Front element size and light gathering

[Edsport]

...snip...

Think of it in terms of two funnels.

One funnel has a wide opening of 12" and the small opening of 1"
The second funnel has a wide opening of 6" and a small opening of 1"

Will both let the same amount of water through ?

More will go through the 12 inch one...

...snip...

False. You're assuming the there's more water in the 12" one, when that may or may not be the case. If there is equal water placed in both, the rate of water through the funnels will be equal. This is also assuming that the length of the little ends are the same, else the longer end will flow slower due to friction and potential turbulence.

Actually if you think about it, the water may flow faster through the 6" one. Smaller diameter, but same volume means the 'smaller' funnel will have to be taller. Taller = more of the water's weight from above pushing it out of the funnel.

And so says the chemical engineering student. /geek moment, apologies for derailing the thread.

The 12 inch funnel will collect more water than the 6. Set it up and test it and you'll see it's not false. We are talking about collecting rain correct? If your're not talking about collecting rain than you should state what the heck the funnel is collecting...

 

[Crystal]

Well I wasn't confused until I started reading everyone's explanation..... Now my head hurts & I'm more confused than ever :meh:

 

[480sparky]

It's not how big the glass is out front.... it's the internal diameter of the lens (aperture) that is important.

That's why manufacturers tout the maximum aperture (f/1.8, f/3.5, etc....) as opposed to the diameter of the front glass.

 

[SNBniko]

...snip...


More will go through the 12 inch one...

...snip...

False. You're assuming the there's more water in the 12" one, when that may or may not be the case. If there is equal water placed in both, the rate of water through the funnels will be equal. This is also assuming that the length of the little ends are the same, else the longer end will flow slower due to friction and potential turbulence.

Actually if you think about it, the water may flow faster through the 6" one. Smaller diameter, but same volume means the 'smaller' funnel will have to be taller. Taller = more of the water's weight from above pushing it out of the funnel.

And so says the chemical engineering student. /geek moment, apologies for derailing the thread.

The 12 inch funnel will collect more water than the 6. Set it up and test it and you'll see it's not false. We are talking about collecting rain correct? If your're not talking about collecting rain than you should state what the heck the funnel is collecting...

I thought we were collecting rainwater in the cookie pans. God dammit. hahaha

 

[SNBniko]

Think of it in terms of two funnels.

One funnel has a wide opening of 12" and the small opening of 1"
The second funnel has a wide opening of 6" and a small opening of 1"

Will both let the same amount of water through ?

No mention of rainwater, but I'm not sure if it's implied. I am so confused now. The answer to the above question though, assuming all else is the same and the only variable is the large end funnel diameter, the answer is yes. They will. (and neglecting a whole boatload of other things like slip and friction. ha)

 

[480sparky]

I thought we were collecting rainwater in the cookie pans. God dammit. hahaha

No, we're using kitchen funnels as lens caps.

 

[SNBniko]

Well in that case, cookie pans may work better... you know, non-stick and all. ha.

 

[Edsport]

Think of it in terms of two funnels.

One funnel has a wide opening of 12" and the small opening of 1"
The second funnel has a wide opening of 6" and a small opening of 1"

Will both let the same amount of water through ?

No mention of rainwater, but I'm not sure if it's implied. I am so confused now. The answer to the above question though, assuming all else is the same and the only variable is the large end funnel diameter, the answer is yes. They will. (and neglecting a whole boatload of other things like slip and friction. ha)

Post # 10 talked of collecting rain then his post # 12 mentioned water so it's easy to assume he was talking of collecting rain as well but now i think everyone in this thread is confused.

 

[Edsport]

It's not how big the glass is out front.... it's the internal diameter of the lens (aperture) that is important.

That's why manufacturers tout the maximum aperture (f/1.8, f/3.5, etc....) as opposed to the diameter of the front glass.

It's a known fact that a telescope that has a bigger lens with the same aperture of one that has a smaller lens will collect more light so the diameter of the aperture isn't the only factor that lets a certain amount of light through to the sensor...

 

[480sparky]

It's a known fact that a telescope that has a bigger lens with the same aperture of one that has a smaller lens will collect more light so the diameter of the aperture isn't the only factor that lets a certain amount of light through to the sensor...

A telescope with a larger lens will usually have a larger aperture to go with it. They may have the same f/number, the the measurement of the apertures are different. Increasing only the front lens size and not changing the aperture will not increase the brightness of the image seen in the eyepiece.......... unless you also increase the diameter of the aperture as well. F/numbers are not units of measure, they are the result of a mathematical equation.

 

[Helen B]

The f-number (or strictly the T-stop) is the determining factor for image brightness. The diameter of the entrance pupil is the determining factor for light gathering (the focal length then comes into play to determine the image brightness, because of its effect on magnification).

For two lenses of the same focal length and entrance pupil diameter (and hence the same f-number) but different front element diameters, the light gathering ability and image brightness will be the same.

The diameter of the front element is determined by the relative positions of the entrance pupil and front element*, and by the angle of view. Ideally the entrance pupil should be fully visible through the front element over the entire angle of view of the lens. This means that the closer the front element is to the entrance pupil, the smaller it can be; and the narrower the angle of view the smaller the front element can be when compared to the entrance pupil. There are telephoto designs for which the entrance pupil almost fills the front element, and wide angle designs for which the front element is very large compared to the entrance pupil.

*There are cases where the front element is also the entrance pupil (simple lenses, telescopes), thus the size of the front element determines the entrance pupil diameter.

Best,
Helen

 

[Edsport]

It's a known fact that a telescope that has a bigger lens with the same aperture of one that has a smaller lens will collect more light so the diameter of the aperture isn't the only factor that lets a certain amount of light through to the sensor...

A telescope with a larger lens will usually have a larger aperture to go with it. They may have the same f/number, the the measurement of the apertures are different. Increasing only the front lens size and not changing the aperture will not increase the brightness of the image seen in the eyepiece.......... unless you also increase the diameter of the aperture as well. F/numbers are not units of measure, they are the result of a mathematical equation.

When talking telesecopes the lens is the aperture. If a telescope has 10 inch aperture that means it has a 10 inch lens so as you say a larger lens will usually have a larger aperture isn't quite right, a larger lens do mean a larger aperture because the lens is the aperture...

Copied and pasted below from Telescope Science: All About Telescope Aperture

Aperture is the size of the main optical lens of the telescope. It can be specified either in inches or millimeters. “Light Grasp” which is how much light an optical system can pull is a function of the area of the aperture, so that, “Light Grasp” goes up and down in squares.
For example, the Light Grasp of a 50mm pair of binoculars is 51, that is each ocular is 51 times brighter than you can see with the naked eye. This is most apparent at night or in low light situations. A 100mm binocular will pull about 4 times more light with a light grasp value of 204.
Light grasp can be calculated by the formula (A/38.495) where A is the area of the objective lens in square millimeters.
Little jump in aperture are significant jumps in light grasp.
end of paste.

A telescope and binoculars lens size matters to collecting light so why wouldn't a camera lens that has a bigger diameter collect more light than a smaller lens? It should be a simple answer instead of a confusing one...

 

[jake337]

It's a known fact that a telescope that has a bigger lens with the same aperture of one that has a smaller lens will collect more light so the diameter of the aperture isn't the only factor that lets a certain amount of light through to the sensor...

A telescope with a larger lens will usually have a larger aperture to go with it. They may have the same f/number, the the measurement of the apertures are different. Increasing only the front lens size and not changing the aperture will not increase the brightness of the image seen in the eyepiece.......... unless you also increase the diameter of the aperture as well. F/numbers are not units of measure, they are the result of a mathematical equation.

When talking telesecopes the lens is the aperture. If a telescope has 10 inch aperture that means it has a 10 inch lens so as you say a larger lens will usually have a larger aperture isn't quite right, a larger lens do mean a larger aperture because the lens is the aperture...

Copied and pasted below from Telescope Science: All About Telescope Aperture

Aperture is the size of the main optical lens of the telescope. It can be specified either in inches or millimeters. “Light Grasp” which is how much light an optical system can pull is a function of the area of the aperture, so that, “Light Grasp” goes up and down in squares.
For example, the Light Grasp of a 50mm pair of binoculars is 51, that is each ocular is 51 times brighter than you can see with the naked eye. This is most apparent at night or in low light situations. A 100mm binocular will pull about 4 times more light with a light grasp value of 204.
Light grasp can be calculated by the formula (A/38.495) where A is the area of the objective lens in square millimeters.
Little jump in aperture are significant jumps in light grasp.
end of paste.

A telescope and binoculars lens size matters to collecting light so why wouldn't a camera lens that has a bigger diameter collect more light than a smaller lens? It should be a simple answer instead of a confusing one...

Read helen b.'s statement above yours. Because we are not using binoculars or telescopes. What we use has a different design then both.

 

[Edsport]

Oh a different design. OKKKK now i fully understand and here i was confused...

 

[table1349]

I'm confused with this also. A telescope that has a bigger lens lets in more light so why not a camera lens...

Well you can, it just ends up looking like this.

:lmao::lmao::lmao: