Because of SD being such a low resolution, besides talking to your eye doctor you have to shrink the image back to what it was back in those days. Some folk have forgotten this issue but it's still here.
I have Samsung ES6200 40 Inches. My viewing distance is > 2 times x screen size ( 40 Inches = 2 * 40 ) ie viewing distance is between 80 - 100 inches but getting eye strain / headache. I too observed that when I see the HD with same settings for HD channels, I am not getting eye strain and headache. But when I view the same for SD channles, I am getting eye strain and headache. My settings are as follows
Viewing Distance - between 80 - 100 inches
Contrast - 100
Sharpness - 100 ( Blurred in SD if I go too near..Awesome in HD )
Colour - 45
Brightness - 65
Picture Mode - Standard
Resolution - 1080i
But for viewing HD channels, I don't have any eye strain / headache even if I set to contrast and sharpness as 100 ( Clarity is awesome ). I don't even get a single bit of eye strain / headache. But when I watch the same for SD channels, I am getting the headache / eye strain. I need proper settings and viewing angle for SD channels in order to avoid eye strain / headache.
Samsung Default settings ( below ) for Picture ( Awesome clarity but getting eye strain / headache ). Eyestrain is avoided if I view at 120 inches or more but still getting a slight headache.
Picture - Dynamic
Backlit - 20 (20/20)
Contrast - 100
Brightness - 45
Sharpness - 55
Advanced Picture Mode - Cool
Please do tell me the viewing angle and if my viewing angle is correct, do I need to change the settings ? If so what will be the best HDTV settings for SD and HD channels ?