Headline - DSLRs have imprecise focusing due to their mirrors

Started Apr 5, 2014 | Discussions thread
WilbaW
WilbaW Forum Pro • Posts: 11,389
Re: Closed vs open loop focusing
1

stevo23 wrote:

WilbaW wrote:

stevo23 wrote:

WilbaW wrote:

stevo23 wrote:

Martin.au wrote:

Both are closed loop. You can test it by starting the focus on a subject, then quickly moving the subject during the focus group's movement, and seeing if it focused on the background, or on the spot where the subject was.

Agreed. Open loop PDAF has been gone for 10 years or so.

PD AF has never been open-loop, see Busted! The Myth of Open-loop Phase-detection Autofocus.

I was reading Roger's article and there is reason to think that earlier PDAF were open loop:

http://www.lensrentals.com/blog/2012/08/autofocus-reality-part-3b-canon-cameras

You can think all you want but evidence always beats speculation. Use the tests in my link above to prove it for yourself.

I've ready your article already and I'm not sure you've proved that PDAF has never been open loop.

Obviously I haven't, but you can disprove it. All you have to do is find a single conventional SLR that behaves in the tests as predicted by the open-loop model. I'd go for a Minolta 7000 (1985), which is (according to Wikipedia), "the first camera to feature... integrated [phase detecting] autofocus".

Given that the first Canon with PD AF (the 1987 EOS 650) behaves exactly the same as the nine other more recent Canon models and the eight from all of the other major SLR manufacturers documented so far, I think it's a safe bet that all conventional PD AF systems are based on the same Honeywell patents.

If you read my comments on Roger's article (search for "Wilba"), you'll see why his idea is guesswork founded on misunderstanding.

This being said, I've never used anything that didn't have some amount of iteration in the focus, so I'm sure I've never had open loop autofocus.

So am I. 

But for the purpose of this thread, I think we're on safe ground in this rabbit hole.

Yep, the Easter Bunny has an SLR with open-loop PD AF and takes photos of Bugs Bunny with it. 

 WilbaW's gear list:WilbaW's gear list
Canon EOS 60D Canon EOS 7D Mark II
Post (hide subjects) Posted by
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
(unknown member)
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow