View Full Version : Polarizer with B&W

brian steinberger
12-Sep-2005, 18:18
I shot a roll of Tri-x 400 yesterday and used a Hoya Circular polarizer for every shot. And all of them look very contrasty. Just a thought, but could it be that polarizer filters transmit more amounts of blue light, which black and white film is most sensitive to? Just wondering if that was why my shots came out overly contrasty. It wasn't my scenes, I used to spot meter to measure and keep them within a 5 stop range.

Ron Marshall
12-Sep-2005, 18:40

Have a look at a page on this site (http://www.largeformatphotography.info/filters.html) which lists the spectral charecteristics of some polarising filters. Some pass more blue, some don't but not enough to affect contrast. They will darken the sky at certain orientations.

CP Goerz
12-Sep-2005, 18:50
If you pop a number of polarizers on a light box you'll se that no two are actually the same colour, most are a little on the warm side which would make a more contrasty B+W neg.

CP Goerz.

John Berry ( Roadkill )
12-Sep-2005, 18:54
As of late I'm leaning more towards a graduated ND as I find I lose shadow detail in proportion to the amount of filtration used.

12-Sep-2005, 20:54
You might be seeing increased contrast if there are objects that are not susceptible to polarization such as sheet metal. As far as admitting more blue - dunno, but not in my filters.

Doremus Scudder
13-Sep-2005, 01:43

More blue light would probably result in a decrease in contrast. More than likely, what is happening is a result of the exposure compensation you are giving. If the film is receiving more exposure because you are over-compensating, it would move the entire luminance range up on the film curve resulting in more shadow separation and higher maximum density. This is generally a desirable thing and you can simply print less contrasty.

If you are giving inadequate compensation, the loss of shadow detail might result in prints that have a "contrastier" look to them when printed for the mid-tones.

Also, the polarizing effect itself can increase contrast by darkening objects that reflect polarized light (this is why we use a polarizer!). Sometimes, it is surprising which objects are darkened. I assume, however, that you took a look through the polarizer to determine the extent of this effect. If not... A polarizing filter should be used discriminatingly for what it does, i.e. remove reflections and darken objects that reflect polarized light (blue sky, for example), not for "every shot" with no thought to what effect it will have on the final image.

Even if your polarizer has a "warm" or "cold" cast to it, it will not be enough color change to make any significant contrast difference with black-and-white film.

Ken Lee
13-Sep-2005, 07:04
What Doremus said.

Next time, shoot a target with well-known colors and shades of grey - with and without the filter. Compare and learn.

If the scene was a landscape, then you should expect greater apparent contrast, since the polarizer will eliminate atmospheric haze, to the degree that you rotate the polarizer, etc. For sky and haze, polarizers give the strongest results when we shoot at a 90 degree angle to the Sun.

Brian Ellis
13-Sep-2005, 07:06
"It wasn't my scenes, I used to spot meter to measure and keep them within a 5 stop range"

I assume you don't really mean this literally since your spot meter obviously can't keep the scene within a five stop range. I assume what you really mean is that you didn't photograph anything unless the contrast range was five stops or less.

Setting that aside, while a polarizer will darken some portions of a scene the effect of that may be to increase contrast or it may be to decrease contrast depending on whether the area darkened is a highlight or a shadow. For example, if a polarizer is properly used it will darken a blue sky and if the sky was the brightest area in the scene then the effect will be to reduce contrast, not increase it.

While Doremus makes some very good points, I disagree with the suggestion that overexposure is the likely cause of the excessive contrast. While overexposure does increase highlight density it also increases shadow density so the end result is a very dense negative with lower overall contrast than would result if everything had been done correctly. It's underexposure that tends to increase contrast (if everything else is done correctly).

How was the film developed (i.e. did you do it yourself or did a lab do it?). Unless you or your lab have done the necessary testing I'd guess the cause of the excessive contrast was overdevelopment, which increases highlight density without causing a corresponding increase in the shadow density (since shadow areas are fully developed about a third to half way through the development process). If overdevelopment was combined with underexposure (e.g. by using too low a filter factor for your polarizer) then you'd get even more contrast.

You don't say what kind of film this was. If by chance it was T Max then whoever processes it must take particular care to keep the developer temperature correct and constant, agitation methods consistent, and times correct. Labs aren't known for doing that kind of thing.