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OT: Film vs Digital Question


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Sorry if this is too off topic, but I know the body of knowledge on this forum can answer this.


Growing up in Rochester NY I have full knowledge of film, cameras, exposures, printing and generally how film works.

I realize I haven't a CLUE exactly how digital "film" works!


Digital cameras (whether movie or "point & shoots") have shutters that open, capture an image, then close. They "save" the captured image to a "source" like a memory card, but how exactly IS that done? Is the memory source set up with pixel "receptors" that decide "red, blue, yellow"?


I'm trying to teach TikiKid how to take (fake) photos of "ghosts" by manipulating her camera and realized I don't understand jack about digital images. I still describe in the antiquated terms of film: "overexposure", "dodging & burning", etc.

In digital film, that simply doesn't apply, does it?

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I was a photographer for many years. A few years ago I had a neighbor kid who was interested in ghost photos. He and his mom would come over here and we?d look them up on the internet. I would explain to him how some of the ghost images appeared in the photos.


First, double exposure is common, with the main image being bright and the second image, the ?ghost? image, being dim. In this case, the "ghost" is a person in costume and makeup.



With many old snapshot cameras, double exposures were common in the old days.


But I don?t know if a digital still camera can do a double exposure on the same frame.


Also, blurred smoke is common. Cigarette smoke from a nearby ash tray can be out of focus and lit up by a camera?s flash, and will appear in the foreground of an image like a tall wavy ghost.



Something small stuck to the front glass of the lens:


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Long exposure, subject moved during exposure:



Dust on negative, similar to dust or small blob of dirt on front of camera lens:



Flash reflection in mirror and lens flares as a result:



Lens flare from sunlight. The lens has a 6-leaf iris:



Flying bugs lit up by camera flash:


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Thanks for the info, Fred. I know how "ghost" photos work on film, I just can't explain how they work on digital film. I know *how* to create all the "ghost effects" just can't explain it.


The digital cameras allow light in the same way as a film camera, but how are the dark/light/color images "burned"? It's not onto light sensitive film that reacts, so what is it?


Whatever it is, the end result works in almost the exact same way. Ah, our new virtual world.

It certainly is an asset knowing _real_ film photography when you sit down and use PhotoShop. All professional photographers use PS on a daily basis now to "fix" their pictures.


It makes REAL photographers such as Karsh & Adams all the more amazing.

I'm hoping this sparks an interest in photography for TikiKid. Whenever we watch a film I point out the photography and she's become pretty aware there's someone behind a camera recording it. Just last night we discussed "magic hour".

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> {quote:title=TikiSoo wrote:}{quote}

> The digital cameras allow light in the same way as a film camera, but how are the dark/light/color images "burned"? It's not onto light sensitive film that reacts, so what is it?



I?ll try to explain it as someone taught it to me:


A CCD chip has individual ?pixels? that are autonomous and separate from other pixels. These are like film ?grains?.


A film grain is a small clump of a chemical known as a silver halide. When light hits it, it becomes unstable. When it is developed in another chemical, the halide separates from the silver, leaving a small clump of black tarnished silver.


Silver grains are very small and are touching one another. Some are slightly larger and some are smaller. They are on the film in a somewhat random manner.


Each pixel is on a CCD chip is square and all are very small and side by side. A CCD camera usually doesn?t have any kind of shutter. When the button is pushed to take a picture, a little electricity is run through the chip and at that time the light hitting the chip causes some sort of electrical reaction and a small amount of electricity comes out of each pixel.


The ?shutter speed? for a CCD chip is actually the amount of time the electricity comes out of a chip. Such as for 1/4 of a second, 1/50 of a second, 1/100 of a second. Etc. A long exposure of several minutes in dim light takes a continuous flow of electricity from the chip and builds up the image gradually.


This is all fairly complicated electronically so that all the electrical signals are lined up in their proper places so that the electricity from each row of pixels is lined up in the proper sequence.


A pixel is just like a film grain, except pixels are all lined up and usually square.





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There are also CMOS sensors, which use less electricity than CCDs. One CMOS chip, made by Foveon, actually senses all three colors on the entire chip, because different colors penetrate to different depths in the chip. I think only Sigma cameras use the Foveon chip. Canons have used CMOS chips for quite a while, and Nikon began using them a few years ago. I think both still have CCD cameras as well. But, the principles Fred cites are accurate. Pixels are roughly equivalent to grain size in film. The more megapixels, the sharper the picture. This is usually accomplished by having larger chips. The chip replaces the film frame, as the objective of the light coming through the lens.

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I think you're all missing the point about digital technology. When a CCD (charged coupled device) is struck by light, the pixels are sent to the camera's microprocessor that translates those impulses into digital information, all expressed as "0"s "1"s, "0" meaning "off," and "1" meaning "on," and then stores them on tape, optical disc, or solid-state flash drive. Hundreds of thousands or millions of these tell the device created to reconstitute those long sequences of on-off flashings what the digital file is: it could be sound (such as music), or data (such as a text file), or images (both still and moving), and in what form.


This is what digital is: everything reduced to only two quantities, "0" and "1." Traditional photography, like LP records or ink on paper are analog, meaning that they deal in subtle gradations, whether they be the density and distribution of silver grain on film, the cut, frequency and depth of the sides of grooves in a record, or the darkness, lightness and direction of ink marks on that paper. Digital came into existence and was thought to be superior because its irreduceable mathematical basis allows for perfect, loss-free reproduction, though as most know by now that doesn't preclude information loss through aging and corruption of the storage medium.

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Wow thanks Fred, Valentine & Sprocket....now I "get" it. In a nutshell, digital cameras work in the same way as film cameras in that; the shutter opens, light registers onto a surface & is "burned" onto that surface in light waves. Some light waves are dark, some light, some colors.

Pretty amazing that it even could be developed into digital information (1's & 0's) that we can see as a picture.


So if I open the shutter for a longer exposure, a headlight will "trail" just like a film camera because the light is hitting the "sensor" for the lack of a better word. Now to read the manual and figure out how to alter shutter speed on a point & shoot.


Wish me luck teaching the kid how to make special effect photos. You certainly can't teach until you can explain why you're doing what you're doing.

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