Idea for new focus system....

[MattSepeta]

I was thinking about how annoying it is when you are shooting wide open at a very low f-stop,m f/1.4 or f/2, and when you employ the focus-recompose method you will often end up with the eyes, or whatever your desired focus point is being off a bit.

I came up with an idea of sorts on how a camera could combat this without the pain of selecting a focus point, which I really do not like doing-

Let's say you are using center point one shot AF. You focus the center point on the eyes, and naturally recompose to a more pleasing composition while your shutter is half pressed. What if the camera would somehow detect that area, and assuming said desired area of focus falls under another focus point once desired composition is obtained, the camera automatically senses this and reconfirms the desired focus using the new, non-manually-selected focus point on the original area of desired focus? I imagine it would do this by employing a very small "snapshot" of the area under the desired focus when you half-depress the shutter, then on-the-fly sensing if this "snapshot" falls under any of the outer focus points while recomposing, where it will finally verify and correct the focus if it does fall under a new focus point.

It's kind of hard to explain, but I imagine with how "smart" AF is getting (Not counting canon's "5" series of course ), this is not unrealistic...

Any thoughts on this? Is it possible? More importantly, is is plausible?

 

[compuwar]

This is basically how focus tracking works.

Paul

 

[mackmgg]

When shooting in Live View, some cameras already offer something like this as compuwar said. The normal phase-detect autofocus wouldn't be able to do this though, because there is nothing being processed

 

[jabbott]

I'm still waiting for light field digital cameras to come out... it would allow you to choose focus after taking the shot:
http://graphics.stanford.edu/papers/lfcamera/

It also provides f/22-like sharpness with an f/4 aperture (not counting diffraction limitations). The tradeoff is lower resolution... but I would often be willing to give up resolution for being able to refocus during post-processing.

 

[VirtualRain]

I'm still waiting for light field digital cameras to come out... it would allow you to choose focus after taking the shot:
http://graphics.stanford.edu/papers/lfcamera/

It also provides f/22-like sharpness with an f/4 aperture (not counting diffraction limitations). The tradeoff is lower resolution... but I would often be willing to give up resolution for being able to refocus during post-processing.

Wow... that's very cool!

 

[MattSepeta]

This is basically how focus tracking works.

Paul

I was unaware that one-shot AF tracked anything, I thought that was simply in AI-Servo mode?

 

[miloblithe]

Do you have $20-50k for a Hasselblad system?

True Focus: Delivering accurate composing at close distance with shallow depth-of-field
True Focus helps solve one of the most lingering challenges in professional photography, true, accurate focusing throughout the image field when working with shallow depth-of-field at closer range. Without multi-point auto-focus a typical auto-focus camera can only correctly measure focus on a subject that is in the center of the image. When a photographer wants to focus on a subject outside the center area, they have to lock focus on the subject and then re-compose the image.

In short distances, this re-composing causes focus error, as the plane of focus sharpness follows the camera’s movement, perpendicular to the axis of the lens. The traditional solution for most DSLRs has been to equip the camera with a multi-point AF sensor. These sensors allow the photographer to fix an off-center focus point on an off-center subject, which is then focused correctly, but such multi-point AF solutions are often tedious and inflexible to work with and do not really solve the problem.

To overcome this problem, Hasselblad has used modern yaw rate sensor technology to measure angular velocity in an innovative way. The result is the new Absolute Position Lock (APL) processor, which forms the foundation of Hasselblad’s True Focus feature.

The APL processor accurately logs page 3/3 camera movement during any re-composing, then uses these exact measurements to calculate the necessary focus adjustment, and issues the proper commands to the lens’s focus motor so it can compensate. The APL processor computes the advanced positional algorithms and carries out the required focus corrections at such rapid speed that no shutter lag occurs. The H4D’s firmware then further perfects the focus using the precise data retrieval system found on all HC/HCD lenses. The True Focus technology and APL (both patent pending) mark a significant milestone for Hasselblad’s high-end DSLR strategy and represent the result of many years of development work.

http://www.dpreview.com/news/1002/10020210hasselbladh4d40.asp

 

[compuwar]

I was unaware that one-shot AF tracked anything, I thought that was simply in AI-Servo mode?

Continuous-servo mode focus tracks, servo mode doesn't. In continuous mode, the camera tries to follow the subject at the original point of focus, predict where it will be when the shutter fires and focuses accordingly.

http://www.nikon.com/about/technology/core/software/caf/index.htm

To whit:

An operation mode called "Continuous-servo AF (AF-C)" maintains continuous focus on a moving subject, but this is not sufficient for taking a sharply focused picture. This is because there is a short time lag between when the shutter is pressed and when the picture is actually taken, which is referred to as the release time lag. To solve this problem, the "predictive focus tracking system" uses special algorithms to forecast the position of the subject at the moment the image is captured based on measurement of the subject's movement, and moves the lens accordingly. Simply put, the predictive focus tracking system detects the subject’s speed of motion and adjusts the focus by taking the release time lag into consideration. Nikon's AF function performs accurate autofocusing operation under any situation by controlling the predictive focus tracking system based on the locus of the subject’s motion. Nikon used extensive data obtained by photographing a large number of moving subjects for the development of the predictive focus tracking system.

Paul