filters

[livin4lax09]

Hey everyone...
I'm interested in getting a few kinds of filters to help my photography out...i've never really used them before, so I was wondering if someone could tell me what kind to look into. also, I have a couple questions... I've heard a few things about ND filters, and from what I can gather, it makes it so you can get good sky photos without underexposing the landscape. Is that true? WHat exactly does an ND filter do? Also, is there a filter than darkens things to allow me to use a slower shutter speed? to give an example...if I want to blur a person walking down the street in the middle of the day, but I'm still at like 1/100 shutter speed at ISO 100 and a fairly small aperture. Is there a filter that allows me to slow it down to something slower, like 1/5? ANy help would be appreciated. Thanks!

[Michael Fanelli]

Hey everyone...
I'm interested in getting a few kinds of filters to help my photography out...i've never really used them before, so I was wondering if someone could tell me what kind to look into. also, I have a couple questions... I've heard a few things about ND filters, and from what I can gather, it makes it so you can get good sky photos without underexposing the landscape. Is that true? WHat exactly does an ND filter do? Also, is there a filter than darkens things to allow me to use a slower shutter speed? to give an example...if I want to blur a person walking down the street in the middle of the day, but I'm still at like 1/100 shutter speed at ISO 100 and a fairly small aperture. Is there a filter that allows me to slow it down to something slower, like 1/5? ANy help would be appreciated. Thanks!

A graduated ND filter lets you reduce the dynamic range by darkening the sky. They come with a "hard" line or the more common gradual change. A "straight" ND filter cuts down on the light evenly.

For the former, you'd get better results using imaging software. Expose one image for the highlights, one for the shadows, and combine them.

[straightarm]

Depends on whether you are shooting black & white or colour.

For black and white, you would use yellow, orange or red filters to darken blue skies to really make clouds stand out. Yellow gives the most subtle effect, red the most dramatic.

Sometime green filters are sued to lighten foliage and in portrait work.

For colour work, you would use warm up filters to give warm orange effect, neutral density filters as described below and polarising filers to eliminate reflections from non – metallic surfaces such as water, and to enhance colours and to dramatically darken skies.

A neutral density filter is essentially a grey filter that blocks out some light (that’s the density bit) without changing the colour balance ( that's the neutral bit) It's bit like wearing sunglasses that had absolutely no colour shift. That would allow you to achieve the objective in your street scene.

A variant of a plain neutral density filter is a graduated neutral density filter, which is clear at the bottom and dark at the top. There are different densities, typically 1, 2 or 3 stops (some time referred to as 0.3, 0.6 & 0.9) This means that the top part is 1, 2 or 3 stops, ie 2, 4 or 8 times darker than the clear part. A second variation is how abruptly the filter changes from clear to dark. An abrupt change is referred to as a hard edge, a more gentle change is called a soft edge.

Whilst you can buy circular screw in graduated ND filters, they are impractical as the position of the transition is fixed. Most people therefore use a square graduated ND filters which slot into a holder that screws into the front of the lens. You can then slide the filter up and down to get the effect that best suits your shot. Another advantage is that the same filter can then be used on multiple lenses simply by changing the adaptor ring. The following people make graduated ND filters, Cokin, Lee, Hi Tech, Singh Ray.

A plain ND filter can be either screw in or square.

As a last resort, you can use your polarising filter as a ND filter.

[photophorous]

Just to add to Straightarm's useful information...you can also use a polarizer with black and white. I never here people say that, but it does the same thing with black and white as it does with color. It blocks reflected light, and it darkens blue skies, similar to the way an orange or red filter will. The difference being that the relative location of the sun is important with a polarizer and not so much with colored filters. If you choose to buy one, get the "circular" kind, so it's effect is adjustable. It is one of the most useful filters you can get.

For your blurred street scene, you'll need a ND filter. In bright sun you'll need a pretty dark one. A polarizer will darken the scene, but not enough to blurr movement in the bright sun. Before you buy a ND filter, you should find out how many stops you need to slow down, and pick the filter accordingly. It might be hard to find a ND dark enough to blur movement in the bright sun (not sure about that). You could stack filters, but you'll loose image quality and you'll need to watch out for vignetting.

Good luck and have fun!

Paul

[another view]

Just to try to make this obvious, there is a big difference between Graduated Neutral Density (GND) and Neutral Density (ND) filters, in the way they're used. The best way to use a GND is to have a square one (like Cokin or Singh-Ray) so the split between clear and ND can be adjusted up and down or turned to match what you need the filter to do. Cokin's P-series is pretty inexpensive and although not truely neutral (it's called grey) it's pretty close. Singh-Ray makes one that's truely neutral, but you're comparing under $20 to over $100.

ND filters come in different values too (somewhat true of GND filters as well). A common ND is a two-stop, which will give you a shutter speed two stops slower than without that filter. Four-stop and other versions are available, and Singh-Ray makes a variable one that goes up to about ten stops (very cool and equally expensive).