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Aperture?
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Jan 29, 2019 08:21:15   #
TSHDGTL
 
My understanding is that a smaller aperture blocks out of focus light. Does this mean wider apertures are using out of focus light to brighten the image?

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Jan 29, 2019 08:29:21   #
rmalarz Loc: Tempe, Arizona
 
Smaller apertures simply let in less light than larger apertures. Smaller apertures provide a larger depth of field. Depth of field is the range at which objects in the scene appear to be in acceptable focus. The general rule of thumb is that of the total depth of field, 1/3 will be in front of the object which is "perfectly" focused and 2/3 will be behind that object.

There is no such thing as focused and out of focus light.
--Bob
TSHDGTL wrote:
My understanding is that a smaller aperture blocks out of focus light. Does this mean wider apertures are using out of focus light to brighten the image?

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Jan 29, 2019 08:39:41   #
jerryc41 Loc: Catskill Mts of NY
 
TSHDGTL wrote:
My understanding is that a smaller aperture blocks out of focus light. Does this mean wider apertures are using out of focus light to brighten the image?


Light isn't in or out of focus. Try this. Make your hand into a loose fist so you can look through it like a telescope. As you tighten your fist, the image will become sharper as extraneous light is reduced. I've been taking advantage of this trick for years.

https://www.healthyerhacks.com/vision-boost-curl-your-hand-fist-and-look-through-telescope
https://www.independent.co.uk/news/science/how-to-see-clearly-without-glasses-using-a-simple-trick-9295548.html
https://www.youtube.com/watch?v=OydqR_7_DjI

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Jan 29, 2019 08:54:09   #
Longshadow Loc: Audubon, PA, United States
 
rmalarz wrote:
Smaller apertures simply let in less light than larger apertures. Smaller apertures provide a larger depth of field. Depth of field is the range at which objects in the scene appear to be in acceptable focus. The general rule of thumb is that of the total depth of field, 1/3 will be in front of the object which is "perfectly" focused and 2/3 will be behind that object.

There is no such thing as focused and out of focus light.
--Bob



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Jan 29, 2019 08:55:20   #
Dikdik Loc: Winnipeg, Canada
 
rmalarz wrote:
There is no such thing as focused and out of focus light.--Bob


for monochromatic light only...

the problem comes in with colours... all colours have slightly different light speeds and are 'bent' in differing amounts when they pass through the lens. With a smaller aperture, only the central part of the lens is used and there is better control of the amount of 'bending' because the light rays are 'hitting' a part of the lens that is nearly normal to the light ray, hence, the depth of the focus is greater. I think that's what causes it.

Dik

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Jan 29, 2019 09:56:52   #
selmslie Loc: Fernandina Beach, FL, USA
 
rmalarz wrote:
... The general rule of thumb is that of the total depth of field, 1/3 will be in front of the object which is "perfectly" focused and 2/3 will be behind that object. ...

A few minutes with a DOF calculator will prove that this is a myth.

It only holds when you are focused at about 1/3 of the hyperfocal distance.

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Jan 29, 2019 10:14:28   #
rmalarz Loc: Tempe, Arizona
 
Well, "professor", I could have written a thesis on the subject of DOF but preferred to just give a general rule of thumb instead.
--Bob
selmslie wrote:
A few minutes with a DOF calculator will prove that this is a myth.

It only holds when you are focused at about 1/3 of the hyperfocal distance.

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Jan 29, 2019 10:23:00   #
selmslie Loc: Fernandina Beach, FL, USA
 
rmalarz wrote:
Well, "professor", I could have written a thesis on the subject of DOF but preferred to just give a general rule of thumb instead.
--Bob

Perpetuating a myth, like fake news, does more harm than good.

You should know that it's a myth and not a "rule of thumb".

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Jan 29, 2019 11:05:26   #
rmalarz Loc: Tempe, Arizona
 
"Is depth of field equally distributed in front and back of my focus point?

No, it’s usually about one third in front and two thirds behind your focal point, but as your focal length increases, it becomes more equal".- https://digital-photography-school.com/understanding-depth-field-beginners/


Again, for the average beginner, which this post seemingly is by, the 1/3-2/3 is good enough. I didn't wish to extend that to a detailed treatise on optics.
--Bob

selmslie wrote:
Perpetuating a myth, like fake news, does more harm than good.

You should know that it's a myth and not a "rule of thumb".

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Jan 29, 2019 12:33:06   #
Longshadow Loc: Audubon, PA, United States
 
rmalarz wrote:
"Is depth of field equally distributed in front and back of my focus point?

No, it’s usually about one third in front and two thirds behind your focal point, but as your focal length increases, it becomes more equal".- https://digital-photography-school.com/understanding-depth-field-beginners/


Again, for the average beginner, which this post seemingly is by, the 1/3-2/3 is good enough. I didn't wish to extend that to a detailed treatise on optics.
--Bob

Agreed. Basic rule of thumb.

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Jan 29, 2019 12:49:30   #
selmslie Loc: Fernandina Beach, FL, USA
 
rmalarz wrote:
"Is depth of field equally distributed in front and back of my focus point?

No, it’s usually about one third in front and two thirds behind your focal point, but as your focal length increases, it becomes more equal".- https://digital-photography-school.com/understanding-depth-field-beginners/


Again, for the average beginner, which this post seemingly is by, the 1/3-2/3 is good enough. I didn't wish to extend that to a detailed treatise on optics.
--Bob

This appears to be a case of the blind leading the blind. I guess you have not given it much thought.

At one extreme, focusing at the hyperfocal distance the ratio is 1/2 the hyperfocal distance to infinity - the distance beyond the hyperfocal distance.

At the other extreme, anyone who has ever captured a closeup or macro image will know that the ratio approaches 1/2 and 1/2.

In between there is only one distance when the ratio is 1/3-2/3. At all other distances the ratio does not hold. It's one of several DOF myths.

If you want to learn more, see Depth of Field Myths: The Biggest Misconceptions. This one tops the list.

To learn more, see DEPTH OF FIELD CALCULATOR at Cambridge in Colour.

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Jan 29, 2019 13:21:03   #
N4646W
 
selmslie wrote:
A few minutes with a DOF calculator will prove that this is a myth.

It only holds when you are focused at about 1/3 of the hyperfocal distance.


Well, yes, "if" you are in a lab, tightly controlled conditions, engineering the design on paper, or you have some magical lens that can compensate for humidity changes, wind current, temp differences between subject and capture element, take into consideration light diffraction from the surrounding, lens and camera are within ideal tolerances, ect.

In the real world not so much. Rule of thumb is about the best guess.

But, this is not what the OP was asking about.

Ron

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Jan 29, 2019 13:33:28   #
selmslie Loc: Fernandina Beach, FL, USA
 
N4646W wrote:
Well, yes, "if" you are in a lab, tightly controlled conditions, engineering the design on paper, or you have some magical lens that can compensate for humidity changes, wind current, temp differences between subject and capture element, take into consideration light diffraction from the surrounding, lens and camera are within ideal tolerances, ect.

In the real world not so much. Rule of thumb is about the best guess.

Ron

Then as a rule of thumb it’s pretty useless.

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Jan 29, 2019 13:56:29   #
Longshadow Loc: Audubon, PA, United States
 
selmslie wrote:
Then as a rule of thumb it’s pretty useless.


No, it's a rule of thumb, like "Sunny 16", a starting point.

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Jan 29, 2019 14:31:42   #
selmslie Loc: Fernandina Beach, FL, USA
 
Longshadow wrote:
No, it's a rule of thumb, like "Sunny 16", a starting point.

Except that in broad daylight, Sunny 16 actually works. It's not a myth.

Other EV settings for different lighting conditions also work nicely for both film and digital. See Exposure value

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