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Through-the-lens focusing cameras had focusing screens — usually ground glass or fresnel lens (related: What is a focusing screen?). View cameras (the old-style large cameras with bellows) projected the image onto the focus screen. The photographer directly inspected the image on the focusing screen (perhaps using a loupe to magnify areas of the image), ...


69

To increase readability and avoid exceeding the answer length limit, this answer has been split across two posts. General information and APS-C cameras are covered in this post; full-frame and APS-H cameras are covered in a separate post below. TL;DR answer In general, Canon DSLRs require a maximum aperture of at least f/5.6 or wider to autofocus, although ...


59

Rarity. There were only approximately 20 of these now out of production lenses ever made. When they were in production they sold for about $90,000 (US). Due to the time needed to grow the large fluorite crystal used in the 3rd element of the lens, once ordered they took about 18 months to produce. Autofocus Capability. These lenses include auto focus ...


55

STM stands for Stepper Motor and is a applied to a new range of Canon lenses which feature a new design of focus motors which, along with a new iris mechanism are designed to eliminate (auditory) noise during video recording. Canon haven't revealed any information about how the new design works but it's probably the same type of motor used in mirrorless ...


48

You're not doing anything wrong. You're just finding the limits of the camera/lens combination you are using. The EF 50mm f/1.8 (in various versions) has been known as the "plastic fantastic" for a long time. For what it can do at what it costs, it is a fantastic value. But it isn't really a fantastic 50mm prime lens when compared to many others that, ...


30

Like many things when it comes to designing hardware for photography, there are always tradeoffs to be considered and made. STM lenses sacrifice a little speed in order to be quieter and smoother (no jerky starts and stops). This is important when using Autofocus while recording video. Lenses with USM focus designs are built for speed first and quiet ...


29

No Canon EOS body needs AF motors because every single Canon EF lens released since the EOS system was introduced since 1987 has a focus motor in the lens. Thus no Canon EOS camera has ever had a need for a focus motor in the body. There are a few manual focus lenses in the EOS system, but they are clearly designated as such by not being named as an EF lens:...


28

In actuality, a cross type AF sensor is just two "normal" AF sensors, one with the lines oriented in a vertical direction and the other with the lines oriented in a horizontal direction, that are superimposed over the same area. Non cross-type AF sensors can be either vertical, horizontal, or even diagonal. Some very early AF film cameras with a single ...


27

It is not just cheaper lenses. Many modern lenses, especially Auto Focus zoom lenses have this characteristic. There are several reasons for it: Unless a lens is parfocal the exact point of infinity focus shifts as the lens is zoomed in or out, and so obviously there will be a point where infinity for one focal length is past infinity for another. As ...


25

Having many autofocus points opens up the camera's capabilities because it can function in different ways depending upon settings and camera features: You can select a single AF point (get precise with exactly which point you want to use, without recomposing at all). You can select a group of AF points (a group of AF points means you don't need to be as ...


25

How did photography work before auto-focus was invented? Pretty well for those willing to learn how to do it with the tools we had at at the time. The same is true now. The only difference is that now we must learn how to tell an AF system to focus on the part of the frame we want it to bring into focus. Presumably everybody used manual focus. But here's ...


23

Aperture limitations are a consequence of the design of phase detect autofocus systems and are not specific to Canon. Phase detect autofocus in SLRs works by directing light to the AF sensor using a second mirror behind the semi-silvered main mirror. The AF sensor uses a pair of lenses to focus light from the subject onto a pair of 1-dimensional sensors, ...


23

Your old D80 had a focus motor built into the body that connects to a mechanical coupling on Nikkor AF lenses to move the focus elements in the lens. Your D5300 does not have a focus motor in the body. To use autofocus your D5300 requires that you use Nikon AF-S or AF-I lenses or the equivalent third party lenses (such as Sigma's HSM or Tamron's USD and PZD ...


22

A few aspects mentioned in your question will be our starting point. Please note, we are not saying each of these issues will be determining factors for every photographer. We're not saying one system is better than the other because of... a or b. Rather they are a response to the question, "...what all should a person consider?" Once considered, each of ...


21

Phase detect autofocus in DSLRs works by comparing patterns of light coming from each side of the lens using pairs of detectors which are separated a certain distance on the AF sensor. This distance is called the baseline, and the greater the baseline the more accurately the distance can be measured. The need for a wide baseline and for light to travel from ...


21

According to it, we should first turn off the camera before turning auto-focus on/off. That's quite cumbersome obviously. That seems pretty ridiculous. Perhaps the authors are serious about their target audience being dummies. I am confused if this might harm my camera or lens in any way? You won't hurt anything. It's fine to turn AF on or off while the ...


20

Sigma 28-300mm F3.5-6.3 DG Macro? You are going to get a $7,000 camera with that piece of glass? Or even any of those Tamron's. I highly doubt anyone in the market for the 1DX even has these in a backup kit. How important is it? Not important at all.


20

Do whatever gives you the best results, don't worry about what may or may not be acceptable to others. I'd say shooting events fully manual is rare these days, though you might want to explore the aperture-priority and shutter-priority modes, each of which are very good for certain situations. I'd also investigate auto-ISO if your camera offers it. My ...


20

I can not imagine damage that would impact focusing without visible damage to the packaging or the camera. These things are pretty sturdy. you would have to damage the mirror or shutter box to really have an impact. So I suspect user error. These images appear to be in focus, but perhaps not where the photographer expected. I see areas in focus in both. ...


19

I don't think you're lacking in sharpness: at full size, the image you post shows sharp eyelashes and teeth. If you are using a large aperture (<F2), that explains the unsharp ears. When you reduce the size at which the image is displayed, apparent sharpness tends to decrease. To get the impression of sharpness back, you'd have to apply some sharpening ...


18

An auto-focus motor is just what it sounds like: a small electric or piezoelectric ("ultrasonic") motor which moves the lens elements to facilitate autofocus. In some camera systems, this motor is in the camera body, and the lens moved by a physical coupling. However, you actually read some misinformation. Canon EOS cameras do not have a motor in the body, ...


17

The auto focus systems are not capable of using the highest precision cross type focusing points if you do not use a large aperture lens. They aren't artificially limiting the precision, they are simply working within the constraints of the maximum aperture. Canon puts these limits in to ensure reliable AF. If you don't believe that theory, add a piece of ...


17

AF-S is AF 'single'- your camera will focus on a fixed object when you press the AF button and will remain focused on that point for as long as you hold the button down. This is best for static subjects. AF-C is AF 'continuous' - the camera will focus on whatever is in the relevant AF points (depending on how you have your AF coverage set up) and will ...


17

There are several custom function options available to the 7D which can be configured to assist with tracking moving objects: C.FnIII -1 AI Servo Tracking Sensitivity You want this set to "Slow" - this will stop the AF system trying to refocus on anything that briefly passes between you and the subject you are tracking - handy with birds where branches etc ...


17

Major reason is that the DSLR lenses are optimized for Phase Detection. Every component of the lens is tailored towards quick movement and stopping the glass in precisely picked moment. Contrast detection on the other hand works best with stepper motors capable of quickly switching directions so that you can move lenses inside back and forth looking for ...


17

There are three parts to the answer to this, which is appropriate, because with Sony, Olympus, Panasonic, Fujifilm, and Sigma focusing on mirrorless designs, there are really only three companies making DSLRs: Pentax, Canon, and Nikon. First, all Pentax DSLRs, even the entry-level models, have built-in autofocus motors. So, if that's really your main ...


16

Phase detect autofocus works by measuring the horizontal displacement between brightness patterns projected onto the AF sensor. To measure the displacement, pairs of 1-dimensional arrays of monochrome pixels are used. This is what the AF sensor in the Canon 5D mkIII looks like: You can see lots of different lines of pixels used by different user selectable ...


15

The fact that Phase-Detection stops at the focus-distance rather than exceeding and then coming back has a big impact (as Stan mentioned in his answer) on video since this motion is visible in the recording. Another impact is that Phase-Detection requires dedicated sensors in fixed positions which is why the number of AF points is relatively small. Contrast-...


15

It really depends on what you want to do with the camera. After all, there are many great photos that have been taken with older cameras, both when they were the hot new model and when they were no longer on the cutting edge. As with all equipment recommendations it comes down to the question of what do the technical demands of the photos you want to take ...


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