focal points canon
Sep 22, 2022 12:47:52 #
lmTrying wrote:
You just mentioned something that I have often wondered about, plane of focus, or arc of focus. Lenses are spherical. If you stretch a string from the lens out to the focal point, it will not define a flat plane. I have noticed that the people on the ends of a long line tend to get distorted. Distortion or focus?
Quite worthy of a whole new thread, using the question just the way you describe it here, string and all.
Sep 22, 2022 12:52:01 #
Tomfl101 wrote:
Use single point focus. For a group of 8-10 use one or two rows. Focus carefully on the front row. Significant depth of field using a small aperture is advised but not necessary. See my example shot at 2.8 with a 50mm lens in evening light.
Nice. Distance allowed your f/2.8. But for only half as many peeps youll be at about half the distance, so f/5.6 (or even 8.0).
Sep 22, 2022 13:09:45 #
Longshadow wrote:
Focus. br The plane of focus follows an arc, even ... (show quote)
Thaz all very wrong. You cannot draw conclusions by rotating the camera to recompose the edge of the subject field into the center. When you rotated the plane you shifted the focus.
When you focus a flat field lens at 10 ft that means 10 ft ON AXIS. It may be focused to 13 ft halfway to corner and 16 ft at the corner (actual numbers depend on FL). Sketch it out if that what it takes to understand it.
The focus plane is a plane, not an arc. Hawgsters are too much talk and not much hands on. How many here really photograph brick walls ? Maybe nobody but me.
Sep 22, 2022 13:11:57 #
User ID wrote:
Thaz all dery wrong. You cannot draw conclusions by rotating the camera the bring the edge of the subject field into the center.
The focus plane is a plane, not an arc. Hawgsters are too much talk and not much hands on. How many actually shoot brick wall ?
The focus plane is a plane, not an arc. Hawgsters are too much talk and not much hands on. How many actually shoot brick wall ?
Yes, the focus plane is flat. If you focus at 10 feet and rotate the camera, the flat plane, at 10 feet, rotates around the 10 foot arc, remaining perpendicular to the camera at the focused distance.
Last I knew aspherical lenses correct aberrations that exist in spherical lenses.
They do not "flatten" the depth of field arc.
Sep 22, 2022 13:32:40 #
Longshadow wrote:
Yes, the focus plane is flat. If you focus at 10 feet and rotate the camera, the flat plane, at 10 feet, rotates around the 10 foot arc, remaining perpendicular to the camera at the focused distance.
The entire flat plane is NOT focused at 10 ft. Only the center is at 10 ft. The corners are actuall focus at a much greater distance, maybe 15 ft (depends on FL).
If you re-aim the camera such that you move the center of your composition over to edge, you moved that away from the 10 ft focus and into the 15 ft focus, but the object is still only 10 ft away .... so acoarst that object goes out of focus.
Going out of focus doesnt prove focus is in arc. It does prove that its a plane.
Again, sketch it out (mark off a few dimensions).
Sep 22, 2022 13:36:47 #
User ID wrote:
The entire flat plane is NOT focused at 10 ft. Onl... (show quote)
The object goes out of focus because it is now in front of the focal plane.
I did sketch it out, in my mind with a compass and paper.
Sep 22, 2022 13:43:02 #
Longshadow wrote:
Yes, the focus plane is flat. If you focus at 10 feet and rotate the camera, the flat plane, at 10 feet, rotates around the 10 foot arc, remaining perpendicular to the camera at the focused distance.
Last I knew aspherical lenses correct aberrations that exist in spherical lenses.
They do not "flatten" the depth of field arc.
Last I knew aspherical lenses correct aberrations that exist in spherical lenses.
They do not "flatten" the depth of field arc.
Plz dont drag in lens element shapes. A flat field is a flat field. Doesnt matter how it got flattened. Think "crop circles".
Sep 22, 2022 13:45:06 #
User ID wrote:
Dont drag in lens element shapes. A flat fielf is a flat field. Doesnt matter how it got flattened.
Exactly, but some people referenced the spherical/aspherical differences in this instance, which is erroneous.
Sep 22, 2022 23:06:40 #
lmTrying
Loc: WV Northern Panhandle
User ID wrote:
Quite worthy of a whole new thread, using the question just the way you describe it here, string and all.
Yes, I thought about that even before I started typing, and after I hit send.
I may yet throw it out there.
Sep 23, 2022 07:07:12 #
User ID wrote:
Nice. Distance allowed your f/2.8. But for only half as many peeps youll be at about half the distance, so f/5.6 (or even 8.0).
You are correct about distance, but I'd say even f-4 would do it. Accurate focus and tight spacing is the key. When we miss the mark on focus we tend to think a wide aperture was the culprit, when focus was the problem all along. Of course bokeh is usually not needed in group photos so choosing a small aperture is always smart when you have sufficient light.
Sep 23, 2022 07:07:32 #
lmTrying wrote:
Yes, I thought about that even before I started typing, and after I hit send.
I may yet throw it out there.
I may yet throw it out there.
It will get wild and wooly with Hawglands various phony experts arguing opposite each other. Im here for the entertainment .........
Sep 23, 2022 07:25:45 #
Tomfl101 wrote:
You are correct about distance, but I'd say even f-4 would do it. Accurate focus and tight spacing is the key. When we miss the mark on focus we tend to think a wide aperture was the culprit, when focus was the problem all along. Of course bokeh is usually not needed in group photos so choosing a small aperture is always smart when you have sufficient light.
When you move in to fill the frame after reducing the group size down to half, you are doubling the image magnification ... and that costs two stops to maintain same DoF as was available at the longer distance.
Thaz how I chose f/5.6 based on your photo at f/2.8. But yes your f/4 might work cuz facial details will be larger and easier to see at the closer distance. But, for truly equal DoF, half the distance means two stops.
Sep 23, 2022 08:41:01 #
MS. DONNA wrote:
How many focal points do you choose when you photograph a family or groups of people ( 8 to 10 )
5d markiv canon
5d markiv canon
One.
Sep 23, 2022 09:09:04 #
User ID wrote:
When you move in to fill the frame after reducing the group size down to half, you are doubling the image magnification ... and that costs two stops to maintain same DoF as was available at the longer distance.
Thaz how I chose f/5.6 based on your photo at f/2.8. But yes your f/4 might work cuz facial details will be larger and easier to see at the closer distance. But, for truly equal DoF, half the distance means two stops.
Thaz how I chose f/5.6 based on your photo at f/2.8. But yes your f/4 might work cuz facial details will be larger and easier to see at the closer distance. But, for truly equal DoF, half the distance means two stops.
Got it. Good point.
Sep 23, 2022 13:14:02 #
amfoto1
Loc: San Jose, Calif. USA
WOW! Did this discussion ever drift off into the weeds! 
How I would shoot a group where I wanted to be part of the shot...
1. Arrange the group in two or three rows, as needed (depending upon how many people there are). Leave a space where I'll be jumping into the shot.
2. Set a focal length on a zoom around 50mm (full frame... 30 to 35mm APS-C). Put camera on a tripod at distance required to frame the group as wanted.
3. Stop down the lens a bit, f/2.8 or f/4, to create enough depth of field to cover the subjects front to back.
4. Select a single AF point and focus upon the front row (if two rows) or middle row (if three). On a Canon camera One Shot can be used. Or, if using back button focusing, AI Servo can be used.
5. Once focus is achieved TURN OFF AF. (It also would be possible to focus manually... even using the rear LCD zoomed in to 10X for precise focusing if wanted.)
6. Re-compose as needed, without changing the distance to the subject. Now that focus is set up and AF is turned off, there's no risk of the camera refocusing away from where you set it.
7. Use any metering method and exposure mode you wish. Fill flash may be needed in some situations (be careful of eyeglasses). Actually this is irrelevant to the focusing question.
8. Either use the 10 second self timer or a wireless remote release to allow myself to get into the shot.
Take several shots in case someone closes their eyes. Tell everyone to stay in place a few minutes longer while you quickly confirm that the shots came out okay. Your main concerns should be proper exposure and good focus. (If someone's eyes are closed in one image, check that they are open in another. No need to re-shoot. You can always copy a face from one image to another in post-processing, if needed.)
How I would shoot a group where I wanted to be part of the shot...
1. Arrange the group in two or three rows, as needed (depending upon how many people there are). Leave a space where I'll be jumping into the shot.
2. Set a focal length on a zoom around 50mm (full frame... 30 to 35mm APS-C). Put camera on a tripod at distance required to frame the group as wanted.
3. Stop down the lens a bit, f/2.8 or f/4, to create enough depth of field to cover the subjects front to back.
4. Select a single AF point and focus upon the front row (if two rows) or middle row (if three). On a Canon camera One Shot can be used. Or, if using back button focusing, AI Servo can be used.
5. Once focus is achieved TURN OFF AF. (It also would be possible to focus manually... even using the rear LCD zoomed in to 10X for precise focusing if wanted.)
6. Re-compose as needed, without changing the distance to the subject. Now that focus is set up and AF is turned off, there's no risk of the camera refocusing away from where you set it.
7. Use any metering method and exposure mode you wish. Fill flash may be needed in some situations (be careful of eyeglasses). Actually this is irrelevant to the focusing question.
8. Either use the 10 second self timer or a wireless remote release to allow myself to get into the shot.
Take several shots in case someone closes their eyes. Tell everyone to stay in place a few minutes longer while you quickly confirm that the shots came out okay. Your main concerns should be proper exposure and good focus. (If someone's eyes are closed in one image, check that they are open in another. No need to re-shoot. You can always copy a face from one image to another in post-processing, if needed.)
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.