Moderators: Dave Moll, Andrew Davie, Steve Anderson
Steve Anderson wrote:Maybe I have this wrong...but here goes...
You're having problems focussing the image from the rotating 'block', correct?
But as I think I understand it the block in time will actually be covered in mirrors, correct again?
If so you'l be focussing on the reflected image which surely be far more distant, I would have thought that this slight difference in sensor-mirror-subject distance as the mirror block rotates would have little impact on the focus.
But again I could have this entirely wrong.
Steve A.
Steve Anderson wrote:I have a small amount of time to myself over the long weekend here (Kings birthday). So I thought I would at least have a look at a good old-fashioned CRT display for SSTV, as per 1950-something.
So I dug out one of the 3" CRTs I have had for the best part of a decade and mused if it would fit into the well and truly beat-up DG7-32 chassis. It will with minor 'adjustments', the tube is about 10mm shorter.
It's a DP7-5 which has a very similar two-stage long-persistance phosphor to the better known US P7 phosphor.
Having bought these (and other) tubes in 2005-6, it's about time I did something with them! But I don't have that much free time at the moment, we'll see...
Steve A.
Steve Anderson wrote:For a flying spot scanner a short persistance tube is better, for SSTV most used a standard P1 CRT which for SSTV is just short enough, but could be improved. If you were to do the same for NBTV a CRT with a P5, P15 or in European speak a DB-something phosphor would be required. e.g. DB7-5, DB13-14.
Most of these short persistance phosphors have a their major output in the blue part of the spectrum which is an ideal match to a PMT, say a 931A which is primarily blue sensitive.
But I don't have any short-persistance tubes as I haven't planned to make a flying spot scanner, though quite simple to do and no modulation of the grid/cathode circuit required.
At a push you could use a standard oscilloscope for SSTV, preferably one without an internal graticule.
Steve A.
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