there is a roll of motion picture negatives in this camera the finished picture will be on another roll known as positive film these delicate strips of with their light sensitive coating on the materials which records and transmit the creations of hollywood to the world this picture is the story of these films and of how the al hollywood makes entertainment out of solar these buildings are some of the movie photo finishers of motion picture laboratories in hollywood where you have taken a snapshot of junior with your own camera you take your roll of film to the photo finish your next day so you're finished pictures this is just what happens to movie film from a studio camera the photographic process and how it brings a picture to you is explained by this diagram originated by dr meis when you look at an object in real life the brain at number one receives an image of it through the eye in photography the object is a large black text two is image by a lens on a light sensitive  the exposure period produces a latent image on the film and four after developing in fixing a visible negative image is formed at five it is called a negative image because it is right where the original object is black and vice versa in order to obtain an image in which the light and dark areas are in the correct relationship this process must be repeated the negative is therefore photographed or printed light shines through the negative and falls upon another light sensitive film at six and produces a latent image it's seven once more of the developing and fixing of the film we veil a permanent image at eight which is this time a positive image of the original object therefore when this positive image at nine in the brain a ten again sees an image which is a faithful reproduction of that obtained from the original subject what happens to the film chemically may be expressed in three equation first a latent images form second it is developed and finally made permanent the photographic emotion is made up of millions of tiny crystals of silver bromide suspended in a thin layer of delton this picture shows how the crystals actually look when magnified several thousand times we want to talk about them for a few minutes in rather technical language because on their peculiar properties is based the whole art photography you will note that the triangle is a charge and the brahman denoted by b r a negative the significant detail about this crystal which makes it a photographic value is a tiny speck best known as the sensitivity spec consisting primarily of silver  probably formed during the manufacture of the emotion let us follow the action when light waves from your favorite movie star pass into the camera to the emotion if you light quanta strike this particular crystal and electric conductor indeed we speak of this property of silver bromide crystals as photo conductance since they conduct electricity when light falls on them electrons within the crystal travel freely and naturally in their wandering they find the sensitivity spec since the molecular pattern of the spec is such that it can trap the electrons like a positive pole in the crystal the electrons released by the action of the light find themselves clustered about the sensitivity spec electrons converts the spec to a negative pole capable of attracting positively charged particles there is at all times within the crystal a movement of ions through the thermal agitation under ordinary conditions the silver and roman irons moved sluggishly about occupying vacant places within the  this particular crystal however something has happened to disturb the normal state after being struck by the light a negative pole was formed at the sensitivity spec and now positively charged silver ions are attracted to the speck we follow the silver ions in their slow path toward the speck since their movement is due to thermal agitation of the molecules this action is faster when the crystal is warm than when it is cold which explains why film is less sensitive in cold weather the silver ions progressively drawn to the spec and as fast as they come within its range they are neutralized by the electrons clustered about the speck eventually one atom of silver is neutralized  for each quantum of light which if the crystal and the sensitivity spect finds itself surrounded by a group of silver atoms it is the aggregate of these clusters of silver present in the crystals which were struck by light which are the latent image in the film this image is called latent because it is quite invisible and of no use to us until a developer reveals that the latent images permanent this crystal pattern being stable at ordinary temperatures and fact film exposed by the andre expedition and abandoned in the arctic was found thirty years later and developed to give satisfactory pictures following the neutralization of the electrons at the spec by the silver ions suspect original ability to trap electrons and on immersion in a developer and ionized molecule hydroquinone bearing a negative charge is attracted to the specter or latent image the secret of the use of certain weight cing agents as developers is that they're like trick potential is of just right order to be attracted to the specs but they are not powerful enough to reduce the silver ions in neighboring crystals which have not been exposed to light one molecule of heidrick unknown appears at the spec and loses its negative charge which is an electron to the group keeps up long enough all the silver ions within one crystal are reduced to metallic silver and we have a black deposit forming part of a visible image the bromide ions move out of the crystal and are released in the developer to show how  of light and dark tones may result from a collection of silver particles let us see what happens when crystals are given exposures of different intensity this crystal receiving much light has many electrons released and many silver atoms formed following development it is completely reduced to metallics over the next crystal receiving a moderate amount of light has fewer ions reduced to atoms and has some of the silver and brahman ions left in their places the third crystal receiving little light has  metallic silver atoms behind but the positive silver making up the visible image actually consists of clusters of these atoms distributed throughout the gelatin layer these particles are not evident in an actual picture but may be seen under enormous magnification as in this photo microgra we have seen how the silver bromide crystals receive install the latent image and learn that a developer is needed to reveal it and of fixing back to make it permanent in a hollywood laboratory thousands of gallons of such developing solutions are in daily use organic reducing agents such as a lawn pyro liason imanol and hard to come down which will convert the latent image to metallic silver here we see some hydrophone added to water and a piece of exposed film agitated in the solution that development takes place promptly but also observe that the solution becomes discolored the discoloration is due to the oxidation of the heineken own and a solution like this would lose strength very rapidly to a piece of exposed film and immersed in the solution will rapidly turn black indicating that the developing power is unimpaired by the sodium sulfite but now we noticed that the solution remains perfectly colorless our developing solution is now practically complete it is desirable however to include a small quantity of potassium bromide to restrain and reducing action of the developer so that it will convert only the desired i mentioned into metallic silver without affecting the surrounding unexposed bromide the ability of potassium bromide to retard the action of the developer is illustrated here in an exaggerated way but its class contain complete developing solutions and excessive amount of potassium bromide has been added to the one on the now we see that the solution with the excess throw mine does not develop at all these then are the ingredients of a developing a the developing or reducing agent say the preservative see the alkali or activator the restrainer in addition to a developer we need affecting ba film transparent where there is no m and it also makes the image permanent since the action of light by itself will gradually cause the un removed silver bromide to darken in this demonstration we observe that a piece of we call that development was carried out in an alkaline solution it is therefore desirable to make the fixing bath acid in reaction so that development will stop promptly when the film is immersed in it