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Sharpness of film


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#1 Sturla

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Posted 21 February 2010 - 02:33 AM

What does it really mean when Kodak says that: "KODAK VISION2 100T Color Negative Film 5212 / 7212 is the sharpest color negative motion picture film". Sharp - How?
They can't just be talking about the fine grain, I'm guessing that the 5201 50D has finer grain? And fine grain doesn't necessarily mean sharp, no? What kind of sharpness are we talking about here? And can one really tell the difference in "sharpness" from the 5217 200T?
Any comments?

Thanks

Sturla

Edited by Sturla Brandth Groevlen, 21 February 2010 - 02:37 AM.

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#2 John Sprung

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Posted 21 February 2010 - 03:49 AM

The way they determine sharpness is by shooting a test pattern and measuring density on the film to create a graph of the Modulation Transfer Function, or MTF.

The test pattern consists of alternating black and white lines, ranging from wide to narrow. On the wide end, you see clear black and white lines, 100% modulation transfer. On the narrow end, the lines disappear into gray, 0% modulation transfer. I don't know off hand exactly how they turn the in-between density readings into percentages, but they come up with a graph that starts out horizontal at 100%, then curves downward until it hits 0. The narrower the lines where the curve heads south, the sharper the film.

A similar thing is done in video, where for lengthy historical reasons, the pattern of fat to skinny lines is called multiburst.




-- J.S.
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#3 Brian Pritchard

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Posted 21 February 2010 - 04:29 AM

The way they determine sharpness is by shooting a test pattern and measuring density on the film to create a graph of the Modulation Transfer Function, or MTF.

The test pattern consists of alternating black and white lines, ranging from wide to narrow. On the wide end, you see clear black and white lines, 100% modulation transfer. On the narrow end, the lines disappear into gray, 0% modulation transfer. I don't know off hand exactly how they turn the in-between density readings into percentages, but they come up with a graph that starts out horizontal at 100%, then curves downward until it hits 0. The narrower the lines where the curve heads south, the sharper the film.

A similar thing is done in video, where for lengthy historical reasons, the pattern of fat to skinny lines is called multiburst.




-- J.S.

The pattern is actually sinusoidal pattern of increasing frequency. Some films produce a result that has MTF of low frequencies that is greater than 100% this can be can be caused by developer edge effects.

You can find a full explanation here http://www.normankor...ials/MTF1A.html

MTF is also used to measure lenses and the results can be multiplied to give the combined result for lens and film and so on.


Brian
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#4 Simon Wyss

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Posted 21 February 2010 - 04:33 AM

Rubbish. The term sharpness belongs to optics, nothing else. Photographic layers are discussed under the aspect of resolution, resolving power. There is nothing sharp or unsharp about a film. A lens is focused, the more or less clear image is called sharp or unsharp. A shame that Kodak folks jumble words like laymen.
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#5 Dominic Case

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Posted 21 February 2010 - 06:51 AM

Sinon are you suggesting that the properties of the film emulsion have nothing to do with the degree to which the image is resolved on the film? (Whether you call it MTF or sharpness or resolution, or even acutance).

If you are, then, respectfully, that's also rubbish. Image spread, halation, developer edge effects, and granularity all play a part in this, and are all effects of the emulsion, not the lens.
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#6 John Sprung

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Posted 21 February 2010 - 03:05 PM

The pattern is actually sinusoidal pattern of increasing frequency.


Thanks for the correction, Brian. That's a very useful site, well worth bookmarking.



-- J.S.
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#7 Brian Pritchard

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Posted 21 February 2010 - 04:08 PM

Thanks for the correction, Brian. That's a very useful site, well worth bookmarking.



-- J.S.

You will find all the information you want to know about film sharpness in the book 'Fundamentals of Photographic Theory' by T H James and George Higgins of the Eastman Kodak Company. Chapter 13 covers 'Structure of the Developed Image', page 280 onward has a section on Turbidity and Sharpness. Basically sharpness is defined as the density gradient across an exposed knife edge. In theory the image should go from black to white, how quickly the change takes place defines sharpness. It is measured by using a micro densitometer across the image.
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#8 Charles MacDonald

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Posted 21 February 2010 - 08:32 PM

When ever this topic omes up, I aways recomend "from Dry plates to Ekatachome film" by Mees. He explains the difference between sharpness and accuance as well as can be. And Yes the MTF approch does border on the way that video is rated and is one of those "grand unifying theories" Just like amplification curves for transistors and vacume tubes look JUST LIKE the curves for film.
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#9 Dominic Case

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Posted 22 February 2010 - 07:46 AM

Just like amplification curves for transistors and vacume tubes look JUST LIKE the curves for film.

I've come across descriptions of the photographic development process as being closely analogous to the behaviour of an amplifier, in particular vacuum tubes or valves. They are very similar.

Interesting, but not much use as a teaching aid, as not many people understand an amplifier at the level of volts and amps, (I struggle with it myself, electronics was a new subject when I did Physics!), and of those, few want to understand development at a molecular reaction level.
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#10 John Sprung

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Posted 23 February 2010 - 02:37 AM

Graphs is graphs. It's all math. There are lotsa things that vary sorta linearly over some limited range, and crap out to constants at both ends. It's a very common pattern.




-- J.S.
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#11 Simon Wyss

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Posted 23 February 2010 - 03:54 AM

No, Dominic, the initial question is

What does it really mean when Kodak says that: "KODAK VISION2 100T Color Negative Film 5212 / 7212 is the sharpest color negative motion picture film".

That is crap. Do tell me what a sharp film is besides sex. The terms have come up, acutance, mathematics, but there is no discussion of such things as long as the picture is out of focus. Sharpness has to do with lenses, focus.
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#12 andy oliver

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Posted 23 February 2010 - 02:10 PM

Rubbish. The term sharpness belongs to optics, nothing else. Photographic layers are discussed under the aspect of resolution, resolving power. There is nothing sharp or unsharp about a film. A lens is focused, the more or less clear image is called sharp or unsharp. A shame that Kodak folks jumble words like laymen.


So if your saying the sharpness of a film is down to the optics only. Please tell me why my 16mm kodachrome 25 footage is sharper with more detail than my kodak 16mm 100D footage filmed using the same lens/camera?? Please explain to me why my super 8 k40 is sharper than kodak 64t using the same 10mm lens on my leicina camera. :huh:
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#13 Scott Bryant

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Posted 23 February 2010 - 04:37 PM

So if your saying the sharpness of a film is down to the optics only. Please tell me why my 16mm kodachrome 25 footage is sharper with more detail than my kodak 16mm 100D footage filmed using the same lens/camera??


Wouldn't this be because the 25 asa has much finer grain than the 100D?

Edited by Scott Bryant, 23 February 2010 - 04:39 PM.

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#14 andy oliver

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Posted 23 February 2010 - 06:11 PM

Wouldn't this be because the 25 asa has much finer grain than the 100D?


and greater resolving power!
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#15 Dominic Case

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Posted 23 February 2010 - 08:24 PM

but there is no discussion of such things as long as the picture is out of focus

I can't follow your thinking here, Simon. Yes, of course the performance of the lens is a part of the final resolution of the image, but so are many other factors, including the ability of the emulsion to record more or less precisely the image that fall on it.

The original question asked whether there was anything other than graininess in an emulsion that determined its inherent sharpness. Clearly the answer is yes there is.

There are a number of measures: acutance, MTF, resolution, acuity, granularity, etc. They all measure different but inter-related properties. A photographic scientist needs to use them very precisely to be sure of clarity. It is possible for one emulsion to have a higher granularity and a higher acutance or sharpness than another.

It is indeed a shame that Kodak (they aren't alone) do tend to "jumble words like laymen", (there is another thread on this site that has mentioned just that) but in their marketing literature , (which is probably what was originally referred to in this thread,) they aren't writing scientific papers, they are addressing the non-scientist. They could have said "KODAK VISION2 100T Color Negative Film 5212 / 7212 is the color negative motion picture film that has the highest acutance"; or "KODAK VISION2 100T Color Negative Film 5212 / 7212 has the best MTF of all color negative motion picture films".

But it doesn't have the same "snap", does it.

BTW, apart from James & Higgs, and Mees (both cited above), I rely on Walls & Attridge, Basic Photo Science.
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#16 Brian Pritchard

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Posted 24 February 2010 - 05:49 AM

No, Dominic, the initial question is


That is crap. Do tell me what a sharp film is besides sex. The terms have come up, acutance, mathematics, but there is no discussion of such things as long as the picture is out of focus. Sharpness has to do with lenses, focus.

As I mentioned in my previous post, sharpness is defined and calculated by exposing a knife edge on the film and then measuring the black to white transition. If the film is 'sharp' then the transition will be 'sharp' if the film is less 'sharp' the the transition will be less 'sharp'. This has nothing to do with lenses or optics and is purely a function of the film emulsion along with all the physical factors of the film's construction and chemical effects of the processing.
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#17 Simon Wyss

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Posted 25 February 2010 - 03:39 AM

Please excuse everyone, I'm after words, alright? Language. Terms.

Who says, a film is sharp?

No professional does. We say the picture is sharp or unsharp. Friends, we are far away from measurements, graphs and calculation. It's Kodak who publish rubbish and a colleague who wants to hear our opinion. Unfortunately, we have become accustomed to that kind of ad texts. Rochester, try not to babble!
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#18 Brian Pritchard

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Posted 25 February 2010 - 06:11 AM

Please excuse everyone, I'm after words, alright? Language. Terms.

Who says, a film is sharp?

No professional does. We say the picture is sharp or unsharp. Friends, we are far away from measurements, graphs and calculation. It's Kodak who publish rubbish and a colleague who wants to hear our opinion. Unfortunately, we have become accustomed to that kind of ad texts. Rochester, try not to babble!


The term 'Sharpness' is a recognised, scientific term used by Film Technologists throughout the world. It is not something invented by Kodak to sell films.

There is an excellent article that can be downloaded from the Internet Archive by Higgins and Jones titled 'The Nature and Evaluation of the Sharpness of Photographic Images' It is in the Journal of the SMPTE Volume 58 April 1952 PP277-290.

This is the Ilford Manual of Photography definition of Sharpness:

Sharpness
The appearance of the edges of well-resolved detail in a photograph
is termed sharpness. When a film is exposed while partially shielded
by a knife-edge, the image after development does not change
abruptly at the knife-edge from a high density to clear film. Instead,
there is a measurable density gradient across the boundary. One
reason for this is the turbidity of the emulsion, which results in the
diffusion of light beyond the knife-edge. Adjacency effects in develop-
ment (page 431) may also affect the image at the boundary. The
quantities acutance and contour sharpness have been defined in the
U.S.A. and Germany respectively as expressions of sharpness in
terms of this density gradient.

Brian
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#19 Leo Anthony Vale

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Posted 25 February 2010 - 04:56 PM

Wouldn't this be because the 25 asa has much finer grain than the 100D?



Yet the 100T EKneg is sharper than the 50D EKneg.

As for the kodachrome, a thinner emulsion is part of the equation.
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