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What you don't see on the Internet
Digital VS film resolution issues


The Internet is a great way to distribute information and images across the globe, but it is limited by the hardware of the end-user. Standard screen sizes are generally between 640X480 and 1600X1200. Designing an Internet page to be viewed at 800X600 is a good compromise to make the page useable by the most viewers possible. That is what I use. However, my panorama photos would be tiny at that resolution, so I expand them a bit to a width of 1200 pixels. If you are using a 800X600 screen, then you will have to scroll to the right to see that part of the picture. Even a 1200 pixel wide image is just a small version of the actual photo.

Here is a sample photo, a view of the Pauling Ranch at Big Sur:

This is a small section from the above 1200-pixel-wide photo.

This is what you see on the Internet.


The negative was originally scanned at 1200 DPI, so the width of that scan was more than 8000 pixels.

Here is the same image, viewed at the higher resolution:

This is a medium resolution scan.

Note that you can now see individual rocks on the top of Salmon Cone. To view the entire photo at this resolution you would need an eight-foot-wide monitor!


Even this does not come close to what the 6X18 panorama camera can capture. A 3200 DPI scan of this same negative resulted in a 23,238-pixel-wide image.

Here is a section of that file:

This is what you see at 3200 DPI.

To view the whole thing would require a huge monitor. Even the CIA doesn't have twenty-foot wide computer monitors! Now you know why we are considered to be digital extremists!


On Paper
Images presented on photographic paper are very different from images presented on the computer screen, even if they are both derived from the same negative. On the monitor, the pixel is a fixed size. To get more resolution, you need to have more pixels. With paper, the "pixel count" is fixed by the negative. (In black and white film this would be grains of silver; color films use dyes.) If you make an 8X10 print, it will have the same "information" as an 16X20 print, but it will look sharper (at the same viewing distance) because the "pixels" are smaller. That is why the 3200DPI sample above looks so "grainy." It is as if you had your nose pressed right up to a twenty-foot wide print. An actual print might be only four feet wide, so it would appear five times as sharp.



UPDATE

The conclusion that the film/digital photographer might make from the above information is that what would be needed was simply the highest resolution scanner available. However, before going out and buying a very expensive scanner, there are some other factors to take into consideration.

THE FILM

Diferent films can give very different degrees of resolution, even for scenes shot under the same conditions and with the same equipment. Most photographers know that, with black and white film, the size of the silver grains determines the "speed" of the film--the larger the silver grains, the faster the film; the smaller the grains, the slower the film--but "slowness" is also correlated with higher resolution. Think of the fast film as a square foot of boulders, while the slow film is a square foot of pebbles. The standard unit of measurement for this factor is lines-per-millimeter. The fast film might be five boulders wide; whereas the slow film might be a hundred pebbles wide (5 rocks per foot VS. 100 rocks per foot.)

This brings us back to scanners. If, in your particular case, you are using film which is the equivalent to "5 rocks per foot" in resolution, then using a scanner with "100 rocks per foot" resolution would not improve your resolution because there were only five rocks to begin with.

From the manufacturer's site, you should be able to download the data sheet for whatever film you are using. Check the resolving power of your film. For example, I have found that Fuji Reala ISO 100 film works the best for the type of photography I do. The film has a l/mm of 125 for contrasty conditions. This translated to 3175 lines per inch, so using a scanner with more than 3200 dpi would not improve the resolution. Other films have different resolving powers, so you will have to check the data sheets for each film you might want to use. Kodak Tmax (ISO100,) for example, resolves to 200 l/mm. (Data sheet here: http://www.kodak.com/global/en/professional/support/techPubs/f32/f32c.jhtml) However, checking the film does not mean that you are done with the resolution issue.

THE LENS

Different lenses have very different resolving qualities. You would not expect to get the same quality photograhs from a Holga as a Haasselblad, even if you used the same film, so you will also have to check the resolving power of your particular lens. For example, the Rodenstock Grandagon-N f6.8 has a resolving power of 67 l/mm, but that is only in the center; the edges are less sharp. By way of contrast, lenses designed specifically for close-up work, such as the Tominon lenses for the Polaroid MP-4 camera, can be expected to have higher resolving powers. (The MP-4 was mostly used for medical and scientific macro photography.)
[ A lens information page is here: http://www.hevanet.com/cperez/testing.html ]

Shooting Reala film with a Rodenstock lens, therefore, means that the film is "better" than the lens, so the lens is the factor which should be matched to the scanner. Scanning that negative at 1800 DPI would yield as much information as would be available. In this situation, buying one of the new 4800DPI scanners would not make much sense because you would not be able to use the higher capacity.



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 Revised last: April 24, 2008