Measuring film acutance visually

[Bayard]

Hi all,

First post, so excuse any verbosity. I had an idea for measuring the acutance of different films. According to the Ilford site, acutance is a measure of the sharpness of the film, and loss of (or low) acutance is caused by the fact that light can bounce off of the silver halide crystals, in the emulsion, and "spread" a little further than the actual, straight-line, exposure of that tone.

Here is the method I am thinking of. Please offer any improvements or critiques.

1. Assume that all films will be properly developed, in the same developer, for the time recommended by the Massive Dev Chart.

2. Using Photoshop, I will create a series of straight gradients, from 0 to 255, with an increasing number of steps. The first line, for example, will be a straight Zone System gradient, where 11 zones are defined. Then, the next gradient will have 22 zones, then 33, then 44...and so on. I will stop around 66 zones, or so, unless I find I need to go further. This may also be limited by the number of steps I can see on the digital print, in the first place. There will be no lines or borders between the zones.

3. Using Program Mode, under studio lighting (controlled) conditions, I will make an image showing all these gradients.

4. After normal development, I will loupe the negs, rather than make a print, so as not to add variables of paper, filter, processing, etc. This may be a weak point, and I would like opinions on whether or not I split filter print, or have the negs scanned.

If I do this, the idea is that, on films that have a higher acutance, I should be able to see the differences, between steps, on the gradients with a higher number of steps. If the acutance is lower, then I would only be able, for example, to see 50 changes on what I know is the 66 step gradient.

Does this trip anyone's logic circuit and, if so, why?

Thanks in advance,
Bayard

 

[Leigh B]

Simplest / best / most accurate way to measure film acutance...

Read the manufacturer's datasheet.

They have far more expertise, much more equipment (properly calibrated), and trained personnel.
Consequently, you can believe their numbers.

- Leigh

 

[ic-racer]

Why not use the conventional 'knife edge' method?

 

[Bayard]

Thanks, Leigh, and I completely agree with you, kind of . The only reason I have for doing this myself may be a very good reason - for something other than acutance - but not, necessarily, a good reason for acutance, itself.

In the end, I may develop my film in exactly the same way as someone else on the forum, but I have no idea who. Similarly, I may or may not develop my film in exactly the way the experts at the manufacturer developed theirs. Now, does doing a few extra inversions, during agitation, or pouring out my developer with 15 seconds left, instead of 5, make a difference? It might not, for acutance, but it might for some other characteristic of a film/developer/process combination.

I am trying to come up with a "magic roll". 24 or 36 frames that I can take, on a given film that, when developed, will give me the most information about how the film behaves for me, if I keep my other variables controlled. From there, I can learn a lot more about what changes in my own development "moves" do to a given combination.

This will allow me to methodically compare any two rolls, with a minimum of time/expense, and maximum information return, all specialized to my personal style of shooting, developing and, eventually, printing. I am not looking for a strict set of methods that I can tell you, for instance, that you should be following. I am just exploring what variables, in a development methodology, truly affect the negatives, and to what degree.

Bayard

 

[Bayard]

Why not use the conventional 'knife edge' method?

Hey ic-racer,

Not trying to be overly difficult, but I don't have a micro-densitometer to accurately measure the results, and I was, specifically, searching for a way to approximate this, visually, using only what was recorded on the film.

Am I being, pardon the pun, dense about that?

Bayard

 

[Leigh B]

Hi Bayard,

Wanting to have a "standard" that can be used to compare other processes is certainly a valid goal.

My suggestion would be to start by trying to duplicate the manufacturer's results.
That may require changes in subject, lighting, exposure, development, or technique.

Once you've achieved that, you can change one element at a time to see how the film reacts.

I would suggest buying a target from Edmund Optics rather than trying to make one yourself.

- Leigh

 

[Bayard]

Thanks, Leigh. You are right. Trying to dupe the results of the expert is the better place to start.

And thanks for the recommendation on Edmund Optics. Why re-invent all the wheels at once?

Bayard

 

[Leigh B]

Some suggestions for achieving the highest possible contrast on the negative.
(You probably already know this...)

Set the target up against a flat black wall (flat meaning non-reflective).
Make sure the entire wall is black, not just the portion visible through the camera lens.

Set the lights on each side at a 45 degree angle to the target.
Locate the camera precisely square to the wall, centered on the target.

A tripod and cable release are obviously required.
If using an SLR, lock the mirror up and use the self-timer to reduce vibration.
Use the largest format you have available (LF if possible).

Turn off the room lights when making the exposure.

These are all just techniques commonly used for copying photographs or paintings.

- Leigh

 

[Bayard]

Some suggestions for achieving the highest possible contrast on the negative.
(You probably already know this...)

- Leigh

Thanks, Leigh and, for the record: with the exception of the tripod mount and cable release, I wouldn't have thought of any of that, so gracias!

Bayard

 

[Leigh B]

One thing I forgot to mention about the setup.

Arrange the camera and lights such that NO light falls directly on the camera lens... NONE... ZERO.
Did I mention none??? Sorry, I meant NONE.

The first option is to put the lights forward of the camera, with hoods over the lights.
Alternatively, you can rig opaque screens between the lights and the lens.

This and the other folderol is to minimize lens flare, which can kill a high-contrast shot.

- Leigh

 

[MattKing]

Welcome to APUG.
I certainly wouldn't look to the Massive Developing Chart for a standard development time. The MDC is like Wikipedia, except it permits multiple, inconsistent entries.
Use the manufacturer's recommendations instead.
I too would recommend an existing test chart.
It is important as well to understand that acutance is just one component of perceived sharpness, and it is perceived sharpness that we tend to value the most.

 

[Bayard]

Welcome to APUG.
I certainly wouldn't look to the Massive Developing Chart for a standard development time. The MDC is like Wikipedia, except it permits multiple, inconsistent entries.
Use the manufacturer's recommendations instead.
I too would recommend an existing test chart.
It is important as well to understand that acutance is just one component of perceived sharpness, and it is perceived sharpness that we tend to value the most.

Hi Matt, and thanks. a few follow-up questions.

1) How good are manufacturer's at publishing times for developers that are not their brand, in general? If they don't, is there a better resource than the MDC for such cross-pollination?

2) I am taking these characteristics one at a time, in a rather clinical fashion. I would be interested in the opinions of you, and others, in an attempt to make up a list of characteristics that a film can have. I got acutance, contrast, and grain. What other things could be looked for?

Bayard

 

[MattKing]

1) How good are manufacturer's at publishing times for developers that are not their brand, in general? If they don't, is there a better resource than the MDC for such cross-pollination?

The main-stream manufacturers are fairly good at publishing times for other brands. It is of course important to understand that the times posted are based on the publishing manufacturer's preferred results. As the different manufacturers use slightly different criteria for desired contrast, it can be difficult to exactly match targets.
The MDC is excellent for one thing. For unusual combinations which the manufacturers don't test - if you are just looking for what people have tried and like, it has a pile of interesting information. It is really hard though to critically compare that information.

2) I am taking these characteristics one at a time, in a rather clinical fashion. I would be interested in the opinions of you, and others, in an attempt to make up a list of characteristics that a film can have. I got acutance, contrast, and grain. What other things could be looked for?

Resolution, spectral sensitivity, latent image retention, reciprocity failure (or lack thereof), dimensional stability, exposure latitude, ability to withstand environmental variables, flatness of film stock, appearance of grain - there are more.
Grain and acutance are somewhat variable, in that the user can change them by changing exposure, type of developer and mode of agitation. Contrast is highly controllable by the user.

 

[Alan Johnson]

From R Henry, "Controls in Black and White Photography" p214:
"Since it is admitted that the sense of sharpness depends not only on acutance but also adjacency effects,,,,,much work would have to be done first to determine the relative importance of the two effects."
So if you measure the acutance it is not much guide to the perceived sharpness and the value of it is not clear.

 

[Gerald C Koch]

If I do this, the idea is that, on films that have a higher acutance, I should be able to see the differences, between steps, on the gradients with a higher number of steps. If the acutance is lower, then I would only be able, for example, to see 50 changes on what I know is the 66 step gradient.

I fail to see any connection between acutance and the image of a step wedge.

 

[Craig75]

Sensitometry for Photographers by Egleston,Development by Jacobsen (i think?) and Controls in black and white photography by Henry (and others - I just found these three understandable to me) I would recommend if you wish to know about film characteristics,their measurement and manipulation.

Testing yourself - I would just say choose one film - shoot photos, bracket, and develop in different developers - some will be really sharp, some very fine grained and you will learn more from that than anything else

 

[Bayard]

From R Henry, "Controls in Black and White Photography" p214:
"Since it is admitted that the sense of sharpness depends not only on acutance but also adjacency effects,,,,,much work would have to be done first to determine the relative importance of the two effects."
So if you measure the acutance it is not much guide to the perceived sharpness and the value of it is not clear.

Hi Alan, and thanks for the reference. Perhaps what this experiment would be measuring is more along the lines of that adjacency effect, as opposed to acutance.

Bayard

 

[Alan Johnson]

There seems to have been two opinions about the relation of perceived sharpness to acutance.
The Kodak workers found the perceived sharpness to correlate with acutance (the article by Perrin 1956 in Image magazine archive is unavailable while Eastman House reorganize)
Others, including Crawley BJP Jan 6 1961, were aware of the contribution of adjacency effects as well as acutance.
Eventually it was found that to take into account both it was needed to make a microdensitometer trace of a series of ever narrowing lines.
It is the latter , successful, method you would need try to work up I believe.