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09-03-2009, 10:54 PM   #16
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Think of the aperture number as a fraction.
eg: 1/1.4, 1/2, 1/3.5, 1/4, 1/5.6, 1/8, 1/11, 1/22.

1/2 is larger than 1/4 which is larger than 1/5.6 etc.

1/2 a pie is a larger slice than 1/4 of a pie.

Instead of the size of a slice of pie, the aperture, that is the hole through which light may enter your camera through the lens, is made small ( 1/22 ° ) or larger
( 1/4 O ).

In photography the "f" is put in front of the fractions to confuse us. eg: f1/4, f5.6 etc.
So think of "f" as the number "1" in the fraction. Thus f5.6 = 1/5.6, f8 = 1/8, f22 = 1/22.
So 1/8 of your pie ( aperture = hole ) is bigger than 1/22 of your pie (aperture = hole ).

I had better stop before I confuse myself.

Mickey


Last edited by mickeyobe; 09-03-2009 at 11:04 PM.
09-04-2009, 08:50 AM   #17
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QuoteOriginally posted by mickeyobe Quote
<snip> ... In photography the "f" is put in front of the fractions to confuse us. eg: f1/4, f5.6 etc. ... <snip>
Mickey
[PEDANTIC]
f/4, replacing with the actual focal length of the lens, yields that aperture diameter in the same units as the focal length.
  • 100/4 = 25mm diameter aperture on a 100mm lens
  • 400/4 = 100mm diameter aperture on a 400mm lens
Thus, using numbers such as f/4 rather than labelling my 100mm lens with 25 as the aperture number, says that if the diameter of the aperture is f/4, the density of photons striking the recording medium will be the same given an identical subject , always provided of course that the light transmission of the collection of glass is the same.

A look at your high school geometry will tell you that the area of the aperture varies with the square of the radius, and thus the square of the diameter as well. That results in a series where doubling the diameter provides 4 times the density of photons.
[/PEDANTIC]
09-04-2009, 09:45 AM   #18
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Dear Pedant,

I really did want to keep it simple.

"...if the diameter of the aperture is f/4, the density of photons striking the recording medium will be the same given an identical subject , always provided of course that the light transmission of the collection of glass is the same."

Could you please translate that into a piece of pie. Apple will do. With cheese..... Cheddar.

Mickey
09-04-2009, 10:45 AM   #19
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QuoteOriginally posted by mickeyobe Quote
Dear Pedant,

I really did want to keep it simple.

"...if the diameter of the aperture is f/4, the density of photons striking the recording medium will be the same given an identical subject , always provided of course that the light transmission of the collection of glass is the same."

Could you please translate that into a piece of pie. Apple will do. With cheese..... Cheddar.

Mickey
Well, I don't know about the Cheddar cheese on the pie. How about this simplification:
[SEMI-PEDANTIC]
The brightness of the image on the sensor/film is directly affected by the diameter of the aperture and the focal length of the lens. The brightness is also affected by the quality of the lens' glass and coatings of course, but we will ignore this complication for the purposes of this pedantic discussion. Modern Photography used to publish the effective value as one of their tests. The way the focal length and aperture affect the brightness of the image at the recording medium, be it film, sensor or eye is determined as below:
  • As the focal length of a lens increases, the angle of view decreasees, and thus decreases the total amount of light the lens gathers.
  • As the area of the aperture increases, the total light transmitted to the film or sensor increases.
  • The ratio between the focal length and the area of the aperture is identical for equal brightness at the sensor or film for all focal lengths. You need a bunch of optical physics to figure this out, of course, but others have done it for us.
  • The aperture diameter changes as the square root of the area.
  • The focal length divided by the diameter of the aperture expressed as an f/stop results in a series based on the square of the diameter.
  • This results in the weird series of f/stops so that doubling the f/stop results in quadrupling the light transmitted.
[/SEMI-PEDANTIC]


09-04-2009, 04:16 PM   #20
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Dear Semi-,

Would you now please simplify E=mc²
- with 6 year old cheddar.

Mickey
09-04-2009, 08:14 PM   #21
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QuoteOriginally posted by mickeyobe Quote
Dear Semi-,

Would you now please simplify E=mc²
- with 6 year old cheddar.

Mickey
For that explanation, the payment would need to be along the lines of a 50 year old single malt Scotch.
09-04-2009, 08:41 PM   #22
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That little misunderstanding aside, this has been very helpful thread. Thanks for the thread , maconmatt (I was in the same place as you were on this) and thanks all for the answers.

09-05-2009, 10:00 AM   #23
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Just a non-so-technical advice. Depending on the focal length and other conditions (aperture-shutter speed ratio, lack of tripod...),you will find yourself having to sacrifice either the foreground or the background sharpness. Whenever that happens you have to think on what it is the most important part for the picture and how detailed is the element on the foreground. For relevant and/or detailed foregrounds make sure that they are on focus. For instance, if you choose some nice flowers as a foreground and you dont have them on focus it will kill the purpose of their inclusion in the picture.

The idea is to optimize focus so a good training is to know what is the right distance for you to place the foreground elements. For instance, if hyperfocal distance for your lens at Xmm and f8 tells you that closer thing in focus will be at 16ft, dont go to choose a foreground element which it is at 5 ft from you
09-05-2009, 09:03 PM   #24
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Hyperfocal distance is the distance that the lens is focused at so that everything appear sharp from infinity back to whatever distance the depth of field allows things to still be in focus.
Since you have a lens with depth of field markings on it you can easily get your head around hyperfocal distances.
St the lens to a fairly small aperture, say f/11. Set the infinity focus mark to the f/11 mark on the depth of field scale. Note the focus distance at the other f/11 mark. that is your closest distance that will appear in focus. Anything closer will be more and more out of focus.
Note the distance that the lens is actually focused at.
That is the hyperfocal distance.
Note that your lens is probably marked for a 35mm film format depth of field, you may find that the hyperfocal distance with your DSLR is slightly different from the lens marking, but it is a good place to start.
09-05-2009, 10:13 PM   #25
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I thought the hyperfocal distance is the point measured from the camera (sensor) to which everything from the point to infinity is in focus; this hyperfocal distance depends on focal length plus lens aperture. As Wheatfield indicated, it also depends on crop factor as well. Hope someone will correct me... thanks.
09-05-2009, 11:00 PM   #26
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Once upon a time....

I used to understand what "hyperfocal distance" meant...now I don"t....
09-05-2009, 11:31 PM   #27
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Hyperfocal distance is that point set on a camera's lens at which everything is acceptably sharp from half the distance at which the lens is focussed to infinity. ∞

Mickey

P.S. Unless you are blotto from drinking too much 50 year old single malt scotch, at which point nothing will be in focus.
M.O.
09-06-2009, 09:56 AM   #28
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QuoteOriginally posted by mickeyobe Quote
Hyperfocal distance is that point set on a camera's lens at which everything is acceptably sharp from half the distance at which the lens is focussed to infinity. ∞

Mickey

P.S. Unless you are blotto from drinking too much 50 year old single malt scotch, at which point nothing will be in focus.
M.O.
Well, for a good friend, a discount - make that 25 year old single malt scotch.
09-06-2009, 10:48 PM   #29
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QuoteOriginally posted by Canada_Rockies Quote
Well, for a good friend, a discount - make that 25 year old single malt scotch.
That sounds more than fair. Indeed, most generous.

But as a non drinker can I use it as an antiseptic?
Or, perhaps, to clean sticky shutters?
Or fuel for my Matrix?

It's good to have friends in high places and there are very few places higher than the Rockies.

Mickey
09-07-2009, 08:33 AM   #30
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QuoteOriginally posted by mickeyobe Quote
That sounds more than fair. Indeed, most generous.

But as a non drinker can I use it as an antiseptic?
Or, perhaps, to clean sticky shutters?
Or fuel for my Matrix?

It's good to have friends in high places and there are very few places higher than the Rockies.

Mickey
It might not be suitable for your Matrix (neat car, BTW). Please check the owner's manual for alcohol fuel ratios that are permitted. My six year old Tundra can't take more than 10 percent.
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