What happened to the focus (Page 4): Please explain how a single focus point 'averages'.

imagesintime Loc: small town, mid-America

Rongnongno wrote:

I will not describe what I think of your understanding of how the averaging works. Your understanding is wrong and since you are not able to back down, even knowing when you are mistaken you keep going like the infamous bunny.

Enjoy your lack of brain cells, you already enjoy being obnoxious most of the time so...

YOU WIN! (not)

(indistinct rumbling)

Please explain how a single focus point 'averages'.

oldtigger Loc: Roanoke Virginia-USA

imagesintime wrote:

Please explain how a single focus point 'averages'.

When the camera chooses one member of a group matrix to focus on, it is not a mathematical average but it is a functional average because the spot chosen is the closest approximation to the combined findings of all the matrix group members.

Apaflo Loc: Anchorage, Alaska

oldtigger wrote:

When the camera chooses one member of a group matrix to focus on, it is not a mathematical average but it is a functional average because the spot chosen is the closest approximation to the combined findings of all the matrix group members.

There is no "functional average" for focusing. Whatever that was supposed to mean. :-)

The "spot chosen" is a "focus point" in the camera. The area of the scene visible in the viewfinder at that "focus point", highlighted in red, is what the camera attempts to focus on, using that one and only that one "focus point". Nothing is averaged, in any way.

If the camera is using AF-Area Mode with either Dynamic-area AF, 3D-tracking, or Auto-Area AF then multiple "focus points" are used to determine which single "focus point" will provide the focus information used to focus the lens. Nothing is averaged! The point selection is made by analysis of the data recorded by multiple focus points, including both distance and color differences, but none of that information is averaged and none of that (saved) matrix is used for actual focus.

Focus averaging does not happen.

davidk2020 Loc: San Diego

Meives wrote:

Howard, The rule that I was taught is that the shutter speed should be equal or greater than the mm of the lens used. Shutter = 1/mm You were at 1/400 and the lens was 1000. This could cause total blur. David I re-read your post and you used a tripod.

That rule applies to a hand-held camera to mitigate the effects of camera shake. Howard used a tripod for a huge lens that hardly anyone would try to hold by hand: the tripod is used to hold up a heavy lens but it also eliminates camera shake.

I hope this helps you understand the shutter speed => 1/focal length rule.

oldtigger Loc: Roanoke Virginia-USA

Apaflo wrote:

There is no "functional average" for foc... (show quote)

thankyou for agreeing my statement was correct.

Apaflo Loc: Anchorage, Alaska

oldtigger wrote:

thankyou for agreeing my statement was correct.

There is no "functional average" for focusing. That is disagreeing with your entire point. The small part that was correct I do agree with.

JoeJoe

Apaflo wrote:

There is no "functional average" for focusing. That is disagreeing with your entire point. The small part that was correct I do agree with.

Looks like people confuse WB and focus... Spot focus is what it says on the tin as I've previously posted and calibrate the lens to the body (sensor) Nikon fine tune in menus.... keep it simple and you'll find it easy once you've done it a few times
I choose where my DoF sits in the focus (that is focus fine tune)

Muddyvalley Loc: McMinnville, Oregon

Downloaded and enlarged, the photo without the extender appears to me to be sharper everywhere, which tells me it is more the tele extender degrading the image, not the focusing, which may be off a bit too.

Howard5252 Loc: New York / Florida (now)

Thank you to all who replied.

Silvermeteor Loc: South Carolina, USA

Howard5252 wrote:

Thank you. I use a single focusing point in the viewfinder and typically focus on the head of the bird. The mode was Auto Focus. I'm not looking for post camera corrections. I will re-create this again.

Howard there is an add on for LR called "Show Focus Points" that will show you the actual active focus points in the image. This might provide you with a little more input.

You can check it out here:

http://www.lightroomfocuspointsplugin.com/

Howard5252 Loc: New York / Florida (now)

Thank you; I use Elements. The camera has an option that shows me the focus point on the playback (while still in the camera). That info goes away upon uploading. Not concerned about it, thanks again.

MtnMan Loc: ID

Apaflo wrote:

There is no focus averaging.

The OP is talking about a Nikon camera. Nikon cameras can have many "focus points", but only one of them is selected to measure the focus. There is no averaging, ever.

We can all agree that a lens can only focus on one plane. ONE. That is what all must keep in mind.

How the camera fixes the distance to that plane varies. I think the Nikon literature is misleading in the way it discusses "multiple focus points".

I am not sure how they come up with the distance when not using AF-S. Several points light up in the viewfinder. That suggests to me that the camera is indeed measuring the distance to those several points and averaging it to set the lens. Some have suggested it chooses the closest of those points. Some have suggested it chooses something like the median; a kind of averaging. If you can find something published by Nikon please share it.

(PS: I only use AF-S single point focus so don't really have to know.)

oldtigger Loc: Roanoke Virginia-USA

MtnMan wrote:

We can all agree that a lens can only focus on one plane. ONE. That is what all must keep in mind.
How the camera fixes the distance to that plane varies. I think the Nikon literature is misleading in the way it discusses "multiple focus points". ...

some write ups suggest focus is determined by blocks of color, some refer to closest large uniform block, some refer to shape of a defined area as in an eye or face, some speak of greatest contrast.
I think it may have evolved over the years, i don't care as long as it remains where i put it.

SonyBug

On my monitor, the first shot is blurry throughout, so I would guess camera movement or too slow shutter speed for the lens equivalent of 1000 mm. On the second, the focus point is definitely in front of the bird. The bird is almost in the DOF, so it looks OK at small sizes.