Create hd curve

yya · May 17, 2024

If I want to use the method of measuring film density to plot an HD curve, I'm encountering some issues.

Based on the estimated ISO, I use a step wedge to expose a white wall at Zone 10, then check the density at Zone 2 to determine if the estimated ISO is correct, and check the density at Zone 7 to determine if the development time is correct.

This is our common method for measuring film density and development time.
My question is: If I want to plot an HD curve based on this film, for the x-axis I need the logarithm of the exposure value. The logarithm of the exposure value is calculated from the light intensity (lux) and exposure time. So, do I need to prepare an illuminometer during exposure?

xkaes · May 17, 2024

You're making it much more complicated than it needs to be. Where are you getting your information from? On one axis is time and the other density. How are you measuring time and density? There are many ways to do it -- some easy and inexpensive, other more accurate and more expensive. Lots of people just use their eyeballs. Check out Richard Henry's book "Controls in Black & White Photography".

RalphLambrecht · May 17, 2024

xkaes said:
You're making it much more complicated than it needs to be. Where are you getting your information from? On one axis is time and the other density. How are you measuring time and density? There are many ways to do it -- some easy and inexpensive, other more accurate and more expensive. Lots of people just use their eyeballs. Check out Richard Henry's book "Controls in Black & White Photography".

that book is excellent but has been out of print for many years and is very hard to use. A public library might be your best guess. The vertical axis D) of the HD graph is density; the horizontal axis (H) is exposure.

Romanko · May 18, 2024

You don't need to know absolute exposure to plot the HD curve. If you are using a step wedge you know the density of each step of the wedge (nominal or individually calibrated). If you plot the density of your film as a function of the density of the step wedge you will get the HD curve. To calculate the contrast index you can even plot film density values re. step number.
The absolute exposure value is only required if you need to measure the ISO speed of the film. And even in that case an exposure reading of your white wall taken with a good light meter could suffice. I would actually recommend this method as you are calibrating your full system including your light meter, the shutter on your camera and your development process.

Alan Johnson · May 18, 2024

Controls in black and white photography : Henry, Richard J. (Richard Joseph) : Free Download, Borrow, and Streaming : Internet Archive

270 p. : 28 cm

archive.org

yya · May 18, 2024

Romanko said:
You don't need to know absolute exposure to plot the HD curve. If you are using a step wedge you know the density of each step of the wedge (nominal or individually calibrated). If you plot the density of your film as a function of the density of the step wedge you will get the HD curve. To calculate the contrast index you can even plot film density values re. step number.
The absolute exposure value is only required if you need to measure the ISO speed of the film. And even in that case an exposure reading of your white wall taken with a good light meter could suffice. I would actually recommend this method as you are calibrating your full system including your light meter, the shutter on your camera and your development process.

Sure, I need the absolute exposure value because plotting the HD curve with the absolute exposure value can confirm the ISO value. You mentioned using a light meter to measure the light reflected off a white wall to get the EV (Exposure Value) at the current ISO setting. However, to convert this to lux, it needs to be at ISO 100, which is where my confusion lies. How do you use a light meter to measure the light reflected off a white wall and then determine the absolute exposure value?

Romanko · May 18, 2024

There must be a way to convert the F-number and shutter speed at a given ISO setting to lux (or whatever is the unit of the exposure). However, this is only relevant if you are measuring the ISO speed of the film according to the ISO standard. For practical use it suffices to know the HD curve in relative exposure units (stops).
Are you trying to determine the individual film speed, the development time or both?

yya · May 18, 2024

Romanko said:
There must be a way to convert the F-number and shutter speed at a given ISO setting to lux (or whatever is the unit of the exposure). However, this is only relevant if you are measuring the ISO speed of the film according to the ISO standard. For practical use it suffices to know the HD curve in relative exposure units (stops).
Are you trying to determine the individual film speed, the development time or both?

Alright, I've given up on measuring the absolute exposure. You're right, I don't actually need to obtain the actual ISO of the film on the HD curve. When plotting the HD curve, my main objective is to understand the impact of development time and different developers on the curve. The actual ISO of the film can be determined directly by checking the density of Zone 2 on the film obtained using a step wedge.

Romanko · May 18, 2024

I would start with plotting densities vs. step number curves which you could later convert to <density film> vs <density step wedge> plots. I did this when experimenting with developers for Kodak Technical Pan using a similar technique - exposing the film in a plate camera through the step wedge. What step wedge are you using? Do you have a densitometer?

yya · May 18, 2024

Romanko said:
I would start with plotting densities vs. step number curves which you could later convert to <density film> vs <density step wedge> plots. I did this when experimenting with developers for Kodak Technical Pan using a similar technique - exposing the film in a plate camera through the step wedge. What step wedge are you using? Do you have a densitometer?

stouffer 4x5 21 step, Yes I have a densitometer

yya · May 18, 2024

Romanko said:
I would start with plotting densities vs. step number curves which you could later convert to <density film> vs <density step wedge> plots. I did this when experimenting with developers for Kodak Technical Pan using a similar technique - exposing the film in a plate camera through the step wedge. What step wedge are you using? Do you have a densitometer?

I will use the density values read from the 21 steps of the step wedge to plot the x-axis, and the y-axis will represent the film densities of the 21 steps.

Romanko · May 18, 2024

Yes, this worked for me. I did not have a densitometer back then so I used the nominal values of the Stouffer step wedge for the x-axis. I then scanned the step wedge itself and the film printed through it and "measured" film densities of the scan by comparison.

yya · May 18, 2024

Romanko said:
Yes, this worked for me. I did not have a densitometer back then so I used the nominal values of the Stouffer step wedge for the x-axis. I then scanned the step wedge itself and the film printed through it and "measured" film densities of the scan by comparison.

Thank you very much for your help. Prior to this, it seems I was caught up in a mystery, forgetting that the values on the x-axis are obtained by subtracting the density of the step wedge from the absolute exposure. Hence, if ISO is not measured, there's no need to consider absolute exposure. I simply assumed, after watching the video by the naked photographer, that the HD curve must be plotted using intensity and time

xkaes · May 18, 2024

RalphLambrecht said:
that book is excellent but has been out of print for many years and is very hard to use. A public library might be your best guess.

I found it very easy to use -- easy to follow and understand, without any expensive equipment needed. That's why I recommend it. Out of print, but very easy to find, too. There are three listed on EBAY alone right now.

Milpool · May 18, 2024

There are a few different ways of doing this depending on the goals, methodology and what kinds of measuring instruments you have.

What film is this? How are you doing the exposure with the wedge? (contacting in-camera, under an enlarger, using a sensitometer)

Ultimately you plot log exposure (either absolute or relative log H) on the x-axis and density on the y-axis. If you are using a reputable film with a known ISO speed, depending on the exposure methodology (enlarger, sensitometer…) you can potentially use a few formulas and assumptions to estimate the exposure the film is receiving (what you’re basically trying to figure out in that case is illuminance, assuming you don’t have a meter that can directly measure it). There isn’t a whole lot to be gained from that exercise though.

If you just want to see how processing affects the gradient and curve shape, you can just stick with relative log exposure on the x-axis and keep it simple. You can then look at the differences between curves. Incidentally unless things are way out of whack, if you develop the film to meet the ISO gradient criterion (see ISO criteria or ISO “triangle”), the ISO speed point of 0.1 above B+F should lie ~3 1/3 stops below the metered exposure.

yya · May 18, 2024

Milpool said:
There are a few different ways of doing this depending on the goals, methodology and what kinds of measuring instruments you have.

What film is this? How are you doing the exposure with the wedge? (contacting in-camera, under an enlarger, using a sensitometer)

Ultimately you plot log exposure (either absolute or relative log H) on the x-axis and density on the y-axis. If you are using a reputable film with a known ISO speed, depending on the exposure methodology (enlarger, sensitometer…) you can potentially use a few formulas and assumptions to estimate the exposure the film is receiving (what you’re basically trying to figure out in that case is illuminance, assuming you don’t have a meter that can directly measure it). There isn’t a whole lot to be gained from that exercise though.

If you just want to see how processing affects the gradient and curve shape, you can just stick with relative log exposure on the x-axis and keep it simple. You can then look at the differences between curves. Incidentally unless things are way out of whack, if you develop the film to meet the ISO gradient criterion (see ISO criteria or ISO “triangle”), the ISO speed point of 0.1 above B+F should lie ~3 1/3 stops below the metered exposure.

Thanks! all done!

Bill Burk · May 18, 2024

yya said:
Sure, I need the absolute exposure value because plotting the HD curve with the absolute exposure value can confirm the ISO value.

You want a repeatable light source that always makes the same amount of light when you use it. That’s called a sensitometer. Later as you use it you can estimate its absolute exposure value (in this case how many meter candle seconds it delivers to the film plane)

After making the sensitometer, use it without knowing and make graphs with only relative labels on the exposure axis. I guarantee you if you use enough light, no matter how much light it was, a graph will appear.

Kind of like if you overexpose or underexpose when taking pictures, if you give the film enough light you’ll get a picture.

So don’t worry about exactly how much. Just hit it hard.

You will be best off buying a Stouffer T2115 step wedge and putting it in contact with film.

You want to hit that step wedge with one or two meter candle seconds of light. That can be something like a bright light for a hundredth of a second, or a candle for a whole second.

The step wedge covers a range of 1:1000.

So the exposure the film gets will be between 0.001 and 1 meter candle seconds. Anywhere in that ballpark will work.

yya · May 18, 2024

Bill Burk said:
You want a repeatable light source that always makes the same amount of light when you use it. That’s called a sensitometer. Later as you use it you can estimate its absolute exposure value (in this case how many meter candle seconds it delivers to the film plane)

After making the sensitometer, use it without knowing and make graphs with only relative labels on the exposure axis. I guarantee you if you use enough light, no matter how much light it was, a graph will appear.

Kind of like if you overexpose or underexpose when taking pictures, if you give the film enough light you’ll get a picture.

So don’t worry about exactly how much. Just hit it hard.

You will be best off buying a Stouffer T2115 step wedge and putting it in contact with film.

You want to hit that step wedge with one or two meter candle seconds of light. That can be something like a bright light for a hundredth of a second, or a candle for a whole second.

The step wedge covers a range of 1:1000.

So the exposure the film gets will be between 0.001 and 1 meter candle seconds. Anywhere in that ballpark will work.

thanks！

Augustus Caesar · May 18, 2024

H&D curves published by film mfrs are made by carefully measured exposure to a calibrated light source. No lenses are involved. Bear in mind that each lens you own will have different characteristics. You cannot get anything close to a true H&D curve at home.

It is not clear to me what you are trying to do. Shutters are not perfectly consistent, and there are many other variables in photography. So long as you have at least the minimum correct exposure, you will be fine. There is no need to measure film speed to five decimal places. It doesn't matter!

yya · May 19, 2024

Augustus Caesar said:
H&D curves published by film mfrs are made by carefully measured exposure to a calibrated light source. No lenses are involved. Bear in mind that each lens you own will have different characteristics. You cannot get anything close to a true H&D curve at home.

It is not clear to me what you are trying to do. Shutters are not perfectly consistent, and there are many other variables in photography. So long as you have at least the minimum correct exposure, you will be fine. There is no need to measure film speed to five decimal places. It doesn't matter!

OK！I understood!

Europan · May 19, 2024

Everybody who commingles H. & D. with I. S. O. is not informed. A step wedge does not exist, because it’s a contradiction. You either have a wedge which is continuous or a series of steps. You don’t get a curve from steps. What a mess in that video! Yeah, and the naked photographer wants daylight on the film but uses an enlarger with incandescent bulb and filter. He’d better built a little box he could use under the sun.

Hurter (the u pronounced German u or like oo in booth) and Driffield, a Swiss and an English, established a scientific method to determine the sensitivity of photographic materials. That was around 1890.

The letters H and D have nothing to do with ordinate and abscissa. We speak of amount of light on one axis and measured density in result after development on the other, in short characteristic (density) curve. The amount of light is the product of intensity of illumination and time. Development is standardised from the chemical formula to time, temperature, to method of agitation or application.

Deutsche Industrienorm, DIN, began in 1917.

ISO photography related work began in 1947.

xkaes · May 19, 2024

Augustus Caesar said:
H&D curves published by film mfrs are made by carefully measured exposure to a calibrated light source. No lenses are involved. Bear in mind that each lens you own will have different characteristics. You cannot get anything close to a true H&D curve at home.

It is not clear to me what you are trying to do. Shutters are not perfectly consistent, and there are many other variables in photography. So long as you have at least the minimum correct exposure, you will be fine. There is no need to measure film speed to five decimal places. It doesn't matter!

Well said. That's exactly why I run my own tests -- and why Richard Henry recommends everyone do the same.

koraks · May 19, 2024

Europan said:
A step wedge does not exist, because it’s a contradiction. You either have a wedge which is continuous or a series of steps. You don’t get a curve from steps.

Weeellll...maybe if you're being very strict. However, a wedge consisting of discrete steps can be (and in practice is often) called a wedge and arguably, as the number of steps approaches infinity, the difference between a true and a 'false' wedge disappears. Also, this is the same reason why you do/can get a curve from steps, but it requires some degree of interpolation. Whether this is problematic, depends on the resolution requirements of the application. In amateur darkroom practice, the curve created with a .15 logD step tablet works quite well to obtain a usable curve, as anyone who has ever done this, can attest to. If you want to study toe- and shoulder behavior in more detail, something like .05 differentiation would be nice, although it's debatable what the real-world gains would be compared to a commonly available .10 tablet.

So technically, yes - but for a first step in the field of sensitometry and/or densitometry (which seems to be what OP's intention is, and what the Naked Photographer arguably caters to - not professionals in the field), using a .15 step tablet to create H/D curves is not a capital sin, nor is it punishable by law to refer to the tablet as a 'wedge'. So maybe cut a guy some slack.

Also, assessments of the Naked Photographer videos might suit better here: https://www.photrio.com/forum/threa...lvergrain-classics.206837/page-2#post-2796915
Post there and you'll be in the company of a few likeminded critics.

Augustus Caesar · May 19, 2024

xkaes said:
Well said. That's exactly why I run my own tests -- and why Richard Henry recommends everyone do the same.

Well, I have done many tests over the last 50 years, using almost every film available in N. America (including DuPont Superior MP film), and I have settled on T-Max 400 (Type II) developed in FX-21. I don't have to worry about developers being discontinued or being out of stock. I have my Leicaflex cameras serviced regularly, so I know they are in good shape.

Create hd curve

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