Nikon 1 in low light with fast native lens....PDAF???

Started Mar 31, 2012 | Discussions thread
mosswings Veteran Member • Posts: 8,115
Re: My experiment data

stasvolik wrote:

Thanks to new beta search feature of DPReview, I found another important piece of information, that is completely in line with my results and Marianne's [wordy] explanation of how to test underlying physics of this phenomenon:

"The AF sensors in a camera are directional. They're aimed at two spots on the "exit pupil" of the lens. That's the lens's aperture, seen from the camera side. If you aim the sensor "beams" along a 10 degree V, you cover the part of the exit pupil that corresponds to f5.6.
1/(2 tan(10deg/2))

If you have a lens faster than f5.6, it doesn't matter, because the parts of the exit pupil that correspond to apertures larger than f5.6 fall outside the 10 degree V of the AF sensor. "

For those who are not afraid of reading too many letters, more info at

Bottom line: faster lenses will NOT help to improve sensitivity of current PDAF systems without a significant overhaul (aiming sensors at 20 degree angle relative to each other - like Canon and Olympus did in theirs).

-- hide signature --

Comments and critiques are always welcome .


Heaven's, I just learned something! What this says is, in effect, for a given separation angle the ability of the AF system to focus in dim light is just a direct function of the AF sensor's light collecting area as long as the light transmission qualities of the lens attached to the camera don't interfere. A complex zoom lens may have lower light transmission characteristics than a simpler prime.

So a useful exercise would be to compare the total light-gathering area of the V1's integrated sensors with the separate AF sensor found in DSLRs. My suspicion is that it's significantly less. Of course, it could be made to be the same area, but that would take up more of the smaller V1 sensor, and the question would then be if sufficient high-speed data paths could be provided to pump out the AF data fast enough to keep AF acquisition speed high. If the AF sensors cannot do double duty as imaging sensors, then an integrated PDAF system must be made necessarily of minimum area to do the job; that job may not be to reliably focus down to EV -2 as the D800 can.

 mosswings's gear list:mosswings's gear list
Olympus XZ-1 Olympus Stylus 1 Nikon D90 Nikon D7100 Nikon AF-S DX Nikkor 18-105mm f/3.5-5.6G ED VR +5 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow