Pixel Magic Systems VPS3800 - Manual (Page 28)

refresh rate. For example, let’s take a 1280 x 720 @ 60Hz timing which has 720 active
lines, a vertical front porch of 3, a vertical sync width of 7 and a vertical back porch of 23.
Total vertical figure becomes 753; multiply this by the vertical refresh rate of 60 and the
answer is 45180. Divide by 1000 for a horizontal scan rate of 45.180 KHz
• Horizontal timing specifications do not affect the horizontal scan rate. They do affect the
pixel clock but this is unlikely to completely prevent a CRT projector from displaying the
resolution. However, models with a low RGB bandwidth may not fully resolve resolutions
that result in a high pixel clock
4.7.1 SWEET SPOT TIMINGS
For CRT projectors people tend to talk about the Sweet Spot for a particular projector. This will
vary considerably between models and it will also be affected by projector condition and setup.
Here are some general guidelines; they will not suit every viewer’s taste and they will not suit
every model of projector but they offer a range to consider:
• 7” tube Electrostatic focus: 480p to 720p
• 8” tube Electrostatic focus: 480p to 720p
• 8” tube Electromagnetic focus: 600p to 960p (1080p some models)
• 9” tube Electromagnetic focus: 800p to 1200p
• The Sweet Spot of any CRT projector is just before the point where individual scan lines
start to overlap. Exceeding this point will produce a soft image which lacks detail
• Electromagnetic focus projectors are capable of higher resolutions before scan line
overlap due to their ability to tightly focus the electron beam, which produces finer, more
defined scan lines
• Spend time trying a few different resolutions; you should find some that suit both you
and your projector
• We all look for different things in our picture; if sharpness is your goal, lower resolutions
may be more suitable. If a smoother more filmic appearance is required, higher
resolutions should be appropriate
4.7.2 48HZ/72HZ CADENCE LOCK
Film is generally shot at 24 frames per second. Since NTSC video is nominally 60Hz vertical
refresh rate and PAL is 50Hz vertical refresh rate, the requirement for 3:2 pulldown (NTSC) and
2:2 pulldown (PAL) is created (you can research this in more detail on the internet). Crystalio II
has the ability to offer 48Hz (24 film frames times two) and 72Hz (24 film frames times three).
Both vertical refresh rates can produce smoother camera pans.
• 48Hz will produce significant image flicker. Flicker tolerance will vary considerably between
individuals; what is quite acceptable for one viewer may be unacceptable for another
• 48Hz flicker will vary between projector models partly due to different phosphor decay
rates of the tubes
• 72Hz will be free of image flicker. 60Hz and above is generally free of flicker for most viewers.
• While you may see flicker at 60Hz on a CRT computer monitor, CRT projectors have
slower phosphor decay rates; this masks image flicker
• Remembering the horizontal scan rate is calculated by vertical lines multiplied by vertical
refresh rate, 72Hz resolution timings can produce unexpectedly high horizontal scan rates
• If you want to define a customized output resolution with 48Hz (or 72Hz) refresh rate,
enter 47.95 (or 71.93), instead of 48.00 (or 72.00), in the Refresh Rate numeric box. 48Hz
(or 72Hz) is used in the industry as shorthand for the actual 48Hz ÷ 1.001 (or 72Hz ÷
1.001) industrial standard refresh rate. For the same reason, while NTSC video is called
60Hz, the actual refresh rate is 59.94Hz
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