A Primer on Incident Metering.

[pdeeh]

What I found particularly instructive was to shoot a number of scenes twice - once incident, once (average) reflective - and compare the results

 

[jstraw]

What I found particularly instructive was to shoot a number of scenes twice - once incident, once (average) reflective - and compare the results

Sometimes it's instructive to simply spot meter, then incident meter and see what difference there is in the suggested exposures, if any and think about why.

 

[pdeeh]

If you have a spot meter, yes no doubt

 

[markbarendt]

Sometimes it's instructive to simply spot meter, then incident meter and see what difference there is in the suggested exposures, if any and think about why.

I've actually done this against every meter I have had the opportunity to even hold for a few moments. This is a great way to learn any new camera meter or ...

 

[Poisson Du Jour]

Sometimes it's instructive to simply spot meter, then incident meter and see what difference there is in the suggested exposures, if any and think about why.

That doesn't make sense. A spot meter has a very limited angle of read, typically 1° to 5° — it is very explicit in just what it is viewing. How great is the tonal range that a spot meter can see andcompared to the blanket 'view' of incident which cannot determine a dark or light tone, or a range of tones?

 

[markbarendt]

That doesn't make sense. A spot meter has a very limited angle of read, typically 1° to 5° — it is very explicit in just what it is viewing. How great is the tonal range that a spot meter can see andcompared to the blanket 'view' of incident which cannot determine a dark or light tone, or a range of tones?

What I believe jstraw is referring to is comparing the derived camera settings from each, that was what I was referring to also.

The tonal range can be defined by an incident meter. One reading pointed at the light source the other at the camera, the difference tells you if it is high medium or low contrast. You can also place the meter in the shade for the shadow reading. BTZS does exactly this. Sure, the math is slightly different than Ansel's ZS but incident meters can and do give very usable numbers.

The spot meter can provide the reference point needed tie a specific tone from scene (like the dark or light point) to a specific point on a negative, a valuable thing if you are literally following Ansel's instructions and shooting landscapes. That though is the special case rather than the norm.

For the grand majority of photography, mid tones trump shadows in importance. When we are pegging the mid tones the incident meter provides an objective measurement.

In general spot meters are used in a subjective manner, the spot meter can be used objectively but it requires a known target to read. Skin can be that target but it has to be oriented properly, like holding the palm of your hand "just so". Measuring a sitters face though is a crap shoot unless you have significant experience.

 

[baachitraka]

Shaded palm is an another...

 

[baachitraka]

I may ask, not to worry too much about the incident metering.

Consider,

"Pegging comes in three basic types; shadow, mid-tone, and highlight. When we peg we are simply picking one of the three as the most important point for that shot." - markbarendt

then spice the illumination. My preferred way is E.I and your negs will never ever disappoint you.

 

[markbarendt]

I may ask, not to worry too much about the incident metering.

Consider,

"Pegging comes in three basic types; shadow, mid-tone, and highlight. When we peg we are simply picking one of the three as the most important point for that shot." - markbarendt

then spice the illumination. My preferred way is E.I and your negs will never ever disappoint you.

I don't understand what you are suggesting here.

 

[baachitraka]

When the exposure is based on shadows and want to keep shadows as shadows then we may need adjustment(spicing up) on the metered value. -1 or -3/2

On contrary when the exposure is based on highlights and want to retain highlights as highlights we may need similar adjustment. +1 or +3/2 stops

On diffused lighting, we may not require to do any such adjustments.

 

[markbarendt]

When the exposure is based on shadows and want to keep shadows as shadows then we may need adjustment(spicing up) on the metered value. -1 or -3/2

On contrary when the exposure is based on highlights and want to retain highlights as highlights we may need similar adjustment. +1 or +3/2 stops

On diffused lighting, we may not require to do any such adjustments.

Yes, simply using an offset to find camera setting.

The exact value of the offset should be based on a personal tests.

 

[jstraw]

That doesn't make sense. A spot meter has a very limited angle of read, typically 1° to 5° — it is very explicit in just what it is viewing. How great is the tonal range that a spot meter can see andcompared to the blanket 'view' of incident which cannot determine a dark or light tone, or a range of tones?

Spot meter something you think naturally falls at Zone V, 18% gray, etc. You can tell how good you are at recognizing that reflectance by doing an incident reading in the same light. If you're dead on, the EV should be the same for spot or incident.

Turn it around. Say your incident reading tells you the EV is 7. Whatever spot meters at EV 7 is middle gray.

 

[baachitraka]

Provided flare is taken care.

 

[Poisson Du Jour]

Provided flare is taken care.

...and spectrals.

 

[markbarendt]

Provided flare is taken care.

...and spectrals.

Good points.

If allowed both flare and spectrals will influence a reflective meter toward "thinking" that the subject being metered is brighter than it really is, the meter will in turn suggest an underexposure. While a spot meter is generally less affected than center weighted or matrix, it still requires some care to get a high a quality reading.

Conversely an incident meter is unaffected by flare and will provide a high quality reading even in a high flare situation. This doesn't mean you will get a perfect shot, the camera is still very much vulnerable to the same type of flare as reflective meters. High flare situations may require a change in EI or offset or lens shading or ...

Testing in the real world is important.

 

[HiHoSilver]

May I join the long list of those who've found Mark's methods quite sound? My shots of the unlit church interiors usually had 1.5 stops difference between my reflected & incident readings (I'm no expert on metering). His comment about most people doing better w/ incident readings in tricky situations are what got me to try & use it on what for me were important shots. Together w/ The Flying Camera's rule of thumb about reciprocity failure (from very fallible memory) was 1 more stop for 30s-1min. Over a min - add a 2nd stop. I had 3 exposures that were 16 min., though most were 30-60s. They turned out better than a rookie has a right to expect. Thank You, Mark. and also TFC.

 

[markbarendt]

Glad it helped.

 

[TheToadMen]

May I join the long list of those who've found Mark's methods quite sound? My shots of the unlit church interiors usually had 1.5 stops difference between my reflected & incident readings (I'm no expert on metering). His comment about most people doing better w/ incident readings in tricky situations are what got me to try & use it on what for me were important shots. Together w/ The Flying Camera's rule of thumb about reciprocity failure (from very fallible memory) was 1 more stop for 30s-1min. Over a min - add a 2nd stop. I had 3 exposures that were 16 min., though most were 30-60s. They turned out better than a rookie has a right to expect. Thank You, Mark. and also TFC.

Nice! It's good folk at APUG, isn't it? A lot to learn and a lot of help when needed.

 

[HiHoSilver]

Some humble, basic questions - I have great powers of confusing myself.
SBR? = Subject Brilliance/brightness Range?
BTZS metering method: Do I understand correctly that puts the dome over the sensor, points at the sun (for a sunlit scene), then points towards the camer location, subtracts the lower reading from the higher - and then what? I searched for the method & haven't found anything yet.

 

[MattKing]

SBR is Subject Brightness Range

BTZS = "Beyond the Zone System"

Both courtesy of Phil Davis

 

[markbarendt]

Some humble, basic questions - I have great powers of confusing myself.
SBR? = Subject Brilliance/brightness Range?

Close enough. It is a Zone system term normally so a bit of reading in Adams' books may help. Essentially it is the difference (in f-stops) between the brightest and darkest points in the scene that you want to print on the paper with detail.

The SBR is typically used to calculate a film development change based on a specific fixed paper grade target.

One thing it is not, but IMO gets conflated with, is the usable range of detail that a film can capture.

BTZS metering method: Do I understand correctly that puts the dome over the sensor, points at the sun (for a sunlit scene), then points towards the camer location, subtracts the lower reading from the higher - and then what? I searched for the method & haven't found anything yet.

BTZS is a zone system variant. It can use an incident meter, it can use a dome, it can use a spot meter... Google is your friend there.

 

[HiHoSilver]

Matt, thank You.

Mark, thank you also. So the metering method is more generic than specific. I'll keep looking. Many thanks again.

 

[markbarendt]

Matt, thank You.

Mark, thank you also. So the metering method is more generic than specific. I'll keep looking. Many thanks again.

It's a whole system with software and testing and ....

 

[Bill Burk]

BTZS metering method: Do I understand correctly that puts the dome over the sensor, points at the sun (for a sunlit scene), then points towards the camer location, subtracts the lower reading from the higher - and then what? I searched for the method & haven't found anything yet.

Here's how I would summarize BTZS metering method...

Point meter at the camera while you are standing in the sunlit part of the scene, then walk to the shaded part of the scene and point at the camera. Add 5 to the difference to obtain your SBR. From the SBR you will find development time and EI (which in the BTZS system floats with development time).

Set the EI on your meter at double the usual EI (only for BTZS not for any other system) and use the shadow-based reading to obtain f/stop and shutter speed. This will "underexpose" the shadow region by one stop, which will make it look dark in the print (which is exactly what you want the shadows to look like - dark).

 

[HiHoSilver]

Bill, Thank You!
I would never have guessed it would first establish time, then EI. 'Very different. 'Also the first I've heard about deliberately making shadows darker, rather than wringing as much detail as possible. I would guess that the wider the SBR, the shorter the time - similar to Zone sys' N-1,2, etc. I can see how it would get elaborate quickly, needing lots of notes, computing or an app for the purpose. There's alot that for now, remains in my future - but it'll come. I'm not afraid of the work. 'Finished Adam's Negative for the 2nd time & will likely have a 3rd. 'Reading the print now.
I sure appreciate your help, Bill. Thank You!