18% calibration???

Why do people refer to 18% "neutral gray" when talking about meter

calibration? I thought the ANSI standard adopted by camera makers and

metering equipment producers was 12-13% reflectance?<BR>

<BR>

Could someone shed a light (sorry!) on this? Thanks!<BR>

<BR>

Donny

<a href="http://www.photo.net/bboard/q-and-a-fetch-msg.tcl?msg_id=000Til">From the archives</a>. I don't think it answers your question dead-on, but it's close.

Something to add to the mix:

 

The manual for the Metz 44 MZ-2 flash (which I downloaded from www.metz.de) states under the topic of manual flash exposure correction:

 

"The automatic TTL flash exposure system of most cameras is matched to a 25% degree of light reflection by the subject (average amount of light reflected by subjects show with flash)."

 

Also, under the topic of maximum flash range indication in TTL and automatic flash mode:

 

"The mecablitz LC display indicates the maximum flash range. The indicated value relates to a factor of 25% of light reflection by the subject, which applies to most photographic situations."

 

What I get from these statements is that if I were to measure the maxiumum output of a Metz 44 MZ-2 with a incident flash meter calibrated to 18 % gray, I would measure 1/2 stop less output.

 

Perhaps other flash manufacturers also use 25 %.

18% grey is related to the Zone System. Roughly 12% is indeed the typical calibration for most light meters. One doesn't necessarily have to do with the other.

 

The shorthand answer is, 18% corresponds to a Zone in the Zone System. The Zone System was developed over time and the Zones even varied a bit over that time, starting out as a nine-zone scale (I-IV) and ending up as an eleven-zone scale (O-X), altho' Zone V, neutral gray, remained a constant *within the Zone System*.

 

Makers of light meters, handheld and TTL, were never obligated to Ansel Adams, Minor White or anyone else to calibrate meters to 18% gray. They were more concerned with consensus standards organizations such as ANSI, ISO and others, just as film manufacturers are.

 

Some handheld meters did include provisions for use with the Zone System. Most didn't. That's why modifications were offered to spotmeters popular among zonies, such as the Pentax Spotmeter V, to make the meters more user friendly to the Zone System.

 

According to at least one report Kodak had considered switching the 18% gray standard to something closer to meter calibration, like a 12% standard. Supposedly upon hearing this Ansel Adams became outraged and made himself a fixture in the Kodak corporate office until they agreed not to change the standard. He didn't expect meters to magically be recalibrated to 18% gray - he just wanted the 18% gray card that had become associated with Zone V of the Zone System to remain 18% gray. True or not, it's an interesting story.

 

As evidence of the difference (not disparity or discrepancy) between meter calibration and 18% gray cards, consider the fact that it is generally recommended to open up one-half to one full stop from the meter reading for photographing most light to medium skin tones. Zone V may be the mid-tone but it's not necessarily the most appropriate zone for placing skin tones.

In graphics arts and lith work; one either used a white card; and used modified by 5x; or an 18% grey card; with a 1x factor. This goes back before ANSI; or even there was a ASA speed system; to before WW2. <BR><BR>Pre WW2 books on copying mention a neutral grey card for exposure control. The card included in a scene; copy board; etc allows a reference point; whether a meter was used at all. The zone system was started after Ansel read the Kodak literature; or copy camera literature; since the grey cards existed at least a decade or two before they brought out the zone system iabout 1939.<BR><BR>The grey cards existed before the zone system; or Ansel.<BR><BR>The zone system just simplfies the H&D curves into zones instead of a photo engineers density and real exposure numbers. Imagine simplifying a football announcers callout to 10 zones of 10 yards; instead of stating the actual ball is on Parkville's 38; with 7 yards to go. Photographers like the simplified model. <BR><BR>

The pre WW2 copy book we had mentioned that the white side was 90 percent reflective; and the "grey side" was about 18 percent refective. This is where the 5x exposure ratio comes from; ie 90/18. Since this card was already in use by printers; probably old Ansel just made it into one of his zones; since the cards were already a reference standard for a decade or two. Meters ; if any; were not any hallmark in accuracy probably at that time. This was well before the norwood director incident light meter of the 1940's. It was common to calibrate reflective meters to incident meters; using 18 percent cards; in the 1960's. This is how the National camera repair course I took had their settup and method. The more recent 12.5 percent meter calibration is well after the B&W asa redefine of 1960. There are USA; din; JIS and ansi standards in photo stuff. At one time the German and Japanese meter standards were different. Long ago; film had different film speeds; for about 3 different meters; GE; weston; etc...