Measuring film resolution

[Rudeofus]

Dan, such H&D curves are quite easy to make by contact printing a Stouffer wedge and exposing with a uniform light source.

BTW very interesting results you posted with Rodinal and Xtol, and good to know that we don't pursue figments of imagination but real differences in results.

 

[RobC]

and good to know that we don't pursue figments of imagination but real differences in results.

Yes and that means you have actually got to print the negs at large sizes and measure the obtainable in print results otherwise its all theoretically achievable stuff which isn't the same thing.

 

[Athiril]

Dan, such H&D curves are quite easy to make by contact printing a Stouffer wedge and exposing with a uniform light source.

BTW very interesting results you posted with Rodinal and Xtol, and good to know that we don't pursue figments of imagination but real differences in results.

Printing a step scale to some slide film now with a film recorder, I'd do it directly to T-Max but I dont know what the light values exactly will hit the film for each step. Can use that to contact print later.

 

[Photo Engineer]

If the light is the same for the step scale and resolution chart there is no problem.

PE

 

[Rudeofus]

Yes and that means you have actually got to print the negs at large sizes and measure the obtainable in print results otherwise its all theoretically achievable stuff which isn't the same thing.

There may be little point in optimizing resolution of TMAX 100, but trust me: there is plenty to do for HP-5+, Tri-X and Delta 3200. When it comes to TMAX 100, Delta 100 and the like, one might still be interested in emphasizing sharpness while accepting higher than normal granularity, see DS-12 vs. DS-10.

If the light is the same for the step scale and resolution chart there is no problem.

You need a lot more light for step wedge exposures than for resolution target exposures if you want to exploit the full range of that step wedge. I use an enlarger as light source, which allows me to trivially adjust exposure levels. I usually calibrate my exposure with some standard developer, then use the same exposure for test developers.

Printing a step scale to some slide film now with a film recorder, I'd do it directly to T-Max but I dont know what the light values exactly will hit the film for each step.

A step wedge exposure as described above will give you no absolute ISO rating, but you can easily derive relative speed of one developer vs. the other.

 

[Athiril]

I have a densitometer to measure the density of the scale I'll be making.

 

[Rudeofus]

If you make your own step wedge from exposed film, doesn't such a step wedge have its own granularity which creates incorrect results? I could imagine that especially weakly exposed regions of the target would respond differently to weak and uniform vs. grainy and weak on average exposure.

 

[removed account4]

never ceases to amaze me how detailed some photographer's systems are .
and the need to know the details of limitations of their materials ...

 

[Photo Engineer]

Rudi, if an exposure grabs the entire range of density on a chart, any chart, it will work with a step scale.

This is my point here!

PE

 

[Xmas]

John, nearly every thread on every forum shows that most pretend to know the details of their materials. What's wrong with a handful of people wanting better information? It doesn't diminish their creative/artistic potentials in the slightest.

Alas I don't claim to have any potential.
But the eg the resolution that you get from a film is degraded by depth of focus, lens aberrations, camera shake,... Etc.,
So the film is only going to be of 'relevance' if you have a well controlled 'environment'?

Does not stop you from photographing test charts, eg there are lots of nice mono films 200-400 ISO.

 

[Rudeofus]

Rudi, if an exposure grabs the entire range of density on a chart, any chart, it will work with a step scale.

With step wedges you go from barely visible exposure all the way to extreme over exposure, which happens where the step wedge is mostly clear. At these extreme levels of overexposure I have seen all kinds of overexposure artefacts (blooming) which would severely affect any sharpness or grain measurements.

 

[Photo Engineer]

Rudi, if a chart shows black and white, then a step scale run to the same density values using the same exposure will give us slope and speed when compared with other films. Thus, it will work. You do not need over and under in this case, you need the center and slope of the center.

PE

 

[removed account4]

John, nearly every thread on every forum shows that most pretend to know the details of their materials. What's wrong with a handful of people wanting better information? It doesn't diminish their creative/artistic potentials in the slightest.

michael
you misinterpreted what I said. :confused:
you are 100% correct.
most threads are as you describe and there is nothing wrong
with anyone wanting better information, or the thesis of this thread
there was no snark included in my comment, just amazement
and, yes, I do realize it has no ill consequence ... :thumbsup:

 

[Rudeofus]

I'm still not clear on what you are trying to measure. Resolution or sharpness? Based on what I've read, resolution on its own is a relatively weak objective correlate to subjective sharpness - hence the acutance measurement, then edge effects, later MTF etc. Of course image structure (granularity, sharpness) can impact resolution to some degree.

An MTF chart together with granularity data gives you both, and then some. You get resolution, sharpness, it gives you Ron's (there was a url link here which no longer exists) and then some. Once you know what a developer really does, you can start optimizing, and you get reliable feedback whether you go in the right direction or not.

Athiril's test chart provides too little area per frequency for determining reliable MTF data from grainy film, but even with all its limitations you see quite well what's going on with his four test developers.

 

[Bill Burk]

If you make your own step wedge from exposed film, doesn't such a step wedge have its own granularity which creates incorrect results? I could imagine that especially weakly exposed regions of the target would respond differently to weak and uniform vs. grainy and weak on average exposure.

Oh I see what you're thinking... No. The step wedge is a separate control test. You check for exposure and processing by reading densities. You don't read granularity/graininess/sharpness/resolution from the step wedge exposure. Instead you include a separately-exposed resolution chart developed at the same time. The combination helps explain the conditions of your resolution test.

 

[Photo Engineer]

Since grain and sharpness vary with density, both of these are measured as a function of density and thus in the final exposure you plot grain vs density and sharpness vs density, the familiar plots we see posted on some manufacturers web sites.

The step scales should be as grain free as possible, but they can be used if the chart itself is used as a reference to remove "noise'.

PE

 

[Athiril]

The measurement area/aperture on the densitometer I'm using is 4mm, way too large to measure granularity, or have it interfere with density results I would think, granularity from everyone's datasheets is measured with a 48 micron aperture.

 

[Rudeofus]

Oh I see what you're thinking... No. The step wedge is a separate control test. You check for exposure and processing by reading densities. You don't read granularity/graininess/sharpness/resolution from the step wedge exposure. Instead you include a separately-exposed resolution chart developed at the same time. The combination helps explain the conditions of your resolution test.

You won't measure resolution with a step wedge, but it's a great method for measuring density vs. exposure and grain vs. exposure from a single contact print. The resolution test would be done with a separate contact print, of course.

 

[Rudeofus]

How do you measure granularity (or acutance) without a microdensitometer?

My scanner allows me to scan in raw mode, from this I can derive density and granularity data with a bit of image processing. As far as acutance and MTF is concerned, I am limited to the few dozen lp/mm that my flat bed scanner can reliably read. For Delta 3200, HP-5+ and Tri-X this shouldn't be a limitation.

 

[Athiril]

My scanner allows me to scan in raw mode, from this I can derive density and granularity data with a bit of image processing. As far as acutance and MTF is concerned, I am limited to the few dozen lp/mm that my flat bed scanner can reliably read. For Delta 3200, HP-5+ and Tri-X this shouldn't be a limitation.

For Delta 3200 I managed to hit 50-60 lp/mm off 120.

 

[Rudeofus]

For Delta 3200 I managed to hit 50-60 lp/mm off 120.

At which speed? Look at SPUR's latest and greatest developer HRX-3 new, they claim all kinds of superior performance with all kinds of film, but with Delta 3200 you get ISO 400-500.

 

[Athiril]

Exposed at 3200.

 

[Rudeofus]

Exposed at 3200.

You can expose Adox CMS 20 and Pan F+ at EI3200 if you want, just don't expect much shadow detail. Since we know that Delta 3200 is ISO1200-1600 at best, but certainly not ISO 3200, it would be interesting if you gave us complete details for these 50-60 lp/mm result, and that includes ISO speed, either as absolute number, or relative to some well known developer.

 

[RobC]

You can expose Adox CMS 20 and Pan F+ at EI3200 if you want, just don't expect much shadow detail. Since we know that Delta 3200 is ISO1200-1600 at best, but certainly not ISO 3200, it would be interesting if you gave us complete details for these 50-60 lp/mm result, and that includes ISO speed, either as absolute number, or relative to some well known developer.

Ilford Delta speed seems to cause huge confusion. It's very simple. Ilford use ID11 for all their ISO speed tests. Using ID11 my tests indicate that yes indeed its ISO speed is 1000. But EI is your own personal speed and is dependant on the devloper used and your own process. I find I get 1600 with DDX and I get 3200 with Microphen. Grain is much bigger with Microphen than with DDX so DDX produces much smooither looking prints than Microphen but certainly not what I would call fine grain.

I may be wrong but my impression is that the closer to neutral PH a developer is, the finer the grain. Its important to remember that the grain we talk about is actually grain clumps and its my belief that the further away from neutral PH(7) a developer is, the greater the grain clumping. The increased hydrogen ionisation cause greater attraction of real grains to each other forming bigger grain clumps. The developer is "more active".

I'm no chemist and I may have got this wrong but look at the facts.

[TABLE="width: 500, align: left"]

Developer
Dilution
PH


PERCEPTOL
stock
7.68–7.82


ILFOTEC DD-X
1+4
8.45 - 8.55


ID-11
stock
8.60–8.70


MICROPHEN
stock
8.67–8.93


ILFOTEC LC29
1+9
8.90 - 9.00


ILFOSOL S
1+9
9.75 -9.85


[/TABLE]















I have used the first four and the grain I get seems to be in the order they are listed.
I have never used LC29
I have only used ILFOSOL once and thought the grain was very great.

So this all seems to bear out my theory that stronger PH increases grain clumping.

The question is, does using a developer with greater Hydrogen ionisation (PH) reduce resolution because its moving charged grains into grain clumps thereby reducing the detail that was in the negative (but increasing acutance at the same time).

I guess there is a fine balance to be found depending on what you're looking for.

 

[Athiril]

It was exposed at 3200, it is a measure of resolution when rating the film @ 3200, the same as if you would use it to take pictures exposed at 3200.