Filter Factor and Development

madNbad · Jul 7, 2022

RalphLambrecht said:
Never thought of that but I would start developing at the filter I still just as you did. What was your experience with that approach?

For many years, I adjusted the ISO to compensate for the filter factor. When I started back developing my own B&W I developed the film at the exposed ISO, such as TMax 400 with a yellow filter factor of 2X, expose at ISO 200, develop for ISO 200. The problem arose when I made the switch to Tri-X. Developing times for Tri-X in HC-110 can be quite short since it's such an active developer. When I did a short roll with a yellow filter, I followed the MDC for TRI-X at 200 and came away with really dense negative, which lead to my original question. I try to nail down development with no filters first, then experiment.

madNbad · Jul 7, 2022

Alan Edward Klein said:
How do you adjust ISO on film. It's fixed?

Divide the box speed of the film by the filter factor and set your meter to that ISO. TMax 400 with a yellow filter factor of 2X is now ISO 200. Or, expose at the box speed ISO then adjust the aperture or shutter speed the necessary number of stops.

Alan Edward Klein · Jul 7, 2022

madNbad said:
Divide the box speed of the film by the filter factor and set your meter to that ISO. TMax 400 with a yellow filter factor of 2X is now ISO 200. Or, expose at the box speed ISO then adjust the aperture or shutter speed the necessary number of stops.

Oh I get it. I just add additional stops to shutter speed and/or aperture but keep the meter at the box speed. Then if I take off the filter, I don;t have to change the meter ISO which I might forget. Of course, I might forget I have a filter on, so my mistakes even out over the long run.

madNbad · Jul 7, 2022

Alan Edward Klein said:
Oh I get it. I just add additional stops to shutter speed and/or aperture but keep the meter at the box speed. Then if I take off the filter, I don;t have to change the meter ISO which I might forget. Of course, I might forget I have a filter on, so my mistakes even out over the long run.

I often forget to change the aperture, the meter is my reminder.

MattKing · Jul 7, 2022

madNbad said:
For many years, I adjusted the ISO to compensate for the filter factor.

Warning - this is really picky.
It helps if instead you say something like: "For many years, I adjusted the ISO setting on the meter/camera to compensate for the filter factor."

Otherwise some people start figuring that you changed the film somehow.

Warning over.

Alan Edward Klein · Jul 7, 2022

MattKing said:
Warning - this is really picky.
It helps if instead you say something like: "For many years, I adjusted the ISO setting on the meter/camera to compensate for the filter factor."

Otherwise some people start figuring that you changed the film somehow.

Warning over.

That's what I thought when he said it. I was getting a little embarrassed thinking I missed something so fundamental after shooting film for 60 years.

Sirius Glass · Jul 7, 2022

MattKing said:
Warning - this is really picky.
It helps if instead you say something like: "For many years, I adjusted the ISO setting on the meter/camera to compensate for the filter factor."

Otherwise some people start figuring that you changed the film somehow.

Warning over.

I agree. I always use the box speed on the meter and then adjust the exposure for the filter and/or Zone System.

madNbad · Jul 7, 2022

MattKing said:
Warning - this is really picky.
It helps if instead you say something like: "For many years, I adjusted the ISO setting on the meter/camera to compensate for the filter factor."

Otherwise some people start figuring that you changed the film somehow.

Warning over.

I just fire up the flux capacitor, dial up a number then drop in the film. Works every time! Warning heeded.

Alan Edward Klein · Jul 7, 2022

Sirius Glass said:
I agree. I always use the box speed on the meter and then adjust the exposure for the filter and/or Zone System.

I write on the filter case the stops needed with a black marker pen such as +3 for three stops required on my red filter. Then if I change to a yellow filter, I know I have to adjust in +1 stop. I don't have to mess around changing the meter's ISO each time, as long as the same film is being used.

madNbad · Jul 7, 2022

The main reason I change the meter is when using a similar filter on multiple lenses. Currently, I have three 022 light yellow and three #15 medium yellow. Occasionally, I will fit each lens with one so I can skip the step of changing filters when changing lens.

gone · Jul 8, 2022

madNbad said:
When using filters in order to compensate for exposure the options are, adjust the f stop, adjust the shutter speed or adjust the ISO

It doesn't matter, one is the same as the other. Your EI is what you expose the film at, and that can vary by each individual, and by each developer choice.

So if you shot Tri-X at 200, for example, and had a filter that ate up a certain amount of light, you would adjust your meter for that. Then you would still develop the film normally. Or, you could make the same adjustment w/ the ISO or aperture/shutter selection, and again, develop normally.

That's what I like about cameras w/ AE. You just set the ISO and the camera takes care of the filter factor.

pentaxuser · Jul 8, 2022

madNbad said:
The card is a standard Kodak gray card, the house is almost the same shade as the card with white trim, the light is filtered through the grove of a dozen hundred foot tall Douglas Firs that are the property line between my yard and my neighbor to the south.

Thanks If the colours are grey then it suggests that filters or different filters are unlikely to have much effect on differentiating. I always felt that filters are only really useful in those scenes where colours that appear close in shades of grey but aren't alike in the colour spectrum need differentiating

pentaxuser

Mainecoonmaniac · Jul 8, 2022

I like Alan and Maris' philosophy if keeping it simple. Too many variables is in invitation for mistakes. Usually, most filers indicate how much exposure compensation is needed. With most modern cameras with TTL metering, it's already calculated for you.

madNbad · Jul 8, 2022

pentaxuser said:
Thanks If the colours are grey then it suggests that filters or different filters are unlikely to have much effect on differentiating. I always felt that filters are only really useful in those scenes where colours that appear close in shades of grey but aren't alike in the colour spectrum need differentiating

pentaxuser

It was a hard decision not to move to a red filter when the sky opened while I was at the air museum. I’m processing the other rolls today.

madNbad · Jul 9, 2022

Learned a few things. Bring more film, be careful with bulk loaded cassettes and Tri-X either has more grain than I remember or my developing skills need improving. First up is Rollei R09, 1:25 for seven minutes, M4, 28 Elmarit ASPH, UV filter, 400TX at ISO 400, metered with a Reveni reflective meter

Moving on here is the Tri-X developed in HC-110 Dilution E (1:47) for five and a half minutes:

Finally, Covingtons favorite for 400TX, HC-110 Dilution E for six and a half minutes. Even though it looked like a dense negative, this scanned the best with the least manipulation:

I'll use up the R09 since I don't have that much left. It seems to give bigger grain and more contrast than the HC-110 and is less likely to show detail in the brighter area of the negative. I wanted to try the HC-110 E at five and a half minutes to reduce the density of the negative but ended up with muddied tones that needed boosting. The sky was great, really wish I had tried a red filter. Thanks for all the advice!

DREW WILEY · Jul 11, 2022

There is simply no way to know the exact filter factor for any specific film in relation to your own metering and development system unless you bracket test a gray card in advance, and ideally make comparisons using a transmission densitometer. If the manufacturer's tech sheet gives you specific filter factors, start with that. Not all films are the same in spectral response, nor are all the same designated filter numbers from different manufacturers necessarily identical. Do not trust TTL metering; their own spectral sensitivity is likely to be somewhat different from black and white film itself.

BrianShaw · Jul 11, 2022

I second the recco for starting with filter factors from film data sheets.

For those who may not have seen this data, there is some spectral sensitivity curves for various meter technologies in this thread that are quite interesting. Not sure if one can estimate the relative effects of various filters on each metering technology or not, though. The data presented is rather old but I assume it to be classic enough that it fundamentally doesn't change too much and represents a reasonable generic perspective. Some individual variability between manufacturers or individual users, surely, may be likely and I would hope that affects only the most specialized of users who need the most precise and accurate metering information.

When did the industry move from ASA to ISO?

The confusion arises because ISO, DIN and ASA are both - they are labels on the box and they are standards as well. The standards coalesced in 1974, all under an official rubric of ISO certification. But for a while, you could say the same thing in three different ways. Sort of like six of one...

www.photrio.com

madNbad · Jul 13, 2022

The Sekonic 398A has a built in calculator for up to +/- two stops. Good enough for my most used yellow or green filters. With the Reveni, I can take a reading, hold the filter in front of the sensor and take another reading for the correct exposure. Just like those new fangled cameras with the through the lens metering. Now for some Tri-X with a yellow filter!

DREW WILEY · Jul 13, 2022

On problem of metering through filters is that panchromatic films have depressed green sensitivity, whereas many meters, especially silicon cell ones, are logically balanced to be analogous to human visual sensitivity, which peaks in the green. Things get even more dicey with respect to red filters. Among so-called pan films you're potentially got extended red, typical pan, and even orthopan (reduced red sensitivity). Then there are ortho and blue-sensitive films per se.

I'm not saying you can't read through filters, but if you do intend to do that, run careful tests with your chosen film first. And of course, the deeper the contrast filter, the higher the risk of being seriously off.

JPD · Jul 13, 2022

madNbad said:
For many years, I adjusted the ISO to compensate for the filter factor. When I started back developing my own B&W I developed the film at the exposed ISO, such as TMax 400 with a yellow filter factor of 2X, expose at ISO 200, develop for ISO 200.

You are still exposing the film at ISO 400 when you do that. If you want to expose the film at ISO 200 while using a filter that steals one stop of light, you should set the exposure meter to ISO 100.

When you compensate for the filter factor you adjust the exposure so that the same amount of light reaches the film as it would if you didn't use the filter. With a filter factor at 2X, one stop, you set your hand held meter to ISO 200 for your ISO 400 film, and you will give it as much exposure as without the filter, at ISO 400.

madNbad · Jul 13, 2022

DREW WILEY said:
On problem of metering through filters is that panchromatic films have depressed green sensitivity, whereas many meters, especially silicon cell ones, are logically balanced to be analogous to human visual sensitivity, which peaks in the green. Things get even more dicey with respect to red filters. Among so-called pan films you're potentially got extended red, typical pan, and even orthopan (reduced red sensitivity). Then there are ortho and blue-sensitive films per se.

I'm not saying you can't read through filters, but if you do intend to do that, run careful tests with your chosen film first. And of course, the deeper the contrast filter, the higher the risk of being seriously off.

The light yellow filter I normally use is a B+W 022 with a 2X factor or 1 stop. I was quite surprised when I held it in front of the little Reveni and the difference was exactly one stop. I'm to the point of using a single film stock, Tri-X, and shortly the developer will be HC-110 Dilution E. Metering will be mostly reflective using the Reveni but I do have the Sekonic 398 for those times when I want to use incident. If I was using a broader range of film stock, then experimentation would be in order.

Sirius Glass · Jul 13, 2022

DREW WILEY said:
On problem of metering through filters is that panchromatic films have depressed green sensitivity, whereas many meters, especially silicon cell ones, are logically balanced to be analogous to human visual sensitivity, which peaks in the green. Things get even more dicey with respect to red filters. Among so-called pan films you're potentially got extended red, typical pan, and even orthopan (reduced red sensitivity). Then there are ortho and blue-sensitive films per se.

I'm not saying you can't read through filters, but if you do intend to do that, run careful tests with your chosen film first. And of course, the deeper the contrast filter, the higher the risk of being seriously off.

And that is why I use the manufacturers' recommendations only.

madNbad · Jul 13, 2022

Sirius Glass said:
And that is why I use the manufacturers' recommendations only.

Thank you for answering my question on the first page.

DREW WILEY · Jul 13, 2022

It's not quite that simple. For example, filter factors can drastically change during long exposures, one filter color relative to another. (And that's in addition to long exp recip corrections themselves.)There are also scene variables. For instance, many people accustomed to slightly hazy lighting might have a rude awakening by just how blue deep shadows can be at high altitude. As a lifelong photographer of mountains and desert areas, I'm keenly aware of that, and it can make a lot of difference between particular pan films, or the choice, say, between a 25 red and 29 red filter, or even 24A or 22 deep orange. In other words, there is simply no substitute for experience shooting and printing, along with preliminary testing.

Filter Factor and Development

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