MP Resolution of 35mm Film?

Started 3 months ago | Discussions thread
Trebor1 Regular Member • Posts: 193
Re: Resolution of 35mm Film & MTF 30?

alanr0 wrote:

grsnovi wrote:

I don't generally read this forum but was wondering (with all of the general interest in the other forums about sensor resolution in MP) if there is a generally accepted number representing the resolution equivalent of a 35mm film frame? B/W? v. color (slide). TIA. Sorry if this has been beaten to death previously - I admit to not attempting a search.

As Erik and Mark have already pointed out, the characteristics of film and digital sensors are very different.

You might find this document by Tim Vitale of interest: It discusses differences between halide particle size and grain size, cloud size in colour emulsions, and has tables comparing the resolutions of different emulsions.

Resolution, measured via Modulation Transfer Function (MTF) at 30% contrast varies from 35 lp/mm for Ektachrome 160 up to 160 lp/mm for T-MAX 100.

Kodak Ektachrome EKT 160 35 lp/mm
Kodak PORTRA 160VC 65 lp/mm
Fuji Velvia RVP 80 lp/mm
Kodak VR100 Color Neg 100 lp/mm
Kodak Plus-X B&W negative 125 lp/mm
Kodak T-MAX 100 B&W negative 160 lp/mm


Kodak T-MAX 100:

From the data sheet for Fuji Velvia RVP100, effective resolution depends on the subject contrast:

Resolution at Chart Contrast 1.6:1 .......................... 80 lines/mm
Resolution at Chart Contrast 1000:1 .........................160 lines/mm (80 lp/mm ?)

If we take the rather simplistic view that we need 2 pixels for each line-pair, then equivalent pixel counts at MTF30 range from 4 - 22 Mp for slide film to 88 Mp for high resolution B&W film.

Useful additional data, regarding true film resolution, at at a specified contast level, can be found if movie film stock (post year 2000) are also considered. In the following link, the film contrast for green, at 80 lp/mm, is 50%, with blue higher and red considerably lower. When the whole camera system (Panavision), including lens, was measured by the ITU, the results were as follows:

Close to limiting resolution at MTF 6% = 106 lp/mm and at the previously considered 80 lp/mm, a contrast of 17% was achieved.

In film scanning there appears to be a semi-arbitrary threshold of 10% MTF, I've always wondered - why not 9% to match the Rayleigh Criterion? The paper suggests that a scanner of up to 11K resolution might be required to capture all the data on film but then the economics start to intrude!

Yesterday, I was looking at the figures for resolution from Super 16 film and the arguments (plus downright lies) from some of the TV broadcast representatives, that were advanced . It was boldly stated back in the day, that Super 16 was only Standard Definition and not capable of HD but this appears to have been more related to deficiencies in the early MPEG2 codecs (complaints of too much moving noise/graininess in static scenes), rather than based on the actual film resolution figure.

This caused a lot of grief for nature photographers in particular, who were effectively forced to abandon this convenient format. Ironically, the early HD video cameras were initially restricted to 1440 horizontal pixels rather than the HD TV standard of 1920 but were allowed anyway.

There were a number of productions shot for the BBC and ITV on Super 16 then broadcast in Standard Definition, as per the (unnecessary) mandated standard but were then later released as HD, on Blu-Ray! These include the first 2 (3?) series of Merlin and also Doc Martin which was latterly repeated on ITV, in 1080i.

Things have moved on and now it is relatively common to scan Super 16mm film at 4K, in order to deliver HD content (But still not permitted for original TV broadcast). This scanning requirement appears sensible because at 80 lp/mm, with a frame length of 11.76 mm (12.52 mm maximum gate), this would need a minimum of 1881 pixels or 2003 pixels at open-gate. Super 35 film is scanned at either 6K or 8K, for UHD/Cinema 4K output.

On a Super 35 mm film camera, an Arriflex 535B for instance, the ground-glass (safe area) when shooting at a 1.85:1 aspect ratio is 21 mm on the long dimension. Scaling to 35 mm full-frame would give a horizontal resolution of 7021 pixels (assuming that the camera lens is equally as good and that the Super 35 scan delivers Cinema 4K, or 4096 pixels. This would equate to 32.87 MP for the 24 x 36 mm format but at a relatively low contrast, because this would be at 97.5 lp/mm.

OTOH, at 50 lp/mm the Super 35 camera plus lens, shown in the first link, delivers 43% contrast, on film and the overall MTF after scanning will still be useful. This would equate to 8.64 MP, on 35 mm full-frame, when using colour film, assuming that there is not a huge difference in the lens performance between the two formats.

What is the low contrast threshold, below which high spatial frequency image detail is not perceptually significant: 20%, 15%?

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