Hot answers tagged autofocus
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The fundamental driver of cost in a lens is not the correction of aberrations, although the correction of aberrations does add to the cost of a lens, and may be a more significant factor in wider angle lenses. Generally speaking, the primary cost of a lens is the "glass". I put glass in quotes, because sometimes it is other materials, such as Fluorite or a ...
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Infinity focus places the plane of focus sufficiently far that light from than plane reaching the lens hit the sensor are all parallel.
To get as much in focus as possible, you should focus at the hyperfocal distance which depends on your sensor-size and lens aperture. If you focus at infinity, there will be less in focus but things may be acceptably sharp ...
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You've probably heard people describe some lenses as "unusably soft wide open, but passable at f/2.8 and excellent from f/4", or similar. That's because, basically, these lenses are already designed in the way you suggest, although additionally constrained by size, weight, complexity, cost, and other design factors. And they also let you use the lens at ...
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The technology in theory is similar, but the implementation isn't exactly the same.
Without knowing exactly which model, or even which manufacturer made your camera, it is difficult to be very specific. There's a large difference in performance between different models and lenses.
It always starts with light, so let's begin there. The amount of light used ...
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There's never going to be a shot which can't be achieved on the 6D or the 5D Mark II due to the lesser AF capabilities of those cameras - with enough precognition (also known as experience), you could have manually focused on exactly where the action was going to occur and not needed any AF at all.
That's not to say that you won't get a higher proportion of ...
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To understand infinity focus, you must first understand both what depth of field (DoF) is as well as what it isn't.
Regardless of the aperture of a lens, there will only be one distance that will be in focus. That is, there will only be one distance at which a point source of light will be focused to a single point on the recording medium. Point sources of ...
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The extra glass in a fast lens is not just there to correct aberrations. The full aperture must be visible across the whole field of view meaning for moderate or wide lenses, you can't just make the aperture larger you'd have to make all elements in front of the aperture much larger as well.
But your idea is sort of in effect with large format lenses. Many ...
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There's one teensy-weensy little flaw in the plan: the aberrations (particularly, but not solely, spherical aberration) are the main culprit for the phenomenon of focus shift. Essentially, that would mean that your "focusing lens" won't have exactly the same focal length as your "taking lens", so images focused perfecctly at the larger aperture will be out ...
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Let's start with phase-detect autofocus. Here, there are a limited number of focus points to choose from. You may choose manually, in which case it doesn't pick anything -- it just tries to focus at that point.
If you chose a mode where the focus point is selected automatically, the camera will decide. Usually, this is initially based on a simple ...
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With Phase Detection Auto Focus it is ultimately about how accurate the system is. To put it another way, it is all about how often the the system is accurate enough. Every system will have variation from one shot to the next. The question is what is the average difference from sharpest focus for each shot.
The best single place I've seen describe the ...
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It appears your camera and lens combination is suffering from back-focus.
Given you have an entry-level camera, there is no way for the user to correct this. You must send your camera and lens to a Canon authorized service center for calibration. If you have other lenses, they can calibrate multiple in one batch.
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Some lenses have a calibration problem, aka, front focus or back focus. You can easily test your lens and find out if that is the problem.
There are some great guides on the web, you may want to google it: "front focus lens test"
Edit: Try to print this photo and shoot it from a low angle while focusing on the line in the middle. Use an open aperture. Then ...
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In short, it looks for high contrast areas.
It usually restricts itself to either a pre-set area or a pre-set array of areas though, and it may also have a slight bias towards the centre of the picture, or at least away from the far edges.
In a shot like this it'll pick the dog, because the other areas are too low-contrast. This is a win, because it's ...
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Traditional phase detect autofocus system runs mainly in an open loop configuration: take measurement, send focus distance to lens. Contrast detect autofocus is closed loop, it has to take a contrast measurement, move the lens, take a contrast measurement, move lens etc. which is clearly much slower.
The reason phase detect on sensor isn't nearly as fast as ...
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