Lens Diaries Go Now
Glamour, Beauty, Nude, Models, Photographers

*    |  Register  


 
Go Back   Garage Glamour™ > Garage Glamour™ Main Forums > Tech Talk Forum
 

Tech Talk Forum Photography & Technical Related Only!

Reply
 
LinkBack Thread Tools Display Modes
Inverse Sqauare Law...
Old 08-05-2006, 12:37 AM   #1 (permalink)
Founder Garage Glamour™

 
rolandogomez's Avatar
 
Join Date: Mar 1999
Member GG#: 1
Location: San Antonio
Posts: 1,802
Comments: 10
My Mood:
Send a message via AIM to rolandogomez

rolandogomez is offline IP: 67.11.199.24
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

My mind is in La La land right now, so I wanted to ask you high-techie photogs to verify something for me.

Simply stated, under the Inverse Square Law, if your light meter measures F/11 when your studio light source is five feet from your subject, by moving the light 10 feet (twice the distance from your subject), you’ve reduced the light by one-quarter of its power, or two full F/stops.

Remember, every time you decrease an F/stop, you have a 50-percent light increase, so from F/11 to F/8 is a 50-percent light increase and from F/8 to F/5.6 is another 50-percent light increase, or 4-times the original light at F/11.
Comments? Thanks, rg sends!
__________________
Photographer & Author author of five photography books. My newest book is Socially Smart: Twitter Plus Facebook, Marketing Multipliers And Brand Boosters Click here for My Tweet Workshop Information and the Photo Blog
  View Public Profile Send a private message to rolandogomez Visit rolandogomez's homepage! Find More Posts by rolandogomez
Last edited by rolandogomez; 08-05-2006 at 06:06 PM..
 
Re: Inverse Sqauare Law...
Old 08-05-2006, 01:45 AM   #2 (permalink)
Bawdy Little Monkey

 
SamBeasley's Avatar
 
Join Date: Jan 2005
Member GG#: 41173
Location: Miami Beach
Posts: 1,387
Comments: 1
Send a message via AIM to SamBeasley Send a message via Yahoo to SamBeasley

SamBeasley is offline IP: 68.18.215.197
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

As quoted from HyperPhysics, from Georgia State University's website:

"The energy twice as far from the source is spread over four times the area, hence one-fourth the intensity."

http://hyperphysics.phy-astr.gsu.edu...sion/isql.html

Sounds like you're right.

Sam
__________________
"Photography's better than a poke in the eye with a sharp stick." -- Thomas Roma
www.sambeasleyphoto.com/
www.sambeasleyphotopart2.com/
http://sambeasley.tumblr.com
http://www.lalluredesmots.com
  View Public Profile Send a private message to SamBeasley Visit SamBeasley's homepage! Find More Posts by SamBeasley
 
Re: Inverse Sqauare Law...
Old 08-05-2006, 11:16 AM   #3 (permalink)
Free Member
 
Join Date: Dec 2002
Member GG#: 35541
Location: Loveland
Posts: 51
Comments: 0

photoaz is offline IP: 67.161.204.20
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

You should be within a few tenths of f stops you mention.

An easier way to remember how to reduce by a stop is as simple as the f stop table. With the light 5 foot from your subject (or better yet five feet, six inches) when you move it back to eight feet you will record one drop in the f stop. Move it back to eleven feet you have another drop in f stop. The next full drop would come at sixteen feet then again at twenty two feet.

For us major right brainers look at it like this.

4, 5.6, 8, 11, 16, 22, and so forth which is the same as f stops.
__________________
Bill Guy
I am not unemployed, I am an Artist!!
  View Public Profile Send a private message to photoaz Visit photoaz's homepage! Find More Posts by photoaz
 
Re: Inverse Sqauare Law...
Old 08-05-2006, 02:01 PM   #4 (permalink)
Lifetime Photographer

 
mcherry's Avatar
 
Join Date: Aug 2005
Member GG#: 45854
Location: Stamford
Posts: 310
Comments: 0
Send a message via AIM to mcherry

mcherry is offline IP: 69.120.103.198
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Dude, as a left brainer I never made the connection between feet and f-stops. Is that where the "f" in f-stop comes from? That's great information to know, thanks!
  View Public Profile Send a private message to mcherry Visit mcherry's homepage! Find More Posts by mcherry
 
Re: Inverse Sqauare Law...
Old 08-05-2006, 04:22 PM   #5 (permalink)
Aspiring Photographer

 
CatCynic's Avatar
 
Join Date: Mar 2006
Member GG#: 50625
Location: Melbourne
Posts: 437
Comments: 0

CatCynic is offline IP: 220.253.37.214
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Quote:
Originally Posted by rolandogomez
My mind is in La La land right now, so I wanted to ask you high-techie photogs to verify something for me.
Simply stated, under the Inverse Square Law, if your light meter measures F/11 when your studio light source is five feet from your subject, by moving the light 10 feet (twice the distance from your subject), you’ve reduced the light by one-quarter of its power, or two full F/stops.
Remember, every time you decrease an F/stop, you have a 50-percent light reduction, so from F/11 to F/8 is a 50-percent light reduction and from F/8 to F/5.6 is another 50-percent light reduction, or one-quarter of the original light at F/11.
Comments? Thanks, rg sends!
Everything is correct, except that you said "F/11 to F/8 is a 50-percent light reduction". Not quite, it's a 50% light INCREASE. You know this, of course, but the pedant in me insists on saying it

BTW: For anyone who ever wondered why one f-stop means multiplying the f-number by 1.4, it's because the square root of 2 is 1.414etc. Strictly speaking, we shouldn't go from f4 to f5.6 - one f-stop from f4 is really f5.656etc.
  View Public Profile Find More Posts by CatCynic
 
Re: Inverse Sqauare Law...
Old 08-05-2006, 05:14 PM   #6 (permalink)
Lifetime Photographer

 
mcherry's Avatar
 
Join Date: Aug 2005
Member GG#: 45854
Location: Stamford
Posts: 310
Comments: 0
Send a message via AIM to mcherry

mcherry is offline IP: 69.120.103.198
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Quote:
Originally Posted by CatCynic
Everything is correct, except that you said "F/11 to F/8 is a 50-percent light reduction". Not quite, it's a 50% light INCREASE. You know this, of course, but the pedant in me insists on saying it
BTW: For anyone who ever wondered why one f-stop means multiplying the f-number by 1.4, it's because the square root of 2 is 1.414etc. Strictly speaking, we shouldn't go from f4 to f5.6 - one f-stop from f4 is really f5.656etc.
Not only is that more than I needed to know, it's more than I can possibly retain...

  View Public Profile Send a private message to mcherry Visit mcherry's homepage! Find More Posts by mcherry
 
Re: Inverse Sqauare Law...
Old 08-05-2006, 06:07 PM   #7 (permalink)
Founder Garage Glamour™

 
rolandogomez's Avatar
 
Join Date: Mar 1999
Member GG#: 1
Location: San Antonio
Posts: 1,802
Comments: 10
My Mood:
Send a message via AIM to rolandogomez

rolandogomez is offline IP: 67.11.199.24
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

I've corrected it, it was the lower half thinking like the first paragraph, which is correct. Thanks, rg.
__________________
Photographer & Author author of five photography books. My newest book is Socially Smart: Twitter Plus Facebook, Marketing Multipliers And Brand Boosters Click here for My Tweet Workshop Information and the Photo Blog
  View Public Profile Send a private message to rolandogomez Visit rolandogomez's homepage! Find More Posts by rolandogomez
 
Re: Inverse Sqauare Law...
Old 08-06-2006, 01:12 AM   #8 (permalink)
Evangelical Ne'er-do-well

 
ChipBulgin's Avatar
 
Join Date: Feb 2005
Member GG#: 42306
Location: Severna Park, MD
Posts: 485
Comments: 0
Send a message via Yahoo to ChipBulgin

ChipBulgin is offline IP: 68.55.248.34
 
Digg this Post!Add Post to del.icio.usBookmark Post in TechnoratiFurl this Post!
Reply With Quote

Quote:
Originally Posted by rolandogomez
My mind is in La La land right now, so I wanted to ask you high-techie photogs to verify something for me.

Simply stated, under the Inverse Square Law, if your light meter measures F/11 when your studio light source is five feet from your subject, by moving the light 10 feet (twice the distance from your subject), you’ve reduced the light by one-quarter of its power, or two full F/stops.
I think a more correct way to say it is that you have spread the light out so that it covers four times as much area. You haven't reduced the power of your light. Because the light covers four times the area, the amount of light illuminating your subject is 1/4th. of what it was.

Quote:
Remember, every time you decrease an F/stop, you have a 50-percent light increase, so from F/11 to F/8 is a 50-percent light increase and from F/8 to F/5.6 is another 50-percent light increase, or 4-times the original light at F/11.
Comments? Thanks, rg sends!
If you're opening up, it's because there is a decrease in the amount of light, not an increase.

-Chip
__________________
People who do stupid things with dangerous substances often die! -me
  View Public Profile Send a private message to ChipBulgin Find More Posts by ChipBulgin
 
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are Off
Pingbacks are On
Refbacks are On


Sponsors


New To Site? Need Help? Photographer & Model Links
All times are GMT -5. The time now is 08:00 AM.

© 1999-2017 Garage Glamour™




Search Engine Friendly URLs by vBSEO 3.2.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94