary advantages of prime lenses are in cost, weight and speed. An inexpensive prime lens can generally provide as good (or better) image quality as a high-end zoom lens. Additionally, if only a small fraction of the focal length range is necessary for a zoom lens, then a prime lens with a similar focal length will be significantly smaller and lighter. Finally, the best prime lenses almost always offer better light-gathering ability (larger maximum aperture) than the fastest zoom lenses — often critical for low-light sports/theater photography, and when a shallow depth of field is necessary.

Also note that just because the maximum aperture of a lens may not be used, this does not necessarily mean that this lens is not necessary. Lenses typically have fewer aberrations when they perform the exposure stopped down one or two f-stops from their maximum aperture (such as using a setting of f/4.0 on a lens with a maximum aperture of f/2.0). This *may* therefore mean that if one wanted the best quality f/2.8 photograph, a f/2.0 or f/1.4 lens may yield higher quality than a lens with a maximum aperture of f/2.8.

Other considerations include cost, size and weight. Lenses with larger maximum apertures are typically much heavier, larger and more expensive. Size/weight may be critical for wildlife, hiking and travel photography because all of these often utilize heavier lenses, or require carrying equipment for extended periods of time.

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Gli esercizi sulla profondità di campo presentati di seguito sono studiati per analizzare come diverse lunghezze focali hanno effetto sulle immagini e sulla profondità di campo.

Focus distance

Understanding camera lenses can help add more creative control to digital photography. Choosing the right lens for the task can become a complex trade-off between cost, size, weight, lens speed and image quality. This tutorial aims to improve understanding by providing an introductory overview of concepts relating to image quality, focal length, perspective, prime vs. zoom lenses and aperture or f-number.

Ripeti infine lo stesso esercizio, ma riducendo lo zoom alla lunghezza focale più corta (quella con l’angolo più ampio). Avanza verso il soggetto, riempi nuovamente mezza inquadratura e procedi nel fare l’ultimo scatto.

Other factors may also be influenced by lens focal length. Telephoto lenses are more susceptible to camera shake since small hand movements become magnified, similar to the shakiness experience while trying to look through binoculars. Wide angle lenses are generally more resistant to flare, in part because the designers assume that the sun is more likely to be within the frame. A final consideration is that medium and telephoto lenses generally yield better optical quality for similar price ranges.

Per realizzare fotografie degne di nota e per essere sempre pronti allo scatto, la profondità di campo è un concetto che deve essere il più chiaro possibile, per cui ecco dei comodi esercizi che mirano proprio a farti comprendere al meglio la profondità di campo.

A zoom lens is one where the photographer can vary the focal length within a pre-defined range, whereas this cannot be changed with a "prime" or fixed focal length lens. The primary advantage of a zoom lens is that it is easier to achieve a variety of compositions or perspectives (since lens changes are not necessary). This advantage is often critical for dynamic subject matter, such as in photojournalism and children's photography.

Durante il nostro corso di fotografia abbiamo affrontato diversi concetti tra cui quello della profondità di campo. Per comprenderlo al meglio, prova ad immaginare il tuo soggetto avvolto da una sfera, ecco in quella sfera tutto è a fuoco, fuori dalla sfera man mano il tuo soggetto o quello che gli sta attorno diventano sempre più sfocati.

Sistema il soggetto in modo che ci siano sfondi vari a profondità riconoscibili, come ad esempio un albero a una certa distanza, una siepe a un’altra e uno steccato a un’altra ancora.