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Thread started 09 Apr 2011 (Saturday) 08:28
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Apertures f/numbers help

 
CanonEOS
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Apr 09, 2011 08:28 |  #1
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What I want to know is the aperture numbers.

What is the larger aperture f/numbers in lens that lets in more light?

What is the lower aperture f/numbers in lens that let less light in?

Because I read this
A larger aperture with a (smaller f/ number) will have a very (narrow) depth of field
A larger aperture will let in more light but will have a very (narrow) depth of field

But are these smaller f/numbers? he is talking about

Also

A smaller aperture with a (larger f/ number) will have a (wide) depth of field.
A smaller aperture will let in less light but will have a larger (wide) depth of field

And again what do he mean in larger f/numbers?

I was told a larger aperture f/numbers start from 1.4, 1.8, 2.0, 2.8, 3.2,3.5,4.0 is this true?
And
A Lower aperture f/numbers start from 3.5,4.5,5.0,5.6,6.3,7.​1,8.0,9.0 is this also true

Also smaller aperture f/numbers start from 10,11,13,14,16,18,20,2​2 is this ture again


I am so lost in all this (dof) and aperture numbers:rolleyes:

Please understand I am new to all this aperture numbers and DSLR cameras but I would like to learn more.

Thank you.:D


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gonzogolf
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Apr 09, 2011 08:37 |  #2

The smaller the number, the larger the aperture. The smaller the number the less depth of field, if everything else is the same. I dont think there is a range of larger apertures, or smaller apertures, or that there is a dividing point like in your above post. They just flow from larger to smaller.




  
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Hermeto
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Apr 09, 2011 09:17 as a reply to  @ gonzogolf's post |  #3
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Ben's Newbie Guide to Digital SLR Photography


What we see depends mainly on what we look for.

  
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mark2009
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Apr 09, 2011 09:20 as a reply to  @ Hermeto's post |  #4

This could help, a useful tool...

http://dryreading.com/​camera/index.html (external link)




  
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CanonEOS
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Apr 09, 2011 10:02 |  #5
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That is the link I was talking about he don't explain what is the lower aperture numbers are and smaller aperture numbers what are they in number.

Like I said

what is larger aperture f/numbers start from 1.4, 1.8, 2.0, 2.8, 3.2,3.5,4.0 ?

What is Lower aperture f/numbers start from 3.5,4.5,5.0,5.6,6.3,7.​1,8.0,9.0 ?

What is smaller aperture f/numbers start from 10,11,13,14,16,18,20,2​2 ?

Are any of these numbers in the right order?

gonzogolf wrote in post #12188803 (external link)
The smaller the number, the larger the aperture. The smaller the number the less depth of field, if everything else is the same. I dont think there is a range of larger apertures, or smaller apertures, or that there is a dividing point like in your above post. They just flow from larger to smaller.

Ok what you mean is this larger aperture f/numbers start from 1.4, 1.8, 2.0, 2.8, 3.2,3.5,4.0??

So what are the smaller numbers and lower numbers?


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Thorrulz
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Apr 09, 2011 10:13 |  #6

As Chris Orwig says, If you want 1 person in focus use f/1. If you want 22 people in focus use f/22.
Apertures start at:
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 and so on.


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suecassidy
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Apr 09, 2011 10:17 |  #7

Take a chocolate bar and divide it into 16 pieces. Take a second chocolate bar and divide it into 2 pieces. You are allowed to choose a piece of one of the two chocolate bars. Which chocolate bar will give you the largest piece to enjoy? Most certainly it will be the one you divided into TWO pieces, not the one you divided into 16 pieces, yes??? That's because you divided the bars into fractions, and 1/16th of a chocolate bar is not a very big piece. Give me 1/2 of the bar any day.

The aperture hole in your camera is measured in fractions of an inch, roughly, for the sake of this illustration. So the size of the hole when it is at f16, is 1/16th of an inch. Not very big and if you looked at the aperture hole when the camera is set to f16, you would see it is approximately 1/16th of an inch. Now change it to f2. The hole is approximately 1/2 of an inch wide, and will let in lots of light. Smaller NUMBER than 16, but bigger hole because you are now thinking in fractions.

Just absorb that concept and then you can learn about the other factors that affect focus/depth of field such as focal length, distance to subject etc. But for now, just understand why f16 is a larger number, but smaller hole that lets less light into your camera than f2. will.


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BrickR
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Apr 09, 2011 11:39 |  #8

I had problems remembering the size with ap numbers at first too, until a friend pointed out that the ap number is a fraction. Look on your 50mm, it says 1:1.8 as the maximum ap. 1:2 is bigger than 1:4, 1:4 is bigger than 1:8, so forth and so on. Its just quicker to say f1.8 than f 1:1.8
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JohnB57
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Apr 09, 2011 12:14 |  #9

suecassidy wrote in post #12189190 (external link)
. The aperture hole in your camera is measured in fractions of an inch, roughly, for the sake of this illustration. So the size of the hole when it is at f16, is 1/16th of an inch. Not very big and if you looked at the aperture hole when the camera is set to f16, you would see it is approximately 1/16th of an inch. Now change it to f2. The hole is approximately 1/2 of an inch wide, and will let in lots of light. Smaller NUMBER than 16, but bigger hole because you are now thinking in fractions.

Maybe I'm confusing an attempted analogy with explanation of facts here Sue but even though the conclusion goes a long way to explaining apertures, the working out sure doesn't!

Aperture numbers are the ratio of the entry pupil - or the actual size of the diaphragm at any one setting - to the focal length of the lens. A 50mm lens with a maximum aperture of 25mm (don't use inches, all lenses are defined in mm these days, even in the US) is therefore f/2 (50/25). This is critical as the f number is a constant regardless of focal length and works as an indication of light transmission for all formats of film, digital etc independent of size. It's also why older and cheaper zoom lenses change aperture as the focal length increases.

Just to confuse further, depth of field varies depending on the format in use for any focal length/f number combination, but that's a whole 'nother story.




  
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CanonEOS
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Apr 09, 2011 12:17 |  #10
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Thorrulz wrote in post #12189164 (external link)
As Chris Orwig says, If you want 1 person in focus use f/1. If you want 22 people in focus use f/22.
Apertures start at:
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 and so on.

That's different apertures so where is the 1.8, 3.2, 3.5, because my 18-135mm IS f/3.5 - 5.6 lens so the f/3.5 is missing from the aperture numbers list that you have.

So is the larger f/ numbers f/18, f/20, f/22, f/24, f/55, f/70 for wide depth of field?

This as confused me from the start:rolleyes:


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BrickR
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Apr 09, 2011 12:21 |  #11

Yep, basically, higher f stop number, wider dof.


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JohnB57
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Apr 09, 2011 14:54 |  #12

CanonEOS wrote in post #12189591 (external link)
That's different apertures so where is the 1.8, 3.2, 3.5, because my 18-135mm IS f/3.5 - 5.6 lens so the f/3.5 is missing from the aperture numbers list that you have.

So is the larger f/ numbers f/18, f/20, f/22, f/24, f/55, f/70 for wide depth of field?

This as confused me from the start:rolleyes:

Hey Pompey!

Fixed f numbers go back to the days of manual cameras and external light metering, when you used a Weston Master light meter (I still have one) or similar and converted the light reading in EV (exposure value) into aperture and shutter speed values appropriate to the film speed, transferring them to your camera by setting the shutter speed on the body and the aperture on the lens. The apertures were normally at full stop "clicks" and conventionally these were f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 and 32 (f/1 would have been a very expensive lens!). One full f stop lower in number lets in twice the light. These days, lenses are capable of more or less infinitely variable f numbers, but we still tend to use the old ones. Curious.

By the way, your 18-135mm lens at max aperture has an entry pupil diameter of 18mm/3.5mm = 5.142857143mm.


I've probably confused you more now but look it up on Wikipedia. It's basic to understanding your camera and will actually enhance your enjoyment and help you to understand why things sometimes go wrong.




  
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Stir ­ Fry ­ A ­ Lot
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Apr 09, 2011 16:23 |  #13

CanonEOS wrote in post #12189591 (external link)
That's different apertures so where is the 1.8, 3.2, 3.5, because my 18-135mm IS f/3.5 - 5.6 lens so the f/3.5 is missing from the aperture numbers list that you have.

So is the larger f/ numbers f/18, f/20, f/22, f/24, f/55, f/70 for wide depth of field?

This as confused me from the start:rolleyes:

Your lens doesn't support those apertures bro. You have what is considered to be a "slow" lens due to its inability to collect the large amounts of light that "fast" lenses do. The lower the number, the more the light, the faster the shutter speed you can use to freeze action and avoid blur due to subject movement and camera shake. Set it on AV mode and try to get some first hand knowledge instead of relying on people the internet to explain it to you. If you use Google Chrome or Firefox install an extension called Exif Viewer. It makes it so that when you hover your cursor over a photograph it will show you what settings were used to take the picture as long as the data is still attached to it.


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Apr 09, 2011 16:32 |  #14

CanonEOS, here is a simply way to understand (let's assume 100mm FL lens...)

If the largest opening of the lens diaphram is 50mm in diameter, that is f/2 or (1/2 * 100mm = 50mm)
If the smallest opening of the lens diaphram is 5mm in diameter, that is f/20 or (1/20 * 100mm = 5mm)

f/2 lets more light pass, has shallower DOF (a big hose attached to the bucket lets water drain out faster and leaves less water left in the bucket)
f/20 lets less light pass, has deeper DOF (a small hose attached to the bucket lets water drain out slower and leaves more water left in the bucket)


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Apr 09, 2011 17:01 as a reply to  @ Wilt's post |  #15

In some very simple terms that might help:

For aperture:
- Lower number = shallow depth of field = more blurry background or foreground (depending on what you're focused on) and more light
- Higher number = more depth of field = Things in the background or foreground tend to be more in focus and less light

Not to be confused with
- Bigger/wider aperture = lower number (when counting)
- Smaller aperture = higher number (when counting)

The reason it feels backwards is because, as someone stated earlier, it's based on a fraction.

- A f/3.5 aperture is really a fraction of 1/3.5
- A f/22 aperture is really a fraction of 1/22

As such, the f/3.5 aperture is a lower aperture # (numerically) but actually considered "bigger/wider" than the f/22 (higher number numerically, but smaller for the purposes of aperture).

Think that's all right and hope it helps a bit. :). Aperture value also affects other stuff like amount of light, etc, but I tried to simplify it as much as possible as a start.


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