Filter Factor for Polarizer

[Ektagraphic]

Hi Guys- Lately whenever I have used my polarizer I used one of my automatic cameras and have not worried about metering. What is the filter factor for a polarizer? How do you adjust when shooting with one and using a handheld meter. As always, I will be shooting slides so there is not really lots of exposure latitude. Thanks

 

[brian steinberger]

I would simply meter through the filter for color. I've always been under assumption that a polarizer is 1 2/3 stops. I dial in +1 1/2 on my MF rangefinders and have good results. For color slide work, as I said, I would meter through the filter.

 

[Ektagraphic]

There has got to be another way than taking the filter off of the camera all the time to put it up to the meter....

 

[Lee L]

B+W and Hoya are spec'd as varying between a factor of 2.3 to 2.8, which is 1.2 to 1.5 stops. Tiffen says 1.5-2 stops. You can meter through the polarizer with your camera meter as long as you don't combine a linear polarizer with a metering system that uses some kind of beam splitter. You're safer with a circular polarizer if you don't know how your camera's TTL meter works, but they are a bit more expensive than linear polarizers.

Metering through the filter with a handheld meter is probably a little less accurate because you may not be holding the filter in the same orientation that you're using it on camera.

Lee

 

[brian steinberger]

There has got to be another way than taking the filter off of the camera all the time to put it up to the meter....

If you don't want to take the filter off the camera I would try adding 1 1/2 stops then bracketing 1/3 or 1/2 each way.

 

[Jeff Kubach]

Up to 2 stops. Like other posts you could bracket 1/3 either way.

Jeff

 

[Colin Corneau]

Why not just figure it out once with the filter atop your meter, put it back on the lens, and be done with it? Then you'll know what the factor is so long as you own that polarizer.

Seems the easiest way.

 

[Poisson Du Jour]

FF-POL is 2.5, or +1.3 stops, when hand-held metering. NO difference irrespective of how much POL is applied.
Reversal film is much less tolerant of errors, so bracket +1.3, +1.6.

Hand held (i.e. spot) meters can take screw-on POL filters to save the mental gymnastics of compensation, but even tiny POL filters are expensive!

 

[Q.G.]

The filter factor should be printed on the rim of the filter.
It, like Poisson mentioned, is a fixed factor: always the same, no matter how the filter is used.

That makes using a filter on an automatic camera (the first question you should ask whenever you are considering thingies with built-in automation is where the off-switch is) a bit tricky, since the meter in such thingies cannot help but also register the varying effect of the filter.
You do not want that: selective filtering is what the filter is used for. You do not want to selectively darken things using the polarizer, then overexpose the bits left unaffected by the filter because a stupid meter, ignorant of selective filtering, thinks it has to.

So the only good way to use it is to use that off-switch (!), meter without filter, and use those readings, corrected for the fixed factor, after you have put the filter back on again.
Alternatively, you could use a hand held meter.

So, how on earth did you manage not using the fixed factor and a hand held meter?

 

[Ektagraphic]

For some reason, none of the filters I have give you the filter factor. They are all fairly new so I guess they must just assume that most people shoot in automatic all the time. Even my polarizer, put out by Tiffen does not say. Even with slides how visible is a 1/2 stop chage? Someone said tiffen reccomends 1.5 to 2 stops. Is there really a very visible diffrence?

 

[Q.G.]

A polarizer 'eats' about 1 to 1.5 stops.
It depends on the foil used.

There is a visible difference, yes. How much depends on the lattitude of the film. Beter than trying to describe it, you should just try: one scene, two exposures, 'straight' (no filters), one half a stop more/less than the other.

 

[Lee L]

Not trying to be rude, but you'll learn a lot more, and about your specific equipment if you test for yourself, take careful notes, and look at the results from your specific film, meters, and camera. In this case a few pictures are worth a thousand internet forum verbal descriptions. Bracket by third and half stops and you'll have the answer to your last question.

Lee

 

[Denis K]

You say you want to use a hand held meter without having to always swap-a-roo the polarizer. One would think that if your normal aesthetic is to use a polarizer to darken skies and/or to selectively reject glare lights, then if you were to use an 'incident' light meter offset by a fixed filter factor that would come as close as any other automatic exposure mechanism. The other option would be to use a hand held spot meter, again offset by the same fixed filter factor. If your existing reflected light meter has a low acceptance angle, you may be able to use it like a semi-spot meter and keep it away from heavily modified areas (e.g. sky, water surfaces, non-metallic reflecting surfaces).

 

[Ektagraphic]

Another thing...I just want to make sure that I have this right. If I want to shoot something + 2 stops I would move up to f/stops or shutter speed. If I want - 2 stops I would go down 2 f/stops or shutter speeds.

 

[Sirius Glass]

I agree with the above posts. The most accurate way is to meter through the lens. You can look up the range of filter factors by looking up the manufacturer, but the actual factor for a given situation can vary widely so see the second sentence.

Steve

 

[MattKing]

Another thing...I just want to make sure that I have this right. If I want to shoot something + 2 stops I would move up to f/stops or shutter speed. If I want - 2 stops I would go down 2 f/stops or shutter speeds.

"+ 2 stops" means 2 stops more light. For this, you would slow the shutter by two stops (e.g. from 1/250 to 1/60) or open up the aperture 2 stops (e.g. from f/16 to f/8)

"- 2 stops" means 2 stops less light. For this, you would speed up the shutter by two stops (e.g. from 1/125 to 1/500) or close down the aperture 2 stops (e.g. from f/5.6 to f/11)

Matt

 

[Ektagraphic]

Thanks Matt! I forgot for a minute that less mean more with aperature. Long week

 

[Denis K]

Like using + instead of : with dilutions, we should probably all say "open the lens up 2 stops" instead of saying +2 stops. That way, after paying big bucks for a f1.x lens, we all instinctively know which direction to twist the aperture ring.

Denis K

 

[Poisson Du Jour]

I agree there is some doubt and confusion about what "open up 2 stops" and variations to that effect. Many years ago, we visual arts students were perplexed as to just what this meant, looking for an "opening" and "stops"!! We were expected to known even though it wasn't explained in details. Published tables (i.e. Hoya's) are often not much more help to those seeking guidance, often giving just filter factors and the stops difference. Ideally, such references should include '+' (much less commonly '–') as the equivalent compensation to the stated EV (FF) factor.

Unless I am in a hurry (i.e. quite often I'm nigglingly tolerating getting very wet, on a slippery perch or some other environmental or technical hazard), the POL will be in-situ on the lens and metered 'there and then' (the onboard meter is deadly accurate); I can always go back and fine-tune metering once I review the results, whichever method of metering I employ. A tiny 30mm diameter POL (costing all of AUD$73 about 18 months ago!) is swapped on my L758 spot/incident meter's receiving lens.

Regarding how visible +0.5 stop is on reversal film, it will be very visible (just as –0.5 will be), often enough to balance the affect of the POL with a pleasing photograph. So too, will +0.6 (2/3), as that is greater than +0.5, of course. I think you should willingly burn a few rolls of film in the name of experience, exposing with a POL to gauge the affect it has. Cut the talk, go out now and shoot, damn it.

 

[Joe VanCleave]

The most obvious problem with using a predetermined filter factor for a polarizing filter is that there is no predetermined filter factor for a filter of adjustable density like a polarizer; there's just a range of factors, and not all manufacturers even supply that range.

Thus the need, when using polarizing filters on non-TTL metered cameras, to either remove the filter, meter through it, then reinstall the filter -- all the while retaining the exact orientation of the filter to its original adjustment on the lens (which is highly impractical for all types of photography except perhaps landscape), or use a predetermined guess.

Another way is to adjust the filter through its full range of adjustment while placed in front of the external meter, and note the range of exposure variations, but especially note the exposure variation at minimum and maximum filtration. Then, with the filter on the lens you can make an educated guess about which side of the filter spectrum the filter is adjusted at (either the mininum or maximum amount) and apply your predetermined factor. This is easier for a TTL viewfinder camera (SLR) whereas with a rangefinder or non-TTL viewfinder camera it's again just a guess.

~Joe

 

[Q.G.]

You only want to correct for the 'neutral' density of the polarizer.
Not for the varying effect you can get it to produce.

So all you ever need to know is that fixed neutral density, and all you ever need to adjust for is that same fixed neutral density.

You never want to meter through the filter (except, perhaps, to find it's neutral density - find something that when the filter is rotated doesn't change. The difference between 'straight' and through the filter will be the factor).