| Author | Thread |
|
|
03/08/2006 01:22:25 PM · #1 |
Ok, here I am drinking, see, and looking out the window in my foggy haze I came up with a question.
Here is the prequil to the question.
The Earth rotates around the sun.
Axis 'A' is winter time on Earth furthest from the Sun, axis 'B' is summer time on the Earth when it is closest to the Sun.
Now, the Sun is a huge light source even from axis 'A'.
Here is the question.
If weather did not exist. If I set up a light meter and everything being even, and metered the axis of 'A' and 'B', will there be a differance in the f stop of light.
|
|
|
|
03/08/2006 01:24:50 PM · #2 |
Hmmmmmmm you need another drink! heheee
|
|
|
|
03/08/2006 01:28:24 PM · #3 |
| flash guide numbers take distance into account ... so the distance from the sun (your flash in this case) does factor in. |
|
|
|
03/08/2006 01:30:55 PM · #4 |
Originally posted by idnic:
Hmmmmmmm you need another drink! heheee |
Sorry idnic I don't agree, he need at least three more, LOL
|
|
|
|
03/08/2006 01:50:43 PM · #5 |
Distance would definitely be a factor, but it would not be enough to cover a whole stop. Seeing that a stop is the doubling or halving of the amount of light, it's pretty obvious that it wouldn't be a whole stop., probably only small fractions of a stop.
Message edited by author 2006-03-08 14:00:43.
|
|
|
|
03/08/2006 01:56:36 PM · #6 |
| I don't know if i'm reading you right, but I know the earth is farther from the sun during the summer months (early july it's furthest). So while the earth is more directly being hit during the summer, it's farther away from the sorce. |
|
|
|
03/08/2006 02:06:39 PM · #7 |
About 94% of the light hits the earth at it's furthest compared to it's closest so that does not account for very much.
Seasons are caused by axial tilt, not distance. Inside the arctic and antarctic cirlces, however, you would see a dramatic difference between the amount of light at high noon at mid-winter and mid summer. |
|
|
|
03/08/2006 02:08:28 PM · #8 |
Originally posted by joebok:
About 94% of the light hits the earth at it's furthest compared to it's closest so that does not account for very much.
Seasons are caused by axial tilt, not distance. Inside the arctic and antarctic cirlces, however, you would see a dramatic difference between the amount of light at high noon at mid-winter and mid summer. |
exactly, well said. |
|
|
|
03/08/2006 02:10:51 PM · #9 |
just because we're on it ... i don't think the sun is a huge light source ... is it?
relatively speaking (relative to how far away it is), it's smaller than a soft box.
BUT ... when the sun's light hits the atmosphere - it bounces all over the place and illuminates just about everything.
if the earth had no atmosphere ... the sky would be black, even during the day ... except for a small light source about the size of your hand melting you to the surface of the now scorched earth.
no? |
|
|
|
03/08/2006 02:12:36 PM · #10 |
Originally posted by hopper:
just because we're on it ... i don't think the sun is a huge light source ... is it?
relatively speaking (relative to how far away it is), it's smaller than a soft box.
BUT ... when the sun's light hits the atmosphere - it bounces all over the place and illuminates just about everything.
if the earth had no atmosphere ... the sky would be black, even during the day ... except for a small light source about the size of your hand melting you to the surface of the now scorched earth.
no? |
Pretty much ... LOL
And at night or in shade, you would instantly freeze.
Message edited by author 2006-03-08 14:13:58.
|
|
|
|
03/08/2006 02:36:45 PM · #11 |
Originally posted by kyebosh:
I don't know if i'm reading you right, but I know the earth is farther from the sun during the summer months (early july it's furthest). So while the earth is more directly being hit during the summer, it's farther away from the sorce. |
Correct, Kyebosh. I don't recall the precession period of the eccentricity of the orbit but it is a very long time, thousands of years. Regarding the fstop of the sun: What does American Horse mean by the question? Photos of the solar disk are made every day using nd filters with rather ordinary cameras. No more firewater for you!! |
|
|
|
03/08/2006 03:16:59 PM · #12 |
Originally posted by kyebosh:
I don't know if i'm reading you right, but I know the earth is farther from the sun during the summer months (early july it's furthest). So while the earth is more directly being hit during the summer, it's farther away from the sorce. |
That would be Summer in the Northern hemisphere, when the sun is highest above the horizon and the rays hit the Earth least obliquely, due (as was mentioned) by the Earth's axial tilt. |
|
|
|
03/08/2006 03:27:10 PM · #13 |
There would be no difference in the meter reading.
|
|
|
|
03/08/2006 03:52:21 PM · #14 |
Put it this way; if you stand on the equator on a perectly clear day in midwinter or in midsummer, the "exposure" is the same. Variation in exposure between midsummer and midwinter, in either hemisphere, increases the further from the equator you travel and is due to the sun's light having to travel more obliquely through the atmosphere to reach the spot where you are at in hemispherical winter, or less obliquely during hemispherical summer.
Robt.
|
|
|
|
03/08/2006 03:54:18 PM · #15 |
Originally posted by Bear_Music:
Put it this way; if you stand on the equator on a perectly clear day in midwinter or in midsummer, the "exposure" is the same. Variation in exposure between midsummer and midwinter, in either hemisphere, increases the further from the equator you travel and is due to the sun's light having to travel more obliquely through the atmosphere to reach the spot where you are at in hemispherical winter, or less obliquely during hemispherical summer.
Robt. |
It would still be an undetectible difference. It would be like moving a softbox/strobe 1/4" closer or farther away from the subject. Actually a lot less than 1/4".
|
|
|
|
03/08/2006 04:18:48 PM · #16 |
The Earth's orbit is not perfectly circular; perihelion, the closest approach to the Sun is 91.405 million miles, and aphelion, the furthest point, is 94.511 million miles, a difference of about 3.3%. Assuming the Sun emits an essentially constant total light flux (close to true in the short term), the light intensity falling on an object falls off with the cube of the distance, so the expected difference in intensity for a 3.3% increase in distance is about a 10% reduction. A 10%change in light intensity is much less than one stop, specifically -0.15 stops.
The differences due to the angle of the sun above the horizon are much more significant.
|
|
|
|
03/08/2006 05:41:15 PM · #17 |
thank you, mister wizard
Originally posted by kirbic:
The Earth's orbit is not perfectly circular; perihelion, the closest approach to the Sun is 91.405 million miles, and aphelion, the furthest point, is 94.511 million miles, a difference of about 3.3%. Assuming the Sun emits an essentially constant total light flux (close to true in the short term), the light intensity falling on an object falls off with the cube of the distance, so the expected difference in intensity for a 3.3% increase in distance is about a 10% reduction. A 10%change in light intensity is much less than one stop, specifically -0.15 stops.
The differences due to the angle of the sun above the horizon are much more significant. |
|
|
|
|
03/08/2006 05:53:51 PM · #18 |
Originally posted by kirbic:
The Earth's orbit is not perfectly circular; perihelion, the closest approach to the Sun is 91.405 million miles, and aphelion, the furthest point, is 94.511 million miles, a difference of about 3.3%. Assuming the Sun emits an essentially constant total light flux (close to true in the short term), the light intensity falling on an object falls off with the cube of the distance, so the expected difference in intensity for a 3.3% increase in distance is about a 10% reduction. A 10%change in light intensity is much less than one stop, specifically -0.15 stops.
The differences due to the angle of the sun above the horizon are much more significant. |
Wow, I was still trying to noodle this out. Figured that change in relation to the total was very small. But, a bigger/quicker brain than mine laid this out nicely.
Kirbic- are you an astrophysicist as well as DPC'er? :)
|
|
|
|
03/08/2006 06:14:03 PM · #19 |
Originally posted by kirbic:
The Earth's orbit is not perfectly circular; perihelion, the closest approach to the Sun is 91.405 million miles, and aphelion, the furthest point, is 94.511 million miles, a difference of about 3.3%. Assuming the Sun emits an essentially constant total light flux (close to true in the short term), the light intensity falling on an object falls off with the cube of the distance, so the expected difference in intensity for a 3.3% increase in distance is about a 10% reduction. A 10%change in light intensity is much less than one stop, specifically -0.15 stops.
The differences due to the angle of the sun above the horizon are much more significant. |
I would have thought it would fall off at the square, rather than the cube, of the distance? (Aren't we talking about area, not volume?) That gives about a 6% reduction in light due to distance. |
|
|
|
03/08/2006 06:30:22 PM · #20 |
3.3% distance increase = 10.9 % light decrease (3.3 squared is 10.89).
Originally posted by joebok:
Originally posted by kirbic:
The Earth's orbit is not perfectly circular; perihelion, the closest approach to the Sun is 91.405 million miles, and aphelion, the furthest point, is 94.511 million miles, a difference of about 3.3%. Assuming the Sun emits an essentially constant total light flux (close to true in the short term), the light intensity falling on an object falls off with the cube of the distance, so the expected difference in intensity for a 3.3% increase in distance is about a 10% reduction. A 10%change in light intensity is much less than one stop, specifically -0.15 stops.
The differences due to the angle of the sun above the horizon are much more significant. |
I would have thought it would fall off at the square, rather than the cube, of the distance? (Aren't we talking about area, not volume?) That gives about a 6% reduction in light due to distance. |
|
|
|
|
03/08/2006 06:41:48 PM · #21 |
Originally posted by strangeghost:
3.3% distance increase = 10.9 % light decrease (3.3 squared is 10.89).
|
No - you can't just square the %. Say the distance at closest is 1. The amount of light reaching the earth depends on the square of the distance (actually the inverse square) - say k/1^2. The amount of light at a further distance, 1.033 (a 3.3% increase) is k/(1.033)^2.
Ratio, the k's cancel and you have 1^2/(1.033)^2 = .937..., or about a 6.287% decrease. |
|
|
|
03/08/2006 06:44:35 PM · #22 |
Originally posted by joebok:
No - you can't just square the %. Say the distance at closest is 1. The amount of light reaching the earth depends on the square of the distance (actually the inverse square) - say k/1^2. The amount of light at a further distance, 1.033 (a 3.3% increase) is k/(1.033)^2.
Ratio, the k's cancel and you have 1^2/(1.033)^2 = .937..., or about a 6.287% decrease. |
OUCH! My HEAD!
|
|
|
|
03/08/2006 06:49:14 PM · #23 |
Originally posted by jmsetzler:
Originally posted by Bear_Music:
Put it this way; if you stand on the equator on a perectly clear day in midwinter or in midsummer, the "exposure" is the same. Variation in exposure between midsummer and midwinter, in either hemisphere, increases the further from the equator you travel and is due to the sun's light having to travel more obliquely through the atmosphere to reach the spot where you are at in hemispherical winter, or less obliquely during hemispherical summer.
Robt. |
It would still be an undetectible difference. It would be like moving a softbox/strobe 1/4" closer or farther away from the subject. Actually a lot less than 1/4". |
That's not true, actually; when you get way north (or south), the difference is considerable, to the point at which when you're near the arctic circle the daylight at "high noon" is as dim as the daylight shortly before sunset is when in the temperate belt.
If you're talking about the light FALLING on the earth-as-a-whole, of course it's true, but when the sun's traveling very obluquely through the atmosphere it gets much dimmer before it reaches the surface in the higher/lower latitudes.
R.
|
|
|
|
03/08/2006 06:56:25 PM · #24 |
Originally posted by Bear_Music:
Originally posted by jmsetzler:
Originally posted by Bear_Music:
Put it this way; if you stand on the equator on a perectly clear day in midwinter or in midsummer, the "exposure" is the same. Variation in exposure between midsummer and midwinter, in either hemisphere, increases the further from the equator you travel and is due to the sun's light having to travel more obliquely through the atmosphere to reach the spot where you are at in hemispherical winter, or less obliquely during hemispherical summer.
Robt. |
It would still be an undetectible difference. It would be like moving a softbox/strobe 1/4" closer or farther away from the subject. Actually a lot less than 1/4". |
That's not true, actually; when you get way north (or south), the difference is considerable, to the point at which when you're near the arctic circle the daylight at "high noon" is as dim as the daylight shortly before sunset is when in the temperate belt.
If you're talking about the light FALLING on the earth-as-a-whole, of course it's true, but when the sun's traveling very obluquely through the atmosphere it gets much dimmer before it reaches the surface in the higher/lower latitudes.
R. |
Yes - since I'm all mathed up - the difference between mid-winter and mid-summer is that the sun will be 47 degrees lower in the winter than the summer (this is since the axial tilt is ~23.5 degrees). So nearer the poles you start noticing the same differences that you see between mornings and evenings (when the sun is low) and mid day (when the sun is higer).
And I shouldn't say "lower" - the angular distance differs by 47 degrees. Outside the tropics of cancer and capricorn that will mean "lower"... |
|
|
|
03/08/2006 07:30:47 PM · #25 |
OOPS. It is an inverse square relationship, goes to show I shouldnt be trying to post while working...
It's actually minus six-point-something percent, and that's about -0.1 stops.
|
|
Home -
Challenges -
Community -
League -
Photos -
Cameras -
Lenses -
Learn -
Help -
Terms of Use -
Privacy -
Top ^
DPChallenge, and website content and design, Copyright © 2001-2025 Challenging Technologies, LLC.
All digital photo copyrights belong to the photographers and may not be used without permission.
Current Server Time: 09/09/2025 11:33:29 AM EDT.
