Kodak grey card usage

[RobC]

Rob C: regarding your question about the density of the 18% subject area the answer is approximately 0.7, however this is only an estimate based on interpolating between the steps of a Kodak step wedge transparency having 0.3 increments.

Well thats within half a stop so quite close. But it does depend on how you print it. i.e. your printing contrast filter settings and paper and dev and dev time so there is never any guarantee it will match exactly unless you force it to be with printing controls. But each paper type will be slightly different so if its within half a stop you're not doing bad at all.
There is no standard negative density which you should be targetting unless you create your own target and can relaibly hit it every time.

 

[Bill Burk]

I agree with RobC on this point. You have a lot of flexibility when you print. The gray in the print of the part of the subject that was originally 18% subject might not be what gets printed at 18%. There might be something lighter in tone that looks good at 18% gray and when you print it down like that, the original 18% might be pushed down to 12% or 7%. We're making illusions of reality, not replicas.

Now this sounds like a great theory that's going to be easy to test. I'll go out tomorrow and take some pictures with and without a gray card/gray scale. When I print them, I can point out (by measuring areas of the pictorial negative that match the gray card), what started out 18% and where it ended up (by measuring on the print with a reflection densitometer).

 

[wiltw]

You can prove the calibration point of film very easily with a gray card if you have a TTL meter. Just put the gray card in the frame, light it evenly, and whatever the in-camera meter wants to put it at, it will put it at that point. Doesn't even have to be gray. It can be any neutral shade between white and black. The meter will adjust exposure until it puts the amount of light on film that it is designed to put at the mid-tone exposure point. Now I would boldly say that I hope a camera meter and a handheld meter are both designed to put the same amount of light on film. If I'm wrong, then there is another whole discussion we have to go into. With all this talk about the difference between incident and reflective... nobody's talked about how both are different from in-camera metering. The in-camera meter doesn't have to assume light loss of the optical system because it is measuring through the taking lens - so instead of using a generic value for light loss, in-camera meters get to account for light loss precisely..

Bill you might start to hate me after I tell you this!:
First some background: For TTL metering in the SLRs of the 1970s and 1980s, some cameras employed half-silvered mirrors deflecting light to a sensor, and other SLRs actually looked AT the film plane. Olympus employed a design in which the sensor not only looked at the film surface, but they also imprinted a pattern on the shutter curtains, so that the photosensor could read the curtain itself even when the entire film area was not revealed, during the shutter 'slit', so that light changes during the exposure interval could be achieve 'off the film' (really, a combinabion of reading both film and curtain pattern!).

Where is the Beef?: What this has to do with me upsetting you is for me to tell you that transparency emulsion is MORE REFLECTIVE than color neg emulsion. And while different film manufacturers' emulsions varied in brightness a bit, universally ALL transparency emulsions were brighter than color neg. Never having measured the brightness of B&W emulsion, I cannot say where THAT fell in relative brightness of emulsion types. As a result TTL flash metering behaved differently for transparency than for color neg. We coped. My Bronica ETRSi employed a similar off-the-film reading, but its in-lens leaf shutter alleviated the need for any pattern on focal plane curtains...but it nevertheless had TTL flash metering affected by the emulsion type.

The upshot, of course, is that the relationship between the TTL metering result and the reflected handheld result -- and even incident handheld meters -- was DIFFERENT for transparency film TTL than for color neg TTL.

 

[Bill Burk]

Bill you might start to hate me after I tell you this!:
First some background: For TTL metering in the SLRs of the 1970s and 1980s, some cameras employed half-silvered mirrors deflecting light to a sensor, and other SLRs actually looked AT the film plane. Olympus employed a design in which the sensor not only looked at the film surface, but they also imprinted a pattern on the shutter curtains, so that the photosensor could read the curtain itself even when the entire film area was not revealed, during the shutter 'slit', so that light changes during the exposure interval could be achieve 'off the film' (really, a combinabion of reading both film and curtain pattern!).

Where is the Beef?: What this has to do with me upsetting you is for me to tell you that transparency emulsion is MORE REFLECTIVE than color neg emulsion. And while different film manufacturers' emulsions varied in brightness a bit, universally ALL transparency emulsions were brighter than color neg. Never having measured the brightness of B&W emulsion, I cannot say where THAT fell in relative brightness of emulsion types. As a result TTL flash metering behaved differently for transparency than for color neg. We coped. My Bronica ETRSi employed a similar off-the-film reading, but its in-lens leaf shutter alleviated the need for any pattern on focal plane curtains...but it nevertheless had TTL flash metering affected by the emulsion type.

The upshot, of course, is that the relationship between the TTL metering result and the reflected handheld result -- and even incident handheld meters -- was DIFFERENT for transparency film TTL than for color neg TTL.

Looks like Olympus had a patent http://www.google.com/patents/US4295720 they tried to deal with it by reading both the curtain and the film. Since there are more patents this must have been an incomplete solution to the problem.

I was made aware of TTL off the film problems with the OM-4 when I would shoot a few frames in Auto with no film in the camera. It would freak me out to see 1/8 in the finder and then hear the shutter stay open for several seconds.

I'll be walking out with one of those... an OM-4 with 50mm f/1.8 (figure other people can replicate my tests because that model and lens are not rare). I can use the TTL in auto mode and also I can use spotmeter to memorize the gray card in Auto mode, and also I can take some shots in Manual mode, electronic mechanical and mechanical manual.

 

[RobC]

my contax 167MT uses off the film(OTF) metering for flash. I always thought it would be variable depending on film type.

 

[Diapositivo]

You can prove the calibration point of film very easily with a gray card if you have a TTL meter. Just put the gray card in the frame, light it evenly, and whatever the in-camera meter wants to put it at, it will put it at that point. Doesn't even have to be gray. It can be any neutral shade between white and black. The meter will adjust exposure until it puts the amount of light on film that it is designed to put at the mid-tone exposure point.

I have the TTL meter but I don't have a densitometre, so that test, even though certainly giving me the correct tone of "middle grey" that I saw in the scene, would not give me the density in the processed slide corresponding to that middle grey.

[As a side note, I am more and more convinced that reflected light meters must be calibrated to a certain kind of grey, and that that grey is 18% grey].

[As a different side note, Minolta X-700 had a different method of taking into account internal reflections, and diaphragm imperfections. Its MPS system closed the diaphragm first, and measured in a tiny fraction of a second the light passing through the lens in stopped-down state, then raised the mirror. That gave the advantages of real-time exposure systems (Olympus OM-2 and Pentax LX) in Automatic mode, measuring the light through the real diaphraghm aperture and not the "simulated" one, without the cost and the problem of different reflectivity of different films.]

 

[RobC]

But a visual comaprison will show you if they are close or not. If they are not close you can then do another test of just one slide metering the wall and photograph it with the card in picture and make an adjustment to exposure to get it closer.

Why do you think you need exact density match anyway?

reflection meters are NOT calibrated to 18% grey. If they are it would be becasue the film speed standard was calibrated to 18% grey but it isn't so you're barking up the wrong tree there.
As I have already pointed out in other topics, the K factor of 12.5 makes an adjustment of 3 2/3 stops from what is metered. On further consideration that 3 2/3 stops is actually 3 2/3 stops more exposure than what is metered and not 3 2/3 less exposure than what is metered as I previously claimed. For the anally retentive, flare if its present which IMO would be miniscule, would be catered for by the fact the meter would have it as well as the camera lens if the claim is that all lenses have it, so the mere fact the meter would be automatically including flare in its reading means that it has taken into account any flare the camera lens has. i.e. the camera lens flare is compensated for by the meter lens flare unless someone is going to try and claim they're different without being able to prove exactly how much flare is in the meter and how much flare is in the camera lens to be able to say so. Flare is NOT an issue.

So suggested exposure is what is actually metered in cd/m2 reduced by the film speed component and then increased by the K factor component.

So taking some sensible numbers we can start with a cd/m2 value of 16 which by itself would be EV4 but that is reduced by the multiplication of the film speed component (using 100 for this example) so we get 16*100 = 1600 which by itself would give EV 10.6438 except that the division by the K factor of 12.5 ( which is 8% of reading*Speed) results in 1600*0.08 = 128 which results in EV 7.

So from an initial cd/m2 of 16 = EV4 we arrive at EV7 as the exposure which is 3 stops more than the actual cd/m2 metered when using 100 speed film.

Now trying a different speed film say 400 we have:

16*400*0.08 = 512 = EV9

so two stops less exposure which is what we expect moving from 100 speed film to 400 speed film but an offset of 5 stops from the actual 16 cd/m2 measured by the meter.

Now lets try 32 as the value of cd/m2 read, which by itself would be EV5, and we get:

32*100*0.08 = 256 = EV8

so again a 3 stop adjustment from reading at 100 speed.

and at 400 speed we get

32*400*0.08 = 1024 = EV10

so again at 400 speed we have an adjustment from cd/m2 read by 5 stops.

so what happens if we use film speed of 12.5 (3 stops less than 100).

using 32 cd/m2 and film speed 12.5 we get:

32*12.5*0.08 (which is same as K factor 12.5)
so we can say
32*12.5/12.5 which means the K factor cancels out the film speed when film speed is 12.5

we get 32*12.5*0.08 = 32 = EV5

So I think we can conclusively say a modern reflection meter uses a baseline filmspeed equal to its K factor and adjusts exposure from there based on film speed.

EV0 = 1cd/m2

if we use that then

1*12.5*0.08 = 1 = EV0

EV0 is 1 second @ f1

I was under the impression that meters used a baseline film speed of 100 but it doesn't look like it. It follows that since using a K Factor equal to the film speed means there is no adjustment from the metered cd/m2 reading, that any adjustment for flare has magically disappeared in a puff of reasoned logic and only reappears when the film speed changes from the K Factor. That's clever isn't it. I mean all your lenses are magically cured of flare when K factor equals film speed. Or perhaps maybe there wasn't any there to begin with.

Oh and I was wrong (which I already mentioned) about exposure being reduced by K factor, it is actually increased by K factor until K = film speed where there is no adjustment but the adjustment kicks in again when film speed falls below K factor. It is the EV value which is reduced (where my error was) by the K factor but a reduction of EV value means an increase in exposure.

That should keep everyone busy for a few days arguing over this. I'm now going into hiding.

 

[Bill Burk]

flare if its present which IMO would be miniscule, would be catered for by the fact the meter would have it as well as the camera lens if the claim is that all lenses have it, so the mere fact the meter would be automatically including flare in its reading means that it has taken into account any flare the camera lens has. i.e. the camera lens flare is compensated for by the meter lens flare unless someone is going to try and claim they're different without being able to prove exactly how much flare is in the meter and how much flare is in the camera lens to be able to say so. Flare is NOT an issue....

Oh and I was wrong (which I already mentioned) about exposure being reduced by K factor, it is actually increased by K factor until K = film speed where there is no adjustment but the adjustment kicks in again when film speed falls below K factor. It is the EV value which is reduced (where my error was) by the K factor but a reduction of EV value means an increase in exposure..

Flare is miniscule, but it's happening in the area around -2.1 log meter candle seconds for 100 ISO film. The speed point is around 0.008 meter candle seconds for that film and is very little light indeed. The flare if you take tedr1's example with Delta 100 and my estimate that there is 0.36 log flare at that low level of light in his graycard camera image... amounts to 0.018 difference. It shifts the shadow from -2.1 to -1.74 and when you get the arithmetic equivalent... it exposes the shadow to 0.0182 meter candle seconds instead of 0.008 what you wanted... This is 0.010 meter candle seconds of flare... not very much light but more than double what you wanted.

There's a cave on the hill I'm climbing today, from a distance it looks like an old mine. I was glad I had a flashlight but when we got up close realized it's just a cavity the right size for a dog to chill out in on a hot day.

Absolutely right. Flare in the spot meter and flare in the camera are similar... Parts of the complicated equations deal with that... I think it's enough to say they thought about that.

And I'm happy to see you kicking around numbers... that's what I think is going to make this work.

 

[RobC]

but did you understand them

and since you are claiming flare is significant I want to see proof that my lenses and meter have it. I also want to know where the source of the information about it came from and when was it written.
I don't want to be told its someones formulas or its in somones publishcation, I want those claiming its significance to post their proof here for everyone to see.

good quality modern lenses don't have a flare problem

http://www.canon.com/technology/s_labo/light/003/03.html

 

[wiltw]

Looks like Olympus had a patent http://www.google.com/patents/US4295720 they tried to deal with it by reading both the curtain and the film. Since there are more patents this must have been an incomplete solution to the problem.

I was made aware of TTL off the film problems with the OM-4 when I would shoot a few frames in Auto with no film in the camera. It would freak me out to see 1/8 in the finder and then hear the shutter stay open for several seconds.

I'll be walking out with one of those... an OM-4 with 50mm f/1.8 (figure other people can replicate my tests because that model and lens are not rare). I can use the TTL in auto mode and also I can use spotmeter to memorize the gray card in Auto mode, and also I can take some shots in Manual mode, electronic mechanical and mechanical manual.

I never discovered any negative aspects of Olympus's patterned curtains...that was entirely use for non-flash exposure, and while the theory from Olympus was that it permitted during-exposure adjusting to lighting intensity changes, if their Marketing dept. didn't tell you that would you ever have noticed?! Your experience with long shutter open times if no film loaded certainly was proof of the principle of during-exposure adjustment of shutter speed in spite of what the shutter-closed metering might have indicated earlier.

As for testing of camera TTL vs. handheld, that immediately gets us into the calibration constant issue, of what K was selected by Olympus vs. the K of your handheld spotmeter vs. the C of your incident meter. What method do you have in mind for eliminating that issue from the comparison?! I still have my OM-4, but I do not have a darkroom set up again since moving as much of my motivation had been lost by so many favorite emulsions being discontinued, as well as loss of Cibachrome!

 

[Diapositivo]

Rob, you are talking incident light if I get your right. Incident light metering measure a certain amount of light (of illuminance) and give a certain amount of slide film exposure, function of film speed, which will render "correctly" a certain range of reflectivity, in the scene, function of the dynamic range of the slide film.

A reflected light exposure, on the other hand, measures a certain amount of light (of luminance) and gives you a certain amount of slide film exposure, function of film speed, which will render "correctly" only a certain, defined shade of grey of X reflectance in a detail of the film on the slide film, or, if you prefer, an exposure that will render in the slide film your subject of that X certain shade of grey, regardless of the tone of the subject.

When talking incident light metering you can abstract from shades of grey.
When talking reflected light metering you cannot abstract from that X shade of grey for which they are calibrated.
I am interested in knowing theoretically which is the corresponding density of this X shade of grey on the slide film.

I have some problem with your explanation although now I begin seeing a "useable formula" which is nice

According to your formula, if I get it right:
Illuminance in cd/m2 multiplied by ISO speed multiplied by 0.08 = EV exposure for given speed.

In your example, let's imagine and ambient light of 0.5 cd/m2 at 100 ISO. Which actual exposure would that bring?

0.5 * 100 * 0.08 = 4.

That does not seem to stick with your example which, using this formula, gives EV7 for a scene with an illuminance of 16 cd/m2.
There shoud be a distance of 5 EV between a 16 cd/m and a 0.5 cd/m2.
Your formula doesn't seem to work for values of light below 1 cd/m2.

 

[RobC]

nope, I'm talking reflected light meters.

 

[Stephen Benskin]

but did you understand them

and since you are claiming flare is significant I want to see proof that my lenses and meter have it. I also want to know where the source of the information about it came from and when was it written.
I don't want to be told its someones formulas or its in somones publishcation, I want those claiming its significance to post their proof here for everyone to see.

http://www.canon.com/technology/s_labo/light/003/03.html

good quality modern lenses don't have a flare problem

http://www.canon.com/technology/s_labo/light/003/03.html

Diapositivo, I am working on an explanation for you. I'm trying to organize my thoughts and distill them down, but it's coming.

FYI, Bill Burk has just uploaded another paper for me. The Incident Light Meter Method of Exposure Determination by D Connelly. It's available at http://64.165.113.140/content/benskin/ along with most of the key papers on exposure. Thanks again Bill.

Flare at the metered point is small. The standards have it as 3%, but in the shadows it is around 1 to 1 1/3 stops for the statistically average scene.

Flare is critical to understanding film development, tone reproduction theory, and exposure. I've posted extensively on flare over the years. Here's an interesting thought, let's put the burden of proof on the doubters. Prove it doesn't exist. Simply not believing in something isn't proof. It's a logical fallacy - argument from incredulity.

Here's a black box test I did. The black box opening was surrounded by targets with different tones. A sensitometric exposure was made and run with the test. The results are plotted on the sensitometric film curve. Without flare all the tests would result in the same density.

 

[RobC]

Rob, you are talking incident light if I get your right. Incident light metering measure a certain amount of light (of illuminance) and give a certain amount of slide film exposure, function of film speed, which will render "correctly" a certain range of reflectivity, in the scene, function of the dynamic range of the slide film.

A reflected light exposure, on the other hand, measures a certain amount of light (of luminance) and gives you a certain amount of slide film exposure, function of film speed, which will render "correctly" only a certain, defined shade of grey of X reflectance in a detail of the film on the slide film, or, if you prefer, an exposure that will render in the slide film your subject of that X certain shade of grey, regardless of the tone of the subject.

When talking incident light metering you can abstract from shades of grey.
When talking reflected light metering you cannot abstract from that X shade of grey for which they are calibrated.
I am interested in knowing theoretically which is the corresponding density of this X shade of grey on the slide film.

I have some problem with your explanation although now I begin seeing a "useable formula" which is nice

According to your formula, if I get it right:
Illuminance in cd/m2 multiplied by ISO speed multiplied by 0.08 = EV exposure for given speed.

In your example, let's imagine and ambient light of 0.5 cd/m2 at 100 ISO. Which actual exposure would that bring?

0.5 * 100 * 0.08 = 4

That does not seem to stick with your example which, using this formula, gives EV7 for a scene with an illuminance of 16 cd/m2.
There shoud be a distance of 5 EV between a 16 cd/m and a 0.5 cd/m2.
Your formula doesn't seem to work for values of light below 1 cd/m2.

the formula for a reflected meter is:

2Ev = (B*S)/K

EV = Exposure Value
B = luminance in cd/m2
S = ISO Film Speed
K = K factor = 12.5 (using 12.5 equates to multiplying by 8% (0.08) hence B*S*0.08)

So
0.5 * 100 * 0.08 = 4 = EV2

4 = 2Ev so to convert from that to EV you must take the log2 of 4 which = 2

so you get

0.5 * 100 * 0.08 = 4 = EV2
16 * 100 * 0.08 = 128 = EV7

a difference of 5 stops

 

[Stephen Benskin]

the formula for a reflected meter is:

2Ev = (B*S)/K

EV = Exposure Value
B = luminance in cd/m2
S = ISO Film Speed
K = K factor = 12.5 (using 12.5 equates to multiplying by 8% (0.08) hence B*S*0.08)

So
0.5 * 100 * 0.08 = 4 = EV2

4 = 2Ev so to convert from that to EV you must take the log2 of 4 which = 2

so you get

0.5 * 100 * 0.08 = 4 = EV2
16 * 100 * 0.08 = 128 = EV7

a difference of 5 stops

Let's not forget an important component.

2Ev = A2/T = (L*S) / K

Ev is for the exposure calculator, but it's important to show the relationship to the camera exposure.

 

[RobC]

I take it to mean you have no proof. You have just copied it from a 45 year old paper. Lens coatings have moved on a very long way since then. But I guess if you're using old an knackered lenses and trying to make whats applicable to them applicable to my modern Zeiss T* coated lenses then you haven't got a leg to stand on. some modern lens coatings as you will see in the link I posted have reflection down to 0.02%. So all lenses but less than 1.5% and not so new lenses and NOT 3% as you have quoted. And the total value depends on the lens, how many elements and what they're all coated with and the more modern low dispersion glass that wasn't available 45 years ago. Its highly variable but virtually non existant in quality modern lenses.
Go get yourself some uptodate data and don't quote ancient and misleading statistics.

Oh, and the burden of proof is on those making the claims which is what you're doing using old statiscal data to justify your claims.

 

[Stephen Benskin]

I take it to mean you have no proof. You have just copied it from a 45 year old paper. Lens coatings have moved on a very long way since then. But I guess if you're using old an knackered lenses and trying to make whats applicable to them applicable to my modern Zeiss T* coated lenses then you haven't got a leg to stand on. some modern lens coatings as you will see in the link I posted have reflection down to 0.02%. So all lenses but less than 1.5% and not so new lenses and NOT 3% as you have quoted. And the total value depends on the lens, how many elements and what they're all coated with and the more modern low dispersion glass that wasn't available 45 years ago. Its highly variable but virtually non existant in quality modern lenses.
Go get yourself some uptodate data and don't quote ancient and misleading statistics.

Oh, and the burden of proof is on those making the claims which is what you're doing using old statiscal data to justify your claims.

This is like Evolution deniers claiming there's never been a transitional fossil. No amount of evidence will be enough. Multi coated lenses have reduced flare by about half. The second example is from a test I did. Rob, I really don't want to get into a fact vs fantasy argument with you again. Here in America, we would simply say to turn off Fox News.

 

[RobC]

This is like Evolution deniers claiming there's never been a transitional fossil. No amount of evidence will be enough. Multi coated lenses have reduced flare by about half. The second example is from a test I did. Rob, I really don't want to get into a fact vs fantasy argument with you again. Here in America, we would simply say to turn off Fox News.

well shut up then.

Oh, and please explain how it that when K = Film Speed there is no adjustment for flare or are you in denial of that.

And while you're at it, how about directing us to some peer reviews of your work on this or is it all copied from someone elses.

 

[Diapositivo]

Rob, thanks, now the formula sticks. Please let the exchange of view between you and Stephen to proceed as a calm and polite conversation so that we can distill from the knowledge of both some useful information.

Stephen, thanks. I have downloaded the paper by Connelly. I will try to distill the juice out of all those formulas.

I am eagerly awaiting from you the answers to my doubts:
- which is the shade of grey that a reflected light meter create on a slide film if one follows its indication;
- which is the density on the slide film which corresponds to the middle grey.

The reason why I am interested in the second question is that it gives a way to clearly interpretation of the characteristic curve of a slide. If I know where "middle grey" is, I can easily see where the shoulder and toe begin relative to middle grey.

 

[Bill Burk]

but did you understand them
...
and since you are claiming flare is significant I want to see proof that my lenses and meter have it. I also want to know where the source of the information about it came from and when was it written.

I had only a few minutes this morning before the hike. You laid the numbers out, so I can look at them...

This simple test will demonstrate the impact of flare in your spotmeter.

Find a suitable dark subject at a distance, say the open door of your home from across the street. I opened my garage door instead because I didn't want my dog to run out of the house while I'm doing this... he's tired now since we just got back from the hike and doesn't look like he wants to budge, but I don't want to take chances.

Now walk towards the open door keeping the meter aimed at the opening. As "Black" becomes the dominant tone of your viewfinder, the flare that elevated the original reading will not be elevating the reading. You will have a lower light level reading as you get closer because the influence of flare is becoming less of a problem.

You can say that the camera and meter will both see the same flare, and that's reasonable. They are both similarly impacted by flare. The more detailed formulas break this out separately... when making a spotmeter the manufacturer can know it's own flare, but has to assume how good your lens/camera system is. Adding TTL and OTF metering gives us variations on the theme - where some of the variables can become known. (Too bad the OTF capable camera designers did not include a small reflection densitometer to read the tail during film loading and store the actual reflectance of every roll of film you load...).

 

[Stephen Benskin]

well shut up then.

Oh, and please explain how it that when K = Film Speed there is no adjustment for flare or are you in denial of that.

And while you're at it, how about directing us to some peer reviews of your work on this or is it all copied from someone elses.

Rob, I am letting this go. I suggest you do the same. Remember what happen in the last thread were you got banned.

Remember, I actually reference peer reviewed papers. The exposure meter standard that you are using the equation from has in Appendix F references to the appendixes. This section references The Theory of the Photographic Process, Jones' Sunlight and Skylight as Determinant of Photographic Exposure, Safety Factors in Camera Exposures, and Reevaluation of Factors Affecting Manual or Automatic Control of Camera Exposure. All books and papers I own, and two papers that are available at http://64.165.113.140/content/benskin/.

Here is a legitimate question /point. You have yet to show how anything you've presented works at the film plane. The noodling around your doing with numbers doesn't connect the dots between Luminance and camera image. After all, this the whole purpose of the exposure meter. Could you simplify your math and show a direct correlation between Luminance and film plane exposure?

 

[Stephen Benskin]

 

[Stephen Benskin]

Here's something else to think about. P/q = K. So 8.11/.65 = 12.5. What if the lens had a lower transmittance and q equals 0.58 instead of 0.65? 8.11/.58 = 14. This is basically K. So a K of 14 will produce a camera setting that will let more light into the camera, but if the lens has a q of 0.58, the same amount of light will hit the film plane as a lens with a q or 0.65 and a K of 12.5. The idea is to create the same exposure at the film plane. Don't forget the ratio from the speed point to the metered exposure point. This and the film speed sets where the exposure should fall.

There's another proof I thought I'd share. The ISO standard has K1 = L*t*S / A2 as the calibration equation. Example, 3200 * 1/100 *100 / 256 = 12.5. Notice how it's basically the exposure equation without q? If you recall P/K = q. The ISO version of the calibration equation clear shows that K is primarily about the camera's optical system.

 

[RobC]

As usual when you are asked to explain or give proof you refuse. I didn't ask for other peoples papers which are peer reviewed, I asked for yours and with your usual eavasive response you have tried to fob me off by quoting someone elses peer reviwed work.

And not only someone elses but as I 've already pointed out, they are very very old. i.e. the data used is out of date with regard to flare in modern lenses and you are now trying to obfuscate that which is your standard way of trying hide what you don't know. Mees and Jones work is at least 75 years old and you are quoting it as your reference data.

You have not found a single error in what I've said but once again are trying to start an argument about it and presenting your own out of date findings about it. You haven't given a single reposnse worth reading.

Once again, explain how it is that there is no flare adjustment when the film speed and K factor are equal.
And please present references to peer reviews of your own work. Failure to give satisfactory answers will tell us all we need to know.

And in your ignorance you have once again missed the whole point which is that if you have calibrated your exposure, dev and printing you don't need to know any of the crap you keep posting about ancient and out of date scientific derivations.

A practical evaluation trumps everything your plagiarised scientific formula are trying to prove.

All I've done is start a topic providing the instructions on how a kodak grey card should be used, or at least how it was with the card I have.

And yes I have put some numbers into the standard reflection meter formula to see what is really happening and you have a problem with that. Anyone with an ounce of sense trying to understand a problem would do exactly what I've done and you want to infer its meaningless. That tells us a lot about you.

I know exactly what I get on film becasue I've calibrated to my own standard which I'm not forcing on anyone like you are trying to do. I know if I meter anything I can place it on any zone and it works because I've tested it. I'm not in the slightest bit interested in disappearing up my own anal tract by trying to convert my meter readings into log values that you want me to give you so that you can tell me they don't match yours. Why would I waste my life on doing something so purile. I use my own standard calibration which I've repeated often on the forum so it should be blindingly obvious to you that it wouldn't mean anything to you since you are so blinkered and it would be pointless comparing to your numbers.

You know I'm not interested in hearing what you have to say but you can't help yourself from trying to force it on me. I'm not interested. I hope that has registered.

I've read it all before from the people who actually did the original research and I know enough about it to know things have changed in the last 75 years since the research was done, especially with regard to lens flare. I think you are stuck in 1940s and the previous 50 years research.

I have an idea, why don't you please do us both a favour and put me on your ignore list instead of inventing meaningless diversions to try and hide what you can't explain.

 

[RobC]

Bill, its dark here now. I will try your little test tomorrow if I get a chance. My bet is I will see no variation but we'll see.

If it requires having meter facing in general direction of primary light source then we're into the realms of backlighting which we all know needs special care to get exposure correct, flare or no flare.

But the point is that a proper film speed, dev and print calibration will take it completely out of the realms of needing to know anything about it. Just like if your meter was consistently out by a third of stop. Its factored into the film speed/dev/print calibration if it was there so its a time wasting exercise considering it except for purely academic interest of which I have zero on the topic of flare.

It has already been suggested my film speed tests are not valid becasue they wouldn't have included any flare so at least its been acknowledged that flare may not exist. We all know that strong backlighting is a potential problem with regards to flare but most of the time we aren't using strong backlighting.