Multipoint AF System

Started 3 months ago | Discussions thread
Enders Shadow
Enders Shadow Veteran Member • Posts: 3,293
Re: Multipoint AF System

Distinctly Average wrote:

There is a big difference between your AF system and those on mirror less cameras that have eye and face detection. On DSLRs, those extra points come in handy in many situations, especially when tracking fast moving subjects such as swallows in flight for instance. For that kind of shot a single point makes things very hard. We also enjoy a single point with a few assistance points around it. Even for static subjects that can come in handy. Yesterday I was doing just that, a single point would not focus on a time my bit of foliage where a bird had regularly been landing. Centre plus the assist points nailed the AF so when the bird did land I was locked on.

with the new mirror less cameras, computational AF can determine specific features picked up by the cameras imaging sensor (OVF AF sensors use a different system which cannot be analysed in the same way or resolution)so hit rates can be improved. Once you lock on to the eye of a subject, such as a basketball player or animal, the AF can then track them and even keep tracking predictively when the subject get occluded. So with that system, the more points you have the better the system can be.

Thanks, your reply saved me a bunch of typing.

The traditional DSLR uses a different AF technology than the current generation of mirrorless cameras. Our old school DSLRs use a separate AF sensor. They used relatively large individual points that offered high accuracy and good low light performance. And, the center point typical offered better sensitivity and features like dual cross type focusing. But, the number of AF points was limited. There weren't many cameras with more than 60 AF points. I got back into ILC cameras with the 5D Mk III and later the 7D Mk II. They had 61 and 65 AF points respectively. My D500 has 153 AF points with 53 that are user selectable. Seemed to be adequate for even for my most demanding action photography. But it was a bit frustrating that they covered such a limited area of the frame. (Yes, I understand why that is) I can't imagine being limited to 19 points of the OP's 70D.

Along came on-sensor PDAF and dual pixel AF used in mirrorless cameras. For OS-PDAF, the PD points are set by a mask that blocks half of a sensel. With DPAF, every sensor site is potentially a AF point. Having 100's of AF points was easy to do as was increased sensor coverage. Along with a higher resolution AF array came enhanced subject tracking that includes capabilities like face recognition and eye tracking. As Distinctly Average mentioned, this automation allows the photographer to concentrate on following the action and composition. I remember when using a DSLR sometimes struggling to keep a small AF zone on a erratically moving subject and missing key shots. I still have AF fails with my mirrorless kit, but they seem to occur less and for different reasons. When it makes sense, I still prefer using a small fixed AF group or even a single point. But I can't think of many reasons against the increased number of AF points used in mirrorless cameras.

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Phil

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