Red Filter compensation

Helinophoto said:

According to this article on wikipedia, 25A has a factor of 5, which is slightly over 2 stops http://en.m.wikipedia.org/wiki/Filter_factor , i have hoya and opening up roughly 2 stops worked fine for me.

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awesome this was great ! Thanks everyone for the input

Helinophoto said:

According to this article on wikipedia, 25A has a factor of 5, which is slightly over 2 stops http://en.m.wikipedia.org/wiki/Filter_factor , i have hoya and opening up roughly 2 stops worked fine for me.

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And according to this one (http://en.wikipedia.org/wiki/Wratten_number) 25A has a filter factor of 8. Thus my comments to check the recommendations of each filter manufacturer.

Another point to consider is that monochrome contrast filters will not have the same factor with all films.

It varies with the spectral sensitivity of the individual film. That's particularly true at the red end of the spectrum.

- Leigh

As stated it's very dependant on film and film speed/developer, the latitude of the film will also take care of minor differences between makes of filter I tend to use +1 stop for yellow, +2 for orange and +3 for red. Seems to work okay.

So what is it?
Metering through a Tiffen 25 takes off about four stops. Do you have to subtract an additional number of stops on top of that (about two judging from the vague, disagreeing posters in this thread)?

Film like Tmax 100/400, the Deltas, FP4 and HP5 and TriX has plenty of red sensitivity into the same band that the typical red filter passes. So it would seem it could be safely taken out as a major factor, with standard development?

I resurrect this thread since it’s the first thing that pops up in a google and also strangely one of the largest in this forum on the topic.

Helge said:

So what is it?
Metering through a Tiffen 25 takes off about four stops. Do you have to subtract an additional number of stops on top of that (about two judging from the vague, disagreeing posters in this thread)?

I resurrect this thread since it’s the first thing that pops up in a google and also strangely one of the largest in this forum on the topic.

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A lot of threads are characterised by disagreeing posters in my experience. HP5+ v Tri-X, F100 v F5, is Acros II worth the price being asked to name but a few After 15 years here I think I can safely say that the only thing I have seen compete agreement on is that fix before developer results in clear film

Now there's a challenge that Photrio users will meet. Out there is someone whose experience has been different. We need to wait to hear from that person

To be fair and to be only slightly more serious, the stock answer on most issue that sounds trite but in this case may be the best answer is to test by bracketing around what the meter says when the red filter is on the lens or what the maker's filter factor says the exposures should be and see which of the 3-4 identical shots at different factors looks best to you

pentaxuser

If your meter had exactly the same response curve as your film, just metering through the filter would solve all problems -- but that isn't the case. Selenium, CdS, silicon, smart phone, DSLR sensor, another brand of DSLR sensor -- all have curves different from one another. You can depend on metering with a DSLR to give a correct exposure, for the DSLR you used, but not really for any of the other kinds of meters. In the end, there's a rule of thumb (at least three stops for red, four or five probably better depending on your film type), and there's bracketing and testing. If you can do so, test your film with your filter before you shoot anything important -- if you can't, then give three stops, and bracket at least +1 stop, preferably also +2.

Film costs more than it used to, but it's still cheaper than a lost shot.

Donald Qualls said:

If your meter had exactly the same response curve as your film, just metering through the filter would solve all problems -- but that isn't the case. Selenium, CdS, silicon, smart phone, DSLR sensor, another brand of DSLR sensor -- all have curves different from one another. You can depend on metering with a DSLR to give a correct exposure, for the DSLR you used, but not really for any of the other kinds of meters. In the end, there's a rule of thumb (at least three stops for red, four or five probably better depending on your film type), and there's bracketing and testing. If you can do so, test your film with your filter before you shoot anything important -- if you can't, then give three stops, and bracket at least +1 stop, preferably also +2.

Film costs more than it used to, but it's still cheaper than a lost shot.

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The band a 25 passes is so wide that any modern pan chromatic film should need about the same compensation.
It starts at about 600 nm and goes into infrared.

All the meters I have tested, from fifties selenium to modern ones, have shown about the same four stop difference.

Tiffens insistence on three stops, maybe have to do with the not wanting to disappoint people with too bright a sky as one thread
complained recently?

You divide the ISO by the filter factor and set the results into your meter. So for film with ISO 400, filter factor of 2, set ISO at 200 (one stop). Factor of 4, set ISO at 100 (two stops). Factor of 8, set ISO at 50 (3 stops)

Helge said:

Tiffens insistence on three stops,

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SUGGESTION

BrianShaw said:

SUGGESTION

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https://tiffen.com/products/red-25-filter
(my emphasis)

Alan Edward Klein said:

You divide the ISO by the filter factor and set the results into your meter. So for film with ISO 400, filter factor of 2, set ISO at 200 (one stop). Factor of 4, set ISO at 100 (two stops). Factor of 8, set ISO at 50 (3 stops)

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That’s the kind of information that is taken for granted, but AFAICS not explained clearly and succinctly in this thread.
Until now that is.
Thank you.

You’re being too literal, Helge. Tiffen isn’t Going to spank or prosecute you for figuring out an exposure compensation that works best for your specific gear, film, or photographic vision.

What they are insisting/suggesting is time-honored approximation the will be “generally good enough” until you can decide what works better for you.

computing via filter factor will get you to the same, just a different way.

Jaime Marin said:

Im going to be using a Tiffen red #25 filter and wanted to know how much filter compensation I should put in my light meter. Does it block out -1 or -2 stops of light????

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I mainly use HP5 and I only need to give 1 and 2/3rd more exposure, to maintain a zone III. I believe that David Kachel wrote an article about this very topic way back in the 90's in the long gone Darkroom & Camera Techniques magazine. I found it quite the eye opener. It's important that you test what works best for you. Start with 3 stops and bracket around that.

Filters affect how the colours in the scene render in the negative, with a red filter leaving reds relatively unchanged and greens and blues being made less dense in the negative (and darker in the print).
The red filter will have some neutral density - which will have a consistent across the board effect on how much exposure to use - but it will also adjust the relationship of the tones in the scene to each other.
The uncertainty that you will see in any of these discussions relates to that adjusted relationship.
Think of it: you have two scenes, with one with a mid-tone subject that is predominantly sand coloured (lots of yellow and red) while the other one has a mid-tone subject that is predominantly green. Assume that you have a situation where if you were photographing these two subjects without a filter they would come out to the same density on the negative, and that you wish to maintain that relationship when you use the filter.
Because of the role that the filter plays, in order to maintain those matched densities, the two shots would need different exposures.
Filter factors are recommendations based on collected experience.
The results of metering through a filter also gives results based on collected experience.
Whatever method you use, consider taking notes about the lighting conditions and the subjects - particularly their colour. As you gain experience with the filter, most likely you will find yourself first either metering through the filter lr applying the filter factor, and then making additional adjustments to take into account the character of the light and the individual particulars of the subject.