OT: Very interesting item re HDV sharpness

riredale wrote on 8/25/2005, 11:01 PM
When I was heavily involved in HDTV technology a decade ago I used to really enjoy talking to a friend in the industry. He began writing a monthly column called "The Masked Engineer" and was always a great source of common-sense video engineering.

I happened across one of his recent musings here tonight. The article talks about what "diffraction limiting" means, and he points out that an HDV camera based on a small 1/3" CCD (read: Sony HDV camcorders) will have real trouble showing full sharpness unless the lens is nearly wide open. In order to use a camera this way he says that neutral density filters should be used all the time.

I never knew that HDV was pushing the edge of the envelope from an optical point of view. Now I do.

Comments

Chienworks wrote on 8/26/2005, 4:44 AM
The problem isn't the optics, it's the size of the CCD. The optics are capable of many thousands of lines of resolution. Good low speed 35mm film is often considered to be able to resolve over 4000 lines. Of course, 35mm film has a diagonal of 43mm as compared to the 6mm of a 1/3" CCD. What that article is pointing out is that due to the way light goes through the small aperature, the wavelengths involved can't form a sharp image in that small a space. Given a larger CCD, a similar optical system would be sharper even at smaller aperatures.
Wes C. Attle wrote on 8/26/2005, 6:12 AM
Sony's new small HDR-HC1 HDV camcorder actually uses CMOS, not CCD. So does anyone know if this changes sharpness at all?
B_JM wrote on 8/26/2005, 8:05 AM
no it will not -- the optical 'hole" would be the same ..

the effect can be seen in physics classes on greater scale with FRAUNHOFER DIFFRACTION experiments ...

the effect in the cameras can be reduced also by limiting the wave lengths (block out longer wavelengths)..

the small sensor and optical hole also limits of course your depth of field ranges .. on the other hand focus is an issue on larger sensors/