|he photos below show how different
scanners perform when displaying test patterns. To see enlarged views of any
photo button, just click on the button.
A separate page has photos
showing how these scanners perform when displaying sample images taken
from the Lightspeed "Creation" show. Click
here to see the Creation photos.
ILDA compliant size
||hese photos show the maximum
angle at which a scanner can correctly reproduce the ILDA Test
at a given speed. The larger the angle, the better.
For the three ILDA 30K-tuned
scanners, there are clear performance differences. The Cambridge 6800 can
correctly scan the ILDA Test Pattern at a much larger angle than the GS
G-120 with TurboTrack 2 scanner amps. In turn, the GS/TurboTrack
combination can scan at a larger angle than the Catweazle.
For faster scanners, the
Cambridge 6800 using Pangolin TrueK 50 and the Cambridge 6210 are roughly
equal in performance.
Scanner amps used with Cambridge 6800 and 6210 scanners must
"power limit" when the
scanner is in danger of overheating.
There are three ways of activating power limiting
to avoid overstressing the scanner:
· In current Cambridge 6800 amps and in the
Pangolin TrueK 50 modifications, if part of the image is too stressful, then the amp
power limits the entire image by reducing signal strength. You see the
image shrink in size a second or two after the image is first displayed.
· In the Cambridge 6210 amps, size is also reduced,
but only for the part of the image which is too stressful. You see parts
of the image shrink in size a second or two after the image is first
· In a few other Cambridge-compatible amps, the scanner
performance is temporarily reduced. The image stays the same size, but
corners and other details become more rounded.
||hese photos show the ILDA Test
Pattern at a 30 degree optical scan angle. In all cases, the
circle-in-the-square test will not work -- the circle will be well inside
the square. This means that none of these scanners correctly shows the
ILDA Test Pattern at 30 degrees. However, these photos do show how well
the scanners can show other aspects of the test pattern.
The Catweazle exhibits slight
rounding, compared with the two other 30K-tuned scanners.
Both of the fast scanners have
trouble with the image. It cannot be shown at 30 degrees without
overheating the scanner. As a result, the TrueK 50 amp power limits all of
the X-axis scanner's signal. This is why the TrueK 50 pattern is narrower.
The Cambridge 6210 takes a different approach. It power limits only part
of the X-axis scanner's signals. This is why the "X" and
"ILDA" parts of the test pattern are reduced towards the center
-- these are the parts that are most troublesome.
ringing and overshoot
About square wave tests
Square waves are important to test how fast a
scanner can move from point to point. The square wave shown here is a
This capability is important for images where the
scanner must jump large distances as fast as possible. Examples are
abstracts, rasters, and star fields.
It is possible to eliminate overshoot by adding
steps to large jumps, essentially converting them to a series of small
jumps. But this works by slowing down the scanner, which can defeat the
purpose of jumping far and fast.
The Pangolin TrueK 50 and Cambridge 6210 both speed up small steps, while leaving large
steps essentially unchanged.
A key question is
whether the small-step speedup balances out the extra steps added to slow
down large jumps.
||hese final pictures show a
wave test pattern at around 30 degrees. The scanner is jumping as fast as
possible, over a very large angle. Ideally, you should see a dot at each
corner. There should be little or no overshoot.
This is achieved by all the
scanner tunings here, except for the Cambridge 6210. It exhibits overshoot
beginning at 22 degrees. By 30 degrees the overshoot is severe -- about 3 degrees,
or 10%, in the X axis.
This page last updated:
Tuesday, June 19, 2007 08:54:17 PM