digicam

It depends on what you are doing with the pictures.

The human Eye cannot differentiate any higher resolution than about 5 or 6 Mega pixels. On digital cameras It is also important to know how many points of focus there are. I have a 5 Megpixel camera with multiple points of focus that produces better quality pictures then my 6 MegaPixel camera with few points of focus.

If you are going to magnify the picture, the higher the number the better.

Hint for best quality pictures, do not use the zoom. Instead adjust the distance of the camera

Hangwaiter,

There is not a "simple" answer to your question. You are looking to compare an analog medium, to a digital one.

Also, are we talking 35 mm negative or transparency film? (Transparency film has somewhat higher resolution, but narrower dynamic range)

If we consider Fuji Velvia (ISO 100) 35 mm transparency film

The stated resolution is:

80 lines/mm resolution - low contrast target – (1.6:1)

160 lines/mm resolution - high contrast target (1000:1)

Given that a 35 mm "frame" is approx. 24 mm x 36 mm, to calculate an approximate pixel equivalent, you would multiply

(24mm x lines/mm) x (36mm x lines/mm).

Using the higher resolution value (160, representing a high contrast target) resolution:

(24mm x 160) x (36mm x 160) = 22,118,400

The result would then be multiplied by 3 (representing 8-bit RGB color) to get the uncompressed file size for the resulting image:

22,118,400 x 3 = 66,355,200 pixels = or 66 megapixels

(That's a LOT of pixels…)

Currently, you can chose from the following top of the line digital SLRs

(35 mm camera format):

Canon EOS-1Ds Mark II – 16.7 Megapixels (Approx. $7,000 for the body alone)

Nikon D2X – 12.8 megapixels (Approx. $5,000 for the body alone)

As you can see by the numbers, you really can not match film resolution with any of the currently available (mainstream) digital camera on the market – The $7,000 Canon will give you approximately ¼ of the resolution that (ISO 100) film can provide (at least in theory).

Additionally, many factors need to be considered when attempting to compare film to digital…

Film, as an analog medium, does not record just 256 discrete shades of gray or the corresponding 16 million colors. Rather, it records a more continuous range of colors and shades. (However, the human eye can't differentiate more than about 100 shades of gray)

Also, with 100 speed color film, the limiting factor for image resolution will often not be the film itself, but rather the lens (optical aberrations), subject contrast, photographic technique, camera vibration, camera/subject motion, etc.

Now, regarding the human eye:

"The eye is not a single frame snapshot camera. It is more like a video stream. The eye moves rapidly in small angular amounts and continually updates the image in one's brain to "paint" the detail. We also have two eyes, and our brains combine the signals to increase the resolution further. We also typically move our eyes around the scene to gather more information. Because of these factors, the eye plus brain assembles a higher resolution image than possible with the number of photoreceptors in the retina. So the megapixel equivalent numbers below refer to the spatial detail in an image that would be required to show what the human eye could see when you view a scene.

Based on the above data for the resolution of the human eye, let's try a "small" example first. Consider a view in front of you that is 90 degrees by 90 degrees, like looking through an open window at a scene. The number of pixels would be

90 degrees * 60 arc-minutes/degree * 1/0.3 * 90 * 60 * 1/0.3 = 324,000,000 pixels (324 megapixels).

At any one moment, you actually do not perceive that many pixels, but your eye moves around the scene to see all the detail you want. But the human eye really sees a larger field of view, close to 180 degrees. Let's be conservative and use 120 degrees for the field of view. Then we would see

120 * 120 * 60 * 60 / (0.3 * 0.3) = 576 megapixels.

Well put.

Horses for courses. The chemical image is an excellent vehicle for keeping high-quality snapshots in an album. The digital image is an excellent vehicle for the speed at which an image can be edited, perhaps, transferred into a document and/or sent to the other side of the world (or even beyond one day?). There is obviously an overlap between the two systems and some compromise might be needed.

Why does the poster replace when one could use both (rhetorical question)? One possibility is to keep the chemical imaging system and start with an entry-level digital imaging system, and take it from there.

Jman describles very clearly. He must be very familiar with camera. I have nothing to add only but a few words except.

Its interested question. Most people is vague. at first, I thnk you have to figure out for what you are using it, where you are using it?
More or less, the new electronic camera cannt compare with the tranditional machine singal reflect camera, either lens or resolution. to match film's resolution, lens would has enough high resolution up to 88 lp or 120lp/mm. but electronic camera less than that, say 32--81lp etc. most of industrial camera lens has less than 32 or 64lp.studio camera has higher lp.(I hvnt remembered the value)
2] most of EC (electronic camera) is "stupid" type, means they have smaller aperture and focus, so that they have larger sence deepth, people , even no skill, can take a wonderful photo.

3] CCD or CMOS device has no same HD curve as film has. the front is sharper and the latter is smooth. so it has different image.besides, very most of EC is singal chip device( adopte space filter) not 3 chips type, so they have less colore replay thna film has.
4]Density of pixels depend on how much size you want to enlarge your picture?
I tell you a simple constant to figure out the device density.
generally speak, our human eys's resolving power is about 0.5 -- 1' for orienge light. average 0.8'=2.3exp(-4)
we observe pictue at 25cm. you can work out relative pixels valus by simple geometry. see #3.
the more the value you calculate the large area the chip you need.
In one word, which type camera you are choice depend on what you are using for.