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7201 vs k25 just curious greater resolving power


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#1 A.Oliver

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Posted 19 October 2005 - 12:30 PM

Which stock will have the greater resolving power, k25 or the new 7201. Here is the mtf curve for k25 http://www.kodak.com...rves/7267MT.pdf

i ask the question as i am not 100% sure on how you read mtf curves.
Andy
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#2 John Pytlak RIP

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Posted 19 October 2005 - 03:03 PM

Which stock will have the greater resolving power, k25 or the new 7201. Here is the mtf curve for k25 http://www.kodak.com...rves/7267MT.pdf

i ask the question as i am not 100% sure on how you read mtf curves.
Andy


Kodak used to only measure MTF for a "visual" response, which integrated the sharpness measurement of the red, green, and blue. So that is the data curve you have for the old K25.

Today, separate MTF curves are published red, green, and blue response. So you can't directly compare the data.

The new 7201 is likely sharper than K25.
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#3 Laurent Andrieux

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Posted 19 October 2005 - 04:35 PM

here's the same curve for the 52/7201 :

http://www.kodak.com...ve/5201_mtf.gif

more technical datas about the new 50D neg film :

http://www.kodak.com....4.4&lc=en#mtf:

The 67 looks a bit better, from the FTM curves, but it's not so easy to compare, since the curve of the 01 is more precise (3 curves, for each of the 3 layers) while the 67's one is a one line only curve (a mean ?)...

Anyway, it's very difficult to compare them...

- 67 is a reversal, discontinued, kodachrome process film, 25 ISO rating ;
- 01 is a negative, (ECN2), recent, 50 ISO rating.

Now, for what is about FTM :

You certainly figure out that the more contrast an object is, the better definition you'll get on the image. (it's easier to read a newspaper than thin scares on a face)

Correlativly, the better the system (lens + film) is, the better it will respect the object's contrast.

The response in modulation, as a shortcut, can be understood as the respect in the object's contrast the system will give. The spatial frequency can be regarded as the fineness of an object.

Let's take an exemple : if you shoot hair, you'll have very fine details, therefore a important spatial frequency. See it as the number of alternative black and white lines. The thiner they are, the higher the spatial frequency is.

Now, you easily figure out that if these lines are black and white, as long as they are not too thin (low spatial frequency, the title on the front page of a newspaper), the system will correctly reproduce the contrast beetween black and white lines, but if the frequency gets high, they might look like a grey modulation, the white being darkened and the blacks being over lit, because of a loss in definition.

The modulation response being the respect of the object's contrast - you can even see it as the image's contrast itself - it will lower with high spatial frequency, when the system finds its limits.

This is why it tipically falls after a value like 20 cycles (couples of black and white lines) per milimeter

Hope I'd have helped, though my poor english...
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#4 A.Oliver

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Posted 20 October 2005 - 06:29 AM

Hi, thanks for the replies, 7267 (k25) still appears to be unsurpassed in term of sharpness. Not bad for a 30 year old filmstock, prior to that KII of course. I am very surprised the new stock is not a lot,lot sharper.
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#5 Laurent Andrieux

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Posted 20 October 2005 - 07:07 AM

I'm not sure you can say K25 is sharper, a noticable manner.

As I and John Pytlack told you, the methods for the MTF diagram is not the same.

I didn't see John's post before I replied, but since I read it, I think you can consider it's "likely sharper than K25".

A negative and a reversal are so different that you can't really compare them. The difference in sensitivity has to be taken in account as well.

But, yes, I agree that the K 25 was a very nice stock too...
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#6 David Mullen ASC

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Posted 20 October 2005 - 09:04 AM

K25 doesn't even exist anyway so this whole debate is impractical. Plus comparing a projection-contrast reversal to a low-contrast negative in terms of sharpness is also apples & oranges. Obviously a high-contrast image will look sharper. Why not also compare them unfairly in terms of exposure latitude too?
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