Spot meter & ZS vs. BTZS & incident light

[Helen B]

Mark,

You are correct. The idea was to show readings taken from a real-world object that one would wish to record detail in, using normal photographic metering techniques. All metering caveats apply. This was not a scientific test, nor is it relevant to anything else apart from that one particular situation. It's just an illustration of the kind of subject that Tim asked about, as far as I understand.

If you did only allow 2½ stops over the fully-illuminated incident reading for the brightest highlight, the actual brightness would be about 2½ stops over your allowance, in this instance.

Best,
Helen

 

[mark]

that is what I figured.

 

[Paul Howell]

Forgive my confusion, I have not delved into the BTZS (nor new math) but when I was trained you took an incident reading from the subject facing the camera, and a reflective reading facing the subject from the camera. I don't know if Helen was pointing both the spot and incident meters from the view point of the camera toward the subject. The spot meter reading seems underexposed to render black top 18% gray.

Confused in Phoenix

 

[esearing]

I think I understand...

If Hellen had taken an actual picture of a gray card with the incident meter reading and the sun behind her the gray card would appear on zone v. Bright spots and shadows fall where they may.

If Hellen had taken the picture of the grey card with the spot meter reading, Wouldn't she have had to open up 3-5 stops to get the bright spot white and the grey card on zone V? Or do you use the long exposure and reduce development dramatically to get it all on a wide lattitude film. I don't see this working at all for color slides.

Thus there is really 2 or less real stops to create the same middle grey exposure. It might have been useful to take a reflected spot reading of a grey card from the camera position to determine the variances between the reflected sunlight on the grey card and the bright wet pavement.

 

[rbarker]

I think I understand...

If Hellen had taken an actual picture of a gray card with the incident meter reading and the sun behind her the gray card would appear on zone v. Bright spots and shadows fall where they may.

Agreed. An incident reading ignores the reflectivity of the objects in the scene, thus rendering them in their "true tonality" - assuming the film or media has sufficient range.

If Hellen had taken the picture of the grey card with the spot meter reading, Wouldn't she have had to open up 3-5 stops to get the bright spot white and the grey card on zone V? Or do you use the long exposure and reduce development dramatically to get it all on a wide lattitude film. I don't see this working at all for color slides.

Thus there is really 2 or less real stops to create the same middle grey exposure. It might have been useful to take a reflected spot reading of a grey card from the camera position to determine the variances between the reflected sunlight on the grey card and the bright wet pavement.

I don't know that we can actually determine this. I'm not clear whether Helen's spot reading was of a maximum-black area of the wet pavement, or of a reflective highlight area. That makes a huge difference in how one would interpret the reading. If the spot reading was of a highlight in which detail was to be retained, one might open up 2-3 stops, for example. If of a black area, the adjustment would be in the opposite direction - closing down 3-4 stops, perhaps.

The key point to remember is that a reflective reading gives the exposure needed to render the area being read as a middle gray (e.g. Zone V). Assuming you know accurately what area is being measured (as you would with a spot meter), you can then adjust the suggested exposure to "place" that value where it should be (or, where you want it), and everything else falls wherever it will accordingly. With B&W films (some responding better than others), you can adjust development to either expand or contract the contrast range for the desired effect. Naturally, that's not really possible with color film. The BTZS and Zone System methods are simply two different approaches to metering and development to achieve the desired result.

 

[Kirk Keyes]

"Incident meter directed straight at the sun: f/11½ (no surprise!)"

Let this be Zone V.

"Spot meter reading off wet blacktop: f/64½"

I get 5 stops here - so this would be Zone X. (Forget about all this 2.5 stops over 2.5 stops stuff.)

This should print as pure white and would qualify as a specular highlight, i.e. a highlight that has no detail.

Kirk - www.keyesphoto.com

 

[Paul Howell]

All meters read 18% gray or zone V, a wide angle reflective meter or an incident meter reads middle gray, assuming that the scene has a normal range of values. A spot meter reads 3% to 1% of the scene and assumes that the photographer will find a middle gray or render the most important element middle gray. If Helen had taken a reading of a gray card on the pavement the pavement would have fallen in zone II to IV. The zone system was designed to let the photographer chose how the most important aspects of the scene will be rendered (previsualization), The church in Toas New Mexico that Ansal Adams took many pictures of is not snowey white, at least the last time I was there in the 70's, it is an off white. The photographer meters for the shadows allowing the shadow to render detail and develops for the high values. Sound easy but it is not, takes a lot of work.

Being lazy and having developed many bad habits of the years I just bracket, some times 3 to 4 stops over and under and fix in the dark room.

Still confused in Phoenix

 

[Helen B]

Hey folks, remember the original question, the history of this thread, and the purpose of the readings.

It was a clear enough question as far as I understood it. Something along the lines of: "Can an incident meter be used to measure the scene brightness range (a.k.a. required exposure latitude) when the scene includes bright reflections (I'll avoid 'specular' because it seems to mean too many different things to different people) from surfaces that we wish to maintain detail in (ie we don't want them to blow out)?"

It's an easy enough question for me to answer for myself, because I carry both incident and spot meters, or a combined incident and spot meter - so I frequently use both types of measurement. Both types have their limitations, but Minor White and Phil Davis (among many others, no doubt) have both given perfectly sound reasons why incident metering can be used for the zone system, as long as you understand the assumptions and limitations. That applies to everything - including the adoption or abandonment of the Zone System itself, surely?

Best,
Helen

 

[Paul Howell]

You can measure the range of a scene with a incident meter, but you must be at the subject facing the camera and meter both the high and low values. The question I still have does it have any practical value? Not having any knowledge or experiacne with the BTZS I just don't know. I do use an incident meter for natural light portraits, but for fast action or landscapes I cannot figure out how to make it work.

 

[DeanC]

Dean,

Er... 2½ stops from f/11½ to f/64½?

Er...

It was early and my brain hadn't had its full dose of coffee yet?

I can't tell the difference between 1.4x and 2x?

I know... Hackers took control of my account and posted that! Yeah, that's it...

In the immortal words of Roseanne Rosannadanna: Never Mind!

Dean

 

[Chuck_P]

You can measure the range of a scene with a incident meter, but you must be at the subject facing the camera and meter both the high and low values. The question I still have does it have any practical value? Not having any knowledge or experiacne with the BTZS I just don't know. I do use an incident meter for natural light portraits, but for fast action or landscapes I cannot figure out how to make it work.

I'm not sure how the incident meter can be used to meter both the high and low values since the diffusing dome is designed to "average" all the light falling onto it when positioned on the side of the subject that is receiving the light. If one intends to meter both the high and low values, then it best be done with a spot meter so that an average of the two can be obtained.
___________

Hellen said earlier that too many people have different views of specular light. To those who take AA's zone system seriously (and I am one), then his definition should be accepted and goes like this: "Polished mirrorlike surfaces yield specular reflections where most of the source light is refelcted in a beam...........Since all scintillations are direct reflections of the light source, they are far brighter than a diffuse area, and they can lend a sense of briiliance to a photograph. Unless the specular areas are large, the duffuse and specular reflections combine to produce an average diffuse luminance value read by the meter. It is usually best in practical terms to try to direct the meter at areas that do not contain strong scintillations" (i.e., specular reflections).

So, what I get from that is this: without a doubt, the spot meter makes the best utilization of the ZS (i have no idea about BTZS), and do not concern yourself too much with specular reflections as long as they can be kekpt to a minimum on the negative.

Chuck