27
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
4.7.3 BASIC CALIBRATION
See
Section
4.6.3
for help with picture calibration. Most of the basic steps for pixel-based displays apply except
for CRT projectors. They may have more control over color balance, which generally involves the ability to
calibrate and store color balance per projector source memory. Setting contrast or peak white level is more
difficult with a CRT projector as the blue tube will normally be close to beam current-limiting at full IRE100
output over the whole screen. This can result in a color balance shift to red at very high output levels and also
prevent the standard test disc methods of setting contrast from working 100% correctly. Some contrast level
setting procedures used on test DVDs rely on the projector’s power supply voltage sagging under the load
imposed. However, the majority of CRT projectors originate as over-specifed commercial units, where the power
supply is unlikely to lower its output under high load conditions. Start with the projector’s contrast setting the
same as you have previously used*, then make adjustments to obtain correct peak white levels on a variety of
source material.
Correct
might be defined as
realistic looking
or
comfortable to view
.
* Some projectors have a very high manufacturer’s default contrast setting (ss high as 80%). Depending on projector model, tube condition and
screen gain a contrast setting of 50-60% is more likely to produce realistic levels. As a side benefit, useable tube life will be significantly extended.
