What the heck is a null indicator?

http://www.kenrockwell​.com/nikon/d3/vs-d300.htm

In this review Ken Rockwell mentions something about a "three-segment null indicator ( > o < ) which can indicate perfect, precise, manual focus."

Anyone know what the heck he is talking about and if any Canon has such a feature?

Basically, this is a "hot/cold" indication of how close you are to what the AF system thinks is perfect focus. Usually, you only get a confirmation light, where the AF blinks when you hit manual focus. I don't know which Canon cameras have this as I don't use manual lenses.

I think he's talking about Nikon's feature that shows you which way the focus needs to be turned in manual focus and a light lights up when you hit perfect focus. Never heard it referred to a nul indicator though.

KR has funny names for a lot of things.

The Canon AL-1 had it 30 years ago back in 1982. They called it "In-focus indicator".

http://www.mir.com.my …ources/SLRs/al1​/index.htm

How it works: http://www.mir.com.my …urces/SLRs/al1/​index1.htm

Kolor-Pikker wrote in post #15670947
KR has funny names for a lot of things.

He sure does. In his review of the 5D IIl (which he likes!) He calls the P mode :"Pro" mode.
But.... he's making money!

Its a very useful feature which I liked when I tried the Nikon D4. I wish Canon implemented something like this on their DSLRs.

Mike R wrote in post #15671200
He sure does. In his review of the 5D IIl (which he likes!) He calls the P mode :"Pro" mode.
But.... he's making money!

Well, lots of people call it that when being ironic. After all, it's the most common mode when a beginner gets a DSLR and wants to be a "professional" and not stay in green-box mode.

^^
I understand your point, but as a reviewer with a wide audience, shouldn't he use the correct terminology as to not confuse people, especially beginners? It's "Program Mode", Ken, Program Mode. Lol

Buylongterm wrote in post #15671689
^^
I understand your point, but I dont think hes being ironic when he uses that term. Perhaps as a reviewer with a wide audience, shouldn't he use the correct terminology as to not confuse people, especially beginners? It's "Program Mode", Ken, Program Mode. Lol

Well, lots of people don't understand irony. So maybe he have somehow picked up this terminology without realizing it's said jokingly or ironic, and somehow made the term his own but on completely wrong grounds.

On the other hand, if you aren't good enough with language, you can decide to shorten "Program" into "pro". That the short form "pro" is normally not expanded into "program" will then instantly result in lots of confusion...

Well if KR has a background in electronic engineering he is maybe relating this with SWR meters that are normally tuned for minimum output, usually with a centred swing needle. Although on some meters there is an LED system that lights the middle LED when the output is zero, and one on either side when there is a +/- output. This will be exactly the type of electronic output from the AF system when used in MF mode. I.E an instruction to turn one way or the other or zero output if the lens setting is correct.

There was a thread about AF accuracy that I was reading earlier today, and a link to a blog post on lensrentals.com describing Canon AF system accuracy. In this it explains that the Phase detection AF system provides an output value that tells the AF system how far, and in what direction to turn the lens ring to achieve focus. Some of the Canon cameras tested turned out to have an "open loop" system whereby the lens ring is turned the estimated "correct" amount and the system then takes the image. Other cameras use a closed loop system where after moving the lens ring, the AF system then rechecks the measurement of the system to check that the lens has turned the correct amount (within a particular tolerance). This is effectively what the above system gives you in MF mode. The latest systems in the 1dx and 5DIII when used with some of the latest lenses have very accurate, and repeatable, AF though. This is because they combine both a closed loop system within the camera, with a system that can accurately measure the position of the lens ring. The AF though will only be this super accurate when combining BOTH the new bodies with the new lenses.

Alan

Some notes about phase-detection AF.

The camera normally order the lens to shift focus to a specific setting. Then it normally makes another check "good enough".

One of the things the lens reports back to the camera is how fast the lens AF system can accelerate/deccelerate and how much play there is in the mechanism. Play means that when the focus motor switches direction, the relevant lens element groups will not directly start to move in the other direction.

So the camera tries to predict what focus position to send to the lens, to have the lens end up at the correct position. As the lens wears, the play can increase, making the camera guestimate wrong orders to send to the lens. In some situations, this can be fixed by sending in the lens and have it recalibrated.

It seems that in newer lenses, Canon have added in extra position sensors in the lens, to better measure the actual position on the focus scale, making camera+lens better decide how long to run the focus motor at max speed, and when to start to break to end up at the exact location that would correspond to the original AF sensor reading (and potentially during the travel time having computed multiple new solutions based on position sensor data and AF sensor data).

But note that phase detection AF is only as good as the calibration between camera and lens. And for a zoom lens, that calibration can change a lot depending on zoom level. And over the years, the camera manufacturers have had huge issues getting the side AF points to give decent focus with different lenses.

Only contrast-based focus will remove the calibration issues between body and lens, or the issues with image flatness (obviously under the assumption that there aren't so much play in the lens that the camera body isn't able to get the lens to "land" at the requested focus position)

Alan, you're right about the way some of these AF systems work, a typical phase AF point is just a 1-dimensional line that either sees a gradient or a sharp transition somewhere along it's length. As the gradient tightens up, the AF point knows this to be contrast, and thus detail it can lock on to. The AF can actually scan back and forth hundreds of times per second, so to us it seems like it locks on quickly, when it has actually confirmed focus at least a few doses times by the time the AF light blinks.

Although null indication is not a commonly used term in photography, using it in the description of this type of indicator it is quite valid.

The word "null" when used in this sense means zero and this is exactly what it signifies, it represents the point on the scale where there is neither a positive or negative offset. Very widely used in scientific and electronic terminology.

Mike R wrote in post #15671200
He sure does. In his review of the 5D IIl (which he likes!) He calls the P mode :"Pro" mode.
But.... he's making money!

I actually love his writing. It's extremely entertaining and you get a colloquial, conversational style. Quirky, very.

He is also one hell of a satirist.