Somebody help me with aperature...

[prodigy2k7]

Also, my understand is that F/2.8 could have a different size opening on a 50mm F/2.8 lens than a 300mm lens F/2.8, but they both gather the same amount of light...

 

[bjorkfiend]

...

 

[Chairman7w]

Well said. I don't have enough time in the day as it is just for taking photos and working with them. Let alone figuring out the ins-and-outs of F-stops and aperatures and whosits and whatnots. They are what they are (to me).

I ran a camera store for a few years so I've taught probably hundreds of people about their cameras. sometimes it's just better to go with it and accept the way it works, like when you were a kid they taught you the arithmetic tables, I remember asking why they were what they were and they answered that you should just memorize them? as you work with it it starts to make sense, or if it never does be confident in the fact that some nerdy guy figured it out so you don't really have to.

 

[Sark]

So my question was, if the aperature can physically open up to 9.8mm at a 55mm focal length to give us f3.5, why is it limited to opening up to 6.86mm when at a 24mm focal length? (Since 24mm focal length / 6.86mm aperature opening = f3.5 - see the example lens in my first post).

To clarify the answer to your original question....Dividing the Focal length by the f-number does not determine the aperture diameter, it determines the apparent diameter of the aperture, when viewed through the front lens elements (this is known as the Lens Pupil).

Imagine using a magnifying glass to view a hole in a piece of paper. Move the magnifying glass backwards and forwards and the hole increases, or decreases in size. That is what is happening when you change focal lengths. The aperture stays the same physical size at the same f-number, but when viewing it through the front lens elements its apparent size changes according to focal length.

So, the aperture does not physically open up to 9.8mm, or reduce to 6.86mm. It is just the rearrangement of the lens elements at different focal lengths causing the change.

Sark

 

[C.Lloyd]

This will either clear things up or firmly solidify the belief that all physicists practice black magic.

I'm betting on the black magic.

To clarify the answer to your original question....Dividing the Focal length by the f-number does not determine the aperture diameter, it determines the apparent diameter of the aperture, when viewed through the front lens elements (this is known as the Lens Pupil).

Imagine using a magnifying glass to view a hole in a piece of paper. Move the magnifying glass backwards and forwards and the hole increases, or decreases in size. That is what is happening when you change focal lengths. The aperture stays the same physical size at the same f-number, but when viewing it through the front lens elements its apparent size changes according to focal length.

So, the aperture does not physically open up to 9.8mm, or reduce to 6.86mm. It is just the rearrangement of the lens elements at different focal lengths causing the change.

Sark

Yes, thank you, that's the flaw in the logic of my original supposition. The difference between the actual size of the aperature and the apparent size of it.