Re: CRT article


Hi Dwayne,
The "ideal" filter in high ambient light conditions is a circularly
polarized filter. The ambient light passing through it is circularly
polarized in one direction (CW or CCW, I don't remember which), but when it
reflects (off the glass CRT in this case) the direction of circular
polarization is reversed. So none of it is able to get back through the
filter. The light from the phosphor goes through the filter (and is also
polarized) but since it doesn't reflect before getting to the viewers eye it
is not blocked.
The filter improves the CONTRAST, but any filter (including this one)
reduces the BRIGHTNESS. There are situations where this is an acceptable
compromise. The viewing hood is another good compromise. For analog scopes
the best solution by far was the Micro Channel Plate. But then with the
advent of digital scopes CRTs were quickly replaced with LCDs which had the
additional advantage of color.
Dennis Tillman W7PF

-----Original Message-----
Sent: Tuesday, February 16, 2016 7:13 AM
Subject: [TekScopes] CRT article
I was also intrigued by the notation that most scopes came with a grey
filter. In my very limited experience, I have not seen one remain with the
scope over the years, or tried one. How effective are they? I found some
used ones (incorporated into a light hood) for my 475 on eBay.
Posted by: Dwayne Verhey <tekscopes@...>

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