Autofocus: how does it work?

All cameras are autofocus, which means they focus automatically. But it’s rare to really know how it works … Will you tell me it doesn’t matter as long as it works? Big mistake! The camera focuses automatically either, but for that it needs certain conditions to be met! And it is there that it is important to know more so as not to have any bad surprises. Because in the heat of the moment, it is already too late to ask questions, and especially to find the answers … There are several types of autofocus with different techniques.

Understanding Autofocus Points


This type of AF works well on low contrast or poorly lit subjects. But the major drawback is based on the fact that if an object comes between the camera and the subject like a window, the camera will focus on the window, and no longer on the subject.


This system equips the vast majority of reflex and compact cameras, it is divided into 2 parts:

Autofocus to measure contrast

It obeys the principle that an image which is not clear has a lower contrast. The autofocus makes several attempts to obtain the most contrasted image possible which will thus be considered clear. This focusing method is slower because it fumbles. This technique is most often used on compacts.

Phase detection autofocus

This system appeared on SLRs in 1986 with the Minolta 7000 AF. It virtually cuts in 2 the rays of light coming from the lens. The analysis of the rays which come from this section makes it possible to determine at what distance is the photographed subject. Each of these technologies has these downsides, it is important to know them in order to use them in the best possible way.


At the camera level, this autofocus will be configurable in several ways. To keep things simple, there will be autofocus mode for still subjects like the landscape, for example. The autofocus for moving subjects , and a predictive AF modefor moving subjects suitable for effective subject tracking. We can already see that there are different modes which implies making a choice and the right one.

At the level of the camera, the autofocus works by collimators which are scattered on the surface of the sight glass. A collimator is a point that will be materialized, most often by a square.

Compacts and bridges

Compact cameras are often set at the factory to focus in the center. For a relatively short time, compacts have been equipped with a face detection mode to focus on the face, which can eliminate the need to worry about where the camera will focus. on point. Practice.Auto-tracking mode to detect subject movement and follow it. On some compacts we can even have a manual autofocus mode , which gives complete control of the focus by indicating precisely where the focus is. With a possibility of fine adjustment.

The reflex

It is on this kind of camera that there is the greatest number of modes or more generally of subtlety for the autofocus! So there are generally the following autofocus modes:

Single AF

It focuses when you press the shutter button halfway, and will not move any more. This mode is particularly suitable for still subjects.

Continuous AF

It focuses by following the subject, allowing a subject to be kept in focus continuously regardless of its movements.


the camera autofocus is one thing, but how will it focus and especially on what? This is where the collimator or AF point comes into play.

A collimator is a sensor that will detect the subject , and will thus focus on the same subject. Each camera will have a different number of points. Depending on the range and what the manufacturer has decided.

For example, there are  51 AF points on the Nikon D300s , on the Nikon D3100there are 11 AF points. On the Canon EOS 7D we find 19 collimators, on the Canon 1100D we find 9 collimators, on the Sony Alpha 900 we find 9 and on a Pentax K-7 we have 11.

In addition to the main collimators, some devices have other assistance collimators which help the main ones. All these collimators will be distributed over a more or less large area of ​​the viewfinder, most often materialized by squares.

Autofocus in a fully automatic mode will determine which subject to focus on. This mode is a mode to make your life easier, but it is rare that it gives complete satisfaction . For example, in the street if you have a house on the left side, a tree in the center and a passerby on the right side. How will the camera do to guess what we want to focus on?

He will “guess” by obeying the micro-program built into the camera, focusing on an element that will be more contrasted than another, for example. But if that does not suit us, it is the same … A program as “intelligent” as it may never be able to guess our wishes as a photographer! The device will focus on what it will judge to be the most discriminating element.

On SLRs, when the camera focuses, the collimator on which the focus can light up, this informs us where the focus will be made. We can modify the choice that the camera makes for us, but the ideal is to tell it from the start, where we want it to focus. It takes less time and it is ultimately more convenient. So it’s up to us to tell him what we want to focus on, and not the other way around! This is why we can manually choose the collimator on which the camera will focus.

To return to the example cited above, we will manually choose the AF point which is either on the house, on the tree or on the passer-by. It also makes it possible to “bypass” the time taken by the camera to determine the subject of our photo, and to establish its sharpness. The ergonomics of the camera will make it easy to change the AF point on the fly, when you have your eye placed on the optical viewfinder.

Modern cameras allow you to choose either a collimator or a group of collimators, to enlarge the area on which it will focus. You may need a single AF point because the subject occupies a small space in the photo. Or if the subject is larger, we may prefer that the focus be done on a larger area.

By knowing these details of how the camera works, we can understand why the camera we have, may not produce images that we are entitled to expect. It is important to understand how it works in order to give it the means to deliver what is expected of it. By indicating where the camera should focus, we will go for sure,


So that the camera can focus on a specific element and follow it if the subject is mobile, the camera needs … light! And that’s the goal that gives it to him. So the more light the lens “captures”, the easier it will be to focus.

In general, if you shoot in low ambient light, you should focus on large aperture lenses.

For example 2.8 or better 2, 1.8, see 1.4! They are expensive lenses, and heavy for some of them. With entry-level optics, therefore zooms which at best at their longest focal lengths will be 5.6 or even 6.3, they will not allow the camera to have sufficient light to focus. fast and efficient point in difficult lighting conditions.

Even if we can push the sensitivity of the sensor, the light will always be lacking, and the device will still encounter difficulties. Some AF points are more effective if you use an optic that opens to 2.8 or better.

So the reactivity of the camera will be slowed down … It will hesitate, without finding the point, the lens will alternate from very blurry to something a little clear and continue its search. But without being able to stop. It is a sign that the light or that the contrast is lacking. Some cameras will project an infrared target in front of them so that the autofocus can catch it and thus better assess the distance between it and the subject. Same thing if you add a cobra flash to your reflex.

Many lenses are equipped with a high-performance autofocus motor such as USM at Canon, AFS at Nikon, HSM at Sigma, SDM at Pentax, and SAM at Sony, but to function well and give their full potential it is necessary to light, anyway!

A camera cannot work miracles, under some very difficult conditions … There is no shame in shifting the lens to manual focus and focusing on your own. In many cases, it is much more effective, and will avoid hassle!

For more information, please visit

Things to know before choosing a lens

At the point when we begin taking pictures, we before long acknowledge that pick carefully the camera lens that will go with us in each circumstance. Among every one of the components of our gear, the camera lens will be the main, the most tedious and the most interesting while picking one. Anyway, what would it be advisable for us to consider prior to purchasing a lens? You need to know unmistakably what you need, since it isn’t the least expensive photograph extra accessible, a long way from it.

Besides, the choice will be definitive with regards to giving quality and character to our pictures. Considering this, what would it be advisable for us to search for when purchasing a lens? Today, we disclose what we consider to be the 5 central issues to think about while picking a photograph lens.

The aperture, an important part of the lens

An aspect that will greatly influence our shots, and this is true for any type of photography, such as social, night or portrait photography, is the maximum aperture of the diaphragm. This subtle fact is decisive in the play of the depth of field and the brightness of the image. Therefore, it is important to take it into account before buying a lens.

Maximum aperture of the diaphragm

Accoridng to DZOptics, lenses with maximum apertures of f/2.8 or less are known as “bright lenses” because they allow more light to pass through to the sensor, but they are also known as “fast lenses” because by having the ability to open the aperture wider, you have more leeway on the shutter speed.

A bright lens can help you in low light situations, such as night scenes or interiors. It can also help you achieve images with a shallow depth of field, which is quite useful and striking in some cases in particular, such as portraits and close-ups.

The number of aperture blades

Another aspect to observe in relation to the diaphragm is the number of blades that make it up. The theory says that the more blades of the diaphragm, the better. Why? Because it improves the quality of the “bokeh” since the blur obtained is created by the defragmentations of the light in perfect circles, which is not the case with a diaphragm composed of few blades.

To obtain an almost perfect circle, we could speak of diaphragms with at least 9 leaves or blades in its constitution. Obviously, this characteristic of the lens fully justifies an increase in its price.

Does the lens have an image stabilizer?

Now we come to another important aspect when buying a photo lens, namely whether it has an image stabilizer or not. This system is based on a set of added lenses that compensate for movement. You can use up to 4 or 5 stops slower shutter speed without the image appearing blurred. A real advantage when you find yourself in a situation where there is little light and you want to remedy this by extending the exposure time.

Nikon usually calls this system IS (Image Stabilizer), while Canon calls it VR (Vibration Reduction). As for Tamron, it has chosen the concept of VC (Vibration Compensation). If you decide to opt for a photo lens incorporating an image stabilizer, you will have to take into account a larger budget.

In case you choose a lens without image stabilizer and you have to face situations in which you have to use shutter speeds slower than 1/60, the most advisable is to use a tripod. In any case, this is a “problem” with a solution.

Other features of the lens

In addition to the aspects just mentioned, these accessories have many other features that can be decisive before buying a lens. I have presented the most general ones, which are important for almost all sub-disciplines, but what if you are planning to practice a specific type of photography?

If, for example, you want to take pictures of flowers and insects, you might be interested in a lens with a macro function and a very short minimum focusing distance. If, on the other hand, you would like to use it for shooting videos, you will be interested in finding one that incorporates a silent focus motor or even a light and silent aperture transition, as well as toothed rings in its structure, to allow for the assembly of Follow-Focus systems.

CCNA Certification Opens The Door of Network Engineer for You

CCNA - Cisco

Taking the certification examination is the only way for many people to seek career development. For most people, it is “absolutely impossible” to have no certificate. In foreign countries, every additional certificate will bring a salary increase. Although the salary level in China is not as high as that in foreign countries, it is quite considerable compared with other industries in China. If we can plan the study and examination of certificate reasonably , we can not only learn comprehensive and systematic knowledge, but also easily find a suitable working environment for us to play our strengths. But there are so many certificates on the market, which one should you take? In the network engineer industry, CCNA.CCNP.CCIE are very good certificates, and they all with good employment prospects and recognition in the society.

CCNA, as the primary certificate of network engineer industry, is also the entry threshold of network industry. CCNP certification is very popular in the Internet world certified by Cisco, but CCNA is often ignored because it is the primary stage. So it really doesn’t matter? I think this statement is totally wrong. Great oaks from little acorns grow. Learners can’t aim high, they should first establish a solid foundation, and then make a gradual cycle. At the same time, some people doubt whether the value of CCNA is devaluing? There is no doubt that CCNA certification is an essential Certificate in some low-level network industries. Although CCNA belongs to a relatively low level, it has a certain gold content. CCNA certification indicates that the holder of this certificate has the ability to install, configure, run medium-sized routing and switching network, and carry out troubleshooting. CCNA certified professionals have the corresponding knowledge and skills to establish connections with remote sites through WAN, eliminate basic security threats, and understand the requirements of wireless network access. The certification can prove that the holder has mastered the basic knowledge of network, and can install and configure Cisco router, switch and simple LAN and WAN by using the interface between LAN and WAN, so as to provide primary troubleshooting service and improve the performance and security of network. It can be seen that CCNA is an essential part of the network industry certification system.

Of course, some people may ask me if there is a bright future for them to obtain only one CCNA Certificate in future employment? What industries can they engage in? Here I would like to introduce to you that CCNA is the certification of Cisco. Cisco is a communications equipment manufacturer and can set foot in the communications industry. Communication is a big industry, including operators (China Mobile, China Unicom and China Telecom, commonly referred to as Party A) and equipment manufacturers (HuaWei, ZTE, Ericsson, Alan, Nokia Siemens Networks , etc., referred to as Party B). The operator is the manufacturer operating the whole communication network. Your mobile phone calls with the operator’s network, so the service charge will be charged; The equipment supplier is the party that sells the equipment to Party A, and there are some third-party companies and so on. In the company, personal work can be divided into many situations: first is to do Party B’s sales – buy equipment to Party A; Second, to provide technical services for Party B; Third, do Party B’s R & D – software development. To put it bluntly, Party A’s work is to focus on the equipment and Party B is to solve the problem. Of course, every job has its significance and value. Communication is the same as other jobs, either technology or management, but generally starting from technology. CCNA certificate is recognized by the industry!

Since CCNA certification still has a very good job prospects. But how to use a better way to learn the content of CCNA certification? First of all, you can choose to self-study or enter training institutions for professional training. If you want to self-study CCNA certification, you have to try to select appropriate CCNA teaching materials, consult CCNA learning guide, make learning plans, etc. then you can continue to study day after day, and you can’t lose your strong interest in learning. The key is to choose reliable CCNA training institutions or schools. You should understand that no matter which way you choose, the most important thing is to have preparation and plan for learning, clearly understand the importance of CCNA, and grasp each key knowledge point in a down-to-earth way. In the process of preparing for the exam, firstly, you can understand the information of CCNA practice exam, such as the address of the exam, the details of the exam, etc., so that you can face the exam calmly and be sure of no mistakes. Secondly, we should have a correct understanding of network technology. In fact, network technology is really not difficult. We should learn to decompose some technologies into organized small knowledge points to understand and apply them, and then be patient in the process of learning. Because with the application of learning step by step, it is easy to encounter many problems in the actual operation; At the same time, the solution is not insurmountable. In the process of meeting and solving problems again and again, we should learn to draw inferences from one instance. We should summarize the key points and put them into practice in the future. Finally, we should have perseverance, where there is a will, there is a way. The knowledge of network technology may be boring. But there may be countless related problems and technologies waiting for you to discover, learn and solve. So you have to choose persistence. In persistence, you can get happiness in the learning network.

CCNA certification can not avoid to do a lot of exercises. But to pursue the efficiency of the exercises, if you take a lot of exercises to hit yourself blindly, do not know the importance of the question bank, it is easy to lose important knowledge points in the question bank. Practice is an important part of the review process, only through practice can we further consolidate and deepen the knowledge, otherwise, the quality of review will be affected. Most of the students can understand it in class, but when they go to practice, they find that understanding is one thing and doing the right problem is another. Many students understand it but can’t do it in the real exam. The root of this problem is that they do less. When it comes to practice, we can’t avoid “sea” tactics, but we have to do them. Doing exercises is not wasting time. Doing exercises has many advantages, such as: doing exercises can check the effect of our learning, in the process of learning, we master the knowledge to what extent, and what defects and deficiencies, most of them have to be tested in the exercises, therefore, doing exercises can more  check the effect of our learning accurately, so it is the most practical reference to test our understanding of knowledge. And by doing exercises, we can deepen our understanding of knowledge. It is impossible to thoroughly understand and master the relevant knowledge only through the elaboration and explanation of textbooks, as well as a few examples and exercises. Therefore, only by doing exercises can we deepen our understanding of knowledge and form a complete grasp of things. In addition, doing exercises help us to improve our ability to analyze and solve problems. The stable and up-to-date question bank in training institutions is very popular with most people. The common questions and error prone questions will appear in the question bank. For CCNA certified questions, we should do experiment questions and logic questions in no hurry.

No matter you are studying or working now, you should develop the attitude of lifelong learning. After all, the times change quickly, and you often update and change yourself. Whether it is to do network technology or other things, we should have the concept of lifelong learning. I have seen too many examples. People who no longer study will stagnate. This study is not only for technical, but also other aspects. For example, in the IT industry, if you are not engaged in the network industry, you may feel that you will never come into contact with the knowledge of the network. However, if you are engaged in other IT industries, you will find that it is closely related to the network industry, Therefore, long-term learning is very necessary. If you are interested again, it is good to learn other knowledge of IT industry. I often discuss a problem with my friends. Most people who are engaged in technology would see a tree. A few people who are engaged in technology or in sales and most people who are engaged in management would see a forest.

How to get certified in CCNA 200-301 test

Cisco tests are certainly perhaps the most troublesome tests on the planet. So to accomplish a confirmation in Cisco, you need massive devotion and difficult work. In particular, you should have the correct skill to turn into a Cisco affirmed proficient. Comparative is the situation with the CCNA 200-301 test. This is a partner level, a guideline based test that incorporates innovation territories; specifically, Networking, Security, and Automation. Besides, it credits your masteries of introducing, supporting, and investigating wired/remote organizations in grouped tracks like Cloud Cyber Ops, Data Center, Routing and Switching, Security, Service Provider, and so on At last, this confirmation assesses your dominance of IP administrations and availability, Network essentials, and so on This test is likewise an essential for the expert level CCNP.

One Stop Hub for all of Your International Educational Testing Needs -  Fortray Networks Canada

Why Take the Cisco CCNA 200-301 test?

Securing a CCNA is the absolute initial phase in the creation of a profession in IT innovations. During the time spent accomplishing this accreditation, CCNA test covers a tremendous range of essentials of IT vocations. This will create horde openings for the replacements. Also, Cisco has a background marked by working interminably with a soul to give the best and ideal answers for networks since 1984. It was worked by Leonard Bosack and Sandy Lerner, the pioneers of LAN(Local Area Networking). This makes it even more sensible and furthermore dependable to pick them.

Who Should take the CCNA 200-301 Exam?

First thing first, the Cisco CCNA 200-301 exam test is principally for Engineers (organization, media communications), experts (organization, network activities), and furthermore, examiners (organization, network tasks focus). Besides, this accreditation is additionally for instructors, educators, content producers, or anybody with the necessary abilities. These abilities are; viz, regular key abilities, similar to relational abilities, investigating abilities, hierarchical abilities, client assistance abilities, insightful abilities, delicate abilities spinning Microsoft Office Suite and Cisco balance, and furthermore the information on industry-explicit devices. This affirmation is additionally prescribed for applicants needing to improve their consistency details and profession development. At long last, the competitors who need to show up for the CCNP test are likewise needed to breeze through this test.

With this, you are presently very much aware of the test and its intended interest group. It’s currently an ideal opportunity to perceive what earlier information and experience is prescribed to take the Cisco examinations, and henceforth get the accreditation.

Suggest Knowledge and Prerequisite for CCNA 200-301

CCNA test requires no specific degree. Nonetheless, we recommend you have one in Computer Science or Information Science. However, in the event that you intend to work straightforwardly in the wake of finishing the affirmation, a degree in the regarded fields referenced above is needed by the associations. Subsequently, an essential comprehension of the multitude of subjects in the test is additionally required.

Presently how about we examine the fundamental construction of the CCNA 200-301 test. Additionally, having a careful information on the test design and the sort of inquiries posed, will absolutely smoothen your test planning. So how about we look at it.

Planning Guide for the Cisco CCNA 200-301

Subsequent to covering the test subtleties and course diagram, we will presently move onto the main way in your excursion towards your objective. You will take a test, that took you significant length of diligent difficult work and steady inspiration. In this way, you should understand what handle you need to work upon harder to make progress. Besides, outlining an appropriate report plan will help you a ton in getting the accreditation.

We’d recommend you to initially amend your IT exercises/ideas routinely, and practice your delicate abilities of Networking, IP basics, administrations, and so on Therefore, survey your delicate abilities of utilizing Cisco, ask help from specialists, and experienced IT experts. Also, Cisco anticipates it’s up-and-comers/workers to proceed as constantly as them with regards to organize arrangements. The accompanying investigation guide will without a doubt help you over the long haul, whenever followed with most extreme devotion and trustworthiness.