Early digicams -- why was autofocus so bad and slow?

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toughluck Veteran Member • Posts: 3,224
Early digicams -- why was autofocus so bad and slow?

This thread is specifically about autofocus performance.
What I am not asking about:
- noise in low light and/or high ISO
- poor resolution
- slow continuous mode
- white balance problems
- AF in SLRs and DSLRs

What is common knowledge is that before OSPDAF, digital cameras had to rely on contrast detection for autofocus.

Common sense has is that, well, it had to be because it was the way it was done with video cameras since forever, that was the only sensor in the camera and there was no other way to do it.

However, compact film cameras didn't even have that sensor and they weren't all fixed focus. Sure, so had active AF systems with ultrasound or laser rangefinders, but those were inferior to higher end models which were equipped with passive autofocus. Not only that, but those cameras had very good AF performance, rivalling or exceeding entry level SLRs.

Let's take an example: https://www.shutterbug.com/content/minolta-freedom-zoom-160bra-new-take-af-tech

I know a bit about Minolta's AF technology in compact cameras and it was great, especially if you consider what limitations it had to deal with. I don't know about Nikon and Canon AF systems in their compact film cameras, but I can't imagine they were noticeably worse.

Now, 35 mm film has fairly shallow depth of field. The AF in those cameras had to be good enough to allow >80% of perfectly focused shots, and less than 5% of completely misfocused shots for them to be acceptable to the consumer.

Now for the obvious: AF based on contrast detection is slow and only works in good light. For any fast action or less than good light, it falls apart, hunts, fails to acquire focus, has all sorts of problems.

So why didn't digicam makers ever introduce passive AF to early digital cameras? Maybe not the first or second generation, those had different problems that needed to be overcome first, but second generation buyers would be well aware of AF problems and if any camera managed to offer a solution, they would line right up.

Okay, so the system isn't perfect. It really only works up to ~200 mm equivalent, it would add to the price (thought that Minolta referenced above cost only $200), and it doesn't work great in low light.

I agree that it wouldn't be a good fit for the cheap digicams or for ultrazooms. But for those that cost upwards of $1000, why not? I'm thinking of high end compacts like Canon Gx series or Olympus C-50x0, or bridge cameras like Minolta 7/Ax series or Sony's F-700/F-800.

Anyone here that could offer a more detailed explanation?

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