UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Television and Video

Notices

Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

Closed Thread
 
Thread Tools
Old 26th Mar 2017, 1:27 pm   #21
Argus25
No Longer a Member
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: Baird v. EMI

Quote:
Originally Posted by Karen O View Post
Also, the flicker is worst in peripheral vision. When you look straight at it, the flicker diminishes quite a bit.
Karen O, you are a very good observer.

It is interesting the research relating to this area. The critical flicker frequency (CFF), which is customarily designated as the boundary where the frequency of the flickering light appears to be fused (continuous light) or flickering, 50% of the time (analogous to many measured physiological variables, like the perception of a sound in audiometric testing) is said, at least, in one of the most well respected textbooks (Adler's Physiology of the Eye) to decrease with fixation away from the fovea or central vision.

For example away from the fovea, at 15 degrees from fixation, their graph(data) shows that for a 2 degree white test field, a CFF value of just under 20Hz and it is about 45Hz with that same stimulus presented at central fixation. (their graph is on page 442 of the 8th Edn).

The implication being, from their experimental data, that peripheral images fuse at a lower CFF.

This is counter your practical experience (and mine) and your observations for a visual target, like a TV screen image, which as you state, definitely flickers more when presented to the peripheral visual fields.

They actually tried to explain this away in Adler's text though (the fact that TV images flicker less with central compared with peripheral view) by stating:

"Differential retinal sensitivities and spacial summations by rod & cone subsystems, as well as receptive field sizes and densities might be responsible...." But this explanation in my view was always a bit wishy-washy and lacking any real substance.

One thing of note though; the CFF is definitely affected by retinal adaptation; the higher the light levels the higher the CFF. So in theory at least, perceived flicker from the TV image should be lower under dimmer room illumination, if the eye has had 15 or 20 minutes to adapt to the lower luminance level. That could be fun to verify.
Argus25 is offline  
Old 27th Mar 2017, 9:18 am   #22
brianc
Rest in Peace
 
Join Date: Jun 2004
Location: Burghfield, Reading, Berkshire, UK,
Posts: 1,055
Default Re: Baird v. EMI

In 1972, I worked for a famous (in TV terms) American company called Ampex. This was a truly international company and we used to exhibit (quad VTRs) at all the international symposia etc. One of the constant things that I heard was that the American personnel were annoyed by the flicker of the 50Hz refresh rate of the PAL/CCIR pictures compared with the 60Hz for the NTSC pictures. However, they practically all said that the flicker became much less objectionable when the offending monitor was not in a peripheral position.
brianc is offline  
Old 28th Mar 2017, 11:22 pm   #23
peter_scott
Dekatron
 
peter_scott's Avatar
 
Join Date: May 2003
Location: Edinburgh, UK.
Posts: 3,273
Default Re: Baird v. EMI

Quote:
Originally Posted by brianc View Post
I have just received from a colleague, an interesting spreadsheet from an issue of the Royal Television Society publication current at the time we are talking about. It makes for interesting reading, especially as it does mention manufacturers using slightly coloured phosphors. Baird, or should I say Bush, does come out extremely well however who designed the sets? Was it Bush engineers or Baird employees because it seems as though they produced some really good pictures.
Mechanically, it's very difficult to judge between the two as they use completely different philosophies in their approach. The EMI school of TV manufacture starts with the cabinet maker and his veneering skills. From what I can see of the Baird school, this interest was dropped very early on as the cabinets simplified quite considerably when getting to the table models (marketing?) whereas the EMI versions (5" and 7") still had the cabinetmakers stamp on it. Anyway, the spreadsheet does make for interesting reading.
There is an interesting report published in the U.S. magazine "Electronics" in Oct 1937 by Lewis & Loughren of the Hazeltine Services Corp. that describes viewing the 14 different Radiolympia sets and some longer term assessment of the test broadcasts from the show.
The only off-screen photo by the reporters was taken with a 2 second exposure and is not worth repeating especially when you read their descriptive text. I suspect their photo was taken from a small screen GEC receiver also photographed in the article.
I have edited the text somewhat but probably the main point that was taken from the British system was the need for good DC restoration that did not exist in the American standards at the time.
If you prefer to see the full text rather than my edited version then see:
http://www.americanradiohistor.....937-10.pdf
Peter
Attached Thumbnails
Click image for larger version

Name:	Electronics1.jpg
Views:	67
Size:	110.9 KB
ID:	140011   Click image for larger version

Name:	Electronics 2.jpg
Views:	62
Size:	110.2 KB
ID:	140012   Click image for larger version

Name:	Electronics 3.jpg
Views:	52
Size:	108.6 KB
ID:	140013   Click image for larger version

Name:	Electronics 4.jpg
Views:	72
Size:	101.2 KB
ID:	140014   Click image for larger version

Name:	Electronics 5.jpg
Views:	49
Size:	95.5 KB
ID:	140015  

peter_scott is offline  
Old 29th Mar 2017, 8:26 am   #24
ukcol
Rest in Peace
 
ukcol's Avatar
 
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
Default Re: Baird v. EMI

Hi Peter,

I couldn't get your link to the full text to work, but this one does.

http://www.americanradiohistory.com/...cs-1937-10.pdf
ukcol is offline  
Old 29th Mar 2017, 8:58 am   #25
bluepilot
Heptode
 
Join Date: Feb 2010
Location: Duffort, Gers, France
Posts: 714
Default Re: Baird v. EMI

Quote:
Originally Posted by Karen O View Post
Also, the flicker is worst in peripheral vision. When you look straight at it, the flicker diminishes quite a bit.
The explanation that I read many years ago it that the brain has a capacity for filtering out annoying things if they are always there. For example if you live next to a busy road, after a while you don't notice the traffic any more. In the case of TV flicker, if the screen is always flickering in the middle of your field of vision then after a while your brain filters out 50Hz flicker at that point. Since you don't generally look at a TV with peripheral vision your brain never learns to filter that out. I suppose you could do a test and watch a TV for several weeks with peripheral vision and see whether you still notice the flicker.
__________________
Stuart

The golden age is always yesterday - Asa Briggs
bluepilot is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 12:28 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.