Depth of field question
Sep 9, 2018 05:55:33 #
Chaostrain wrote:
Any more explanation would just be confusing.
Of course, but isn't that what we live for here?
Sep 9, 2018 07:01:33 #
CHG_CANON wrote:
It's science. There are not easy terms.
Now, now, now...CHG CANON! I am a science guy, now retired. Talking science can be just like talking dirty. Just as fun if you know the terms....and just as easy.
LOL
Sep 9, 2018 07:40:41 #
billnikon
Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont
Inthewoods wrote:
Maybe I'm overlooking something obvious, but I wonder if someone could explain in somewhat simple terms why it is that a smaller aperture creates greater depth of field.
Ever squint your eyes to see something more clearly. There you go. When you squint, you narrow the iris of your eye so that the opening becomes smaller, resulting in you seeing better, more clearly. Same works in photography, the more you stop down, the smaller the lens opening, the sharper the image (sort of). This is as simple as it gets.
The other thing to keep in mind with depth of field is that it increases faster going away from the camera. So, if one object is slightly behind the other and you want to make sure both are in focus, stop down and focus on the one in front, that will usually get them both in focus.
One last point, if your camera has a depth of field button, USE IT. It is really helpful to see exactly what will be in focus.
Sep 9, 2018 07:49:14 #
Maybe this has been answered, I haven't looked over all the other posts.
The lens focuses the image as points of light. Since a "point" is theoretical the actual point of acceptable sharpness is really a circle, often referred to as the circle of concussion. Think of it this way, the reflected light coming from the image you are photographing comes through the lens on to the film plane (sensor) as an infinite number of cones of light. A smaller the lens opening makes for a cone of a smaller angle. These cones have a longer distance of acceptable sharpness than a wide angle cone.
Maybe this is more confusing. In any case there is much information written about the subject on the internet. I also suggest getting a hold of Adams "The Lens" book
The lens focuses the image as points of light. Since a "point" is theoretical the actual point of acceptable sharpness is really a circle, often referred to as the circle of concussion. Think of it this way, the reflected light coming from the image you are photographing comes through the lens on to the film plane (sensor) as an infinite number of cones of light. A smaller the lens opening makes for a cone of a smaller angle. These cones have a longer distance of acceptable sharpness than a wide angle cone.
Maybe this is more confusing. In any case there is much information written about the subject on the internet. I also suggest getting a hold of Adams "The Lens" book
Sep 9, 2018 07:52:40 #
Sep 9, 2018 08:09:25 #
camerapapi wrote:
I have a good advise for you: learn basic photography.
To tell you the truth, I'm not inclined to value the opinion of someone who doesn't know the difference between the word "advise" and "advice"...and who doesn't see the difference between a theoretical and a practical question. But, thanks, anyway.
Sep 9, 2018 08:28:59 #
Sep 9, 2018 08:29:15 #
peterg
Loc: Santa Rosa, CA
jerryc41 wrote:
Exactly. When I forget my glasses and can't read the menu, I squint. A pinhole camera has a very small aperture and everything's in focus.It's for the same reason that squinting makes things look sharper.
Sep 9, 2018 08:30:50 #
Dikdik
Loc: Winnipeg, Canada
With a small lens opening, you are using only a portion of the lens, the least amount of curvature, and the most uniform thickness. As you use more of the lens there is more of the area to bend the light, and it passes through a greater thickness of 'glass'. The light rays bend slightly differently when the outer portions of the lens are used. This is called spherical aberration and leads to the 'fuzziness' when a large lens opening is used.
Dik
Dik
Sep 9, 2018 08:35:00 #
Inthewoods wrote:
To tell you the truth, I'm not inclined to value the opinion of someone who doesn't know the difference between the word "advise" and "advice"...and who doesn't see the difference between a theoretical and a practical question. But, thanks, anyway.
Don't ya just love snarky assholes?
Sep 9, 2018 09:22:42 #
rubble43
Loc: Oyster Bay, Long Island NY
The aperture number is a fraction. It is calculated by dividing the focal length by the aperture opening. for example, f/4 for a 100mm lens is representative of 100/4 or a 25mm opening. At f/16 the opening is 1/16th of 100mm, or 6.25mm, a much smaller size. As the focal length gets larger, so will the physical size of the opening for the same f/ number.
Sep 9, 2018 09:36:15 #
I recently discovered this photographer’’s videos , Chris Bray, on You Tube and I find his answers easy to follow. On aperture and DOF he writes:
“Think of aperture like this: Small F number small DOF and large F number large DOF”
“Think of aperture like this: Small F number small DOF and large F number large DOF”
Sep 9, 2018 10:18:39 #
jerryc41 wrote:
Of course, but isn't that what we live for here?
Yeah, I've noticed. It's like somebody on here posted elsewhere. You ask some people what time it is and they'll tell you how to build a clock.
Sep 9, 2018 10:37:27 #
orrie smith wrote:
You are possibly misunderstanding aperture. A smaller number aperture is actually a larger aperture, or more open if you will. 1.4 aperture would relate to a larger opening and would bring less into focus than an 8.0 aperture, resulting in more depth of field. Hopefully that helps.
A smaller "aperture" means smaller opening. A smaller F stop means larger opening.
Sep 9, 2018 11:05:59 #
Chaostrain wrote:
Yeah, I've noticed. It's like somebody on here posted elsewhere. You ask some people what time it is and they'll tell you how to build a clock.
I didn't answer the OP question but the OP question requires a very highly technical answer. The OP asked WHY as he already knew what happened to the DOF with different aperture. His question is WHY and that's not easy to answer. The answer that small aperture has less lens curvature is wrong but I don't want to point that out because you will say I try to tell the OP how to build a clock.
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