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09/21/2005 02:32:49 PM · #1 |
OK, I really feel like a total idiot, but for some reason I'm having a really hard time wrapping my brain around aperture and DOF. I've tried to read on it a few times, but talking about "stopping down" and so forth for some reason loses me. I don't know why, I'm a smart guy, but it's kind of like when my wife talks... I hear the words, but they don't connect with my brain for some reason.
I work for an ophthalmology clinic and have a pretty good working knowledge of the eye and how it functions, and I know the camera is very similar in function. When the pupil is dilated (open), near objects become blurry and the eye is more sensitive to light (more gets in). I understand this principle. Smaller pupils or restricting light to the eye makes objects clearer and crisper. The earliest "corrective lenses" were pinholes in a sheet of paper to correct for low degrees of myopia. So why oh why am I having such a hard time with aperture?
Can someone please help me understand aperture, f-stops and DOF in layman's terms. Maybe something will help make that proverbial "click" in my noggin!
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09/21/2005 02:37:06 PM · #2 |
In a nutshell:
Small aperture = smaller hole for light to go through = bigger f-number = Deeper DOF
Large aperture = bigger hole for light to go through = smaller f-number = Shallower DOF
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09/21/2005 02:37:43 PM · #3 |
Perhaps becaus the number used to express it is actually the reciprocal of the area, so "stopping down" mean changing from (say) f4.5 to f8, making the "hole" several times smaller, admitting less light but with a greater DOF -- more thingsd in-focus.
Stopping down = higher number = constriction = deep DOF
Opening up = lower number = dilation = shallow DOF |
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09/21/2005 02:43:17 PM · #4 |
And when in doubt just remember that the smaller the hole... the more you can get in (focus). Opposite of real life! :)
Message edited by author 2005-09-21 14:43:51. |
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09/21/2005 02:46:02 PM · #5 |
Originally posted by GeneralE:
Perhaps becaus the number used to express it is actually the reciprocal of the area, so "stopping down" mean changing from (say) f4.5 to f8, making the "hole" several times smaller, admitting less light but with a greater DOF -- more thingsd in-focus.
Stopping down = higher number = constriction = deep DOF
Opening up = lower number = dilation = shallow DOF |
I think this is what's throwing me the curve ball... For years I've worked with pupil sizes and I think in terms of higher numbers, larger "holes"... the crossover makes my head hurt.
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09/21/2005 03:00:50 PM · #6 |
this dude explained to to me this way awhile back and it stuck.
think of your camera as an oven...and the higher the f stop (eg f/22)
the longer you cook your picture....getting a more thorough range of detail througout (depth of field).
the lower the f stop (eg f2.8) the faster you cook your picture, effectively only cooking one spot (the focus area) giving you only limited detail...and a shallow depth of field.
the wider the focal length, the less depth of field applies...for example if i shoot at 2 f2.8 with my 10.5 mm fisheye, still almost everything in focus, if you shoot a f2.8 at 300 mm, your image looks flat as a board. |
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09/21/2005 03:14:16 PM · #7 |
Hate to sound like such a novice, but why pretend I'm something I'm not, right?
Can anyone explain to me the meaning of 'depth of field'?
Edit: wait a second, I was reading it all over again, and read 'shallow' and 'deep', I'm guessing that a higher depth of field, or deeper, means that you can focus on something at close range, whilst also having a lenient range of focus, so shallow depth of field let's say is a range of 15-16cm, and deep would be 10-20.. Like that? Or... Am I just guessing at something and am totally wrong? :)
Message edited by author 2005-09-21 15:17:36. |
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09/21/2005 03:16:17 PM · #8 |
| Instead of "f" imagine a "1" in its place - i.e. 1/4 instead of f4, 1/8 instead of f8, and so forth. 1/4 is larger than 1/8 and 1/8 is larger than 1/11. |
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09/21/2005 03:17:28 PM · #9 |
Originally posted by Virus610:
Hate to sound like such a novice, but why pretend I'm something I'm not, right?
Can anyone explain to me the meaning of 'depth of field'? |
How much of the view of the camera from close to far off is in focus. The virtual depth that the focus goes into the scene.
edit - //photoinf.com/General/Klaus_Schroiff/Perspective.htm
Message edited by author 2005-09-21 15:20:17.
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09/21/2005 03:17:50 PM · #10 |
Originally posted by Virus610:
Hate to sound like such a novice, but why pretend I'm something I'm not, right?
Can anyone explain to me the meaning of 'depth of field'? |
It's the amount of the area in front of your lens which is in-focus.
For example, in a shallow field, only things between 4 feet and eight feet from the camera would be in focus; everything closer than that or farther away would be blurry.
With a deep DOF, everything from ten feet away on out to infinity might be in focus. |
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09/21/2005 03:19:41 PM · #11 |
| it is just the amount of your picture that will be in focus low # just the nose high # the whole head |
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09/21/2005 03:21:22 PM · #12 |
Originally posted by maryba:
Instead of "f" imagine a "1" in its place - i.e. 1/4 instead of f4, 1/8 instead of f8, and so forth. 1/4 is larger than 1/8 and 1/8 is larger than 1/11. |
Eureka! That's the switch I needed... thanks maryba
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09/21/2005 03:23:16 PM · #13 |
Here is a depth of field calculator:
//www.dofmaster.com/dofjs.html
There are many of these of the web.
Luminous Landscapes has an online tutorial:
//www.luminous-landscape.com/tutorials/understanding-series/dof.shtml
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09/21/2005 03:37:08 PM · #14 |
I always think of DOF and aperture in terms of how a water hose works. If the water hose is really big around, the water pours right out and only travels a very short distance. If the water hose has a very small diameter, the same amount of water will shoot out really far. It's the same with light - the smaller the aperture on your lens (the hose), the farther into the shot the focus will extend. Or something like that. :-)
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09/21/2005 03:46:43 PM · #15 |
Well remember it's a fraction, but to save limited space on lenses they omit the 1/ part. So f8 is really 1/8 and f4is really 1/4 and 1/4 is larger that 1/8.
Also 1 "stop" is equivalent to double (or half) of the light.
So say you shoot a picture that is too bright and you want to correct it. You think about half the amount of light would be perfect. That's called moving down 1 stop. To move down one stop you can either:
A. Increase your shutter speed
B. Decrease your aperature
Depending on what you're trying to accomplish you'll prefer changing one over the other.
For example, lets say you are taking a portrait shot. You want a nice bokeh (that's the blurry part behind your subject). Your subject is posing for you and you need to go down 1 stop. Would you increase shutter speed or decrease aperature in this situation?
You'd increase the shutter speed. Increasing the shutter speed doesn't affect anything in this situation other than the amount of light that hits the lens.
If you're taking a stop action shot and need to *increase* the amount of light you might not want to decrease the shutter speed so you'd increase the aperature instead.
Hope this helps
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09/21/2005 03:49:05 PM · #16 |
but it's kind of like when my wife talks... I hear the words, but they don't connect with my brain for some reason.
I do this its called selective hearing lmao. |
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09/21/2005 03:50:50 PM · #17 |
I like Philip's hose illustration. That makes sense to me.
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