Can telephoto lenses be used in street photography?

On this issue, I often feel puzzled when I just came into contact with street photography. From the first day of the street sweeping, some older men patiently told me: The young man, he must use a wide-angle fixed focus head to sweep the street, and then he came face-to-face with the names of some photographers, using the 28mm focal length to sweep the streets of Moriyama, with Elliott Erwitt, who sweeps the streets in 35mm focal lengths, and Bresson, who sweeps the streets with a 50mm focal length, and more. So for a very long period of time, whoever asks me to use what focal length to clean the street is better, and I only drift through these three numbers in my mind. Until one day I saw the following set of photos on the Internet.

The photo was taken by street photographer Nick Turpin. These photos were from his photography project â€œThrougha Glass Darklyâ€. Nick was born in the UK and studied art and design during college and also studied photography. He once worked as a professional photographer at a newspaper office, and then later photographed a lot of different types of photography, portraits, advertising, fashion, etc. have been involved, he fell into interest in street photography.

Most street-swept enthusiasts may not be familiar with such a photographer, but I am very familiar with his contribution to street photography because we are doing similar things in different countries. He is also relying on his own. Power spreads the charm of street photography internationally. We will talk about this later and go back to Nick's photo. He applied telephoto lenses and chose to take long distances to take pictures of passengers in the bus. After a long period of shooting, a series of photos was formed. After this series of photos was published on the Internet, the response was large. Many large-scale domestic photography websites have also been reproduced. This group of street photography works also has a lot of enlightenment for me. I will share with you one by one below.

1, holding a telephoto, sweep the street calmly.

Nick uses his work to prove to us that the telephoto lens is not just a snap weapon for the paparazzi. He shot this group of photos without the help of a tripod. Instead, he held it in a handheld manner. The shutter speed was kept to 1/40S. This speed is far below the safety shutter speed for telephoto lenses. Care must be taken to keep the camera stable. This is also the key point we should pay attention to when we use the long focal length to sweep the street, especially at night. Telephoto is more space-saving than wide-angle, but because of the space-compression it generates, it is very good for photographing street portraits, which is helpful for some emotional details.

2. "Street" is not only on the streets

All of Nick's photos were taken in the carriages of the bus. Some people might say that this is not street photography, but what is it not on the street? The definition of street photography in Wikipedia says that the street is not Specifically referring to streets and alleys, any photograph taken in a public space can be called street photography. So when you next time in the exhibition hall, in the mall, on the beach, in the train, and so on in any public place, don't forget to bring a camera, it is possible to shoot satisfactory works there.

Actually, I am very interested in the choice of bus as a public place because it is open first, but because each passenger enjoys a private space, I think it is a relatively private public space. Photography is in this specific space. It is easy for a teacher to shoot extremely natural street portraits. What is particularly emphasized here is the need to pay great attention to respecting the privacy of the person being photographed while filming and must not infringe on the privacy of the subject because of the art.

3, increase mystery art for the work

A careful analysis of the success of this group of photos is not just the use of telephoto for street portraits. There are two more important points: one is to choose to shoot in the winter, and the other is to choose to shoot at night. A lot of water mist condenses on windows in winter, and some windows cover everything in the car with a thin layer of gauze, and some windows give people a feeling similar to painting because they are wiped off by the passengers. In addition to shooting at night, the lights in the car serve as background light, adding a bit of atmosphere to the work. The mysterious texture of the water mist on the windows, the varied passengers, and the soft lights constitute a looming picture, which can not help but imagine the story of the passengers in the car.

PCB Material Fr4 Substrate PCB Board Manufacturing Service

As you know, the Printed Circuit Board plays a vital role in electronic products, so you need to consider how to choose the right material in your PCB Manufacturing. JHYPCB can offer you the lowest possible costs and the very finest in high-quality PCB fabrication and high-quality PCB Assembly . However, there are many different types of PCB materials, such as FR-4 material, HDI material, Rogers PCB material, and so on. In general, we use the standard FR-4 material for the Printed Circuit Boards to reduce product costs, which is a good option because FR-4 material is affordable and useful for many applications. However, FR-4 material is not the only type of PCB material; comparing to PCB material, FR-4 material, and Rogers material is essential.

What is FR4?

FR4 is a standard defined by the NEMA (National Electrical Manufacturers Association) for a glass-reinforced epoxy resin laminate.

"FR" indicates the material is flame-retardant, and the "4" indicates woven glass-reinforced epoxy resin. Single or double-sided PCB structures consist of an FR4 core and top and bottom copper layers. Multilayer PCB boards have additional prepreg layers between the center core and top and bottom copper layers. The core consists of a substrate with copper covering, also referred to as a copper-clad laminate(CCL). The core, laminate, and prepreg may all be FR4 with the copper sheets between the signal and ground layers. FR4 is the most common material grade that comprises fabricated circuit boards.

FR-4 or FR4`s properties and characteristics make it very versatile at an affordable cost. Before the explosion of multilayer PCBs, there were many alternative board materials to FR4. These included FR2, CEM 1, and CEM 3, which were paper-based. However, the strength of FR4, especially for multilayer PCB boards, was a significant factor in separating it from alternatives to become the industry standard. Therefore, Most PCBs are made using FR4 as the base material.

FR4 materials and characteristics

Its glass transition (TG) is 115Â°C to 200Â°C for the High TGs or HiTGs, depending on the manufacturing methods and the resins used. A standard FR-4 PCB will have a layer of FR-4 sandwiched between two thin layers of laminated copper.

FR-4 uses bromine, a so-called halogen chemical element that is fire resistant. It replaced G-10, another less resistant composite, in most of its applications.

FR4 has the advantage of having an excellent resistance-weight ratio. It does not absorb water, keeps high mechanical strength, and has an excellent insulating capacity in dry or humid environments.

Examples of FR-4

Standard FR4: as its name indicates, this is the standard FR-4 with heat resistance of the order of 140Â°C to 150Â°C.
High TG FR4: this type of FR-4 has higher glass transition (TG) of around 180Â°C.
High CTI FR4: Comparative Tracking Index higher than 600 Volts.
FR4 with no laminated copper: ideal for insulation plates and board supports.
There are more details of the characteristics of these different materials later in the article.

Factors to consider when choosing the thickness

Compatibility with components: even though FR-4 is used to produce many types of the printed circuit, its thickness affects its components. For example, THT components are different from other components and require a thin PCB.

Space-saving: space saving is essential when designing a PCB, particularly for USB connectors and Bluetooth accessories. The thinnest boards are used in configurations in which space-saving is crucial.

Design and flexibility: most manufacturers prefer thick boards to thin ones. Using FR-4, if the substrate is too thin, it would be at risk of breaking if the board dimensions were increased. On the other hand, thicker boards are flexible and make it possible to create V-grooves.

The environment in the PCB that will be used must be considered. For an electronic control unit in the medical field, thin PCBs guarantee reduced stress. Boards that are too thin - and therefore too flexible - are more vulnerable to heat. They can bend and take on an undesirable angle during the component soldering steps.

Impedance control: the board thickness implies the dielectric environment consistency, in this case, FR-4, which facilitates impedance control. When impedance is an essential factor, the board thickness is a determining criterion to be taken into account.

Connections: the type of connectors used for a printed circuit also determines the FR-4 thickness.

The Different Types of FR-4 Available From JHYPCB

JHYPCB STANDARD FR-4 MATERIAL PROPERTIES

High Glass Transition Temperature (Tg) (150Tg or 170Tg)
High Decomposition Temperature (Td) (> 345Âº C)
Low Coefficient of Thermal Expansion (CTE) ((2.5%-3.8%)
Dielectric Constant (@1 GHz): 4.25-4.55
Dissipation Factor (@ 1 GHz): 0.016
UL rated (94V-0, CTI = 3 minimum)
Compatible with standard and lead-free assembly.
Laminate thickness available from 0.005" to 0.125"
Pre-preg thicknesses available (approximate after lamination):

(1080 glass style) 0.0022"
(2116 glass style) 0.0042"
(7628 glass style) 0.0075"

Standard FR4

FR4 SHENGYI family S1000H
Thickness from 0.2 to 3.2 mm.
FR4 VENTEC family VT 481
Thickness from 0.2 to 3.2 mm.

FR4 High TG

FR4 SHENGYI family S1000-2
Thickness from 0.6 to 3.2 mm.
FR4 VENTEC family VT 47
Thickness from 0.6 to 3.2 mm.

FR4 High IRC

FR4 SHENGYI family S1600
Standard thickness 1.6 mm.
FR4 VENTEC family VT 42C
Standard thickness 1.6 mm.

FR4 with no copper

This material is an epoxy glass with no copper, designed for use in insulation plates, templates, board supports, etc. They are manufactured using Gerber type mechanical drawings or DXF files.
Thickness from 0.3 to 5 mm.

The Difference Between FR-4 Material and Rogers Material

1. FR-4 material is cheaper than Rogers material.
2. Comparing to FR-4 material, Rogers material is great with high frequencies.
3. FR-4 material has a high Df or dissipation factor than Rogers material, suffering more signal loss.
4. In impedance stability, Rogers material has a wider range of Dk values than FR-4 material.
5. For dielectric constant, FR-4 features a Dk of about 4.5, which is lower than Rogers material with around 6.15 to 11.
6. In temperature management, Rogers material has a less variation comparing to FR-4 material.

When is FR4 Not the Best Material For Your Board?

FR4 is indeed a good standard or default option for your board material in most cases. However, there are cases where FR4 is not the best material for your board, as listed below.

If lead-free soldering is required

If your boards will be distributed in Europe and must adhere to The Restriction of Hazardous Substances Directive (RoHS) or your client necessitates that lead-free soldering be used, then you may want to explore other material options. This is due to the fact that reflow temperatures for no-lead PCBA(Lead-free PCB Assembly) may reach as high as 250Â°C, which substantially exceeds the Tg for many versions of FR4.

If high-frequency signals are used

At high frequencies, FR4 boards are not able to maintain a constant impedance and reflections may occur that negatively impact signal integrity. This is a consequence of the relatively high value for dk.

If the board will be exposed to extremely high temperatures during operation

It is also ill-advised to use FR4 if the PCB will be required to operate in an environment under extremely high temperatures. An example would be near the engine compartment of an aerospace vehicle.

FR4 is rightly the most used material in PCB construction. Boards made from FR4 are strong, water resistant, and provide good insulation between copper layers that minimizes interference and supports good signal integrity. However, at high frequencies and in environments, FR4 is not the best material to use for your boards. At JHYPCB, the industry leader in fast, high-quality PCB Prototype and low-volume manufacturing, we are capable to meet your board material needs for any case. We will work with you to help you select the materials that will best implement your design intent.

And to help you get started on the best path, we furnish information for your DFM checks. If you are ready to have your design manufactured, Try to contact us via email.

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