240-lines on the "Argus"

[Panrock]

A couple of quick snaps taken today of my Argus, working on 240-lines.

Even with the lag of the CV2810 tube, there is some 25Hz flicker visible on this standard.

This Argus uses a 6-inch 'flowerpot' magnifier. It has displaced the picture from the centre due to incorrect camera position... and no, I am not now going to faff around to make it 'perfect'. I readily admit I am a second rater at this game. The photo reveals some hum on the line scan too - I didn't spot this beforehand by eye. Could it be some of the magnetic field from the mains transformer?

Anyway, if you build an Argus to the original spec, in general these are the sort of results to expect.

Steve

[peter_scott]

Hi Steve,

That looks good. What is your source of 240/25?

Peter

[Panrock]

Thanks Peter. A WC-01 World Converter from Darryl. Also useful for the 120-line colour mirror screw.

Steve

PS. A question for the tube experts.... The CV2810 has a short persistence violet phosphor irradiating a long persistence light green phosphor in front. The two add up to a 'sort of' black and white. Should we expect this 'transfer' of picture detail from one to the other to extract a price in maximum definition?

[peter_scott]

Clearly you are still seeing flicker but what do you think about the persistence of the phosphor with moving images? Do you think there would have been any mileage for the 25 Hz frame rate with a longer persistence?

Peter

[Panrock]

I haven't got this currently hooked up to a DVD, but I recall the CV2810/VCRX263 type of tube gives pale green smearing on rapid picture changes. Personally I don't find this objectional. Since it is the violet phosphor that is short persistence, strictly this is 'colour flicker' I must be seeing.

Looking at the table at https://en.wikipedia.org/wiki/Phosphor it could well be that this tube has the P7 phosphor mix.

The P4 white phosphor is of short persistence. I see the P40 is also white but of 'long' persistence. However, I suspect it was hard to create a white phosphor of just the right persistence to counter flicker on 25Hz television without also smearing rapidly changing detail. Instead, we had interlace, and the rest is history.

Steve

[peter_scott]

I would like to see 240/25 displayed on a Cathovisor 15 MW2 to see if it's as bad as it looks on an Emiscope 6/6.

Peter

[Panrock]

Probably worse. A good 15-inch Cathovisor gives a really bright picture (from my memories of the 1980 Science Museum exhibition) and the brighter the picture, the worse the subjective flicker.

This was also brought out with my experience of the Mirror Screw (which also runs at 25Hz), whose flicker noticeably worsened when I improved the brilliance of the 'line of light' (seen reflected in it to make up the picture).

Steve