B&W film speed for artificial lightings/ tungsten?

[kl122002]

I remember when I was learning photography in old days, especially in B&W , I was told under different lighting condition (daylight vs tungsten) has different Exposure Index like Ilford FP4 has EI125 for daylight while and 80 for Tungsten. But now I can't find any.

Today the one that still showing 2 film speed on the box is only Ilford Orho , 80 for daylight and 40 for tungsten.
Have we changed the manufacturing process which we could now ignore the lighting condition for film speed?

 

[koraks]

Have we changed the manufacturing process which we could now ignore the lighting condition for film speed?

No. But it's still dependent on the spectral sensitivity of the film and the nature of the artificial lighting. There's variation in both, and this variation has increased quite spectacularly in the latter. However, the principle still applies as much as it ever did. You could work out the details using the datasheet of the film used and the spectral distribution of the artificial light - or just use a healthy safety margin when making the exposures and call it good

 

[Mr Bill]

Hi, without giving this much serious consideration, I'd be inclined to guess that it's more likely to have been an exposure meter consideration.

If you have any of those older film data sheets I'd guess that they are just saying to set the exposure meter to such-and-such (lower) exposure index for tungsten lighting. Which roughly means that a "normal" metered exposure is fine for "daylight," but would tend to cause underexposure under tungsten light. So, to correct for this they recommend setting the meter to some lower "film "speed."

I'm guessing that modern exposure meters have a spectral response more similar to a (panchro) film, and thus changes to the meter's "film speed" are no longer needed. But... in the case where the meter's spectral response is different from that of the film (ie your case of Ilford "ortho" film) then some adjustment to the meter setting is still called for.

 

[Stephen Benskin]

It's pretty much the spectral sensitivity of the photo cell in the exposure meter and what color temperature to which it was calibrated. Stimson, Allen, An Interpretation of Current Exposure Meter Technology, Photographic Science and Engineering, Vol 6, No 1, Jan-Feb 1962.

You can find more papers at http://beefalobill.com/benskin/content.

 

[Ian Grant]

The Tungsten light speeds were given because it was once very common to use Tungsten "Photoflood" studio lighting. Studio flash largely killed off tungsten lighting, and these days people used Daylight balanced LED.

If shooting in warm balances modern LED lighting you still need to adust the film speed.

Ian

 

[BrianShaw]

For panchromatic film the difference is about 1/3 to 1/2 stop.

 

[ic-racer]

It's pretty much the spectral sensitivity of the photo cell in the exposure meter and what color temperature to which it was calibrated. Stimson, Allen, An Interpretation of Current Exposure Meter Technology, Photographic Science and Engineering, Vol 6, No 1, Jan-Feb 1962.

View attachment 327445

You can find more papers at http://beefalobill.com/benskin/content.

That paper is from 1962, is there anything more current?

I'm working on a light-meter calibration light source and am seeking more info.

 

[Stephen Benskin]

That paper is from 1962, is there anything more current?

I'm working on a light-meter calibration light source and am seeking more info.

There's a good chance but I'm not aware. What about the exposure meter standard? It has a section or two on the light source.

 

[ic-racer]

What about the exposure meter standard? It has a section or two on the light source.

Do you mean these?
ISO 2721:2013 Photography — Film-based cameras — Automatic controls of exposure
ISO 2720:1974 Photography — General purpose photographic exposure meters (photoelectric type) — Guide to product specification

 

[Mr Bill]

That paper is from 1962, is there anything more current?

I'm working on a light-meter calibration light source and am seeking more info.

As Stephen just pointed out, the exposure meter standard. (I thought he had posted a copy of the 1971(?) ANSI standard somewhere, but don't see it listed.) I know that standard had been recertified multiple times, and might even still be current (in the ISO version).

In short, the light source standard was at, as I recall, 4700 degree K correlated color temperature. This was achieved via a tungsten light source filtered through a specified chemical solution. Aside from the difficulty of the "filter" it was also necessary to have a "calibrated" tungsten light source at something like 2856K (CIE illuminant A, I think). Back when I was practically a kid we (the large photo outfit where I worked, QC department) did paper testing with a Kodak-built sensitometer. It used a very expensive calibrated tungsten lamp. The certification with the lamp specified both the mounting position (the sensitometer had a graduated scale for the lamp holder assy) as well as an ammeter setting (the sensitometer was adjustable). Under these conditions there was a known color temperature and light output at the platten. I have no idea where to go for such a lamp today.

I checked the IS&T Handbook of Photographic Science and Engineering (1997); they confirm the same light source and color temperature for the then-current ISO 2720 standard.

Fwiw my understanding is that the color temperature was selected as a compromise to minimize errors between "daylight" and tungsten metering. I would guess that it's not that significant with modern sensors.

As I recall Richard Henry's book (Controls in B&W...?) had a fairly long discussion about his attempts to establish a light source for metering. My fuzzy recollection is that he ended up with a specific GE 100 Watt light bulb.

I'll be glad to look up any questions you have about these references.

 

[ic-racer]

I'll be glad to look up any questions you have about these references.

I might take you up on that. I don't have any of the ISO documents or the ANSI either, so I was scanning the internet for articles that paraphrase them, but, not surprisingly, many search hits lead back PHOTOTRIO! In fact, that is how I came back to this thread; via google.

This is the device I'm making from plans on Github. One issue is the creator only is supplying pre-compiled .hex 'firmware.' Not the editable Arduino sketch to run it. I'll be kind of locked in to the creators interpretation. Though he indicated a "Peter Woodford" tested it's behavior. I don't see him on Phototrio, but on cinematography forums.
The creator did make a calibration function with values held in EPROM. I suspect it will work OK for my purposes, but since it is LED based, I was initially concerned. However, when you think of it, most indoor lighting will be LED soon anyway, so LED is probably best.

 

[Stephen Benskin]

 

[Mr Bill]

I was just looking through Henry's book, Controls in Black and White Photography (2nd edition, 1988) and came across some comments that may help explain the original question.

Per Henry the 1957 ANSI standard for exposure meters (ANSI PH 2.12-1957) used a calibration light source of between 2680 and 2850K (meaning a tungsten bulb).

The 1961 standard (ANSI PH2.12-1961) changed the light source to 4700K color temp. Per Henry, the Foreword to this new standard includes: "This change improves the performance of meters in daylight and makes tungsten film speeds unnecessary for many panchromatic negative materials."

That's all I know and it doesn't seem entirely sensible to me but... it presumably is where the separate tungsten film speeds started to become unnecessary. Most likely the actual 1961 standard explains the reasoning more thoroughly and it probably makes sense; I'm just not seeing it.

A second note on Henry's book, regarding the GE bulb I mentioned. It's pretty much irrelevant. He used it as a method to make a crude check for 1 degree spot meters. At the time, ~1985, the GE lighting division told him that these bulbs would be within 5% of the rated lumens 95% of the time. So he came up with some test conditions for the lamp, etc., and a typical reading for the spot meter. He pointed out that other testers would need to use the exact same bulb - nothing else would suffice, in order to compare results. So 35-40 years later I'm a little skeptical that one would find the identical incandescent bulb.

 

[Stephen Benskin]

That's all I know and it doesn't seem entirely sensible to me but... it presumably is where the separate tungsten film speeds started to become unnecessary. Most likely the actual 1961 standard explains the reasoning more thoroughly and it probably makes sense; I'm just not seeing it.

An Interpretation of Current Exposure Meter Technology which ic-racer referred to in an earlier post answers the question as to the color temperature change in the calibration light source.

 

[BrianShaw]

For panchromatic film the difference is about 1/3 to 1/2 stop.

Perhaps I should have stated, some panchromatic films. Some of the Tri-X data sheets, 2002 for example, don't mention a color temperature differential for EI. See these film data sheets which do specify a differential. Doesn't seem to be a difference in the date of the standard as some films have both EIs listed on the same data sheet. It could be just as easily assumed that the tungsten speed ceased being documented because use of the film became predominately daylight lighting.

https://125px.com/docs/motionpicture/kodak/5231-PLUS-X.pdf

EXPOSURE INDEX/DIN (For development to a gamma of 0.65 to 0.70.)
Daylight—80/20
Tungsten (3200 K)—64/19

https://www.kodak.com/content/products-brochures/Film/TRI-X-7266-Technical-Data-EN.pdf (Although this is motion picture film and there may be a typo)

Exposure Indexes
Tungsten (3200K) - 160
Daylight - 2001

To me, the EI difference, assuming that the Tri-X reversal daylight EI was intended to be 200, seems in the noise from a practical perspective and barely worth mentioning.

 

[Stephen Benskin]

 

[Mr Bill]

An Interpretation of Current Exposure Meter Technology which ic-racer referred to in an earlier post answers the question as to the color temperature change in the calibration light source.

Thanks Stephen. I'm sure I've read this before but without appreciating the significance of the change in calibration light source. Which, according to the graph you just posted, helped to balance the "color temperature errors" between two classes of then-existing exposure meters - those that were substantially red-sensitive vs blue-sensitive.

 

[albada]

Studio flash largely killed off tungsten lighting, and these days people used Daylight balanced LED.

It appears to me that, more and more often, the standard light-spectrum for various purposes is CIE standard illuminant D65. Is that true of the latest meter standard?
The 4700K was a compromise to handle both tungsten and daylight, and it has some inaccuracy for both, so I find it hard to believe that the current standard for meters is 4700K. But maybe it is.

BTW, does anyone know of a manufacturer of D65 LED emitters? The common "white" LEDs have a valley in light blue, and try to compensate with a spike at royal blue (~ 550 nm). For accurate work, that's not good enough.

Mark

 

[RalphLambrecht]

Hi, without giving this much serious consideration, I'd be inclined to guess that it's more likely to have been an exposure meter consideration.

If you have any of those older film data sheets I'd guess that they are just saying to set the exposure meter to such-and-such (lower) exposure index for tungsten lighting. Which roughly means that a "normal" metered exposure is fine for "daylight," but would tend to cause underexposure under tungsten light. So, to correct for this they recommend setting the meter to some lower "film "speed."

I'm guessing that modern exposure meters have a spectral response more similar to a (panchro) film, and thus changes to the meter's "film speed" are no longer needed. But... in the case where the meter's spectral response is different from that of the film (ie your case of Ilford "ortho" film) then some adjustment to the meter setting is still called for.

+1