How/why does small aperture work

[vvizard]

I'm a little ashamed for admitting not knowing this, but since I think many others don't know it either, I'll do them a favour of not having to ask themselfs :)

When I stop my lens down to let's say f/22, and hit the DOF-preview on the cam, while looking into the lens, then I can see how this big opening changes into a very small one. How come that the light travelling into the lens, still can cover the whole image-sensor?

Is there some glass-"magic" here, so that the light get's "compressed" into a small beam before going through the tiny aperture-opening, and then beeing "decompressed" on the other side, to reach out to every corner of the sensor again?

I really don't understand how this works, so if somebody could enlighten me, I would be happy :)

[robertwgross]

Probably nobody has the space to explain it thoroughly here. A good class in Physics will have one section on Optics, and that should teach how lenses work. Anything like this should be found in pieces on the web, and it is the diagrams that will make the best sense, which is why you need to see those first. Try a search.

Some introductory photography classes cover this a little, also. You need to understand just a little of the basic optical stuff going on inside your camera just to be a good user of the camera. However, you don't need to be an expert on it just to take good pictures.

---Bob Gross---

[scottbergerphoto]

vvizard wrote:
I'm a little ashamed for admitting not knowing this, but since I think many others don't know it either, I'll do them a favour of not having to ask themselfs :)

When I stop my lens down to let's say f/22, and hit the DOF-preview on the cam, while looking into the lens, then I can see how this big opening changes into a very small one. How come that the light travelling into the lens, still can cover the whole image-sensor?

Is there some glass-"magic" here, so that the light get's "compressed" into a small beam before going through the tiny aperture-opening, and then beeing "decompressed" on the other side, to reach out to every corner of the sensor again?

I really don't understand how this works, so if somebody could enlighten me, I would be happy :)
Consider the pin hole camera. Take a piece of cardboard and put a small hole in it. In a dark room, shine a flash light through one side of the hole. The light doesn't stay in a narrow beam like a laser. It spreads out. Now I know that's oversimplified and the lense is specially ground to focus the rays of light. But, those little light boogers will go just about anywhere that they can.
Scott

[Scottes]

scottbergerphoto wrote:
But, those little light boogers will go just about anywhere that they can.

Light boogers. ROFLMAO. Photons, man, just like in the torpedos. But I may never use that word again - they'll be "light boogers" from now on.

[scottbergerphoto]

scottes wrote:
scottbergerphoto wrote:
But, those little light boogers will go just about anywhere that they can.

Light boogers. ROFLMAO. Photons, man, just like in the torpedos. But I may never use that word again - they'll be "light boogers" from now on.



Sorry, I didn't mean to use technical jargon ;)!
Scott

[gsmx2]

I don't know the technical explination, but if you are near-sighted and wear glasses, I can give you a practical demonstration.

Get a piece of paper and use a pin to punch a very small hole in it. Now take off your glasses and look at something in the distance to see how out of focus it is. Now look through the hole with the paper right up to your eye. It wil be clearer.

Scott

[DonCoon]

gsmx2 wrote:
I don't know the technical explination, but if you are near-sighted and wear glasses, I can give you a practical demonstration.

Get a piece of paper and use a pin to punch a very small hole in it. Now take off your glasses and look at something in the distance to see how out of focus it is. Now look through the hole with the paper right up to your eye. It wil be clearer.

Scott


Then wouldn't cheap pieces of thin plastic with pin holes in them make great reading glasses. Just think of the money I could save

I know, i know... less light --- but couldn't resist ;)

[DaveG]

vvizard wrote:
I'm a little ashamed for admitting not knowing this, but since I think many others don't know it either, I'll do them a favour of not having to ask themselfs :)

When I stop my lens down to let's say f/22, and hit the DOF-preview on the cam, while looking into the lens, then I can see how this big opening changes into a very small one. How come that the light travelling into the lens, still can cover the whole image-sensor?

Is there some glass-"magic" here, so that the light get's "compressed" into a small beam before going through the tiny aperture-opening, and then beeing "decompressed" on the other side, to reach out to every corner of the sensor again?

I really don't understand how this works, so if somebody could enlighten me, I would be happy :)

Interestingly enough the smaller the aperture the bigger the image circle.

A lens throws a cone of light onto the film. The lens manufacturers want that cone to just cover the size of the film/CMOS. The smaller the coverage needed the sharper they can make the lens. The average 35 mm lens resolves many more lines per millimeter than a medium format lens, which in turn resolves more than a large format lens. The larger film sizes make up for the "inferior lens" performance.

The image circle is also affected by aperture. If you read any product literature for a LF lens it will give the image circle size in millimeters and will also say "@ f22".

The importance of image circle with LF lens can't be understated. It is the LF ad writers equivilent of megapixel size! The bigger the image circle the more desirable the lens.

The chief advantage of LF is the lens movements. The lens sits out at the end of the camera on a flexible bellows. If you tilt the lens down, while keeping the back upright, the depth of field, can be made to "lay down". That way with a large aperture you can still can keep near and far objects in focus. Think of flowers in an alpine meadow with the mountains sharp in the background.

Sideways tilt (actually called swing) can be used to change (say) the depth of field from being close to you on the left and then heading off on a diagonal. This could have the practical use of standing next to a building and being able keep it all in focus as it "moves" away from you, and again at a large aperture.

You can "rise" the lens and this will correct the "falling over backwards" error that you get when you tip the camera up to photograph a building.

There are a lot more movements but they all depend on the negative being inside this great big image circle, and the bigger the image circle the greater the movement possibility. As you use movements you are just using a different part of this image circle. The image circle on the Canon Tilt/Shift lenses are a lot bigger than regular 35 mm lens and for the same reasons.

[samdring]

So is it the case that the speed of your lens is determined by whether or not your boogers are light or heavy?

[scottbergerphoto]

samdring wrote:
So is it the case that the speed of your lens is determined by whether or not your boogers are light or heavy?
I can only refer you to: KE(kinetic energy) = 1/2 M(Vsquared), where m= mass of the booger and v = booger velocity. You can extrapolate from there.
Scott;)

[Scottes]

scottbergerphoto wrote:
samdring wrote:
So is it the case that the speed of your lens is determined by whether or not your boogers are light or heavy?
I can only refer you to: KE(kinetic energy) = 1/2 M(Vsquared), where m= mass of the booger and v = booger velocity. You can extrapolate from there.
Scott;)

Which means that if you have a booger on your aperture then (Vsquared) = 0 which means that no light gets through.

Amazingly enough this makes sense....

[scottbergerphoto]

scottes wrote:
scottbergerphoto wrote:
samdring wrote:
So is it the case that the speed of your lens is determined by whether or not your boogers are light or heavy?
I can only refer you to: KE(kinetic energy) = 1/2 M(Vsquared), where m= mass of the booger and v = booger velocity. You can extrapolate from there.
Scott;)

Which means that if you have a booger on your aperture then (Vsquared) = 0 which means that no light gets through.

Amazingly enough this makes sense....
Exactly! :)
Scott

[kfong]

scottbergerphoto wrote:
scottes wrote:
scottbergerphoto wrote:
samdring wrote:
So is it the case that the speed of your lens is determined by whether or not your boogers are light or heavy?
I can only refer you to: KE(kinetic energy) = 1/2 M(Vsquared), where m= mass of the booger and v = booger velocity. You can extrapolate from there.
Scott;)

Which means that if you have a booger on your aperture then (Vsquared) = 0 which means that no light gets through.

Amazingly enough this makes sense....
Exactly! :)
Scott


No, no, no. The above is only true for SLOW tardyons. You've got to remember that these boogers are relativistics. Boogers are actually luxons, hence E=hf, but attempt to extrapolate will transform these luxie-boogers into tachyons, with imaginary consequences.

Ken

[scottbergerphoto]

kfong wrote:
scottbergerphoto wrote:
scottes wrote:
scottbergerphoto wrote:
samdring wrote:
So is it the case that the speed of your lens is determined by whether or not your boogers are light or heavy?
I can only refer you to: KE(kinetic energy) = 1/2 M(Vsquared), where m= mass of the booger and v = booger velocity. You can extrapolate from there.
Scott;)

Which means that if you have a booger on your aperture then (Vsquared) = 0 which means that no light gets through.

Amazingly enough this makes sense....
Exactly! :)
Scott


No, no, no. The above is only true for SLOW tardyons. You've got to remember that these boogers are relativistics. Boogers are actually luxons, hence E=hf, but attempt to extrapolate will transform these luxie-boogers into tachyons, with imaginary consequences.

Ken
What you talkin 'bout Willis?
Scott

[Belmondo]

You might think it's a light booger,

but it's snot.

[ilya]

belmondo wrote:
You might think it's a light booger,

but it's snot.




All I know is that square boogers are hard to roll.

[Ikinaa]

gsmx2 wrote:
I don't know the technical explination, but if you are near-sighted and wear glasses, I can give you a practical demonstration.

Get a piece of paper and use a pin to punch a very small hole in it. Now take off your glasses and look at something in the distance to see how out of focus it is. Now look through the hole with the paper right up to your eye. It wil be clearer.

Scott


You don't need a piece of paper...
As I'm nearsighted, I don't see the clock (1m diameter, 50 meters away) when I go for a swim.
So what I do, I put my fingers of both hands together to make a tiny hole and peer through it, the clock which is otherwise only a white speck is sharp enough to be read, so the fingers are my lense...
just think about it: simply take a SLR-body, no lens, put your finger before the CCD and make sharp pictures... now... who needs L-lenses :D

[BearSummer]

Which all goes to show the following

1, You dont need to know how the lens works to be able to take good pictures

2, when babbling its a good idea to be a nerd so that you can baffle them with technical bulls#!t (torpedoes lol)

3, saying slow tardyons is like saying hot fire, of course they are slow they are tardy (luxie-boogers, to funny)

4, ke=.5mv^2 lol, v=c, c^2 is always explosive, end result your camera would get very hot and would probably need the new giza tripod (limited number available) just to keep it still. And how many pictures of sand would you like.

If you really want to know then a course in optics (not the kind behind a bar) would probably be a good idea. Thanks to everyone else for such a funny thread.

Regards

BearSummer

[Ikinaa]

I found this :
http://www.cis.rit.edu/~jsapci/Courses/PDF%20Slides/04_The%20Camera.pdf
I find it relatively easy to understand
It's about the pinhole camera and apertures...

[Scottes]

BearSummer wrote:
Which all goes to show the following

2, when babbling its a good idea to be a nerd so that you can baffle them with technical bulls#!t (torpedoes lol)

I am NOT technical!

4, ke=.5mv^2 lol, v=c, c^2 is always explosive, end result your camera would get very hot...

Yeah, it happens sometimes, but if you get the Phoenix lenses you just have to wait a bit and you'll be OK.

[ron chappel]

1) Lenses ARE 'magical'.What they do is amazing-
imagine a thin beam of light shining towards a lens.No matter what part of the lens surface it hits,it will allways end up at the one point on the film/sensor.
Any part of a lens projects a complete image!
What an aperture does is to stop the outer periphery of the glass from being used.So every part of the lens surface can project a complete image-the aperture just cuts down on how much of the lens surface is used
2)Depth of feild works because of the angle light hits the front of the lens.
The center of the lens sees the image straight on while the edges of the lens don't.
Situations that give a shallow DOF are:large diameter lenses,aperture wide open,focussed very close(huge difference in the angles that light has hit the lens surface)
Situations that give a huge depth of feild are:aperture stopped right down,focussed at infinity(light rays are allmost parellel-every part of the lens surface can focus easily)

This is a simple explanation and i may have used the wreong words here are there but it should give you a basic idea

[Tom W]

Ikinaa wrote:
I found this :
http://www.cis.rit.edu/~jsapci/Courses/PDF%20Slides/04_The%20Camera.pdf
I find it relatively easy to understand
It's about the pinhole camera and apertures...

Good resource - there's a lot more there to look at.

Thanks!

[BearSummer]

scottes wrote:
BearSummer wrote:
Which all goes to show the following

2, when babbling its a good idea to be a nerd so that you can baffle them with technical bulls#!t (torpedoes lol)

I am NOT technical!

4, ke=.5mv^2 lol, v=c, c^2 is always explosive, end result your camera would get very hot...

Yeah, it happens sometimes, but if you get the Phoenix lenses you just have to wait a bit and you'll be OK.



Look, using the words "photon torpedos" is technical, "burning, stick, boogers" is non-technical. You may have been faking it was technical. :)

Ahhh, that explains the sphynx, guy must have been reading the plans wrong, was supposed to be pheonix lens, turned into lion bird question asking monster, just be glad you dont have to carry it in your camera bags. Are you sure you want to use me at that aperture, I wont autofocus unless you tell me the middle name of the 12th popes brother. Yeah could be problematical.

Best regards

BearSummer

[Motorsports Photo]

What a wacky thread!

How does it really work?

Squint...

Did you see something better? I CAN see things with my coke bottles, I mean glasses off.

Does that explain it?

-Pete

[Duncreavy]

Want some boogers with that Canon?
Little did I know I was joining a comedy club when I joined this forum. A twofer