Surface & Internal Image theory

[Pere Casals]

emulsions with external or just-under-the surface developing centers are practically more sensitive since the developer can get to the latent silver atoms easier

Jason, I don't understand that this has much effect... developer reaches quickly the emulsion inside, modern emulsions include wetting agents to help it. Also in color films we have all 3 layers (or 4 some cases) de layers, developing at the same time...

It is about developing centers or about image centers ?

[koraks]

Pere, note the difference between emulsion and individual grains. Wetting agents won't do much in terms of penetration of grains.

[Nodda Duma]

Yep. Also, I should have added that the effective sensitivity difference becomes apparent with dissolving vs. non-dissolving developers.

The link I posted above to the wikipedia page on latent image says it better and has references that provides further detail.

[Dan Fromm]

Papi, n lines give n-1 line pairs.

||| Three lines. First pair: || Second pair: ||

[Pere Casals]

Papi, n lines give n-1 line pairs.

||| Three lines. First pair: || Second pair: ||

Dan, here it says: "be aware that numerically L/mm is double LP/mm"

https://luminous-landscape.com/mtf/

Is this wrong ?

[Nodda Duma]

Papi, n lines give n-1 line pairs.

||| Three lines. First pair: || Second pair: ||

Actually the first illustration shows 6 lines and thus 3 line pairs. Each white line and each black line counts as 1. Per convention, the pattern starts with the white line to the left and ends in a black line to the right (er...note I’m looking at this thread as white text on a black background).

Further detail: When used in optics, the value(s) or plot with units line pairs / mm is referring to spatial frequency, not an actual count of the pairs of lines in a pattern. A 3 bar pattern a half mm across isn’t 3 line pairs / mm, but is actually considered to be 6 line pairs / mm. A subtle but distinct difference. It is a count of how many pairs (consisting of a white bar and a black bar) of lines can fit in a mm, not the actual number of pairs.


To get even more complex, a repeating bar pattern actually consists of multiple spatial frequencies (accurately called cyc/mm, but often erroneously interchanged with lp/mm). .. just like the Fourier Transform of a square wave audio signal has multiple harmonic frequencies.

It’s important to note the distinction for generating contrast and modulation transfer functions, which are simply plots of the best contrast at which an imaging or lens system can image, respectively, bar patterns or spatial frequencies (sinusoidal patterns) of different widths.

[Dan Fromm]

Dan, here it says: "be aware that numerically L/mm is double LP/mm"

https://luminous-landscape.com/mtf/

Is this wrong ?

Here's the problem. Consider a single black bar: | Where's the adjacent white bar and how wide is it?

One way of measuring resolution uses target patterns of evenly spaced bars (alternately dark and light, all the same width) at a range of spacings (closer spacing, narrower bars). With the sort of test, resolution is the smallest spacing at which the bars are separated. For practical purposes, n bars/mm is usually close enough to n-1 bars/mm. But lines/mm is not twice line pairs/mm.

[Nodda Duma]

Here's the problem. Consider a single black bar: | Where's the adjacent white bar and how wide is it?

One way of measuring resolution uses target patterns of evenly spaced bars (alternately dark and light, all the same width) at a range of spacings (closer spacing, narrower bars). With the sort of test, resolution is the smallest spacing at which the bars are separated. For practical purposes, n bars/mm is usually close enough to n-1 bars/mm. But lines/mm is not twice line pairs/mm.

Sorry Dan, it's rare that you are incorrect but in this case you have it wrong. See my post above. By convention, a single black bar is considered 1/2 of a pair of lines or combined with the background to be considered one full cycle. Either way, the spatial frequency value is the same: If the single black bar is 1mm wide (1 line / mm), than the corresponding first harmonic is 0.5 cyc/mm, and the bar pattern is 0.5 line pairs / mm.

Think of it in terms of the pixel magnitudes across the pattern: A plot of a row of the values will be one cycle of a square wave.

[Pere Casals]

Well, what happens is that there is some confusion there, technically "a resolution of 10 lines per millimeter means 5 dark lines alternating with 5 light lines, or 5 line pairs per millimeter (5 LP/mm)" https://en.wikipedia.org/wiki/Image_resolution

But there is confusing literature around... depending on epoch. Some say that lpmm is line pairs per mm, some say lpmm is lines per mm because line pairs per mm is lppmm... and this is a source of confusion...

Today in photography we usually find lp/mm or cycles/mm.

I guess that kodak did not want to say 31 lp/mm as this is a lot less than what modern LF lenses can resolve, but it has to be explained that this is a great number because it is measured with 1.6:1 contrast, when lenses (I'd say) are measured with 1:100 contrast in the target, that's what a printed chart may have. So Kodak said 63 lines/mm in the datasheet.

In the ADOX CMS 20 datasheet they are proud of the 800 lp/mm the film has. Well, it's a microfilm recording medium, not a pictorial film... developed for pictorial usage...

they say:

Resolution:
Resolution in high contrast 1000 : 1 = 800 Lp/mm (line pairs/mm).
(Do not confuse with lines/mm)
http://www.adox.de/Technical_Informa...structions.pdf

800 it's a nicer number than 31.5

[interneg]

quoting: "T-Max has a combination at the top of the emulsion are two layers of 'tabular' grains that are larger at the top record and smaller in the lower one they are uniform in size (monodisperse).
Beneath that is a layer of 3D grain (Kodak speak for cubic type) that is finer and slower probably polydisperse."

For simplicity I didn't mention that the T outer layer is in fact composed of two layers...

Yes, but that's TMY-II that you are describing there. 20 years newer in design than TMX or TMZ. The grain growth & sensitising techniques used in TMY-II are shared with cinema & still colour neg films I believe, though I also think many of those techniques significantly post-dates the arrival of TMX in the mid-late 80's. Compare the MTF curves of TMX & TMY-II between 5 & 30 cycles/mm & it's quite obvious how the use of absorber dyes & grain growth technologies etc have evolved. Furthermore, I also understand that if you can (ie you're making a sub 200 speed BW film) you don't multilayer coat the discreet emulsions for a variety of reasons, not least because of the problems of interlayer artefacts/ reflections and sharpness, instead you can blend two or more emulsions & end up with potentially better performance. Worth noting too that colour films may have three discreet layers for R, G & B, but 5 or more emulsions in those 3 layers, for a total of 15 or more in the finished product. Same principle applies to BW - would not surprise me if TMY-II had 5 emulsions in its structure.

Well, the spectral sensitivity curve does not show a flat spectral sensitivity... anyway TMX is suitable for color separation with the right illumination and calibration.

It is specifically reccomended as a separation film in several Kodak technical documents relating to Dye Transfer - and it is explicitly stated that this is because of its favourable response for accurate separation making. Indeed, TMY (not II, the first one) is specifically reccomended against for not having the right spectral response.

Please read comments in the flickr link, that sample does not show actual film images but how a film grain simulation tool uses different (scientifically measured) curves for density vs grain_size. Just to show the shape of that curve.

For real samples you can see this TX image, you may note that on the car the darker areas have more grain, see similar HP5 shots and you'll see that peak graininess is more in the mids, anyway this depends on exposure.

I don't need irrelevant 'real' samples, I've made plenty of prints from pretty much all of the current 400 speed films in the market & the immediate identifiers are spectral response & characteristic curve. Not grain. Indeed, grain 'character' is pretty easily manipulated at various stages of the process. Most of those 'film simulation' plugins seem to be astonishingly poor at actually representing the real behaviour of various films. Tri-X & HP5+ exposed in similar lighting conditions, processed to the same CI & contact printed (taking grain completely out of the way) will tell you far more about their relative characteristics & identifiers than spending time playing around with plugins.

No... because the possible ortho layer is of extreme low ISO and works only with extreme highlights, showing textures of glares and illumination sources, that are usually neutral in color. I'm not completely sure that the cubic (very low ISO) deep layer is ortho, IIRC it is. A factor to not sensitizing it panchro would be a simpler process, and not increasing emulsion speed, as that emulsion is responsible for the linearity in the extreme highligts, where TMX/Y is extremly linear compared to other films that have more or less a shoulder.

I doubt it's orthochromatic in the historic sense, but it's likely tuned to a specific sensitivity which will not adversely affect the ability to hold a range of specular lighting colours or cause strange tonal shifts at the point the emulsions cross over.