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Resolution of ASA 100 film


dan_roe1

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M'er's

 

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I'm directing this to you because we believe we have excellent cameras, but are they too excellent? Please consider this. In the February issue of Digital Camera ( vol 5, issue 23) a columnist reviewing a Nikon Coolpix 5000 on p.39 makes this statement,

 

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"... experts generally agree that standard 100 speed 35mm film has a nominal resolution of about 6 megapixels."

 

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I figure that out to be about 2000dpi. I believed that my M6 combined with a 4000dpi scanner could produce about 24 megapixels of data.

 

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( 35 mm film is approx. 1.5" by 1". At 4000dpi that's 6000 dots by 4000 dots or 24 million dots ( data points ) per frame.

 

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If the reviewer is correct, our Leica systems are massive overkill. a 4000dpi scanner is translating approx. 1 "data point" on the film into 4 "data points" in the TIFF file which basically buys us nothing.

 

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Is the reviewer correct about this film? Are all films this good (bad)?

 

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My faith is not shaken, but there is a slight twitch.

 

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Dan

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I don't agree that the "resolving" power of 100ISO film is necessarly

about 6 megapixels. I am not sure as to the size of one grain of B&W

film, or the edge accutance of even large grain B&W or the size of

dye clouds in color film or edge accutance of that. But with a

little math, there is an argument that "resloving" power of ISO film

is about 6 megapixels. If you assume that the "resolving" power of

100ISO film is 80 lines per millimeter, that means that there are

6400 "resolution" points in a square milimeter. As I recall, 35mm

film cameras frame about 24 X 36 mm. That's 864 square millimeters

per frame with 6400 "resolution" points each. That means, by this

analysis, 5,529,600 "resolution" points or about 5.5 megapoints. The

fallicy of this argument is that lines of resolution in film is made

up of many more "points" than 80 per millimeter. If there were only

80 points per linear millimeter or 6400 points per square millimeter,

then there would be visibly jagged diagonal lines in the image. So I

really think that the resolving power of digital imaging would need

to be much greater to match the resolving power of film. I have

heard that the megapixel point where digital matches film is

somewhere over 12 megapixels. That said, the 12.5 megapixel power of

my Coolscan IV can produce some mighty sharp prints up to 12 X 15 or

perhaps greater using algorithms of Genuine Fractals. In addition,

film simply has a different depth and character than digital stuff.

This is not a bad or good thing, just different. Where we will go on

this - only the invisible hand of the market knows.

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On the surface, 6 megapixels sounds reasonable for 35mm film if one

makes certain assumptions. For discussion, let's assume that that the

lens and film combination is capable of a resolution of 90 lines/mm.

At an image size of 24mm x 36mm, that works out to 2,160 x 3240

pixels, or, about 6 megapixels.

 

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The standard line target, however, is made up of black lines separated

by white space. Hence, a minimum of two pixels are required to resolve

the line - one black pixel for the line, and one white pixel for the

adjoining space. Thus, the 24mm x 36mm image area would actually

equate to 4,320 x 6,480 pixels at 90 lines/mm, or about 28 megapixels.

 

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Lens resolution will, of course, vary from the 90 lpmm rating, as will

the ability of the film to record what the lens projects.

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Scanning a 35 mm silde or neg into Photoshop using a Nikon LS4000

with Silverfast or Vuescan at HR setting (48 bit) produces a file of

about 115 meg. Now that's a lot of data with which one can use for

color correction and levels. I too have heard that 12 megapix is

needed to equal 35 quality.

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After I posted, I realized that the black lines have to be separated

by white lines. Thus for a linear 80 lpm resolution (actually 80

line pairs per millimeter), you would need 160 pixels per mm. So my

computation is too small by a factor of 4. That means you would need

about 22 megapixels to match 35mm resolution at 80 lpm. I agree with

Ralph's analysis. Although I have heard 12 megapixels as the match.

That would be about 60 line pairs per mm - or about the resolution

that a good autofucus system is geared to hone in on.

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I believe Martin has it correct. Since we all (probably) use decent

film in our fine cameras, we can expect to resolve about 200 (just a

median number) lines per mm. 90 and 100 seems really low. That's some

crap film. 150 - 220 is good. The resolution required to match this

is very very high. I can't imagine at all where that 6mp number came

from. Sounds like something just plain made up. In order to record

the same amount of information contained in a 35mm neg/slid, you'd

need much more than 6mp. A hell of alot more. My numbers were like

Martin's last time I worked this out. So don't worry Dan. Even when

they have 50mp 35mm cameras, I bet some film and a Leica will still

take a hell of a better photo. No need to twitch the faith. And don't

read that mag! It sounds very poor.

 

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-Ramy

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Ummm. If you allow 3 bytes (that's only 8 bits) per color channel,

you need to multiply by 3. 12 bits (more common in high quality

scans) multiply by 4.5. And some schemes use 4 channels, not 3. I

fugure. Figure about 78 Megabytes per frame at 150 lines per

milimeter, for 4 channel, 12 bits per channel film. It'll happen, but

give it a few decades.

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I read somewhere, can't remember where exactly, that the resolution

of a professional slide film goes towards 1B (yes Billion) pixels.

 

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The 5M pixel camera's provide pretty good results upto maybe A3

format.

So if that is the max size you're using, I see no reason not to

consider

digital. But before you go digital also consider facts like response

time, battery consumption, cost, etc etc. As we all have discussed

many time before. As for now I still see no reason to trade in my R4s

and lovely "new" Hexar AF.

 

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Reinier

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1 billion pixels in professional slide film? That's just 1000

Megapixels. Within reach of Velvia in 8x10, but certainly not

available in 35mm due to the wavelengths involved.</p>Things look a

bit different at contrasts lower than 1000:1. At 1.6:1 and similar

realistic values, most films can't resolve more than 100 lp/mm, and

the wide majority is around 40-50 lp/mm. Still, to say that 'standard

100 speed 35mm film has a nominal resolution of about 6 megapixels'

is to lie. As the 1.3 Mp digicams some years back rendered

`photorealistic' quality', shouldn't we say that ISO 100 film has a

nominal resolution of about 1.3 Mp ;-) ?

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Kodak supposedly enlarged some 35mm Kodachrome frames to mural size

in Grand Central. My question is, how would 6MP digital image look at

that size?

 

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I think it will still take a long time before digital reaches film

quality because in my mind digital is good only up to a certain level

of enlargement, even better than film for lack of grain. But when you

overdo it, film is still very much better. I suppose our eyes are

somehow used to large grainy images, but over-enlarged 'digital

grain' is much harder to accept.

 

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Just my view.

 

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Ilkka

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  • 1 year later...

I find this a very important question. I do almost all of my "darkroom" work on the computer now with Photoshop. About a year ago I purchased the Nikon Coolscan IV ED which scans 35mm at 2900 dpi. This produces a 2870 x 4200 pixel image that at 8 bit is a 34.6 Megabyte TIFF file of excellent quality both color and black and white.

 

I made the decision to purchase the Coolscan IV because I love my Pentax MX 35mm camera and manual lens setup. I thought that this would be the best of both worlds, which for the most part it is.

 

The software that comes with the Coolscan "Digital ICE" I beleive, does an excellent job of taking scratches and dust off of all negatives and slides except Kodachrome and Black and White film (it works on Kodak T400CN B&W). I like to shoot Black and White especially Kodak Tri-X 400 and Kodak T-Max. This film requires hours of cloning work to remove dust particles in Photoshop.

 

I will never give up my film cameras or scanning in that film. It is a great method to have your cake and eat it too you might say. But I could not resist giving in to the technology of a 5 megapixel digital camera for under $500.00. I justified the purchase of the Nikon Coolpix 5000 because I have another child on the way in less than a month and wanted to save money on film and processing as well as get more instantaneous results out to family etc.

 

The Coolpix 5000 gives me a 2560 x 1920 pixel image that saved at at 8 bit is 14.1 megabytes (at 16 bit it is 28.2 M). I take all photos at the RAW setting and have Photoshop convert them into TIFFs after I make my adjustments. I am finding that when I get a good photo with good lighting it nearly matches that of the full film scan image. The 5 megapixel images are very sharp and have excellent color. There is no "second generation" blurriness however slight that you might get with the film scanner.

 

So my long winded contribution would be both, if you have the opportunity. The downside of the digital lens on my "prosumer" camera is that it has an enormous depth of field even at 2.8, so it will never be able to replace my Pentax MX for certain types of shots.

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