Empirically Determining Film Speed

michael_r said:

Without a densitometer I suggest OP take the opportunity to not do the silly EI test, which is little more than a densitometry exercise in the first place.

The practical way to determine if you need an EI that differs from ISO is by making negatives and printing them. If you consistently find yourself struggling with thin shadows, decrease EI. If you consistently find yourself printing down, increase EI.

It should be a determination from tone reproduction rather than an arbitrary criterion.

EDIT: TYPOS

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This.

The speed point is just the attempt to make a formula out of a consensus of what makes a good print. It's not some objective measurement to the material. So might as well just skip it and make a bracketed shot and choose what you like.

Danner said:

Reading 'The Negative' (A.A. 1981), Ansel describe metering for Zone I, shooting slight variations in exposure, then, using your standard developer, temperature, dilution, and agitation to develop the film. And, measuring density using a densitometer to find the one closest to 0.1 density, and that exposure determines the 'true' film speed.

I have no access to a densitometer, so here is another idea, and I wonder if it will work.

Meter a slightly texture surface at Zone V, and then shoot exposures for Zones 0 through X. Print the Zone V exposure to match a standard gray card in density (visual comparison), and then use that enlarger setting to print all 11 Zones. Look a the prints, particularly Zones I, II and VIII, IX, to see how the texture is rendered. Assuming its unbalanced (texture missing where it ought to be, or too much texture where it shouldn't be, then adjust exposure by changing the meter ISO setting to balance out the texture in the those extreme zones. And, when the texture becomes balanced, the ISO setting on the meter that worked is the true film speed.

Does this make sent, or an I nuts?

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> See attached doc explaining how speed is determined:
https://www.kodak.com/uploadedfiles...en_motion_education_sensitometry_workbook.pdf

> Speed is determined with a formula using the exposure in the Speed Point when development is made to deliver the standard ISO contrast (0.62). When you use the Standard ISO speed you start having detail at 3.33 stops, nominally.

> If using the ISO determined speed, light in a 0+/- metered spot is just x10 times the light in the Speed Point, 3.33 stops deliver x10 more light. For this reason when you underexpose 3.33 stops (if using ISO speed) you should be in the Speed Point, building 0.1D over Base+Fog

> Not having a densitometer ? Purchase an Stouffer T2115 density wedge and scan it alongside your negative, then compare gray level values.

> If you are interested in Practical Sensitometry then Beyond The Zone System (Phil Davis) book is a very good recommendation, used are quite cheap, and you will master all that in depth.

@138S. Thank you for your thoughtful reply. I have reviewed the Kodak reference, and it's a head full of science to digest. Although, my base level of knowledge has grown since I posted their thread. There seems to be a gulf between and acceptable print and a fine print. I will keep trying...

Danner said:

There seems to be a gulf between and acceptable print and a fine print. I will keep trying...

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There is, and the first step in crossing this gulf is learning to see the difference. I freely admit, I find it hard to see the subtle dodging and burning done by master printers -- but I know from experience that the more you print, the more you can see the results of manipulations in the print.

Danner said:

There seems to be a gulf between and acceptable print and a fine print. I will keep trying...

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Yes... a sound authentic darkroom print is quite more challenging to get than a digitally edited one, but a darkroom print can be more a handcrafted art object where the artist's hand can be seen, some may say that only the final image counts, others may value a lot the crafting path, those are always very personal considerations... still there is no doubt that a sound pure optic processing tells a lot about an artist.

Craig75 said:

This.

The speed point is just the attempt to make a formula out of a consensus of what makes a good print. It's not some objective measurement to the material. So might as well just skip it and make a bracketed shot and choose what you like.

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Poetic and sounds good to the ear, but I would say it's literally incorrect to say of the speed point that it's "not some objective measurement".

Craig75 said:

This.

Adding to Bill's post...

The speed point is just the attempt to make a formula out of a consensus of what makes a good print. It's not some objective measurement to the material. So might as well just skip it and make a bracketed shot and choose what you like.

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Speed Point it is a totally objective measurement made in some particular conditions. It is not an attempt to make a formula, but it is the exposure required to increase density 0.1D over fog+base, so it describes a key property of a material in the test conditions.

A photograper may find the precise Speed Point location of a film under the conditions of his particular processing...

...but if using the Speed Point specified in the datasheet then some variables should be kept in mind:

> We may use a different developer or Contrast Index which can displace the Speed Point by some 0.5 Stop, but a proficient photographer (in the darkroom) may make a good guess about that shift (depending on the nature of his processing) thus reducing the error to (say) less than 1/3 stop.

> Speed point doen not tell how toe is, but a proficient photographer knows how the toe of his film is, and many modern films are pretty linear so many behave similarly around the Speed Point.

> Color Filtration and LIRF may have an impact.

> Our metering system may have "personality".

> Our aperture/shutter may lack accuracy.

> Film aging (expired) may vary the Speed Point position.

Craig75 said:

This.

The speed point is just the attempt to make a formula out of a consensus of what makes a good print. It's not some objective measurement to the material. So might as well just skip it and make a bracketed shot and choose what you like.

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The speed point IS an objective measure of the material that ATTEMPTS to match the experimental consensus of what were seen to be good prints. Nothing wrong with bracketing. Many cameras make it easy. Even with large format, you always get two exposures in each holder.