Carl A Loc: Homosassa FL

Old lighter meter is ASA and ISO the same

jerryc41 Loc: Catskill Mts of NY

Unless there is some tiny technical difference, Yes!

AndyH Loc: Massachusetts and New Hampshire

Not precisely, but it is definitely close enough to use for a working number, especially as the settings were often not all that precise, even on some high end gear.

All vintage light meters were not created equal, though. In film days, I used to make adjustments on several of my prized meters when using at the higher or lower end of their ranges. I still have a Gossen in my bag, which I have been known to pull out and use on occasion. Also have Sekonic/Norwood incident meters in several bags and a pretty good number of Weston Masters from various timeframes. The last time I counted I had about 25 meters. Most are in film camera bags, and some are just gathering dust displayed on a shelf.

Andy

BebuLamar

ASA and ISO are the same as far as light meter is concerned. The old Weston meter did have different speed but those are not ASA. Meters do read differently because although they use the same ASA or ISO (which are the same) but they use different K factor for reflected and different C factor for incident. Minolta and Pentax use K14 while Sekonic uses K12.5. I can't verify which K factor Gossen uses. Minolta uses C330 for incident and I think Sekonic uses the same.

camerapapi Loc: Miami, Fl.

Agree with Andy. The new, more digital oriented exposure meters are better for digital photography than old exposure meters. ISO and ASA are exactly the same.
You can use an old exposure meter but even if it is well calibrated its readings are not necessarily accurate for digital photography.

John_F Loc: Minneapolis, MN

My light meter is an older Sekonic that uses a selenium panel: light incident on selenium generates a current that swings a needle ( a small scale galvanometer ) across a number scale. Now as light is a flux of different wavelengths ( color ), does the selenium generate different currents for different wavelegths? My long ago contact with physics says Yes, but what are the facts? What do modern light meters use for the sensing element and is it wavelength variable?

larryepage Loc: North Texas area

I've found that the biggest challenge with all non-spot reading light meters, but especially older ones, is to make certain that you know the "acceptance angle," or field of view of the meter you are using. I have one older meter (and yes, it is a reflected light meter) that has almost a 180 degree acceptance angle for light. It's hard to use that meter for much of anything and get close to a valid reading.

RWR Loc: La Mesa, CA

I’ve experienced no difference - at a given ISO, exposure is the same for film or digital. The meter in my DSLR is no more accurate than my 50+ year old Luna Pro. Measurements of the same target in the same light are exactly the same. I could give a detailed explanation of how I arrived at that conclusion, but it would take more than 6 or 7 lines and I prefer not to sound like a verbose gasbag.

larryepage Loc: North Texas area

There are at least two families of photosensitive cells. The oldest were photoresistive..their resistance varied in a predictable way, generally as the inverse of the light that fell on them. They were generally made of cadmium sulfide and required an external battery connected in series with them as well as a milliameter also connected in series. Current would be higher when the incident light was brighter, and the meter could be calibrated and marked in any of several different ways. Photovoltaic cells actually developed a voltage across their terminals, and this voltage would cause a current to flow through a connected meter. It was possible to connect either a voltage indicating meter or a milliameter (with an appropriate series resistor) which could be calibrated and marked.

Most modern meters likely use photoresistive sensors, hence they end up requiring an external battery to power the system. Instead of directly driving a mechanical meter, they are connected to any of a number of different types of circuits that can extend their usable sensitivity to very low light levels and can produce very accurate readings.

In the "old days," the selenium cells were less expensive, but the silicon cells produced several times the amount of energy with the same cell area and incident light. The selenium cells, though, seemed to function in a more useful fashion at lower light levels.ble abount of electrical energy.)

george19

Also note you may occasionally see a DIN scale, but I’ve long since forgotten the conversion to ASA/ISO.

More importantly, my light meter is always trouble with TSA...they think it looks suspicious.

amfoto1 Loc: San Jose, Calif. USA

For all practical purposes, ASA and ISO have become synonymous.

Prior to ISO, for many years in N. America we rated film using ASA... "American Standards Assoc."

Many other parts of the world used DIN... the "European" system or "Duetsches Institut fur Normang".

ASA is an arithmetic progression.... while DIN is logarithmic.

Much film, many light meters and some cameras showed both scales throughout most of the 1960s through mid-1980s.

ISO or "International Standards Organization" was first discussed in 1974, published in 1979 and began being adopted in 1984. Initially it was a combination of ASA and DIN. For example, ASA 400/DIN 27 rated film was instead shown as ISO 400/27.

But over time the DIN portion of that number has been dropped so we now only see the ASA equivalent being stated almost universally. There's almost no reference to DIN any more. ISO 400 is the same as ASA 400.

Historically, ASA was introduced in 1943 and DIN in 1934. Prior to the late 1950s when those two became the most widely used standards, there were a number of other systems in use. Weston and General Electric each manufactured light meters and had their own, similar scales. Those two had a lot of influence on ASA. BSI or "British Standards Institute" is another sensitivity scale, pretty closely related to DIN. The Soviet Union had their own GOST, which was similar to ASA. The earliest was Warnerke, named for the inventor of the first sensitometer around 1880, which used a standard of measurement developed along with the device. There were a couple other now-archaic sensitivity measurement scales in use prior to WWII.

Much more info here: https://en.wikipedia.org/wiki/Film_speed

The consolidation and standardization of sensitivity ratings have been driven by two major factors. As film and other photographic products were being improved to offer greater sensitivity to light, new measuring methods and scales were necessary. In addition, increasing globalization of products, especially after WWII, also served to narrow the field.

Makes me wonder if we'll see something new in the future, now that some digital cameras have sensors with ISO sensitivity in the hundreds of thousands or even over one million! The numbers are getting so big and cumbersome that someone has probably already proposed changes to the way we talk about light sensitivity. Or maybe we'll just use Auto ISO all the time and not worry about it!

John Geyer

ISO AND ASA ARE IDENTICAL

John Geyer

DIN is old German speed rating and IS different

photogeneralist Loc: Lopez Island Washington State

The discussion about the spectral response curve of various types of meters seems to me akin o the old argument in the early Catholic Church about how many angels could dance on the head of a pin-- interesting philosophically but of no practical importance . The question is , were the meters close enough to the film's (or now sensor's) spectral response curves to be usable? The answer then was and now remains -- drumroll-- yes

Curmudgeon Loc: SE Arizona

I agree. I have been going through some old Kodachrome slides. Before I got my first FTn metering system almost all of them are either under or over (usually under) exposed. Effective use of a light meter is one skill I never mastered.