Filter Factor and Development

madNbad · Jul 4, 2022

This has probably been answered a hundred times but here's one more. When using filters in order to compensate for exposure the options are, adjust the f stop, adjust the shutter speed or adjust the ISO. Now when it's time to develop the film, say Tr-X, is the development time at box speed or do you develop at the filter ISO? Normally, I adjust the ISO but don't want to over develop film that has already been over exposed. This is either a case of over thinking it or sometimes you just have a noob question. Thanks!

Andrew O'Neill · Jul 4, 2022

At box speed...but... For me, it depends on the filter and which film. Years ago, after very careful testing, I found the the factor for a #25 kodak wratten red filter of 8 was too high, when using HP5. A factor of 4x is better for me. Another important factor is how the filter effects the films contrast. With HP5, if I give my normal development, I'll end up with a negative that looked like it was given N-1.5. So, I have to develop longer. I also have to adjust the dev time when using TMY, but I can't remember by how much as I haven't shot it for a while.

madNbad · Jul 4, 2022

Thanks. I had a short roll of Tr-X today using a yellow filter on my Retina IIa, developed it at exposed speed, ISO 200 and it was way over developed. I'll try a few more short rolls and make some adjustments.

Rick A · Jul 4, 2022

Develop normally, I've found there's no need to adjust for filters.

nmp · Jul 4, 2022

By taking into account the filter factor, you are exposing "normally" based on the actual amount of light falling on the film, then you should not have to change your development. If you didn't compensate, you would be underexposing, then over-developing would make sense.

projectbluebird · Jul 4, 2022

Since you are using a Retina, I assume you are using some sort of external meter?

Changing the ISO on an external meter to include the filter factor is one (easy) way to provide exposure compensation. For example, shooting HP5 (400 ISO) with a medium yellow filter (-1 stop) you could set your meter ISO to 200 and you’re good to go - Note that you are not actually changing the ISO of the film.

Sirius Glass · Jul 4, 2022

Rick A said:
Develop normally, I've found there's no need to adjust for filters.

There is no need to adjust the development time.

madNbad · Jul 4, 2022

projectbluebird said:
Since you are using a Retina, I assume you are using some sort of external meter?

Changing the ISO on an external meter to include the filter factor is one (easy) way to provide exposure compensation. For example, shooting HP5 (400 ISO) with a medium yellow filter (-1 stop) you could set your meter ISO to 200 and you’re good to go - Note that you are not actually changing the ISO of the film.

I divide the filter factor by the box speed and enter that into the Reveni meter and expose at that reading. I'm trying not to over develop, thanks to the answers, in the future, development will be at box speed.

MattKing · Jul 4, 2022

projectbluebird said:
Since you are using a Retina, I assume you are using some sort of external meter?

Changing the ISO on an external meter to include the filter factor is one (easy) way to provide exposure compensation. For example, shooting HP5 (400 ISO) with a medium yellow filter (-1 stop) you could set your meter ISO to 200 and you’re good to go - Note that you are not actually changing the ISO of the film.

+1
Some meters, like the Gossen Profisix, have a dial adjustment designed specifically for dialing in a filter factor. They are a great way to approach the issue, provided you remember to set the adjustment back to zero when you have finished.

projectbluebird · Jul 4, 2022

Just to follow up - as someone who has used a variety of older equipment, including filters, I have found the various filter factor notations to be quite confusing at times.

What I have ended up doing is a great deal of sleuthing to find (or calculate) filter factors for the filters I use in f-stops - and then adjusting those through exposure testing.

madNbad · Jul 4, 2022

Sirius Glass said:
There is no need to adjust the development time.

Thank you. That’s all I wanted to know.

Doremus Scudder · Jul 5, 2022

madNbad said:
This has probably been answered a hundred times but here's one more. When using filters in order to compensate for exposure the options are, adjust the f stop, adjust the shutter speed or adjust the ISO. Now when it's time to develop the film, say Tr-X, is the development time at box speed or do you develop at the filter ISO? Normally, I adjust the ISO but don't want to over develop film that has already been over exposed. This is either a case of over thinking it or sometimes you just have a noob question. Thanks!

To elaborate a bit on the above:

Exposure compensation for filters is needed only when you take a meter reading without the filter. Many users of hand-held cameras with built-in meters simply mount the filter and then let the auto-exposure meter do the rest.

If you're using a separate hand-held meter or metering first without the filter in place, then you need to compensate by changing the exposure from the meter reading by the appropriate amount.

In either case, the film is being correctly exposed and development doesn't need to be changed from the usual.

People change development from "normal" when they are "pushing" film (i.e., intentionally underexposing and then compensating by overdeveloping to get some kind of printable negative) or when they are tailoring a negative for the particular contrast range in the scene (á la Zone System). Using filters is neither of these things.

Best,

Doremus

madNbad · Jul 7, 2022

Thanks to all for the advice! I ran a short roll of Tri-X through the Retina IIa a few days ago starting with no filter, moving to a light yellow, then a green and finally a red. I adjusted the ISO to compensate for filter factor. It was developed in HC-110 using the dilutions and times for Tri-X rated at 400 as listed in Covingtons and the MSD charts. I used Dilution E (1:47) for six and a half minutes, fixed with Ilford Rapid fix. Other than the fact my focus was off on most of the roll, due to a combination of tiny viewfinder, bad vision, an achy leg that made it hard to squat down long enough to find the patch and just enough sunlight filtering through the trees to cause glare, the results were spot on. After scanning the roll with the Sony, I made almost no adjustments in post processing except for inverting the image. Since I know the crowd will demand images, here they are in all their fuzzy glory:

pentaxuser · Jul 7, 2022

madNbad, interesting set of pics with different filters. What's the colour of the card leaning against the cherub and the colour of the wood on the side of the house by the door?

The lesson for me would be that none of the filters really help to differentiate the colours in this scene. The colours of the scene as rendered by the film without filters does this In the event that the highest shutter speed was necessary then all the filters do in this scene is to affect shutter speed

Unless filters help differentiate colours in b&w, are needed for an artistic effect or to reduce shutter speed then they add nothing to some scenes

pentaxuser

madNbad · Jul 7, 2022

This was more for my own verification to adjust for filter factor but develop at box speed. There has been the argument for always using a yellow filter with B&W film but with the modern films being so well balanced across the light spectrum, that may not be the case. I’ll keep a set in my bag and when the right lighting calls for enhancements, then I’ll get one out.

pentaxuser · Jul 7, 2022

madNbad said:
This was more for my own verification to adjust for filter factor but develop at box speed. There has been the argument for always using a yellow filter with B&W film but with the modern films being so well balanced across the light spectrum, that may not be the case. I’ll keep a set in my bag and when the right lighting calls for enhancements, then I’ll get one out.

Thanks Any idea about the answers to my questions on colour of the card and wooden side of the door?

pentaxuser

madNbad · Jul 7, 2022

pentaxuser said:
Thanks Any idea about the answers to my questions on colour of the card and wooden side of the door?

pentaxuser

The card is almost spot on with no filter. If you look, you can see the Sekonic 398 sitting next to the setup. The incident metering was on the cherub and allowed the door to fall into shadow. I’m about ready to head to the Evergreen Aviation Museum, home of the Spruce Goose, for a photo outing. I’ll just be using my M4, a 28, 35, 50, UV filters and the Reveni reflective meter. It’s an overcast day so the light may be a little flat.

George Collier · Jul 7, 2022

But what color is the card, per Pentaxuser's question? If it is neutral gray, then using the card in adjusting all versions (making the card the same in each image - in scanning, PShop, however) can indicate the real effect of the filters. Or, you might say theoretically, if the filter factors were correct, the neutral object will be the same negative density in all images - a good test of the filter factors. Especially since different films can respond to color differently.
Also, (I hear you about kneeling down) you can always take a careful measurement between the lens and the object with a tape measure, then set the focus ring accordingly - I used a Retina II in high school, I know what you mean about the viewfinder.

Sirius Glass · Jul 7, 2022

If you are going to do more comparison testing please consider:

Including the sky with clouds
Multicolored subjects such as collections of flowers of red, orange, yellow, blue and green foliage

Then you will see the filter effects better.

pentaxuser · Jul 7, 2022

Thanks for your second reply,madNbad. Useful info but it is the kind that answers my questions. I am assuming that the house wall colour and card against the cherub are familiar and known to you but if this was a scene you just came across and haven't seen again so you cannot recall those colours then that's OK as well but just let me know

Thanks

pentaxuser

Mainecoonmaniac · Jul 7, 2022

madNbad said:
This has probably been answered a hundred times but here's one more. When using filters in order to compensate for exposure the options are, adjust the f stop, adjust the shutter speed or adjust the ISO. Now when it's time to develop the film, say Tr-X, is the development time at box speed or do you develop at the filter ISO? Normally, I adjust the ISO but don't want to over develop film that has already been over exposed. This is either a case of over thinking it or sometimes you just have a noob question. Thanks!

I think that when adjusting your exposure for the filter factor, there shouldn't be any adjustment to your development. The overall exposure should be the same. The only exception is if you're using a long exposure to compensate for your filter. An example would be a timed exposure with an ND filter that causes reciprocity failure.

madNbad · Jul 7, 2022

pentaxuser said:
Thanks for your second reply,madNbad. Useful info but it is the kind that answers my questions. I am assuming that the house wall colour and card against the cherub are familiar and known to you but if this was a scene you just came across and haven't seen again so you cannot recall those colours then that's OK as well but just let me know

Thanks

pentaxuser

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. I may put the effort in to matching the gray on the card with the gray on the negative someday. We have had a fairly wet spring, so cloud cover and diffused light has been the norm. Just returned from the aviation museum and the gray sky gave way to blue with puffy clouds, I'm hoping for some good results.

RalphLambrecht · Jul 7, 2022

madNbad said:
This has probably been answered a hundred times but here's one more. When using filters in order to compensate for exposure the options are, adjust the f stop, adjust the shutter speed or adjust the ISO. Now when it's time to develop the film, say Tr-X, is the development time at box speed or do you develop at the filter ISO? Normally, I adjust the ISO but don't want to over develop film that has already been over exposed. This is either a case of over thinking it or sometimes you just have a noob question. Thanks!

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?

Alan Edward Klein · Jul 7, 2022

madNbad said:
This has probably been answered a hundred times but here's one more. When using filters in order to compensate for exposure the options are, adjust the f stop, adjust the shutter speed or adjust the ISO. Now when it's time to develop the film, say Tr-X, is the development time at box speed or do you develop at the filter ISO? Normally, I adjust the ISO but don't want to over develop film that has already been over exposed. This is either a case of over thinking it or sometimes you just have a noob question. Thanks!

How do you adjust ISO on film. It's fixed?

Maris · Jul 7, 2022

I tend to work filter factors the other way around.
When I test a filter to discover its exposure factor that factor must deliver the negative I want at a normal developing time.
If it doesn't I'll try another filter factor until it does.
Changing the filter factor, changing exposure, and changing development is too many simultaneous variables for me.

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