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I would like to expose some B/W chemical photopaper directly in a large format camera to obtain paper negatives.

What is the maximum effective resolution I could obtain on said paper? assuming a following digital scan is performed at sufficient resolution.

I found some scientific measurements of the effective resolution of film, but not of paper exposed directly (therefore without film->paper exposure).

I'm already aware that the dynamic range would be lower than that one of film.

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    There are other variable involved, such as the resolution limits of the lens you use, and the resolution of your digital scanner. Without knowing these variables, your question is not answerable. – Michael C Mar 28 '18 at 13:47
  • @MichaelClark in other words, the resolution of paper is not the limiting factor? like with film, I assumed a certain maximum value of lines/mm can be achieved (well, according to the contrast/resolution curve). – FarO Mar 28 '18 at 14:09
  • Really interesting question! Probably the one that will answer this is you, doing some tests. – Rafael Mar 28 '18 at 16:03
  • @FarO The limiting factor is whichever factor has the lowest resolution limit. It could be the lens, it could be the paper, it could be the scanner. – Michael C Mar 28 '18 at 18:09
  • Are you only interested in the resolution of the paper negative? If your intent is to contact print to another paper, a loss of resolution will occur in the transfer... – Hueco Mar 28 '18 at 18:12
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According to CTEIN

The typical color-negative paper can record about 65 line pairs per millimeter (lp/mm), but a black and white (B&W) paper can reach 125 lp/mm. Ilfochrome and R-3 papers fall midway between at 80 to 100 lp/mm... (Post Exposure, Second Edition 2011)

To put this into perspective, CTEIN states later in the paragraph that paper normally only needs to produce 30 lp/mm of resolution. So, while the specs say you can get over 100 lp/mm few are doing so in practice. This means that your sensitometric control and chemical process control will likely need to be more accurate than normal practice. For some photographic materials, the sensitometric range for optimum resolution may be only 1 stop in width. This could mean that the correct exposure for optimum resolution looks nothing like a "good print" by traditional definitions. keep in mind that you are creating an intermediate medium with this paper and look to optimize resolution by finding the resolution inflection point along the D-LogE curve

If you are not advanced to expert level in photo processing I recommend further reading (or just some good old experimentation) to help you determine how to get the most out of whichever silver colloid you choose. I like Salvaggio's Basic Photographic Materials and Processes for general background on sensitometric and chemical control.


Out of Scope Footnote: In case you are wondering, the appropriate resolution to faithfully scan a given image is image_resolution x 2 x 25.4 x 1.43 = scanner_resolution. This assumes image resolution is in lp/mm while scanner resolution is in samples per inch (spi) The factors of 2, 2.54, and 1.43 are nyquist sampling, mm to inch conversion, and kell factor respectively.

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Here are some differences between paper and film that will affect the image resolution acutance, resolution, and resolving power.

Paper: The emulsion normally used for paper is relatively insensitive silver chloride in a colloidal suspension, orthochromatic (blue sensitive), thickly applied to a fibre base with a baryta layer for brightness and a starch binder to hold the emulsion to the base. The ability of the image to enter the emulsion and re-expose from the base by reflection reduces the acuity of the image. The image tends to "bloom" and the point-spread-function increases more than doubling. This reduces the effective resolution. There might be some loss due to the paper base itself; but, I suspect minimal.

Film: The emulsion normally used for film is more sensitive larger crystals of silver iodide in colloidal suspension, panchromatic (red sensitive), thinly coated on a dimensionally stable flexible plastic (PET) base, a protective transparent over-coat, a "binder" to hold the emulsion to the base. In addition, an anti-reflection coating is applied to the back of the base to prevent halation (double exposing the film emulsion due to retro-reflection of the source.)

It sounds like an intriguing experiment comparing the performance of the two.

  • I like this answer but disagree on 1 point: I believe the paper base to heavily influence the perceived resolution such that RC would have better resolution than FB and FB would do better than Canvas (for example). – Hueco Mar 28 '18 at 18:00
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    @Corey YES. I did ignore the texture of the base. There are too many to make a definitive statement. All my comments are confined to smooth/glossy surfaces. Thanks for mentioning this important factor. Chances are pretty good that a canvas texture paper wouldn't be considered as a high resolution paper negative material anyway. – Stan Mar 28 '18 at 18:49

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