A new method of AF

Started Apr 19, 2014 | Discussions thread
All forumsForumParentFirstPrevious
Enginel Contributing Member • Posts: 725
A new method of AF

I looked thru patents and haven't found anything similar. I don't feel I'm in condition to make a proper publication, but I decided to tell about it somewhere. I think many older cameras can be retrofitted with that feature just by reprogramming.

The basic idea is to reuse already available components for a new use, that is, focal plane shutter and CMOS arbitrary pixel read/reset, while adding no new components. The focal plane shutter is offset from the sensor itself, which gives problems for very short exposures with Electronic First Curtain Shutter (when gap between physical curtains in otherwise conventional shutter is comparable to distance between shutter and image planes). However, it can be turned into advantage.


Imagine (see figure) physical shutter curtain goes down while electronic "curtain" (a line which is being reset) goes simultaneously downwards too, doing aforementioned very short exposure. So if we divide rows of sensor in triplets and each of three subimages has its separate electronic curtain, one runs ahead, and one runs behind (actually we need to reset only one row at time, though, not sequentially).  Each of three subimages not only get different exposures, but each with different point spread function. Images will be shifted vertically proportionally to defocus amount.

Advantages, compared to conventional DSLR PDAF: it works with all apertures and for all image field. Not sensitive to small misalignments. It will work as fine with small apertures (provided enough light is avalable).

Advantages, compared to mirrorless onsensor-pdaf: that we can use every pixel instead of very few dedicated masked AF pixels, and this method is precise enough without having to rely on CDAF to fine-tune focus position. It will work with every exit pupil location (unlike many pixel-mask implementations don't work with some lenses). No need to compromise static IQ.

There is a drawback, that is firing shutter is required to focus. However, we don't need to read out entire sensor, only small areas of interest. Where sensor readout is flexible enough, it can be incorporated in normal frame readin

g - special areas of interest are reset and read multiple times.

 Enginel's gear list:Enginel's gear list
Pentax Q Sony Alpha NEX-5N Sony E 18-55mm F3.5-5.6 OSS Sony E 50mm F1.8 OSS
All forumsForumParentFirstPrevious
Post (hide subjects) Posted by
All forumsForumParentFirstPrevious
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow