Filters and Metering

SodaAnt · Aug 17, 2023

Is it best to meter a scene (spotmeter, in my case) and then apply filter factors, or meter through the filter(s) and use the reading directly?

I've heard that the latter procedure is problematical because the sensor in many meters doesn't mimic film spectral sensitivity closely enough and can result in incorrect exposure readings. Is this really enough of a factor to worry about?

(I have a Pentax Digital Spotmeter, but not one of the Zone VI modified ones.)

wiltw · Aug 17, 2023

Your question is likely to be rather dependent upon the vintage (and which photocell is employed in it) of the meter in question. Newer photocells (e.g. SBC) response is improved over older technology

BrianShaw · Aug 17, 2023

Filter factor.

Paul Howell · Aug 17, 2023

If you have a newer camera with matrix metering I would not hesitate to use TTL metering with filters, the matrix metering my my F4 and Minolta A mount bodies do a very job of metering with all the black and white filters I use. On the other hand, not that sure about color correction filters with any TTL meter. Using an older body with CdS cells I use a hand held meter and filter factors. With a Miranda EE, I get up a stop of difference between the TTL reading and a hand held meter. The Miranda is heavy bottom weighted pattern on the mirror. With my Minolta 102 just over a 1/2 stop which could be do the age of the cells.

xkaes · Aug 17, 2023

SodaAnt said:
Is it best to meter a scene (spotmeter, in my case) and then apply filter factors, or meter through the filter(s) and use the reading directly?

I've heard that the latter procedure is problematical because the sensor in many meters doesn't mimic film spectral sensitivity closely enough and can result in incorrect exposure readings. Is this really enough of a factor to worry about?

(I have a Pentax Digital Spotmeter, but not one of the Zone VI modified ones.)

Regardless of age, if you meter a midtone GRAY area (with & without the meter) you will get the filter adjustment.

If you meter a RED area with a RED filter you will get the same exposure even though you put the red filter on to ligjhten the red areas.

If you meter a GREEN area with a GREEN filter you will get the same exposure even though you put the green filter on to ligjhten the green areas.

Meter a gray card with the filter or use the filter factor -- or better yet, use an incident meter.

Sirius Glass · Aug 17, 2023

Paul Howell said:
If you have a newer camera with matrix metering I would not hesitate to use TTL metering with filters, the matrix metering my my F4 and Minolta A mount bodies do a very job of metering with all the black and white filters I use. On the other hand, not that sure about color correction filters with any TTL meter. Using an older body with CdS cells I use a hand held meter and filter factors. With a Miranda EE, I get up a stop of difference between the TTL reading and a hand held meter. The Miranda is heavy bottom weighted pattern on the mirror. With my Minolta 102 just over a 1/2 stop which could be do the age of the cells.

Many light meters of all types do not properly meter through darker filters. Always use the filter factor. When I took a class from Alan Ross at Yosemite, he demonstrated the inaccuracies of metering through filters.

Klaus_H · Aug 18, 2023

I am using a Zone VI modified Pentax Digital Spotmeter.
I do not use filter factors, but allways measure with a filter on the spotmeter (filters #5, 8, 11,13,15,21,25).
For me this produces better results than the use of filter factors.
I think most of the published filter factors result in too long exposure times for todays films.

Paul Howell · Aug 18, 2023

Sirius Glass said:
Many light meters of all types do not properly meter through darker filters. Always use the filter factor. When I took a class from Alan Ross at Yosemite, he demonstrated the inaccuracies of metering through filters.

Was that with Matrix or older averaging meters?

ic-racer · Aug 18, 2023

I’m guessing this thread will generate 100+ posts…

Doremus Scudder · Aug 18, 2023

I've written about this before, so a search here will turn up possibly more detailed information.

Here's the short version:

If you use your spotmeter to meter through filters (I do), then you need to be aware of the problems and how to deal with them.

First, you have to understand enough about the physics involved and how filters work to meter intelligently. As mentioned above, if you meter a red object through a red filter, the filter will have little effect on the reading. Conversely, if you meter a green or blue object through the red filter, they will read significantly darker than without the filter. Knowing which color filters pass and darken which other colors is important. Only by knowing that can you effectively place an important value for determining exposure and then find where everything else falls. So read up on color theory and study your filters so you know which wavelengths they block and pass.

Secondly, the spectral response of the meter and the film you are using likely doesn't match exactly. That means that the readings you get when reading through the filter will not translate exactly to the actual exposure the film gets or proportionately to density differences on the film for different colors. The stronger the filter, the more pronounced this effect. Furthermore, very strong filters (red, green and blue) expose only the part of the film's emulsion. Depending on how the emulsion is sensitized to different wavelengths, exposing with just one basic color can affect the contrast that the film develops to, i.e., your "Normal" with no filter might end up being N+1 or N-1 with a strong filter. This also varies from film to film.

The answer here is to run some basic exposure and development tests with the different strong filters you use (usually only red and green for most people) and the films you use most and come up with some adjustments in exposure and development. For example, 320Tri-X and a #25 filter needs 2/3 stop more exposure and a development of N-1 to get to my "Normal." So, when I meter through that filter and am using that film, I make those adjustments. Yes, I know, it's just like applying a filter factor, except I get the advantages of being able to see and measure what my filter will do in every part of the scene, something you don't get with just applying a filter factor. And, the red filter doesn't behave the same way with TMY, so I have a different set of adjustments for the #25 with that film.

The advantages of reading through the filter, however, outweigh the trouble I have to go through to fine-tune the process for me. Not only can I get a better visualization of how the densities will actually be distributed on the negative, but I can ensure better exposure in many cases than just applying a factor.

That's not to say that one can't get good results using the filter factor. However, we must also remember that filter factors are approximations and arrived at assuming standard lighting with the aim of rendering a neutral gray object the same density with and without the filter. It really tells you nothing about how much (or little) a colored object will be affected by the filter. And, when the lighting is not standard, things become much more of a crap shoot. I like to be able to see that that blue sky will actually be darker than those green trees by getting a meter reading from both of them through the filter.

Here's an example where reading through the filter wisely will result in better results than just applying the filter factor: We ZS users place an important shadow value to determine exposure. Shadows are often lit by very blue light from the open sky. A yellow, orange or red filter will darken shadows that are predominantly lit by blue light. Just applying the filter factor does not take this into account (factors are based on neutral gray under standard lighting conditions) and often results in underexposed shadows, especially with stronger filters. In this case, reading through the filter, especially if you've done your testing, gives a more accurate reading of what the exposure should be.

Hope this helps,

Doremus

SodaAnt · Aug 18, 2023

Doremus Scudder said:
Shadows are often lit by very blue light from the open sky. A yellow, orange or red filter will darken shadows that are predominantly lit by blue light. Just applying the filter factor does not take this into account (factors are based on neutral gray under standard lighting conditions) and often results in underexposed shadows, especially with stronger filters. In this case, reading through the filter, especially if you've done your testing, gives a more accurate reading of what the exposure should be.

This is the common case I was concerned about because I like dramatic skies and tend to use orange and red filters a lot, and, as you say, they really impact the shadows lit by the blue sky. Looks like I need to do some experimentation.

Paul Howell · Aug 18, 2023

Good points, I seldom use a red, light orange, dark yellow, and green are my usual filters. I had forgotten that AA discusses how filters affect shadow details, I think he provides a few examples in book 1, now that I think about Minor White gave very similar discussion when I took his summer class in the 60s. Although not a BZS person I need to reread Phil Davis to see what he writes abouts using filters and metering using his method.

SodaAnt · Aug 18, 2023

I use a viewfinder app on my iPhone to check framing before I set up my camera, and one of the features it has is the ability to display the scene in black and white. It would be really cool if it could display the scene as it would appear with filters.

Sirius Glass · Aug 18, 2023

Paul Howell said:
Was that with Matrix or older averaging meters?

We tested it with Matix and both new and old averaging meters and all were not accurate with dark orange, red and green filters.

Sirius Glass · Aug 18, 2023

Doremus Scudder said:
I've written about this before, so a search here will turn up possibly more detailed information.

Here's the short version:

If you use your spotmeter to meter through filters (I do), then you need to be aware of the problems and how to deal with them.

First, you have to understand enough about the physics involved and how filters work to meter intelligently. As mentioned above, if you meter a red object through a red filter, the filter will have little effect on the reading. Conversely, if you meter a green or blue object through the red filter, they will read significantly darker than without the filter. Knowing which color filters pass and darken which other colors is important. Only by knowing that can you effectively place an important value for determining exposure and then find where everything else falls. So read up on color theory and study your filters so you know which wavelengths they block and pass.

Secondly, the spectral response of the meter and the film you are using likely doesn't match exactly. That means that the readings you get when reading through the filter will not translate exactly to the actual exposure the film gets or proportionately to density differences on the film for different colors. The stronger the filter, the more pronounced this effect. Furthermore, very strong filters (red, green and blue) expose only the part of the film's emulsion. Depending on how the emulsion is sensitized to different wavelengths, exposing with just one basic color can affect the contrast that the film develops to, i.e., your "Normal" with no filter might end up being N+1 or N-1 with a strong filter. This also varies from film to film.

The answer here is to run some basic exposure and development tests with the different strong filters you use (usually only red and green for most people) and the films you use most and come up with some adjustments in exposure and development. For example, 320Tri-X and a #25 filter needs 2/3 stop more exposure and a development of N-1 to get to my "Normal." So, when I meter through that filter and am using that film, I make those adjustments. Yes, I know, it's just like applying a filter factor, except I get the advantages of being able to see and measure what my filter will do in every part of the scene, something you don't get with just applying a filter factor. And, the red filter doesn't behave the same way with TMY, so I have a different set of adjustments for the #25 with that film.

The advantages of reading through the filter, however, outweigh the trouble I have to go through to fine-tune the process for me. Not only can I get a better visualization of how the densities will actually be distributed on the negative, but I can ensure better exposure in many cases than just applying a factor.

That's not to say that one can't get good results using the filter factor. However, we must also remember that filter factors are approximations and arrived at assuming standard lighting with the aim of rendering a neutral gray object the same density with and without the filter. It really tells you nothing about how much (or little) a colored object will be affected by the filter. And, when the lighting is not standard, things become much more of a crap shoot. I like to be able to see that that blue sky will actually be darker than those green trees by getting a meter reading from both of them through the filter.

Here's an example where reading through the filter wisely will result in better results than just applying the filter factor: We ZS users place an important shadow value to determine exposure. Shadows are often lit by very blue light from the open sky. A yellow, orange or red filter will darken shadows that are predominantly lit by blue light. Just applying the filter factor does not take this into account (factors are based on neutral gray under standard lighting conditions) and often results in underexposed shadows, especially with stronger filters. In this case, reading through the filter, especially if you've done your testing, gives a more accurate reading of what the exposure should be.

Hope this helps,

Doremus

Thank you for a concise response. I have found that figuring out all the possibilities of colors for each dark colored filter time consuming and I prefer using the filter factors instead.

Bill Burk · Aug 18, 2023

Search for Hutchings Filter Factor.

There is a chart called Gordon Hutchings Filter Factors

Meter through filter then increase exposure by...

#8 no increase - Medium Yellow
#11 one stop - Lt. Yellow-Green
#12 no increase - Dark Yellow (AKA Minus Blue)
#16 one stop - Medium Orange
#21 one stop - Light Red
#25 two stops - Medium Red
#29 two stops - Deep Red
#44A one stop - Cyan (AKA Minus Red)

RalphLambrecht · Aug 18, 2023

SodaAnt said:
Is it best to meter a scene (spotmeter, in my case) and then apply filter factors, or meter through the filter(s) and use the reading directly?

I've heard that the latter procedure is problematical because the sensor in many meters doesn't mimic film spectral sensitivity closely enough and can result in incorrect exposure readings. Is this really enough of a factor to worry about?

(I have a Pentax Digital Spotmeter, but not one of the Zone VI modified ones.)

I had bad experience metering through the filter, especially with the modified Zone VI meter but never had a problem with metering without metering and then applying the filter factor.

Bill Burk · Aug 18, 2023

RalphLambrecht said:
I had bad experience metering through the filter, especially with the modified Zone VI meter but never had a problem with metering without metering and then applying the filter factor.

Was your bad experience from using readings as-is?

I know my underexposed photos taken with a red filter were from using an SLR in auto mode.

I have been using SLR in auto mode lately

That’s what keeps me intrigued by Hutchings factors

I agree reading without a filter and applying the published factors is the gold standard

DREW WILEY · Aug 18, 2023

Filter Factor, always. And by that I mean a personally tested filter factor with with respect to each specific film and filter combination. The published filter factors on the Tech Sheets are a good starting place. But exact filter densities vary from brand to brand, or due to age and fading. So if a particular filter is new to you, it's always wise to do a trial exposure with a gray card and then read the developed neg with a densitometer, before any important project.

Reading through a meter, or even using TTL in-camera metering with the filter in place, is that those don't see all colors equally. You'll probably get away fine with something only slight like Skylight filter or even pale yellow. But as filter density increases, the more likelihood of the reading being significantly off.

Even allegedly similar panchromatic films can differ significantly in actual filter factor. For example, Delta 100 needs fully half a stop more filter factor than than TMax when a medium green filter is being used. Then compare that to Acros, which is actually Orhtopan sensitivity, and you'd be way off.

Bill - you aren't doing anyone a favor by quoting that Hutchings list. Who knows what kind of meters were behind that, or whether or not those filters were used for skeet shooting events first, or dog frisbee. Was the film made fresh in a wash basin, or found in someone's old attic? Never know, when someone back in the redwoods is making moonshine with pyrogallol.

Soda Ant - in the pack I have a pair of red laser glasses. Simulates a red filter. But it's really more for fun, when someone asks me what I'm taking a picture of, and doesn't understand how filters interact with black and white film. So I just tell them to put on those red glasses and look the same direction my camera is pointed, standing beside it. Then it's, Wow!

Bill Burk · Aug 18, 2023

Drew I could probably verify whether or not it’s valid with some tests. But I think it passes the smell test.

It’s presented on Page 28 of Steve Simmons “Using The View Camera” from 1987 when they had the Pentax Digital Spotmeter.

Looking through the acknowledgements I half expected to see your name.

A snippet I could grab…

“This filter-factor system was developed by Gordon Hutchings of Orangevale, California. He designed it to make sure that a scene's shadow areas receive enough exposure and aren't thin and underexposed on the negative.”

A short interview with John Paul Caponigro reveals that Gordon Hutchings develops in Pyro and that he’s a Buddhist.

Gordon Hutchings - John Paul Caponigro

www.johnpaulcaponigro.com

—
JPC Sounds like beginner’s mind.
GH You’re speaking to a Buddhist.
—

Sirius Glass · Aug 18, 2023

DREW WILEY said:
Filter Factor, always. And by that I mean a personally tested filter factor with with respect to each specific film and filter combination. The published filter factors on the Tech Sheets are a good starting place. But exact filter densities vary from brand to brand, or due to age and fading. So if a particular filter is new to you, it's always wise to do a trial exposure with a gray card and then read the developed neg with a densitometer, before any important project.

Reading through a meter, or even using TTL in-camera metering with the filter in place, is that those don't see all colors equally. You'll probably get away fine with something only slight like Skylight filter or even pale yellow. But as filter density increases, the more likelihood of the reading being significantly off.

Even allegedly similar panchromatic films can differ significantly in actual filter factor. For example, Delta 100 needs fully half a stop more filter factor than than TMax when a medium green filter is being used. Then compare that to Acros, which is actually Orhtopan sensitivity, and you'd be way off.

Bill - you aren't doing anyone a favor by quoting that Hutchings list. Who knows what kind of meters were behind that, or whether or not those filters were used for skeet shooting events first, or dog frisbee. Was the film made fresh in a wash basin, or found in someone's old attic? Never know, when someone back in the redwoods is making moonshine with pyrogallol.

Soda Ant - in the pack I have a pair of red laser glasses. Simulates a red filter. But it's really more for fun, when someone asks me what I'm taking a picture of, and doesn't understand how filters interact with black and white film. So I just tell them to put on those red glasses and look the same direction my camera is pointed, standing beside it. Then it's, Wow!

I found the higher quality filters, Hasselblad, B+W and Heliopan filter factors to be accurate as well as Tiffen and Hoya. Other filters, not as accurate.

DREW WILEY · Aug 18, 2023

Tiffen? Yeah, they still offer a huge selection, and I own a number of them; but I sure wouldn't place them in the same quality league as Hoya, B&W, or Heliopan, especially their multicoated versions. Tiffen filters have to be almost constantly cleaned due to lack of coatings. But at least Tiffen tries to equate to Wratten specifications, making it easier to compare specs in the old Kodak filter guide books.

Alan Edward Klein · Aug 19, 2023

Doremus Scudder said:
I've written about this before, so a search here will turn up possibly more detailed information.

Here's the short version:

If you use your spotmeter to meter through filters (I do), then you need to be aware of the problems and how to deal with them.

First, you have to understand enough about the physics involved and how filters work to meter intelligently. As mentioned above, if you meter a red object through a red filter, the filter will have little effect on the reading. Conversely, if you meter a green or blue object through the red filter, they will read significantly darker than without the filter. Knowing which color filters pass and darken which other colors is important. Only by knowing that can you effectively place an important value for determining exposure and then find where everything else falls. So read up on color theory and study your filters so you know which wavelengths they block and pass.

Secondly, the spectral response of the meter and the film you are using likely doesn't match exactly. That means that the readings you get when reading through the filter will not translate exactly to the actual exposure the film gets or proportionately to density differences on the film for different colors. The stronger the filter, the more pronounced this effect. Furthermore, very strong filters (red, green and blue) expose only the part of the film's emulsion. Depending on how the emulsion is sensitized to different wavelengths, exposing with just one basic color can affect the contrast that the film develops to, i.e., your "Normal" with no filter might end up being N+1 or N-1 with a strong filter. This also varies from film to film.

The answer here is to run some basic exposure and development tests with the different strong filters you use (usually only red and green for most people) and the films you use most and come up with some adjustments in exposure and development. For example, 320Tri-X and a #25 filter needs 2/3 stop more exposure and a development of N-1 to get to my "Normal." So, when I meter through that filter and am using that film, I make those adjustments. Yes, I know, it's just like applying a filter factor, except I get the advantages of being able to see and measure what my filter will do in every part of the scene, something you don't get with just applying a filter factor. And, the red filter doesn't behave the same way with TMY, so I have a different set of adjustments for the #25 with that film.

The advantages of reading through the filter, however, outweigh the trouble I have to go through to fine-tune the process for me. Not only can I get a better visualization of how the densities will actually be distributed on the negative, but I can ensure better exposure in many cases than just applying a factor.

That's not to say that one can't get good results using the filter factor. However, we must also remember that filter factors are approximations and arrived at assuming standard lighting with the aim of rendering a neutral gray object the same density with and without the filter. It really tells you nothing about how much (or little) a colored object will be affected by the filter. And, when the lighting is not standard, things become much more of a crap shoot. I like to be able to see that that blue sky will actually be darker than those green trees by getting a meter reading from both of them through the filter.

Here's an example where reading through the filter wisely will result in better results than just applying the filter factor: We ZS users place an important shadow value to determine exposure. Shadows are often lit by very blue light from the open sky. A yellow, orange or red filter will darken shadows that are predominantly lit by blue light. Just applying the filter factor does not take this into account (factors are based on neutral gray under standard lighting conditions) and often results in underexposed shadows, especially with stronger filters. In this case, reading through the filter, especially if you've done your testing, gives a more accurate reading of what the exposure should be.

Hope this helps,

Doremus

How does the red filter behave with Tmax 400?

Alan Edward Klein · Aug 19, 2023

SodaAnt said:
I use a viewfinder app on my iPhone to check framing before I set up my camera, and one of the features it has is the ability to display the scene in black and white. It would be really cool if it could display the scene as it would appear with filters.

Many digital cameras provide that option. You switch to BW mode and then select the color filter. You use the camera as a director's viewfinder. I use my Olympus E-PL1 micro 4/3 digital camera for these things. See the instruction manual section below. What's nice is you can snap the picture and save it for reference as a jpeg while saving the RAW in color at the same time without the BW and filter effect. The digital camera can be used to select the right lens on my LF camera as well as doing preliminary composition. I record the settings verbally in video mode for transcription later at home and use it as a meter as well since it has center, matrix and spot metering options.

Alan Edward Klein · Aug 19, 2023

B+W filter manual. Use the manufacturers' filter factor. These vary among different producers.

https://schneiderkreuznach.com/application/files/1116/7471/9462/Broschuere-B-W_EN_without_UV_reduced_size.pdf

Filters and Metering

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