Polarizer or Neutral Density?

[Colin Sato]

I have a somewhat urgent question. I been reading up on ND filters and have seen some suggest that a polarizing filter can be used in its place. I have a polarizing and want to shoot a time lapse sunset. Do you think this is safe? I'll wait till the sun is very low, possibly only 3-5 minutes before it actually sets, and then into the evening.

If it's too bright will I know (its too bright) because the LCD won't show anything but white? If is see this I will stop right away, but if not, can I assume I have enough darkening to safely shoot a few minutes of late sun? BTW, the camera is an HC-85 and I'll lock down the focus and exposure before I start the time lapse. I'm thinking I'll just use the manual exposure vs. the Program AE settings (moon). Any thoughts and suggestions are appreciated.

[Cole McDonald]

since you're dealing with a tight time window, I would test options one day, then shoot on another after reviewing your tests and selecting the look you want to go for. I would probably start with a polarizer, and add ND filters to suit your needs, although stopping down the iris in this case probably wouldn't hurt you. I am, however, unsure of the framing you'll be using, so you may want more control over your DoF (wide open iris).

[Colin Sato]

Thanks for the reply, I'll take it into consideration!

[Bill Davis]

Colin,

The two filters do different things. Any neutral density filter is designed to reduce the AMOUNT of light passing through it while having negligable effect on the full spectrum characteristics of the original light. In other words you get the SAME light, only less intense hitting your sensor.

A polarizer, on the other hand, does precisely what it says. It takes the scattered rays of light hitting the lens from many directions, and filters out all except those rays hitting the lens from a particular angle of incidence.

Take a cloudy day. Add a neutral density filter and you get a somewhat darker version of that same cloudy day picture.

Add a polarizer and suddenly the clouds take on a whole new look. This is because the cloudy sky scatters light rays from all the cloud surfaces into the lens and obscures any definition those clouds might have. By polarizing the light coming from the clouds, you remove much of the scattering effect and suddenly CLOUD DETAIL jumps out of the scene.

Same with shots of water surfaces. The reflective nature of water scatters light rays and to a camera, the water looks mirrored. Add a polarizer and the scatter goes away, suddenly giviing the camera the ability to "peer into" the water.

Two different filters. Two different jobs.

While a polarizer will necessarilly cut down the amount of light passing through it as it does it's job. The NATURE of the light changes as well.

Rotate a polarizer and expect the scene to change as the filter affects more or less of the light depending on the prevailing angle of incidence. Rotate a ND filter and nothing changes.

Hope that helps.