Focus ONE spot or multiple?
Apr 16, 2019 14:13:03 #
Apr 16, 2019 14:16:03 #
therwol wrote:
Recomposing after using the center focus point on a subject that isn't in the center can change the plane of focus such that your subject isn't perfectly focused any longer. I usually use 3D focus tracking on my Nikon D810, and as I move the camera, the focal point stays on the subject.
Are you saying that, if you focus on a main subject which is, say, thirty feet away and lock focus, that if you move the field of view horizontally or vertically by, say, fifteen feet, that the focussed distance (lens to main subject) will change
Apr 16, 2019 14:19:23 #
elliott937 wrote:
For years, in using my Canon DSLRs, I've always turned off the gazillion focusing squares and elected for just one in the center. I suppose if photographing a moving subject, moving either toward or away from the camera would be a perfect time to have the gazillion squares turned on. For me, I prefer to have just one focusing square and have total control. Am I missing something? Or, do many of you turn off all but one of the focusing squares?
I could never understand the competition to have more and more focus points. The camera can focus on only one plane at a time, generally the one closest to the camera. I've always preferred one central focusing point. Unfortunately, that doesn't work in Auto for most cameras, so if someone likes shooting in Auto mode, he's out of luck.
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Apr 16, 2019 14:19:41 #
nadelewitz
Loc: Ithaca NY
Delderby wrote:
Are you saying that, if you focus on a main subject which is, say, thirty feet away and lock focus, that if you move the field of view horizontally or vertically by, say, fifteen feet, that the focussed distance (lens to main subject) will change
Yes, if the center spot is now on a subject a different DISTANCE away. The more you change the angle of view, the more the distance to a specific spot changes.
Simple geometry.
Apr 16, 2019 14:28:50 #
elliott937 wrote:
For years, in using my Canon DSLRs, I've always turned off the gazillion focusing squares and elected for just one in the center. I suppose if photographing a moving subject, moving either toward or away from the camera would be a perfect time to have the gazillion squares turned on. For me, I prefer to have just one focusing square and have total control. Am I missing something? Or, do many of you turn off all but one of the focusing squares?
The center is the fastest and most accurate ! But, for BIF I try to have a small multiple array in the center enabled.
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Apr 16, 2019 15:26:40 #
Longshadow wrote:
On many cameras, including mine, "single" spot uses the center point only.
My phone has a movable focus point, but not my cameras. (No tilt, swivel, touch.)
My phone has a movable focus point, but not my cameras. (No tilt, swivel, touch.)
Yes - I understand - with an optical VF you cannot adjust the screen with touch - but what I thought was that you could still lock the focus and adjust your composition by tilting and swivelling the tripod?
Apr 16, 2019 15:34:59 #
nadelewitz wrote:
Yes, if the center spot is now on a subject a different DISTANCE away. The more you change the angle of view, the more the distance to a specific spot changes.
Simple geometry.
Simple geometry.
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Apr 16, 2019 15:43:07 #
Delderby wrote:
Yes - I understand - with an optical VF you cannot adjust the screen with touch - but what I thought was that you could still lock the focus and adjust your composition by tilting and swivelling the tripod?
That's what I do using BBF. Select the focus area, then compose the shot (either hand-held or on the tripod). I'm not worried about any angle (and I do understand the geometry involved) as the depth of field will usually take care of that.
Apr 16, 2019 16:10:39 #
therwol
Loc: USA
Delderby wrote:
Are you saying that, if you focus on a main subject which is, say, thirty feet away and lock focus, that if you move the field of view horizontally or vertically by, say, fifteen feet, that the focussed distance (lens to main subject) will change
The focus distance doesn't change if it is locked. What's changed is that the subject you focused on is no longer in the plane of focus. It may be too slight to notice, but at close distances and a wide aperture, it may make some difference.
Apr 16, 2019 16:11:34 #
therwol wrote:
The focus distance doesn't change if it is locked. What's changed is that the subject you focused on is no longer in the plane of focus. It may be too slight to notice, but at close distances and a wide aperture, it may make some difference.
Apr 16, 2019 16:13:59 #
I think the main thing to keep in mind is that focus in not a point, but it is a flat plane parallel to the flat plane of the sensor. So if you take a group photo 30 feet away and they stand in an exact straight line parallel to the back of your camera, if one person is in focus then they all are in focus, but if they stand in a semicircle and you focus on the cute kid in the middle, the old people on the ends will be out of focus. We don't usually care though, because depth of field makes it seem acceptable, but depth of field is also parallel to the same plane.
That is the best thing about view cameras. They can tilt the lens and tilt the film plane. Google the Scheimpflug principle to make your head spin!
That is the best thing about view cameras. They can tilt the lens and tilt the film plane. Google the Scheimpflug principle to make your head spin!
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Apr 16, 2019 17:01:10 #
bleirer wrote:
I think the main thing to keep in mind is that foc... (show quote)
It is just the opposite from the way you describe - people in straight line, the ends will be out of focus because they are further away - people in a semi-circle WILL be in focus ...
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Apr 16, 2019 17:05:59 #
therwol
Loc: USA
Longshadow wrote:
Okay, this is very crude. I did this in Paint. I hope it makes the point.
If you use a single, central point of focus to focus on your subject A and then rotate the camera to put A in the periphery of the picture, then A is no longer in the plane of focus. Your camera is focused on B, and the plane of focus is now beyond A.
You can step sideways parallel to the original plane of focus.
You can move the focal point in the viewfinder to the subject A after composing the picture.
You can have your camera automatically refocus on A as you move the camera. The setting may be different on different on different cameras, but I use 3D focus tracking on my Nikon. No matter how I move the camera, it continues to focus on the subject.
Note that all of this doesn't really matter if your subject is far enough away and you have adequate depth of field so it isn't noticed.
Apr 16, 2019 17:12:08 #
wdross
Loc: Castle Rock, Colorado
imagemeister wrote:
It is just the opposite from the way you describe - people in straight line, the ends will be out of focus because they are further away - people in a semi-circle WILL be in focus ...
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It is more dependent on if the lense has a flat focal plane. Copy lenses have a flat focal plane for documents and paintings. Most lense designs actually curve the focal plane in towards the camera at the edges. That is why some lenses work better than others at the same focal length / focal distance than others for copy work. It is dependent on how flat the focus plane really is.
Apr 16, 2019 17:12:37 #
therwol wrote:
Okay, this is very crude. I did this in Paint. I... (show quote)
Very good graphic depicting how it works!
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