I must have missed that post. I just dropped Gary a note asking to buy one.
Not sure I understand what to do with it, but I'll ask, I guess, when I get
it.
Tom
> Several weeks ago Gary Reese offered one of his test slides to the list
> for two bucks. I ordered one of these slides and Gary suggested that I
> report my results back to the list. Perhaps others will be inspired to
> do the same. (Come on, Tom, we need to know how that 4000 dpi Xerox
> actually performs).
>
> I case you're not familiar with Gary's test setup: The test shot is a
> US Geological Survey map of the Grand Canyon. National Bureau of
> Standards resolution charts are taped to the center and corners of the
> map. The resolution charts consist of multiple, progressivly smaller
> and smaller targets with both horiziontal and vertical line patterns.
> The targets are marked with numbers which must then be multiplied by the
> magnification factor (41) to arrive at the actual resolution on the film
> in line pairs per millimeter (lppm). The charts (in the range relevant
> to this discussion) are labeled 1.0, 1.1, 1.25, 1.4, 1.6, 1.8, 2.0,
> 2.2. This particular test slide is taken with a Zuiko 50mm f/1.4 at
> f/5.6 and shows both center AND corner resolution of 90 lppm. This is
> determined by finding the smallest target where one can count the lines
> (even though they may not be 100 leanly resolved along their entire
> length). With suitable microscope magnification this is found to be the
> chart labeled 2.2. Multiplying by 41 yields 90 lppm.
>
> The first thing I did after receiving the slide was to attempt to verify
> the 90 lppm resolution of the test slide. I dragged out an old student
> microscope I had bought in a garage sale about 15 years ago which had
> been hiding in the closet ever since. I first reported to Gary that the
> scope was only able to show me 1.8 (74 lppm) but I was using too strict
> a standard expecting the lines to be 100% resolved along their entire
> length. I also realized that the scope was dreadfully dirty and the
> illuminator didn't work since the battery box was full of corrosion.
> After disassembling and thorougly cleaning the scope and battery box,
> using the bright light of the illuminator and applying the new standard
> at 120X magnification I was able to confirm the 2.2 (90 lppm) resolution
> of the test slide.
>
> Next, on to the Acer Scanwit. The Scanwit was tested using both
> MiraFoto and Hamrick's VueScan. I had never scanned any slides with
> MiraFoto and the first surprise was the discovery that MiraFoto2 does
> not contain any film profile information for color slide films. I never
> did ask Gary what film he used but VueScan produced a pleasing result
> using one of the Ektachrome profiles. MiraFoto2 did a lousy job on the
> color rendition using its generic color slide profile. The predominant
> light green of the survey map was rendered as a greenish straw color.
> Perhaps MiraFoto's web site has more film profile information available
> but I haven't checked that yet. Maybe one of you Scanwit using list
> members knows the answer. But this is a resolution discussion and I
> couldn't see any resolution differences between MiraFoto and VueScan.
> Using VueScan's ability to do multiple passes actually muddied the
> resolution slightly at 5 passes.
>
> The next surprise was that the Scanwit does not exhibit the same
> resolution both horizontally and vertically. The horizontal resolution
> is 1.6 (66 lppm) but the vertical resolution is fully two steps down at
> 1.25 (51 lppm). At this level one can count the lines but getting the
> line fully separated along 80-900f its length requires backing down
> one grade and 100 lean separation requires backing down two grades.
> Post-processing the image via sharpening does improve it (by making the
> lines easier to see) but the improvement is not sufficient to claim a
> change in resolution to the next highest grade chart (eg: from 1.6 to
> 1.8). The same is true of using higher color resolution. I did the
> first scans at 24 bit and another test scan at 36 bit. I didn't expect
> any difference at all since I didn't think the monitor (set at 32 bit
> color) was capable of showing a difference. In fact, there is a slight
> improvement in visibility of the lines independent of sharpening.
> However, combining both the higher color resolution and sharpening makes
> a better image but still doesn't get one over the hump to the next
> grade. The net result is that I'm going to stay at 24 bit color. There
> isn't enough improvement in the image to justify doubling the file size
> (a 36 bit scan has to be saved as a 48 bit image).
>
> So, what's the actual resolution of the Scanwit on real world
> photographs instead of horizontal and vertical test charts? I assume
> that its performance is somewhere in between the horizontal and vertical
> results... say, 55-60 lppm.
>
> The next surprise was when I hauled out the old Kodak Carousel with its
> 102mm f/2.8 Ektanar C. This test needs to be redone under dark
> conditions and at greater magnification. However, done in subdued
> daylight and projecting only about 10 feet the best I could see was
> about 1.1 (45 lppm). This was in the center only but was cleanly
> resolved lines. Using the same standard as with the Scanwit I guess
> might take the results to the next grade of 1.25 (51 lppm) and, of
> course, the corner results were worse. So, the biggest surprise of all
> was finding that the Scanwit appears to outdo my slide projector.
> However, Gary tells me that his 102mm f/2.8 Ektanar C does 1.8 (74 lppm)
> in the center and 1.4 (57 lppm) at the corner. I'll have to come back
> to this one later. Just haven't had a chance to do any more yet.
>
> So, there you have it. Some very interesting results from a $2
> investment.
>
> Your turn, Tom. What does the 4000 dpi Xerox do?
>
> Chuck Norcutt
> Woburn, Massachusetts, USA
>
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|