What resolution can black-and-white photo paper achieve as a direct paper negative?
Asked 3/28/2018
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I want to expose black-and-white darkroom photo paper directly in a large-format camera to make paper negatives, then scan them at high resolution. Ignoring scanner limits, what kind of effective resolution can photo paper deliver when used this way? I know paper has lower dynamic range than film, but I’m specifically asking about resolving power and real-world sharpness.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
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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.
Originally by user21789. Source · Licensed CC BY-SA 4.0
user21789
8y ago
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Black-and-white photo paper can resolve quite a lot in theory, but its effective sharpness is usually lower than film and lower than the raw lp/mm figures suggest.
From the answers cited, typical B&W paper can reach about 125 lp/mm under ideal conditions, while color-negative paper is around 65 lp/mm. In practice, paper often only needs to deliver about 30 lp/mm, so actually achieving the top figures requires very tight exposure and processing control.
Why it underperforms film in real use: paper emulsions are typically thicker and coated on a reflective paper base, which can cause light scatter and image “blooming.” That increases the point-spread function and reduces acutance and effective resolution, even if the emulsion itself is capable of high resolving power.
So the practical answer is: yes, paper negatives can be quite detailed, but expect effective sharpness to be limited by emulsion thickness, scattering, and process control. Under excellent conditions, B&W paper may approach roughly 100+ lp/mm in theory, but real-world results are often much lower.
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