2/3 inch, 35 mm CCD and sharpness...

[Krstic Zoran]

I was reading about MTF response and CCD's resolving power.But after all, I did not make some precise conclusion about it.

 

Story begins:

 

Lenses have response limit at 200 lp/mm.Ok.Every lens have itself MTF response.Example:at 10lp/mm MTF response is ~90%,at 100 lp/mm is ~70%,etc.We saw that MTF response is falling down for higher spatial frequencies.

 

CCD has limited spatial resolution at some value.For 2/3 inch CCD, 100 lp/mm is limiting value.Now if we include consideration about lens and CCD, conclusion is that all spatial frequencies above 100 lp/mm could not be resolved.And if lens have MTF response ~70% at 100lp/mm it means that MTF response above 100 lp/mm is cutted.

 

But,what happened with 35 mm CCD in Sony F35? Resolution of it is same, 1920 px (5760px, but three for every primary;1920 effective pixels), but CCD's width is 24 mm and spatial resolution is limited at 40 lp/mm. It is same story, MTF response above 40 lp/mm is cutted.

 

If my consideration is right, resolving power of 2/3 inch CCD is better than with 35mm in F35.What it exactly mean?Does F23 give picture with better sharpness (measurable resolution) than F35?

Edited March 24, 2009 by Krstic Zoran

[John Sprung]

The 2/3" chip is 9.6 mm wide. 9.6 x 100 = 960 line pairs across the whole picture. For F35, it's 24 x 40 = 960 line pairs across the picture. The Nyquist limit for 1920 photosites across the chip, in both cases, is 1920/2 = 960. We don't need any more line pairs per millimeter in either case. In fact, we'd be in trouble if we had them.

 

Where we do see a difference is in diffraction. 2/3" is diffraction limited at stops deeper than f/8, 35 is diffraction limited at stops deeper than f/22.

 

 

 

 

 

 

-- J.S.

[David Mullen ASC]

But,what happened with 35 mm CCD in Sony F35? Resolution of it is same, 1920 px (5760px, but three for every primary;1920 effective pixels), but CCD's width is 24 mm and spatial resolution is limited at 40 lp/mm. It is same story, MTF response above 40 lp/mm is cutted.

 

If my consideration is right, resolving power of 2/3 inch CCD is better than with 35mm in F35.What it exactly mean?Does F23 give picture with better sharpness (measurable resolution) than F35?

 

No, I think what it means is that you only need a lens with a 40 lp/mm on a 35mm sensor to get the same level of detail as a lens with a 100 lp/mm on a 2/3" sensor. Basically the larger the capture area, the lower the MTF of the lens can be to capture the same level of sharpness -- you need less lines per mm because you have more mm's total...

[John Sprung]

Basically the larger the capture area, the lower the MTF of the lens can be to capture the same level of sharpness -- you need less lines per mm because you have more mm's total...

 

Yup, we're saying the exact same thing. Just with or without arithmetic. ;-)

 

 

 

-- J.S.

[Michael Collier]

John- could you explain the diffraction limitation between 2/3 and 35mm? I don't generally shoot deeper than an F8 on any format, but I am intrigued...what do you mean by diffraction limitation?

[John Sprung]

... I am intrigued...what do you mean by diffraction limitation?

 

If this link works, here's the basic stuff on diffraction:

 

http://www.cinematography.com/index.php?sh...mp;#entry278263

 

 

-- J.S.

[Michael Collier]

Excellent link. I knew that lenses had a sweet spot and that at too deep of a stop they will suffer resolution loss, but didn't know the reason or math behind it. I thought it had more to do with lens design and how the aperture is built and positioned rather than theoretical optics science. Very interesting seeing how wavelength affects airy disks size.

 

Double checking the math you have done, this only relates to digital 1080P imagers of 2/3 and 35mm correct? In film it would be the circle of confusion that would be the limit, not the nyquist limit? And an digital imager of the same size, but with a higher resolution, and ability to reproduce finer detail without ailising would have to adjust the math to find the correct upper limit for either film or a higher resolution chip of a similar size, correct?

 

Good info, thanks for that John.

Edited March 25, 2009 by Michael Collier