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Author Topic: The workings of photography, How & Why?  (Read 5247 times)

Offline Karen W.

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The workings of photography, How & Why?
« on: 24/10/2006 03:52:59 »
I want to know and understand how light makes impressions on the film to create the pictures we take? Simply how do the images become trapped on the film with such detail?

Karen


 

ROBERT

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Re: The workings of photography, How & Why?
« Reply #1 on: 24/10/2006 12:59:55 »
This is a micrograph of part of the array of red/green/blue photosensors in a digital camera:-



The resolution of a digital image, (the amount of detail recorded in the picture),
 depends on the number of the photosensors, (a.k.a. pixels), in the array.
« Last Edit: 24/10/2006 13:18:56 by ROBERT »
 

Offline daveshorts

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Re: The workings of photography, How & Why?
« Reply #2 on: 24/10/2006 13:37:08 »
In a conventional camera the film is covered with a layer of transparent silver chloride. If Silver chloride is exposed to light it converts to silver metal, which is opaque and dark grey. So a picture is formed, unless you very heavily expose it this picture is still invisible though, as only a few atoms of silver will be converted in each crystal. In developing you add a chemical to convert silver choride into silver, it will tend to do this faster to crystals which have been disrupted by exposure to light. Once it has been developed, you remove the remaining silver chloride with a fixer, leaving a picture in silver.
 

Offline Karen W.

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Re: The workings of photography, How & Why?
« Reply #3 on: 24/10/2006 14:38:36 »
What is silver Chloride?

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Offline science_guy

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Re: The workings of photography, How & Why?
« Reply #4 on: 24/10/2006 16:25:24 »
you just said it: a bond between the elements silver, and chlorine.

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Offline daveshorts

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Re: The workings of photography, How & Why?
« Reply #5 on: 24/10/2006 16:36:54 »
If you burn sodium in chlorine the two will react forming sodium chloride - what we know as table salt. If you burn silver in chlorine you get silver chloride. There are easier ways of making it - dissolve silver in hydrochloric acid for example.
 

Offline Karen W.

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Re: The workings of photography, How & Why?
« Reply #6 on: 24/10/2006 16:51:55 »
That was an explanation I understand DAve.. Thanks for breaking it down like that, I have a hard time understanding unless it is broken down like that! LOL Thanks to both of you!

I still don't get how the picture is transferred to the paper..from the solid object that you are shooting are the lights coming from the objects surroundings or from how much light enters the camera and how does that happen... reflecting back into camera?

Karen
 

Offline daveshorts

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Re: The workings of photography, How & Why?
« Reply #7 on: 25/10/2006 09:07:51 »
Ok this would be a lot easier with diagrams, but that will have to wait till I have written the software...

Start of thinking about shadows:
If you think about the shadow of a stick produced by a light, it will move as you move the light. If you add another light you will get a second shadow in another direction - this is why you sometimes have two shadows when walking under streetlights.

Now instead of thinking about a stick think about a hole in a cardboard box. Now if you look inside the box (without letting in any light youself) and shine a light at the hole you will see a bright anti-shadow of the hole on the back of the box. If you add another light shining from another angle you will get another bright spot somewhere else. If you add a third light that is green, you will get a green antishadow.

Because light is bouncing off all the things in an image you can think of it as being made up of loads of different coloured lights. Each of these lights will make a different bright spot on the back of the box, making an image of what is outside. This priciple was used by artists in the 15th and 16th centuries by getting a dark room, and making a hole in it, thus allowing them to trace the image, hence getting the perspective right. The latin for dark room is Camera Obscura... hence where the name camera comes from.

The problem with just having a hole is that if you want more light to get through you want a bigger hole, but this will mean that each point in the real world will produce a large spot in the image, so the spots will overlap producing a confused fuzzy image. So a lens is used, this is a specially shaped piece of glass that at a certain distance will take all the light hitting the lens from one point and focus it back to one point on the screen, the problem is that it will only work for one distance. This is why you have to set a camera for the distance the object you are photographing is away, or focus it.

I hope that helps..
 

Offline lightarrow

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Re: The workings of photography, How & Why?
« Reply #8 on: 25/10/2006 18:29:05 »
If you burn sodium in chlorine the two will react forming sodium chloride - what we know as table salt. If you burn silver in chlorine you get silver chloride. There are easier ways of making it - dissolve silver in hydrochloric acid for example.
Sorry if I seem nitpicking, but...I like inorganic chemistry, so... I have to correct you a little:

You can't dissolve silver in hydrochloric acid. You need something else, which is oxidizing (silver is called a "noble metal" just for this reason), e.g. nitric acid. Then you have a solution of Ag+ ions, to which, adding Cl- ions (example: NaCl = common salt) you get AgCl (because it's insoluble and precipitates).

About chemicals for photographic films, you can use other silver alogenides, for example AgBr (I think is the most common).
 

Offline daveshorts

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Re: The workings of photography, How & Why?
« Reply #9 on: 25/10/2006 18:31:51 »
I stand corrected.
 

another_someone

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Re: The workings of photography, How & Why?
« Reply #10 on: 26/10/2006 00:07:26 »
This is a micrograph of part of the array of red/green/blue photosensors in a digital camera:-



The resolution of a digital image, (the amount of detail recorded in the picture),
 depends on the number of the photosensors, (a.k.a. pixels), in the array.


Just to be picky, the number of photosensors is a fairly clearly defined concept, but the number of pixels can have all sorts of interpretations.  Usually, what is meant by the number of pixels is the number of discrete points at which we collect colour and luminescence data, but usually this actually contains 4 photosensors (2 greens, 1 red, and 1 blue sensor); but then there is Fuji, that also uses separate sensors for high intensity and low intensity light in order that it can extend the dynamic range of its sensors.
« Last Edit: 26/10/2006 00:27:50 by another_someone »
 

Offline Karen W.

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Re: The workings of photography, How & Why?
« Reply #11 on: 27/10/2006 16:12:14 »
I need to try the whole in the box thing, I seem to understand that some better! Thanks Dave and the rest of you too! Have to read this again a couple more times to try to digest it!...
« Last Edit: 27/10/2006 16:14:11 by Karen W. »
 

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Re: The workings of photography, How & Why?
« Reply #11 on: 27/10/2006 16:12:14 »

 

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