Comparing Spectral Sensitivities

[Leigh B]

Unripe orange??? Are you asserting that ten unripe oranges picked at random will exhibit the same reflectivity?
I'm sure his subjects were chosen to exhibit the greatest possible variation.

Fred Picker was a businessman. His newsletters (I have and have read all of them) were intended to support his marketing efforts.
His newsletter was his blog (before such things existed). It was not a peer-reviewed journal, nor in any way vetted.

So the meters he tested were right more than 75% of the time. His mods only reduced the error by 50%.

You need to assess the information being presented, not just buy into the marketing hype.

Photography attempts to establish processes and standards that work in most situations involving light and objects
that are totally uncontrolled. As such assumptions and generalizations must of necessity be made, as in any physical science.

It's like the use of an 18% gray card. You can find innumerable scenes with reflectances that differ from that standard.
So what?

As to your last statement... I have not said one word about Zone VI meter mods.

In any technical discipline, you're expected to use tools and methods appropriate to the task.
When you choose to do otherwise, your results are yours and yours alone.
The Macbeth chart was never designed for use in the IR or UV ranges, as I stated previously.

- Leigh

 

[MattKing]

So lets see if I've got this right.

It seems to me that the problem that arises is not so much that the human eye, film and meters respond markedly differently to light within the visible spectrum.

It is that the film and the meters are influenced and affected by UV light and IR light - i.e. light outside the visible spectrum

 

[Leigh B]

Actually, films and meters are both affected by IR and UV, in varying degrees.
Human vision is generally insensitive in these regions.

You have spectral response variation in film emulsions, and in meter sensor technologies.

The subject under discussion is how best to match meter spectral sensitivity to that of a particular
film, and beyond that, how to assess the accuracy of that correlation.

Every meter is different, as is every film.

- Leigh

 

[Bill Burk]

I don't take Fred Picker's word for everything. I use Ilford Galerie for example, and he hated that paper.

But I think it is wrong to use the Macbeth color reference to debunk Fred Picker's claims. Particularly because he claimed to have improved the correlation between meter and film in the infrared region. You know that chart wasn't designed to do that.

I try to consider any effect that only causes a 10% error trivial enough to ignore. But Fred was showing that Soligor Spot Sensor II made a 2 stop error in several cases. That caught my attention.

 

[Leigh B]

But I think it is wrong to use the Macbeth color reference to debunk Fred Picker's claims.

Bill,

You need to drop this.

You are the ONLY person in this thread who has mentioned the use of the Macbeth chart for IR or UV testing.
I've stated repeatedly that such is an improper and invalid use of the product.

My comments about Picker's methodology had absolutely nothing to do with the Macbeth chart.

- Leigh

 

[Bill Burk]

Bill,

You need to drop this.

You are the ONLY person in this thread who has mentioned the use of the Macbeth chart for IR or UV testing.
I've stated repeatedly that such is an improper and invalid use of the product.

My comments about Picker's methodology had absolutely nothing to do with the Macbeth chart.

- Leigh

Here's how I see it.

Matt's trying to understand whether a Zone VI modified meter is worth looking into. It is alleged to have a better correlation to film in the extended regions.

He saw a website that debunks the modified meter. That external referenced site makes a convincing case that the meter modification is useless. I defended Fred Picker on a problem I saw in the tests.

You and I have been disconnected since then even though I am sure we agree.

 

[MattKing]

Here's how I see it.

Matt's trying to understand whether a Zone VI modified meter is worth looking into. It is alleged to have a better correlation to film in the extended regions.

He saw a website that debunks the modified meter. That external referenced site makes a convincing case that the meter modification is useless. I defended Fred Picker on a problem I saw in the tests.

You and I have been disconnected since then even though I am sure we agree.

Actually, I am trying to figure out how important the spectral sensitivity issue is, because of an outside APUG discussion wherein it was asserted that the Zone VI modified meter is essential, because all other meters were markedly incorrect or unreliable, due to the issue.

 

[Leigh B]

OK. Yes, I think we do agree.

The disconnect happened at post #14 where you were talking about the article (which I have not read).
Apparently it relied on the Macbeth chart for out-of-range analysis.
As I've stated repeatedly that's not a proper use of the product.

My concern with the use of 'live' subjects for analysis is lack of consistency. This is why the Macbeeth chart exists.
You can easily shoot a landscape and produce a photo. Try moving that landscape into a studio to shoot under strobes.
This is the purpose of the Macbeth chart. It can be moved inside with minimal effort.

And the Macbeth chart will yield the same results five years from now. I challenge you to guarantee that with any landscape.
I replace my Macbeth chart every ten years, and cannot tell the difference between any of them.

- Leigh

 

[Leigh B]

...it was asserted that the Zone VI modified meter is essential, because all other meters were markedly incorrect or unreliable, due to the issue.

That is patently incorrect, based on my 50+ years of shooting, mostly black&white.

Most meters are quite accurate. I use a "modified" zone system, spot metering particular areas of interest if I think they are significantly different from what I would expect, thus requiring exposure adjustment.

Some folks will go ballistic if they think a meter reading is off by 1/10th of a stop (I don't know how they know that).
This is total hog wash. The film and the rest of the process would never notice such an error.

As to the actual magnitude of the UV/IR problem, let's look at the solar spectrum at the Earth's surface (red curve):

Ref: Wikipedia Sunlight/Composition: http://en.wikipedia.org/wiki/Sunlight#Composition

Note the UV/Visible/Infrared captions at the upper left of the graphic.
Note also the extremely low amplitude of the UV energy as compared with the visible.

Infrared energy extends quite a distance below visible, but that greatly exceeds the spectral sensitivity of general-purpose film.
The film sensitivity curves that PE posted in #4 and those that Bill posted in #5 show no sensitivity below 700nm.

Bottom line:
If any UV/IR sensitivity exists, the available energy is only a small fraction of the visible energy that controls the meter.

My assessment: Picker found a solution looking for a problem, and provided biased analysis to support his product sales.
Yes, there might be a slight difference between meter readings in the general case, but not enough to worry about.

- Leigh

 

[Usagi]

Couple of years ago I did this graph of the spectral sensivity of my Gossen Spotmaster 2 meter simply by placing spectral response curves of some films above the exposure meter's curve.


The difference was smaller than I thought forehand.

 

[Bill Burk]

OK. Yes, I think we do agree.

The disconnect happened at post #14

Yes, we agree and that's what happened.

 

[MattKing]

Thanks again everyone.

 

[RalphLambrecht]

somethinglike this?

 

[benjiboy]

My best advice on the subject Matt from someone who has been shooting film for more than fifty years is to not tie yourself up in knots with the technicalitys, just go out and shoot film and enjoy it.

 

[MattKing]

Ben:

I couldn't agree more.

But after 40 plus years of shooting, it is fun to stumble upon an issue that hadn't really seemed too important before, and wonder if I should pay more attention.

I think I remain most curious though about how the various types of meters compare, and whether I should be more careful about switching back and forth.

And Ralph, thanks for that.

 

[Photo Engineer]

Frankly, this is a non-issue! Without any concern for it, there have been millions of accurate and beautiful photos take over the last 100+ years.

PE

 

[RalphLambrecht]

yes, thanks for thesobering words of wisdom!

 

[Leigh B]

Frankly, this is a non-issue!
Without any concern for it, there have been millions of accurate and beautiful photos take over the last 100+ years.

Absolutely true.

- Leigh

 

[Bill Burk]

I agree the problems can be totally avoided by incident metering with a touch of judicious spotmetering.

I don't have a Zone VI modified meter, but I think it is worth estimating the problems the modifications tried to resolve. If I find the problems only cause one stop of issue, I'm probably going to drop it in with other "one stop" issues that tend to cancel each other out.

The article about meter modification in Zone VI Newsletter Number 37 was written by Paul Horowitz. I have to admit I like Paul's style more than Fred Picker's. He seems impartial and scientific, yet he writes clearly. (Paul gave us the stabilized cold light head. I wish I had one, I undestand those live up to the advertising claims).

Paul introduces the problem clearly... "Objects placed on Zone V sometimes wound up on the print as Zone III, sometimes Zone VII. There seemed to be some persistent errors -- foliage always underexposed from one to three zones, sky consistently overexposed, typically a stop or more. Late afternoon often seemed to produce underexposure. And shadow areas that metered as Zone II often "dumped" into total black."

My Sekonic L758-DR is sensitive to infrared. I get EV 12 when I meter the illuminating LED on the ATN-Viper. This is near infrared, but I've tested that it doesn't significantly fog TMY-2 in 15 minutes.

Foliage is an interesting problem. It's green, but reflects infrared. I hunted the backyard with my first-generation infrared viewing scope looking for illogical examples. Maybe because it's late summer, I didn't find any extremes (except a red apple looked light).

I tried to find infrared by metering first with my spotmeter (responds to infrared) then with the SEI photometer (it shouldn't respond to infrared - it uses my eye as a sensor). As Leigh points out, the angle of measurement can affect readings and natural subjects are inconsistent. I didn't find any significant departures. Sometimes I'd find one stop difference but other times I'd meter the same.

Then I got to thinking... What do photographers sometimes do when they want to darken leaves? A red filter of course... What does a red filter do to the infrared. Trick question - it does nothing. What does it do to the visual image of a green leaf? It darkens it.

This is where I think meters do poorly - through red filters looking at foliage!

I aimed the Sekonic at a gray target and metered with and without the red filter. Three stops difference. I aimed the Sekonic at a dark green leaf with and without the red filter. Two stops difference.

If I meter foliage through the red filter, the recommended exposure will be off by one stop. It will be underexposed.

Now the fun begins. Meter places the leaf on Zone V but I previsualize a bit darker, so I place it on Zone IV. But due to the error it falls on the print at Zone III.

 

[RalphLambrecht]

after several dissapointing experiences witha pentax spotmete(unmodified and modified)and metering through filters, i gave up on metering through filters and aplly the filter factor sfter metering without filters.

 

[Bill Burk]

after several dissapointing experiences witha pentax spotmete(unmodified and modified)and metering through filters, i gave up on metering through filters and aplly the filter factor sfter metering without filters.

Thanks Ralph!

And I use the "ISO 2" setting on my L758-DR to apply the filter factor so that may be why I never had the problem!

Some people deal with this issue by using the "Hutchings" factor after reading through the filter that is written in Steve Simmons' view camera book.

 

[Mustafa Umut Sarac]

Matt ,

If you want to dissect and anatomical analysis of old electronics parts , its virtually impossible. Only you can do is to buy several famous lightmeters , disassemble it , look for the light sensor part number , find it at old factory manuals , look for the electronic circuit ....and list goes on.

You have to know that they bought what is available from catalogs , test them approximately and try to be sure part would be available next few years and cheap.

They were not NASA and not sending man on to the moon.

There was no such technology at consumer goods and thats why we hate digital cameras and modern lenses even today

But Leica was always different from Gossen and others.

Umut

 

[Bill Burk]

Umut,

You would probably appreciate the build quality of the SEI Photometer. The only issue in this discussion is that it has a sensor (the eye) that does not correlate 100% to film. I wonder what sunglasses I would have to wear to approximate the response of Tri-X.

Probably something pale Magenta to pull down the Green. Next time you see me in the field, I'll be wearing rose-colored glasses.

 

[Mustafa Umut Sarac]

Hello Bill,

Neodymium glasses , greatest eyeglasses color, I think you are talking about them. There is a glass studio called Cam Ocagi at Istanbul and when I went there , people were wearing these glasses to protect their retinas from radiation of hot glass.



I really loved the color ,I think I must find the seller. Second thing is the amber , real natural amber deep yellow glasses.
I will try to buy it when I visit Russia.


Thank you reminding me them.

Umut

 

[Bill Burk]

I hunted the backyard with my first-generation infrared viewing scope looking for illogical examples. Maybe because it's late summer, I didn't find any extremes (except a red apple looked light).

Here's the trick that makes IR anomalies visible: Put a black E-6 slide over the lens of a night-vision device such as the ATN-Viper.

Now I see scenes in broad daylight similar to how they appear in infrared black and white prints.

I am really enjoying this view of the world. Live IR!

And I see the extreme examples I was looking for.

Looking through the infrared viewer, foliage in shade is as bright as foliage in the sun. So I am focusing my attention on shaded foliage.

Adding the red meter over the Sekonic only reduces the reading of green foliage in shade by one stop.

By carefully choosing an edge case, I have found a problem that could lead to a two stop underexposure.

Solution: Meter without filter and apply filter factor afterwards.

I think I will bring the night-vision device in the field to help me see how much infrared is in my scenes.

Who am I kidding. I'm bringing the ATN-Viper to have fun.