Error in filter factoring?

[rick_durbin]

Being new to LF, I started reading Steve Simmons' book on using view cameras. He recommends holding the filter in front of the exposure meter when taking readings, and then adding a filter factor to the exposure determined from the reading (p,28, rev. edit.). What am I missing? Doesn't this method add the filter factor twice? Is this idea of holding the filter in front of the meter a good method to use?

[david_goldfarb]

That looks like a proofreading error to me. Yes, that would be adding

the filter factor twice.

 

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You could use the method of holding the filter in front of the meter

with a spot meter or other reflective meter, but obviously not with an

incident meter with a dome-type diffuser. There might sometimes be

differences, though, between the spectral sensitivity of the meter and

the spectral sensitivity of the film, so it isn't a bad idea to do

your own tests with different films and light sources, or use the

factors recommended on the film's technical data sheet, usually

available on the manufacturer's website.

[steve_gangi2]

Doing that would cause you to add the filter factor twice. Either

you can meter through the filter, or you can meter and then add the

filter factor, but not both at the same time. I don't meter through

the filter. I meter without it, and the add the filter factor.

Sometimes I even remember to NOW put the filter on the lens. I'm

almost as bad about that as I am about remembering to pull out the

darkslide. But I still somehow manage to muddle through

it :)

[john_hennessy1]

Probably this second factor is "Hutchings Fudge Factor" (a la Gordan

Hutchings). The concept is that the meter does one thing but it is not

enough perceptually. The HFF is different for different filters right?

As low as zero for some filters as I recall even if the filter's own

factor is not zero. My HFF chart is in my camera case but from memory

the highest HFF is less than 2x. It is not a typo.

 

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As far as metering through the filter: that is a good idea especially

if you are out under strange light (e.g., early, late, stormy etc.)

but usually I just use the filter's published factor and usually use

the HFF too.

[jason_greenberg_motamedi]

Hi Richard,

 

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I have always heard that since meters do not 'read' color and light the same

way film does (particularly films like infrared, or polarlizing filters), one is best

off using the published filter factor, rather than what the meter says... My own

experience has affirmed this.

 

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jason

[jorge_gasteazoro4]

you can do it that way but the best way is to take a zone V shot with

your filters and then read which negative has the correct density.

For example when I use a red filter, although the published factor is

8x I use 3 and 1/2 stops instead of 3 stop, because when I took a pic

of a gray card the negative that most closely came to a density

of .65 for Zone V was the one with 3 and 1/2 stops more exposesure,

not 3 as specified by manufacturer. Until you do a personal test you

will always have a little bit of fudge factor built in.

[xx]

but isn't the reason we have to use filter factors based on the idea

that the filter subtracts that particular color from the scene when

put to film? How could the filter factor always be the same since that

same color is not equally present in every scene.

[jorge_gasteazoro4]

Exactly Mark that is why you test with a neutral gray subject! This

way you can see how much light is being substracted without worrying

about the color.

[xx]

Jorge, are you saying you carry a grey card around with you and check

it every time? or test once with grey card and then use that

correction every time. frankly neither is very accurate since the

color that you filter for will be different at every shooting session

and will be different where you are as opposed to where your subject

may be. why not just get an adjusted meter (zone 6) which makes a

world of difference and not have to ever worry about it?

[jorge_gasteazoro4]

I disagree with you Mark, it is the most accurate way to test filter

factors. I guess I will have to explain the method, I thought it was

evident.

Ok, I take a red filter, focus on a gray card and take 3 sheets of

film, one at the manufacturers recommended factor, one at 1/2 stop

over and one at 1/2 stop under, the one that comes closer to the zone

V density (0.65)is my "corrected" factor. SInce you have no color you

are only measuring light absorbtion by the filter. Once you are

taking a real subject you are correct, some colors get absorbed and

some get through the filter, but remember in adition to this

phenomena there is an even amount of light absorbtion across the

spectrum, which is why we use the factors.

Look if you wish to continue using the factors it is not a bad way to

go, but if you ever come across underexposure or overexposure you

will remember what I am telling you.

[xx]

Jorge, I never said I use factors, nor will I use your method, both of

which I find simplistic and inaccurate. I use a zone 6 corrected spot

meter which takes care of these problems.

 

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I and others have shown in film tests that different amounts of a

color affects the factor that will correct an exposure. Can you

honestly say that in the same scene if you have a dark yellow and a

light yellow subject that they will transmit the same amount of light?

This is why filters work in the first place!

 

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I know why we use factors, but this doesn't totally account for this

change of values.

 

<p>

 

 

Of the 15 years or so that I have been shooting bw I have had the

adjusted meter for many years and haven't come across any under/

overexposure problems due to this method.

 

<p>

 

I understood you completly, I just disagree with you, I thought this

was evident.

[steve_gangi2]

To further complicate matters, is your subject in open shade, full

shade, indoors, or in full open sunlight? What about the time of

day? You're starting out with different "base" color temperatures

then. I suppose you could drag gray cards, densitometers, color

meters, light meters etc etc etc everywhere, but why? Folks, it

really is not that critical. After re-reading that section of the

Simmons book, it appears he was talking about the "Hutchings fudge

factor" which is an attempt to allow that meters (and filters) don't

treat all colors or wavelengths the same. If they did, there would

be no filtering. But again, why overanalyze everything? I and many

others have never held a filter over a meter, nor have we tested

everything to death, or used the fudge factor. As an engineer, there

is enough testing and measuring and recording at work every day. I'd

rather be out shooting. Really, lots of people shoot black and white,

which is sort of a departure from "reality" anyway. Even your choice

of film is a manipulation. Then factor in the different tones that

each film and paper have, variations in processing, variations from

one batch of film to the next, and there you go. You're doomed from

the start if you're searching for the perfect definitive magic

numbers. So, have fun, make the best pictures you can, but don't

agonize over it. Some of the most famous photos ever made were those

where the person only had time to guess at everything and expose the

film.

[jorge_gasteazoro4]

Mark you use your zone VI meter in an attemp to do what I simply did

with a little sensitometry. I also thought it was evident, sure

different hues of a color complimentary or suplementary to the filter

will overexpose or underexpose the film but, as I said there is an

OVERALL light absobtion. But look you wanted to spend your money on a

meter fine, I am glad it works for you, OTH just becuase you think a

method is simplistic and/or inaccurate does not make it so, maybe it

is because you dont understand the theory. In the end I agree with

Steve G, this is a test I made about 12 years ago and have used "my"

FF since then without a problem. I am glad the zone VI meter works

for you but dont say other methods dont work or are inacurate when it

is clear you dont understand the sensitometry and color theory.

[brian_ellis3]

It isn't a typographical error. He published a table in "View Camera"

magazine a while back with the same idea. I tried it and it works

very well. Filter factors aren't precise because there is no way of

predicting in advance how much of a particular color will appear in a

particular scene. For example, the "filter factor" when using a red

filter to photograph the side of a red barn would be very different

than the "filter factor" when photographing the side of a green barn

with a red filter. The red filter would block very little light when

the subject is red, but would block a lot of light when there is

little red in the subject. So filter factors are rough guides at

best. Metering through the filter is also not very precise because

your meter and your film aren't equally sensitive to the same color.

I've gotten much better results with orange and red filters with the

sky and clouds using Steve's table (which calls for one additional

stop with an orange filter and two stops with a red filter after

metering through the filter) than I used to get either by using

filter factors alone or by relying solely on reading through the

filter with the meter. I don't know how well the method works when

using it with things other than the sky, e.g. using a green filter to

lighten foliage.

[steve_gangi2]

Filter factors are an approximation, probably based on some average

scene. Usually, they are close enough. In the example of a green

filter, used to photograph green foliage, any green portions would

appear light because the filter is passing that color through. Any

red colors would appear darker because the filter is blocking them.

How much of each there is, the overall percentage, could be said to

shift the filter factor as you say. The main thing is to know when

it is time to stop testing and start photographing. For pictures of

clouds and skies, the primary reason for filters is because without

them the sky would just be a blank off-white patch. When all is said

and done, no matter how much or how exactly you test, there are still

going to be judgement calls based on how you want the final product

to look - how you see it happening. That's the art.

[jorge_gasteazoro4]

Brian and Steve I agree with you completely, all I am saying is that

for my film, lens meter combination I have come up with a very

reliable method, now I wont go as far as Mark and tell you I have

never had any under or over exposures......as the both of you stated

the factors rely on many variables to be able to take into account

with one test, but I sure as heck find testing more reliable than

trustin a meter no matter how well it was tinkered with at Zone VI....

and for a test that I did 12 years ago, to still have reliable

results no matter what meter I use....well I think I am on the right

track.

[steve_gangi2]

If it works, then keep doing it. You've had enough time to know it

works, and that's good. If you were not getting good results you

would have tried something else, so there's no way I can argue

against that. Everyone has their own approach and every person who

posted had valid points, mine is just a little more casual and works

for me. To be honest, my paycheck does not depend on photography, so

I can afford to be a little more lax. I was more concerned with the

fact that the original question was posed by someone new to large

format and all of us (myself included) were maybe starting to get a

little too technical. Learning is like eating. It's better to take

small bites than to choke while trying to gulp it all down at

once.

[xx]

Steve, if I said,"close enough" about something related to engineering

would you have a problem with that? This isn't a hobby for me, and I

don't put "fudge factors" on the wall. this is a big part of how I

make my living, so yes, it does matter.

 

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Jorge, if "close enough" is good for you, then thats fine, just admit

it. To say that I don't understand sensitometry or color theory is

laughable, especially if you knew my background and education. What

you say is correct about absorption, except for the fact that you fail

to compensate for variations in the amount of color transmitted by the

scene. I don't know how to say it any more plain than that. If that

additional variance isn't big enough for you to be concerned then

thats fine, but don't claim to know what my education in these matters

based on this conversation. I also never claimed to not have ever had

under/overexposure problems before, I said that I haven't had over/

under problems due to filter usage when using the spot meter.

 

<p>

 

Brian, yes it is true that metering with filters in front of the meter

is unreliable, unless you have a meter calibrated for that purpose. I

use the pentax spot meter calibrated by Zone 6, its extremly accurate

for this type of situation.

[steve_gangi2]

Mark, we have a funny saying, "There eventually comes a time to

shoot the engineers and get on with production".

No I would have no problem at all if you said "close enough",

since engineers are expected to know when something is close enough.

We call it the design tolerances. You earn a living at this,

so you have to be more exact than I do. Your tolerances are more

stringent. As an amateur I can get away with saying "close enough",

as can most people here. You could say we have looser design

requirements. I was attempting to speak from my perspective and

would not presume to speak for you. There are always unavoidable

variations or tolerances which must be allowed for, no matter what

the field of work.

One advantage to not being paid is that I only have to please

myself. No budgets, time constraints, impossible customers,

unfriendly critics... plus the luxury of not having to show anyone my

really crappy pictures (only the good ones). Wider tolerances. More

leeway in what is "close enough".

[jorge_gasteazoro4]

Mark, I fail to compensate for the color variations the same way your

ZOne VI fails to compensate, why dont YOU admit it that my way is

just as good and cheaper than buying a Zone VI meter. YOu seem to

think that you know everything and your background of which you are

so proud of allows to make the statements you made about the testing

I have made. I dont know, seems to me you are unwilling to learn and

listeng to new ways, plus the fact that even though you might be the

greatest optics engineer you still failed to grasp the concept of

filtration. SO look, I was once told dont argue with a fool, people

looking at you dont know which is which, so in that vein I give you

the absolute reason, you are completely correct, I AM WRONG, and I

wish you luck in your blisfull ignorance.

[xx]

Jorge,

 

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1.The meter compensates for both absorption and variations in color

2.no your way isn't as good because it doesn't compensate for color

variations.

3.How is it that I don't grasp the concept of filtration?

4. the proof is in the pudding as they say, lets see your work.

[jorge_gasteazoro4]

LOL...if I dont wish you argue with you any more, what makes you

think I am going to get into a "I'll show you mine if you show me

yours" deal??

1.- since you rely on a gizmo to do your thinking, I have no interest

on either showing you my stuff or knowing your opinion. Please read

my statement about arguing with a fool!

2.- I have admited to all you are correct, so this will be my last

post on this matter, have a good life Mark!

[photo_bob]

If Mr. Lindsey makes a living from what he shows on his web site, I

would think that he would starve.

[steve_gangi2]

I'd actually enjoy seeing this "Big Shootout" and would be willing to

toss in one or two of my own, just for laughs. I wouldn't expect to

win, have no great secrets to pass on, there's no pressure on me, so

what the heck. Just be warned, I'm a stubborn SOB who's been playing

with film since the late 50s so no matter what, I will still do

things my way. Now, how do we do it?

[c.j._wong2]

Enjoying reading this thread. I learned a lot. One question

though:

 

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Am I correct that published filter factor is based on Zone V ?

And we usually expose for Zone III/IV ....

 

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An accurate filter factor should be the one that makes Zone III/IV

as it should after a filter is applied ....and it certainly is not the

published factor, Yes ? No ?

 

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Regards,

C.J. Wong