Screen Filters for Argus

[Argus25]

I have been experimenting with tinted screen filters for my Argus and just updated my article on these. Scroll to page 35 of the article to see the filters.

I wasn't certain about this idea before I tried it, but it has surprised me and a screen filter definitely improves the contrast and viewing the screen in room light:

http://worldphaco.com/uploads/ARGUS.pdf

[dominicbeesley]

Good work - I'll have to print that out and read it through. I was playing with my own ACR97 screen last night and I can't get results anything like that sharp....I suspect I need to get hold of a better tube as mine is suspiciously rattly and quite blurred.

As to filters, they really do work wonders I'm surprised more set makers didn't include them. I've added smoked (grey/black) acrylic to several projects (CRT, LED matrix) and even though they reduce the brightness noticeably they improve the perceived contrast more. The eye is far more sensitive to the darker shades and any background light either from reflections, the unlit colour of the phosphor or from secondary emission in the CRT make a picture look washed out. The filter tones tames these more than the brighter parts of the picture (it doesn't but it does by perception as our eyes have a non-linear response to light) leading to much improved perceived contrast.

If I'm using my BBC micro I sometimes lean a large sheet of smoked acrylic in front of the sony monitor to give my eyes a rest as I can turn the brightness down a long way and reduce perceived flicker and have sharper text).

D

[Argus25]

Thanks D. I had to buy acrylic from all over the place (world) to find that light leaf green material that suited the VCR97 spectral phosphor output, it came from the UK actually from the ebay seller dropswell_uk and the label on it says ZHONGDA CAST ACRYLIC, its 3mm thick. All of the other 3mm thick transparent green material I could find was far too dark. 2mm is more difficult to get.

[dominicbeesley]

It may be worth trying some black/gray as making the filter colour dissimilar to the phosphor may also increase contrast? Though I've not tried - it may just make the green look even more green!

If I get anything to the stage of actually making a cabinet I was thinking of trying dark red/burgundy or purple (like the VT4). Like you say getting hold of acrylic in small quantities can be tricky, a friendly sign maker might be worth a try for offcuts? I used to have a set of huge binders containing acrylic samples that I found in a skip when I was younger, I have no idea where they ended up!

D

[Panrock]

Gratifying results there Hugo (Argus25), and I do like the acrylic enclosure too! Your productions are a feast for the eyes.

You'll already have seen my own arrangement but for others who may not, I'm showing it here. This also happens to increase subjective contrast. It is a 6-inch bench magnifier lens mounted in a plastic flowerpot. Since I am using a CV2810 tube (giving the equivalent of a black-and-white picture) the green filter method is not appropriate.

Steve

[Argus25]

Steve,
Does the magnifying lens limit the viewing angle much in practice...do you have to be directly in a line in front of it for a good view ?

[Panrock]

I've got the lens distance set so that the round tube just nicely fits the (round) magnified view at most viewing distances, using both eyes. It doesn't feel at all critical, though if you veer off to the side too much, the edge of the flowerpot gently starts to obstruct the view.

Steve

[Radio Wrangler]

Someone at work had been looking into shaded filters for a display to get it to resemble the colouring of a different unit and he'd left behind a set of samples from Lee Filters. It was like one of those car colour matching sets from ICI , a hundred or so shades on samples about 70mmx30mm punched in the corner and held as a set by a rod. Photographic grade.

Anyone experimenting could always contact Lee. They have a very good reputation in photographic circles.

David

[Argus25]

Thanks for that information Radio Wrangler & Steve.

(Also when I added the images of the Argus in its cabinet I edited them into an older version of the Argus article by mistake. I have corrected that now, so the bit about the filters and case are now on page 37, not 35 of the article http://worldphaco.com/uploads/ARGUS.pdf )

Hugo.

[Karen O]

This is interesting because one or two members of the NBTVA have used colour filters to reduce subjective flicker on Baird 240 line receivers (home built ones, that is).

IIRC, red filters had the best flicker reducing effects while blue had the least.

[Panrock]

Originally Posted by Karen O

This is interesting because one or two members of the NBTVA have used colour filters to reduce subjective flicker on Baird 240 line receivers (home built ones, that is).

The CV2810 tube has a green phosphor above a violet one (giving a sort of black-and-white). My Argus displays 240-lines (among other standards) and the green phosphor is already laggy, so this soaks up the flicker. The 'subdued' (dim) picture helps too!

Steve

[dseymo1]

Reflections really are attenuated by a filter, simply because, while transmitted light from the tube passes through the filter once, reflected external light does so twice.