Early in 1998 the idea surfaced on APML to run a test of the various film scanners used for astrophotography. After some discussion it was decided to send around a set of negatives and a resolution target for the various volunteers to scan. Instructions were given to use the scanner and its included software to make the scans. It was not permitted to use Photoshop to enhance the scans as we wanted a comparison of the various scanner/software packages and not a comparison of the volunteers' skills with Photoshop. Results from each scanner are presented as is with no analysis or comments. Below is a summary of what was scanned and the purpose of each scan. Following that are links to pages with the results.
The main point of this test was to verify that the resolution of the scanner was not less than that claimed by the manufacturer. The target was scanned at the maximum resolution of the scanner in B&W. The target is arranged by Element and Group. There are six Groups in each Element. The smallest set of horizontal and vertical lines that are resolved give the approximate resolution of the scanner in DPI (Dots per Inch). Below is a table showing the Group/Element and corresponding DPI. We also performed a color scan of the target to see how much color fringing was visible and if that degraded the resolution. You'll probably need to download that image and view it under high zoom to see the color fringing.
| Group | Element | DPI | Group | Element | DPI |
|---|---|---|---|---|---|
| 5 | 1 | 1626 | 6 | 1 | 3271 |
| 5 | 2 | 1824 | 6 | 2 | 3684 |
| 5 | 3 | 2047 | 6 | 3 | 4094 |
| 5 | 4 | 2301 | 6 | 4 | 4597 |
| 5 | 5 | 2585 | 6 | 5 | 5131 |
| 5 | 6 | 2920 | 6 | 6 | 5791 |
A test negative from a 1 hour color lab was scanned to match as closely as possible to a print made from the negative at the same lab. This was a reference test to see how well the scanners could match the print.
This negative was chosen to test the dynamic range of the scanner. The negative ranged from almost clear to nearly black. This is not a quantitative test. We simply wanted to see how well the scanners could handle a negative with a wide dynamic range.
This photo, taken on Kodak PPF, is a typical low contrast astro-negative. The purpose of this test was to see how good of a scan could be obtained by the scanner/software package on a negative typical of what astrophotographers get. A guideline was given for adjusting the scan to reduce operator interpretation.
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