How To Understand Densitometer Readings

[IanBarber]

I have been lent a densitometer to experiment with.

Has anyone got any good online resources which I can read to better understand how to use them.

For example, With the emulsion side up. I have done measured a deep shadow on the negative and its reading 0.13 but at the moment I am not quite sure what that is telling me

Any information would be helpful

[Michael R]

Ian - you cannot do much better than this:

https://www.kodak.com/uploadedfiles/motion/US_plugins_acrobat_en_motion_education_sensitometry_workbook.pdf

It is an excellent, easy to follow introduction to sensitometry/densitometry, which is what you're doing.

To make a long story short, for transmission densitometry (reading densities of negatives), the densitometer reading is a measure of the opacity of the film. The higher the number, the more dense the film, and the more light it blocks. Low numbers would be relatively clear (shadow areas) and high numbers would be relatively dense (highlight areas).

Whether the negative should be read emulsion up or down depends on the densitometer type.

The densitometer may or may not need to be calibrated.

0.13 would be a very thin deep shadow. Assuming the densitometer is calibrated, you should first take a reading of an unexposed region of the film. This will give you the lowest density (film base + fog). Then you subtract that number from all your subsequent readings to give you the effective "net" density. The net density can be thought of as image density. For example suppose you read an unexposed part of the negative and the densitometer indicates 0.05, that would be your base+fog density. Then you would subtract 0.05 from all your other readings. 0.13-0.05=0.08, meaning the area you read has a net (image) density of 0.08. In Zone System terms that would be a very deep shadow on the low side of Zone I.

[IanBarber]

Thanks Michael, I shall investigate that link you sent.

At this stage, I guess I am more interested to make sure I have enough density in the shadow areas to reveal some texture. I have read that Zone 1 is 0.1 above film base and fog so I am guessing that Zone 3 should be about 0.9 above film base and fog but I could and are probably wrong there

[Michael R]

Actually Zone III would be much lower than 0.9, closer to 0.4 depending on EI and contrast index.

Zone I is typically targeted at ~0.1 above film base + fog.

Keep in mind a densitometer reading can only be a guide, since "detail" is a function of contrast, not density. Most films will have good local contrast at Zone III densities if you are calibrating to a Zone I density of 0.1. Ultimately you have to judge shadow detail by looking at your prints (or digital output), not densitometer readings.

[IanBarber]

Ian - you cannot do much better than this:

https://www.kodak.com/uploadedfiles/motion/US_plugins_acrobat_en_motion_education_sensitometry_workbook.pdf



This has to be one of the best documents I have read to date

[IanBarber]

The densitometer may or may not need to be calibrated.

0.13 would be a very thin deep shadow. Assuming the densitometer is calibrated, you should first take a reading of an unexposed region of the film. This will give you the lowest density (film base + fog). Then you subtract that number from all your subsequent readings to give you the effective "net" density. The net density can be thought of as image density. For example suppose you read an unexposed part of the negative and the densitometer indicates 0.05, that would be your base+fog density. Then you would subtract 0.05 from all your other readings. 0.13-0.05=0.08, meaning the area you read has a net (image) density of 0.08. In Zone System terms that would be a very deep shadow on the low side of Zone I.

Are there any charts that map densities to zones ?

[Leigh]

Whether the negative should be read emulsion up or down depends on the densitometer type.If a transmission densitometer gives different readings for emulsion-up v. emulsion-down, the meter is broken.
Or else you have extremely bright ambient light sneaking into the measurement aperture.

This would be analogous to producing different enlargements depending on emulsion orientation.
It doesn't happen (except for the image being reversed).

- Leigh

[Leigh]

To answer the original question...

Density is one way of expressing the amount of ambient light transmitted through the emulsion.
This is of significance during printing (or viewing of a transparency).

The units is logarithmic. A factor of 2 equates to a value of 0.3, 4 = 0.6, 8 = 0.9, 10 = 1.0.
Each step of 0.3 equates to one aperture stop.

A density of 0.6 would equate to closing an aperture by 2 stops, or speeding the shutter by 4x.

- Leigh

[Drew Wiley]

A helpful book from the heyday of densitometers is Sensitometry for Photographers by Jack Eggleston.

[Greg]

Highly recommend the following book:

Photographic Sensitometry: The Study of Tone Reproduction
by Hollis N. Todd, Richard D. Zakia | Hardcover

You can easily find a copy up for auction for $5-10.00. When I was at RIT, became good friends with Hollis Todd. The book at first seems overwhelming at first but once you skim its contents, it becomes easy reading.

[Luis-F-S]

Highly recommend the following book:

Photographic Sensitometry: The Study of Tone Reproduction
by Hollis N. Todd, Richard D. Zakia | Hardcover

You can easily find a copy up for auction for $5-10.00. When I was at RIT, became good friends with Hollis Todd. The book at first seems overwhelming at first but once you skim its contents, it becomes easy reading.

+1!!!

[Jerry Bodine]

Are there any charts that map densities to zones ?

Here's a screenshot of a table from Way Beyond Monochrome Ed.2:

171073

[Pere Casals]

Are there any charts that map densities to zones ?


First see here pare 10 and 11 of the file pointed byMichael file:///C:/Documents%20and%20Settings/P.PC6/Escritorio/PS/US_plugins_acrobat_en_motion_education_sensitometry_workbook.pdf

In ISO conditions (standard development for ISO), if ISO Speed is 100 then Zone V has a density Base density of base + 0.72, every zone you move up or down it has a constant density shift, an exposure step (a zone) is twice the light, so in the Hor log scale it moves 0.3 units, the density increase/decrease it would be 0.3 * curve stepness this is 0.3 * 0.6 = 0.18, so (with standard ISO development) every additional zone moves 0.18D.

It also happens with other ISO speeds, curve is has the same stepness, so ISO norm says that Zone V has a density = 0.72D + film base density. Film base density is the one of the areas that received no light. Add/Substract aprox 0.18D for each additional zone.


But this depends on your development (that cannot be the same than ISO norm)... and it is related to Scene Zones, not to print zones. In fact you can place a Zone of the scene in another zone of the print...

I think I'm not mistaken, other users should review that.


Regards


PD: edited to replace 0.9D by 0.72D, it was a great mistake

[Pere Casals]

Here's a screenshot of a table from Way Beyond Monochrome Ed.2:


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171073

PD: here I was is wrong.

Hmmm, I don't understand why Z-V do not says 0.9D + base (This is Way Beyond Monochome book !!!)


https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/ISO6speedMethod.png/540px-ISO6speedMethod.png

https://en.wikipedia.org/wiki/Film_speed


"Speed point" is at 0.9D over base (0.8+0.1), since year 1960.

This table shows speed point in Z-VI, instead Z-V ....

Until I know photometers aim "n" point in the graph...

Do the photometers aim to "n" point ?

Do the photometer aim to Z-V ?

[Michael R]

Pere - point n is not the metered exposure and is not Zone V.

[Pere Casals]

Pere - point n is not the metered exposure and is not Zone V.

Hello Michael,

You are right... I was mistaken.

Please look this chart:

http://www.largeformatphotography.info/forum/attachment.php?attachmentid=166063&d=1497314127

We dicussed that in this thread: http://www.largeformatphotography.info/forum/showthread.php?139495-Question-On-Subject-Brightness-Range&p=1395912&viewfull=1#post1395912


Point (4) is the ISO Speed point.

Point (5) is at 10x more lux than Point (4), at it is the point where meters are calibrated for the rated speed resulting from the graph.

So 10x is 2.3 stops or zones, and +1H

IMHO Zone V is at point (5) ,

Then... where "n" point is? It should be at +1.3 H, at the right of Point(4).

So "n" point is 0.3H at the right of Z-V point, and this is an stop.

So the "n" calibration point is one stop overexposed from the meter reading point.


In the past (before 1960) n point and meter point were the same point, but norm changed in 1960, ASA PH2.5-1960 simply mutiplied speed of all existing films by 2.

Is because this that there is exactly one stop from n point to the meter point.

Regards.

[Michael R]

The metered exposure is 1 log H (3 1/3 stops) to the right of Hm. Point n is 1 stop higher.

[Pere Casals]

The metered exposure is 1 log H (3 1/3 stops) to the right of Hm. Point n is 1 stop higher.

This is, exactly 1 stop. I was wrong.

[neil poulsen]

Thanks Michael, I shall investigate that link you sent.

At this stage, I guess I am more interested to make sure I have enough density in the shadow areas to reveal some texture. I have read that Zone 1 is 0.1 above film base and fog so I am guessing that Zone 3 should be about 0.9 above film base and fog but I could and are probably wrong there

I don't think it necessarily works out that way. Zone 3 film density is the negative density that results when the film receives a Zone 3 exposure and then developed at "Normal" development.

Determining "Normal development" requires some testing. Indeed, you first determine THE ASA that places a Zone 1 exposure on the film at 0.1 density units above fb+f. Then based on my past testing, Normal development becomes that length of development time such that a Zone 8 exposure on the film yields a negative density of 1.35 density units with the light meter set at the above ASA.

Just to clarify, a Zone 1 exposure is 4 stops darker than the light meter reading, a Zone 3 exposure is 2 stops darker than the light meter readings, and Zone 8 exposure is 3 stops brighter. (e.g. determine the aperture and shutter speed on an area to expose using a light meter, and before exposing, open the aperture by 3 stops.

[Luis-F-S]

There's little interesting information in Zones 1-3, I'd be more concerned with getting the Zone VII exposure (1.15 above fb+f) correct. There are entire books written on photographic sensitometry, it may be worthwhile reading. One was referenced above. Also I assume that Neil's post above supposes that you are using a spot meter, otherwise, all bets are off. If you haven't already done so I'd get the Zone VI Workshop by Fred Picker.

[neil poulsen]

. . . Also I assume that Neil's post above supposes that you are using a spot meter . . .

At the very least, reflected light readings.