Ogni oggetto, illuminato da una o più sorgenti luminose, riflette parte della luce che lo colpisce. Se proviamo ad illuminare un oggetto di colore rosso e lo poniamo molto vicino ad una superficie bianca, parte delle riflessioni andranno a cadere sulla superficie bianca che diventerà colorata parzialmente di rosso.

Once the show design is finished, the file is exported to a format that includes the color data for each of the lights. A typical show will also have a refresh rate between 20Hz and 40Hz, which means the output file contains the status of every bulb for every frame during the show.

Nell'immagine qui in alto potete osservare chiaramente come lo stesso valore di f su due obiettivi (gli stessi Nikon e Yashica di prima) con lunghezza focale fissa, rispettivamente pari a 50 mm e 80 mm, si tradurrà in aperture molto diverse: circa 12,5mm nel 50mm Yashica e circa 20mm nel Nikon da 80mm. Il "circa" è obbligatorio poiché la misura del diametro è approssimativa sia per disegno e numero delle lamelle, sia per le differenze nella costruzione. Negli obiettivi più complessi questa approssimazione è ancora più incerta. In ogni modo, impostando il valore f = 4, l'obiettivo Nikon avrà di conseguenza minore profondità di campo poiché l'apertura del diaframma sarà nettamente più grande. Per avere la stessa profondità di campo di un obiettivo da 50mm con f impostato 4, su un 80mm dovremo chiudere l'apertura del diaframma fino al valore di f 6,4 poiché 80/6,4 equivale a 12,5mm. Ricordate che il valore di f è inversamente proporzionale al diametro dell'apertura, quindi a valori più grandi di f corrispondono aperture più piccole. Per approfondire l'argomento sull'apertura del diaframma vi consigliamo l'articolo su Wikipedia in lingua inglese e i suoi preziosi riferimenti bibliografici: en.wikipedia.org/wiki/F-number

It's certainly too late this year to put one up, but there are plenty of resources to teach you everything you need to know. There's a great YouTube series that can teach you the basics to get you started. Depending on how much effort you want to put into the display and how good you are with a soldering iron, you can either make your own show elements or buy some ready-to-run.

Controllers and Power All those lights are great, but they need controllers and power supplies. A typical show that you may see will have two types of controllers: the first is a show computer that stores the file from the sequencing software and transmits it to all of the elements. The second type of hardware used to run the show are the controllers that interface directly with the lights. These controllers come in many different shapes and sizes but all do essentially the same thing. They convert the data from the show computer into the WS2811 protocol which directly drives the lights. The controllers receive data from the show computer using a protocol called E1.31. This protocol is a way to stream lighting data over a traditional IP based network. The pixels are grouped into "universes" of 170 lights which all get routed to the same controller. Each light needs to have a red, green, and blue intensity value to determine what color it should be. If you are familiar with DMX for theatrical productions, it's the same idea. Each controller has an IP address and knows what configuration of lights are connected to its output. When it receives a data packet from the show computer, it makes sure it is addressed to the right universe, decodes the WS2811 data that is in the packet, and outputs the data stream to the pixels. In terms of controllers, there are two main styles that people will use in a light show. The first is a centralized, very powerful controller with lots of outputs. The second is numerous smaller controllers positioned closer to the elements. Both have their benefits and while centralized controllers are the most popular style now, the smaller decentralized controller style is gaining in popularity. The controller I have here is a professional-grade board made by Advatek Lighting. This device can control up to 32 individual pixel strings outputs for a total of just over 16,000 pixels. Thanks to its beefy power connectors, it can also supply hundreds of Watts to keep the pixels bright. Rather than using Wi-Fi, which can get crowded if you have lots of devices, this controller has a dedicated Ethernet connection. If you are serious about holiday lighting, this is the type of controller you want. It is also powerful enough to be used in commercial displays like at a theme park. Taking a tour around this board (photo above), we start with the main power connectors on the left side which power the lights. Pixels use either 5V or 12V, so a standard high-wattage computer power supply can be used or power supplies specifically designed for LED lights. This board can handle both voltages at the same time. Around the top and bottom we have 16 removable plugs for the pixel connectors to plug into. Most of the common pixel types, like WS2811, use three wires: power, ground, and data. However, some other pixel types have a clock pin as well. At the center of all of this is a microprocessor that handles the connectivity and signal required to interface with the pixels. There are also four driver ICs that boost the signal-level output from the processor to one suitable for driving pixels a long distance from the controller. Finally, on the right hand side, we have external connectivity. This includes legacy DMX outputs as well as Etherne. There are many other controllers from companies like Falcon and HolidayCoro but they all have a similar format. Running the Show Once you have all the required components and everything is put together, running the show is fairly simple. On the controller side, you just need to tell it what configuration of pixels are attached to what output port. You can also adjust things like brightness and pixel ordering. Each controller will have its own configuration either via a web interface or through a dedicated program. The last thing you'll need is a computer to store the sequences and audio data for the show. You can use a laptop, but one of the most common types of show computers due to its cost and accessibility is a Raspberry Pi with the Falcon Pi Player software. Every night during the show, it loads the sequences we programmed earlier, plays the audio associated with it, and sends the lighting data out to the controllers in the display. This computer also needs to know about the specific controller setup, so that it can send data to the right address. The audio output is usually fed into a portable FM radio transmitter, so that people in their cars can hear the show. To recap, the lighting effects are first created in software, then that software is exported into a show file which contains the color data for each pixel at every moment of the show. The show file is played from a show computer which outputs the light data using the E1.31 protocol to controllers. The controllers receive packets addressed to them and finally output the resulting WS2811 data to the pixels. There's a lot of technology behind the scenes to create these displays and it still has lots of room to improve. Pixels are becoming more accessible and easy to setup. Controllers are getting more powerful but at the same time, more user-friendly. Interested in setting up a display of your own? It's certainly too late this year to put one up, but there are plenty of resources to teach you everything you need to know. There's a great YouTube series that can teach you the basics to get you started. Depending on how much effort you want to put into the display and how good you are with a soldering iron, you can either make your own show elements or buy some ready-to-run. The displays can be a bit expensive getting started, but the price is dropping year after year. For example, a strand or strip of 50 pixels will cost around $10 from China and a good controller will cost around $200. Besides that, basic tools like PVC pipe, metal conduit, zip ties, and hook-up wire aren't very expensive. I've been doing light shows for a few years now, the video at the top of the article is my 2018 show if you'd like to see what the final product looks like. Happy holidays everyone! If you enjoy our content, please consider subscribing. Ad-free TechSpot experience while supporting our work Our promise: All reader contributions will go toward funding more content That means: More tech features, more benchmarks and analysis

Running the Show Once you have all the required components and everything is put together, running the show is fairly simple. On the controller side, you just need to tell it what configuration of pixels are attached to what output port. You can also adjust things like brightness and pixel ordering. Each controller will have its own configuration either via a web interface or through a dedicated program. The last thing you'll need is a computer to store the sequences and audio data for the show. You can use a laptop, but one of the most common types of show computers due to its cost and accessibility is a Raspberry Pi with the Falcon Pi Player software. Every night during the show, it loads the sequences we programmed earlier, plays the audio associated with it, and sends the lighting data out to the controllers in the display. This computer also needs to know about the specific controller setup, so that it can send data to the right address. The audio output is usually fed into a portable FM radio transmitter, so that people in their cars can hear the show. To recap, the lighting effects are first created in software, then that software is exported into a show file which contains the color data for each pixel at every moment of the show. The show file is played from a show computer which outputs the light data using the E1.31 protocol to controllers. The controllers receive packets addressed to them and finally output the resulting WS2811 data to the pixels. There's a lot of technology behind the scenes to create these displays and it still has lots of room to improve. Pixels are becoming more accessible and easy to setup. Controllers are getting more powerful but at the same time, more user-friendly. Interested in setting up a display of your own? It's certainly too late this year to put one up, but there are plenty of resources to teach you everything you need to know. There's a great YouTube series that can teach you the basics to get you started. Depending on how much effort you want to put into the display and how good you are with a soldering iron, you can either make your own show elements or buy some ready-to-run. The displays can be a bit expensive getting started, but the price is dropping year after year. For example, a strand or strip of 50 pixels will cost around $10 from China and a good controller will cost around $200. Besides that, basic tools like PVC pipe, metal conduit, zip ties, and hook-up wire aren't very expensive. I've been doing light shows for a few years now, the video at the top of the article is my 2018 show if you'd like to see what the final product looks like. Happy holidays everyone! If you enjoy our content, please consider subscribing. Ad-free TechSpot experience while supporting our work Our promise: All reader contributions will go toward funding more content That means: More tech features, more benchmarks and analysis

Per dimostrare questa evidenza, prima di dedicarci al tema principale di questo articolo, è necessario aprire una parentesi sul diaframma. E per capire cosa è il diaframma bisogna partire dalla camera oscura.

Designing the Show Designing a show is a lot like composing for an orchestra. The lights are arranged in props like trees, arches, stars, snowflakes, and more. Different props can be grouped like instruments in an orchestra as they light up with the music. Choreographing the different elements to music requires special software that knows how to interface with the lighting protocol. The most common program is xLights which is free and open-source. Shows are designed sequentially along a timeline where each show element has a different track. There are many different effects that can be applied to individual elements or to groups. Each show is unique and the different effects can be endlessly customized. The software creates a grid of where the lights are located using a reference photo of the venue. From here, complex patterns can be applied to the grid to create the effects. Some effects might only light up a single strand while others might move across the entire house. Once the show design is finished, the file is exported to a format that includes the color data for each of the lights. A typical show will also have a refresh rate between 20Hz and 40Hz, which means the output file contains the status of every bulb for every frame during the show. Controllers and Power All those lights are great, but they need controllers and power supplies. A typical show that you may see will have two types of controllers: the first is a show computer that stores the file from the sequencing software and transmits it to all of the elements. The second type of hardware used to run the show are the controllers that interface directly with the lights. These controllers come in many different shapes and sizes but all do essentially the same thing. They convert the data from the show computer into the WS2811 protocol which directly drives the lights. The controllers receive data from the show computer using a protocol called E1.31. This protocol is a way to stream lighting data over a traditional IP based network. The pixels are grouped into "universes" of 170 lights which all get routed to the same controller. Each light needs to have a red, green, and blue intensity value to determine what color it should be. If you are familiar with DMX for theatrical productions, it's the same idea. Each controller has an IP address and knows what configuration of lights are connected to its output. When it receives a data packet from the show computer, it makes sure it is addressed to the right universe, decodes the WS2811 data that is in the packet, and outputs the data stream to the pixels. In terms of controllers, there are two main styles that people will use in a light show. The first is a centralized, very powerful controller with lots of outputs. The second is numerous smaller controllers positioned closer to the elements. Both have their benefits and while centralized controllers are the most popular style now, the smaller decentralized controller style is gaining in popularity. The controller I have here is a professional-grade board made by Advatek Lighting. This device can control up to 32 individual pixel strings outputs for a total of just over 16,000 pixels. Thanks to its beefy power connectors, it can also supply hundreds of Watts to keep the pixels bright. Rather than using Wi-Fi, which can get crowded if you have lots of devices, this controller has a dedicated Ethernet connection. If you are serious about holiday lighting, this is the type of controller you want. It is also powerful enough to be used in commercial displays like at a theme park. Taking a tour around this board (photo above), we start with the main power connectors on the left side which power the lights. Pixels use either 5V or 12V, so a standard high-wattage computer power supply can be used or power supplies specifically designed for LED lights. This board can handle both voltages at the same time. Around the top and bottom we have 16 removable plugs for the pixel connectors to plug into. Most of the common pixel types, like WS2811, use three wires: power, ground, and data. However, some other pixel types have a clock pin as well. At the center of all of this is a microprocessor that handles the connectivity and signal required to interface with the pixels. There are also four driver ICs that boost the signal-level output from the processor to one suitable for driving pixels a long distance from the controller. Finally, on the right hand side, we have external connectivity. This includes legacy DMX outputs as well as Etherne. There are many other controllers from companies like Falcon and HolidayCoro but they all have a similar format. Running the Show Once you have all the required components and everything is put together, running the show is fairly simple. On the controller side, you just need to tell it what configuration of pixels are attached to what output port. You can also adjust things like brightness and pixel ordering. Each controller will have its own configuration either via a web interface or through a dedicated program. The last thing you'll need is a computer to store the sequences and audio data for the show. You can use a laptop, but one of the most common types of show computers due to its cost and accessibility is a Raspberry Pi with the Falcon Pi Player software. Every night during the show, it loads the sequences we programmed earlier, plays the audio associated with it, and sends the lighting data out to the controllers in the display. This computer also needs to know about the specific controller setup, so that it can send data to the right address. The audio output is usually fed into a portable FM radio transmitter, so that people in their cars can hear the show. To recap, the lighting effects are first created in software, then that software is exported into a show file which contains the color data for each pixel at every moment of the show. The show file is played from a show computer which outputs the light data using the E1.31 protocol to controllers. The controllers receive packets addressed to them and finally output the resulting WS2811 data to the pixels. There's a lot of technology behind the scenes to create these displays and it still has lots of room to improve. Pixels are becoming more accessible and easy to setup. Controllers are getting more powerful but at the same time, more user-friendly. Interested in setting up a display of your own? It's certainly too late this year to put one up, but there are plenty of resources to teach you everything you need to know. There's a great YouTube series that can teach you the basics to get you started. Depending on how much effort you want to put into the display and how good you are with a soldering iron, you can either make your own show elements or buy some ready-to-run. The displays can be a bit expensive getting started, but the price is dropping year after year. For example, a strand or strip of 50 pixels will cost around $10 from China and a good controller will cost around $200. Besides that, basic tools like PVC pipe, metal conduit, zip ties, and hook-up wire aren't very expensive. I've been doing light shows for a few years now, the video at the top of the article is my 2018 show if you'd like to see what the final product looks like. Happy holidays everyone! If you enjoy our content, please consider subscribing. Ad-free TechSpot experience while supporting our work Our promise: All reader contributions will go toward funding more content That means: More tech features, more benchmarks and analysis

Le prime camere oscure non avevano lenti ed erano costruite proprio come lo schema del precedente paragrafo: un piano con un piccolo foro interposto tra la scena da riprendere e lastra fotografica. Il problema maggiore era rappresentato dalla luminosità del sistema: l'immagine riflessa non era molto luminosa.

Depending on where you live, you've likely seen a house with crazy flashing Christmas lights that change color and dance to music. Almost every neighborhood or town has "that one house" that goes all out for the holidays each year. In my neighborhood, that house is mine. If you've ever wondered how those displays work and what you need to make your own, this will be a short overview of all the components and how everything works together.

La profondità di campo è l'ampiezza in profondità in cui risulta nitida la scena ripresa, a cavallo del piano di messa a fuoco. Nell'immagine di apertura, qui in alto, abbiamo lo stesso soggetto ripreso con due profondità di campo molto diverse: a sinistra una profondità di campo molto ridotta; a destra una profondità di campo decisamente più ampia. Secondo autorevoli articoli tecnici, la profondità di campo è in relazione ad alcuni parametri che ne determinano l'ampiezza: il diaframma, la focale e la distanza del piano di messa a fuoco. In realtà il solo ad essere responsabile della profondità di campo è l'apertura del diaframma.

The displays can be a bit expensive getting started, but the price is dropping year after year. For example, a strand or strip of 50 pixels will cost around $10 from China and a good controller will cost around $200. Besides that, basic tools like PVC pipe, metal conduit, zip ties, and hook-up wire aren't very expensive.

To recap, the lighting effects are first created in software, then that software is exported into a show file which contains the color data for each pixel at every moment of the show. The show file is played from a show computer which outputs the light data using the E1.31 protocol to controllers. The controllers receive packets addressed to them and finally output the resulting WS2811 data to the pixels.

The lights are arranged together to form different props like leaping arches, snowflakes, stars, megatrees, and more. You couple those lights with controllers and power supplies to make them work as expected. There is specialized computer software that tells the controllers when to turn on and off the lights according to the music being played. These components are at the heart of every light show and I'll go into detail about each one. While you won't be able to go to Walmart and pick this stuff up, there are many companies and a large, helpful community eager to help.

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Il sensore cattura l'immagine che arriva ed è responsabile - assieme alla successiva elaborazione - della presenza o meno di rumore digitale, della dinamica, della fedeltà dei colori, della risoluzione e di tutti i parametri legati alla conversione in formato digitale. Il sensore dunque fa solo questo, cioè, non modifica le caratteristiche della lente, come la profondità di campo. Un sensore grande catturerà un angolo di campo maggiore. Un sensore più piccolo catturerà un angolo di campo inferiore. Nell'esempio qui in basso, abbiamo scattato due foto dalla stessa posizione, con il medesimo obiettivo (un 90mm con attacco Canon EF) e con lo stesso valore di apertura f = 4, con due fotocamere diverse per dimensione dei sensori: Canon 5D Mark II full frame e Canon 60D APS-C.

Vi ricordo che l'apertura del diaframma è espressa in rapporto alla lunghezza focale, quindi è naturale che aumentando la focale diminuisca la profondità di campo, perché per avere pari luminosità si avranno aperture più grandi. D'altra parte non è esatto dire che aumentando la focale diminuisca la profondità poiché sarà l'apertura del diaframma a ingrandirsi. Anche la distanza del soggetto messo a fuoco è legata al diaframma. Infatti è normale che a parità di apertura, più ci allontaniamo dal punto di fuoco e più grandi saranno i circoli di confusione.

La sequenza dei valori di f è tale che ad ogni step l'area dell'apertura del diaframma si dimezza a parità di lunghezza focale. Nella tabella qui in basso ci sono due esempi con lunghezze focali rispettivamente di 100mm e 50mm. Nel primo caso, con 100mm di focale e apertura di 5,6 avremo un diametro di circa 17,86mm, quindi un'area di circa 200mm². Con lo stesso procedimento troveremo che l'area per f = 8 sarà di circa 100mm² e per f = 11 sarà di circa 50mm². In altre parole, supponendo che l'area dell'apertura diaframma sia uguale ad 1, dimezzando ad ogni passo l'area, avremo questa sequenza:

L'inserimento della lente ha portato altre problematiche. Se per ipotesi spostiamo il piano di messa a fuoco, l'immagine non sarà più nitida poiché i raggi non si concentreranno più sul piano focale, creando i cosiddetti "circoli di confusione". Con l'introduzione di una lente si può ottenere un'immagine nitida solamente su un piano focale.

The software creates a grid of where the lights are located using a reference photo of the venue. From here, complex patterns can be applied to the grid to create the effects. Some effects might only light up a single strand while others might move across the entire house.

Benché esista soltanto un piano dove l'immagine sarà a fuoco, entro un certo margine l'immagine sarà comunque nitida, poiché i circoli di confusione saranno ancora talmente piccoli da "ingannare" l'occhio umano. Questo margine, davanti e dietro l'oggetto messo a fuoco, in cui l'occhio percepisce l'immagine nitida, è detta profondità di campo: "pdc". Chiudendo all'estremo l'apertura nel diaframma, ci avvicineremo al foro stenopeico in cui tutto sembrerà a fuoco e la profondità di campo sarà massima.

The most common program is xLights which is free and open-source. Shows are designed sequentially along a timeline where each show element has a different track. There are many different effects that can be applied to individual elements or to groups. Each show is unique and the different effects can be endlessly customized.

I've been doing light shows for a few years now, the video at the top of the article is my 2018 show if you'd like to see what the final product looks like. Happy holidays everyone!

La profondità di campo, termine spesso abusato sia in fotografia che in ripresa video, è l'ampiezza in profondità in cui risulta nitida la scena ripresa, a cavallo del piano di messa a fuoco. Nella guida dimostreremo come la profondità di campo sia legata solo ed esclusivamente all'apertura del diaframma.

Il limite del singolo piano focale si ha anche al contrario: la lente ha un preciso punto di fuoco (che chiameremo "F"). Tutto quello che si troverà distante da esso creerà circoli di confusione sul piano focale PF.

xLights

These type of lights and their protocols were originally designed for digital signage and for theatrical productions. The same WS2811 protocol is used in modern individually addressable PC RGB lighting strips that you might have in your gaming rig. The only difference is that holiday lights have a waterproof coating, are available in strings up of roughly 10-15ft, and cost considerably less.

Taking a tour around this board (photo above), we start with the main power connectors on the left side which power the lights. Pixels use either 5V or 12V, so a standard high-wattage computer power supply can be used or power supplies specifically designed for LED lights. This board can handle both voltages at the same time. Around the top and bottom we have 16 removable plugs for the pixel connectors to plug into.

Le dimensioni dell'apertura nel diaframma hanno effetto non soltanto sulla luce ma anche sui circoli di confusione. Un'apertura maggiore comporta un aumento del diametro dei circoli di confusione distanti dal piano focale. Con un'apertura più limitata i circoli di confusione saranno più piccoli.

In terms of controllers, there are two main styles that people will use in a light show. The first is a centralized, very powerful controller with lots of outputs. The second is numerous smaller controllers positioned closer to the elements. Both have their benefits and while centralized controllers are the most popular style now, the smaller decentralized controller style is gaining in popularity.

All those lights are great, but they need controllers and power supplies. A typical show that you may see will have two types of controllers: the first is a show computer that stores the file from the sequencing software and transmits it to all of the elements. The second type of hardware used to run the show are the controllers that interface directly with the lights. These controllers come in many different shapes and sizes but all do essentially the same thing. They convert the data from the show computer into the WS2811 protocol which directly drives the lights.

Each controller has an IP address and knows what configuration of lights are connected to its output. When it receives a data packet from the show computer, it makes sure it is addressed to the right universe, decodes the WS2811 data that is in the packet, and outputs the data stream to the pixels.

La profondità di campo viene spesso associata alle dimensioni del sensore, oltre che alle dimensioni del diaframma. In realtà l'unica cosa che fa un sensore è quello di catturare le immagini che arrivano dalla lente, senza modificare la profondità di campo. Per spiegare questo concetto, nelle immagini qui in basso potete osservare l'obiettivo Nikon da 85mm con la massima apertura (f 2) mentre riflette su uno schermo bianco l'immagine della finestra (capovolta e invertita). A noi interessa la profondità di campo di quella immagine creata dall'obiettivo sul piano focale, poiché l'immagine che attraversa uno specifico obiettivo, proiettata su un sensore da mezzo pollice o su un muro di 5 metri, è identica.

The controllers receive data from the show computer using a protocol called E1.31. This protocol is a way to stream lighting data over a traditional IP based network. The pixels are grouped into "universes" of 170 lights which all get routed to the same controller. Each light needs to have a red, green, and blue intensity value to determine what color it should be. If you are familiar with DMX for theatrical productions, it's the same idea.

Designing a show is a lot like composing for an orchestra. The lights are arranged in props like trees, arches, stars, snowflakes, and more. Different props can be grouped like instruments in an orchestra as they light up with the music. Choreographing the different elements to music requires special software that knows how to interface with the lighting protocol.

Computer Caselights

Once you have all the required components and everything is put together, running the show is fairly simple. On the controller side, you just need to tell it what configuration of pixels are attached to what output port. You can also adjust things like brightness and pixel ordering. Each controller will have its own configuration either via a web interface or through a dedicated program.

Poiché l'area del diaframma è direttamente proporzionale al quadrato del diametro (A =  ¼ π d²), basta fare la radice quadrata dei denominatori per avere il diametro del diaframma stesso, quindi:

There are many types of pixels and many different protocols for communicating with them. The most common type of pixels use a protocol called WS2811. Essentially, the pixels in a strand receive data sequentially, decode the data intended for them, and pass through the data for all of the subsequent pixels down the line. The actual data that is transmitted consists of a red, green, and blue intensity value for each bulb.

AV Raw s.n.c. P.iva: 02040960672 AV Magazine - Testata giornalistica con registrazione Tribunale di Teramo n. 527 del 22.12.2004 Direttore Responsabile: Emidio Frattaroli Editore: AV Raw s.n.c. - Iscrizione ROC n. 33221

LEDLightsfor Computer screen

Most of the common pixel types, like WS2811, use three wires: power, ground, and data. However, some other pixel types have a clock pin as well. At the center of all of this is a microprocessor that handles the connectivity and signal required to interface with the pixels. There are also four driver ICs that boost the signal-level output from the processor to one suitable for driving pixels a long distance from the controller. Finally, on the right hand side, we have external connectivity. This includes legacy DMX outputs as well as Etherne. There are many other controllers from companies like Falcon and HolidayCoro but they all have a similar format.

The last thing you'll need is a computer to store the sequences and audio data for the show. You can use a laptop, but one of the most common types of show computers due to its cost and accessibility is a Raspberry Pi with the Falcon Pi Player software.

In questo articolo metteremo da parte il rapporto di riproduzione che ha effetti nella percezione soggettiva della profondità di campo. In altre parole, la stessa identica immagine, osservata con diversi rapporti di riproduzione, sarà percepita con profondità di campo differente: più l'immagine sarà piccola, più sembrerà che tutto sia a fuoco e quindi con profondità di campo più elevata. In questo articolo ci concentreremo sulla profondità di campo dell'immagine svincolata dal rapporto di riproduzione e di come sia legata solo all'apertura del diaframma.

L'apertura del diaframma - sarebbe più opportuno chiamarla "rapporto d'apertura" -  è misurata tramite il valore f che è il rapporto tra la lunghezza focale e il diametro dell'apertura del diaframma, con entrambi i valori espressi in millimetri. In altre parole, f = F/d con F che rappresenta la lunghezza focale e d che rappresenta il diametro. Applicando la formula inversa, conoscendo il valore della focale e di f, è possibile calcolare l'area dell'apertura: d = F/f. Ad esempio, con f = 1/4 su una focale 50mm, il diametro dell'apertura del diaframma è 50/4, ovvero 12,5mm. Con f = 1/4 su una focale 85mm avremo un'apertura pari a 85/4 quindi 21,25 mm. Questa apparente complicazione serve in realtà a semplificare un parametro che è più importante in fotografia rispetto all'apertura del diaframma: la quantità di luce che attraversa l'obiettivo, indipendentemente dalla lunghezza focale.

Se tra l'oggetto e la superficie bianca poniamo un ostacolo, un diaframma (dal greco "διάϕραγμα", separazione) con un foro al centro, le riflessioni sulla superficie bianca saranno concentrate su un'area limitata: soltanto alcuni fasci luminosi arriveranno ad illuminare la superficie e le riflessioni tenderanno a formare la stessa immagine dell'oggetto illuminato con i contorni poco definiti. Supponiamo adesso che il foro sia piccolissimo (nell'ordine dei decimi di millimetro): in questo caso i fasci luminosi che attraversano il foro e arrivano sul piano saranno pochissimi e rifletteranno l'oggetto esattamente com'è nella realtà, con l'immagine proiettata sul piano bianco ma capovolta (sopra-sotto) e invertita (destra-sinistra).

Every night during the show, it loads the sequences we programmed earlier, plays the audio associated with it, and sends the lighting data out to the controllers in the display. This computer also needs to know about the specific controller setup, so that it can send data to the right address. The audio output is usually fed into a portable FM radio transmitter, so that people in their cars can hear the show.

A typical holiday light display using this technology might have had a few dozen of such relays controlling an equal number of light strands. This technology was fine for a few years, but eventually things started to get more elaborate.

There's a lot of technology behind the scenes to create these displays and it still has lots of room to improve. Pixels are becoming more accessible and easy to setup. Controllers are getting more powerful but at the same time, more user-friendly.

HolidayCoro

The controller I have here is a professional-grade board made by Advatek Lighting. This device can control up to 32 individual pixel strings outputs for a total of just over 16,000 pixels. Thanks to its beefy power connectors, it can also supply hundreds of Watts to keep the pixels bright. Rather than using Wi-Fi, which can get crowded if you have lots of devices, this controller has a dedicated Ethernet connection. If you are serious about holiday lighting, this is the type of controller you want. It is also powerful enough to be used in commercial displays like at a theme park.

L'introduzione di un sistema ottico composto da più lenti (semplificato in figura) permette di spostare il punto di fuoco a piacimento, variando la distanza fra le lenti che compongono il sistema. Inoltre, il centro ottico "C" ora si trova tra le lenti e non all'interno di una lente. Questo permette l'inserimento di un diaframma con un foro come per la camera oscura con foro stenopeico, stavolta per modulare la quantità di luce che passa nel sistema ottico, in modo da regolarne la luminosità: più chiudiamo il diaframma meno luce arriverà sul piano focale.

L'immagine acquisita dalla Canon 60D  ha un angolo di campo inferiore poiché il sensore è più piccolo. Ritagliando l'immagine della 5D Mark II per portarla allo stesso angolo di campo e alla stessa risoluzione della 60D, osserviamo la stessa identica profondità di campo. Se con la 60D volessimo riprendere la stessa inquadratura della 5D con un obiettivo zoom, saremmo costretti a variare la lunghezza focale. Ma in questo caso, impostando lo stesso valore di f in entrambi gli obiettivi, avremmo comunque due aperture differenti.

L'introduzione della lente in luogo del foro stenopeico ha permesso di risolvere il problema della luminosità. Come descritto nel disegno qui in alto, i raggi che prima venivano fermati dall'ostacolo adesso vengono rifratti e concentrati sul piano focale ricreando l'immagine nitida e più luminosa rispetto alla camera oscura con il solo foro stenopeico. In questo caso il centro ottico si trova all'interno della lente.

Il punto dove si trova il foro e si "incrociano i fasci luminosi" è chiamato centro ottico "C". Il piano dove è proiettato l'oggetto è il piano focale "PF". La distanza tra il centro ottico C ed il piano focale PF è la distanza focale (conosciuta anche come lunghezza focale o più semplicemente focale). Quella che vi ho descritto è esattamente una camera oscura con foro stenopeico.

Una replica della camera oscura di Niépce dalla collezione di Stephen Johnson - click per la fonte e per le immagini ingrandite -

These lights are then arranged in props which is where the artistry comes into place. Different shapes can be created using corrugated plastic, pipe, and custom structures to create almost any design imaginable. While the lights are standardized, the props are unique and involve considerable design effort to figure out where to place the pixels. They must also be able to withstand an entire winter season outdoors without falling apart.

La stessa scena scattata con Canon 5D Mark II (a sinistra) e Canon 60D con lo stesso obiettivo (focale fissa di 90mm) e apertura posizionata al valore f = 4 Le immagini originali (8,5 MB) sono disponibili qui: 5d_original.jpg e 60d_original.jpg - click per ingrandire -

The most common type of lights you see at Christmas are traditional incandescent bulbs or more recently, LEDs. These strings turn on with 120V (in the US) when you plug them into the wall and stay lit until you unplug them. Those are regular Christmas lights. Around 10-15 years ago though, people started connecting them to electronic switches called relays which allow the lights to be turned on and off with a simple microcontroller. This is essentially the same technology found in today's smart wall plugs, but with a more festive approach.

Turning on and off a single strand of lights was boring and people wanted more colors, more brightness, and fancier effects. LEDs had become very popular and and a new type of light technology started to hit the market called "Pixels". These pixels are essentially an entire strand of modern "smart" RGB light bulbs. Each pixel has a tiny microchip that tells the LED when to turn on and off and what color to light up. They are connected in a strand and can each light up individually to form complex patterns and effects.