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When adapting non-Sony lenses to an A7, the electronic protocol for body/lens communication has to be translated as well. Between Sony and Canon/Nikon/etc. the commands to focus the lens are very likely to be incompatible, or are so radically different in how they're represented that the adapter has an issue translating them between the camera body to the ...


1

With phase detect autofocus, it is possible for the camera to know more about how far out of focus an image is, so it can make a better guess of how far it has to move. If it knows how to get all the lens details, then it can quickly give instructions to move close to the target point. If it doesn't, then it has to more iteratively move the focus in to ...


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Take it to a store and see if it works on other cameras. Then try another 28-70mm on your camera just to be sure. The lens may just need a cleaning, but it also may be related to your camera. Doing both will not isolate the issue 100%. If the lens does this on other cameras, get it serviced. If not, you may need to have the camera checked out.


1

It depends entirely on context. If you need to track something around the scene, the more cross type AF points you have, the better as they will provide more reliable tracking, but that said, having the most sensitive points you can have is also desirable, particularly for low light. Both give advantages in their own way and both are most useful in ...


2

Limiting strictly at your question: At the time of writing, Canon 6D has the most sensitive cross-type sensor in the middle rated at -3 EV. Nikon 4Ds is only -2EV. Most cross-type AF sensors are in Canon 1D X / 5D Mk 3. If these are the only factors for you to rate the AF performance (generally they are not - see the others' answers), then you have: For ...


3

There are too many variables involved to make any kind of meaningful generalizations about the best AF implementation for the applications you mentioned. Autofocus performance depends on a lot of factors: AF point layout AF sensitivity (i.e., the f-number) Type of AF point (cross, linear, etc) Camera CPU speed AF algorithm efficiency Optical performance ...


2

In a cross-type sensor, two sensors are at right-angles to each other, and they together determine either the phase or the contrast along the horizontal and vertical axes of light. The rule of thumb is when dealing with illumination (which includes low light, bright light, high contrast scenes), the sensitivity and the dynamic range of sensors factor ...


4

While is doesn't test the premise you lay out, there are some interesting conclusions in this experiments: http://nikonrumors.com/2011/03/28/auto-focus-accuracy-a-scientific-cross-brand-analysis-guest-post.aspx/ Such as: Camera brand does not matter. Individual body does matter. Max Aperture matters; around F2.8 is best. both F1.x and slow lenses perform ...


1

This malfunction can be caused by a variety of component failures, so it is impossible to know for sure without opening up the lens. You can try cleaning the electrical contacts, but it is also possible that there is an electronic or mechanical fault with an internal component. For example, there could be a problem with the circuit board. Or there could ...


1

This question is kind of old, but it doesn't look like anyone's mentioned the recently released Canon 70D. The Canon 70D has a new type of AF built into the imaging sensor ("Dual-Pixel CMOS AF"), so can do phase-detect focusing while recording (or in Live View). While many other cameras can do contrast-based focusing (even during recording), this is a big ...



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