GND filters

[simmonsrandal]

How do GND filters work when a scene isn't even? it seems to me in theory on a landscape it would leave some darkening/ lightening on areas that didn't need it?

What the best way to determine how many stops you need to have on your GND filter?

And last, what the best brand and best place to pick up gnd filters?

[ssim]

That is exactly when you want to use a GND, when the variation between the highlights and the shadows is exaggerated. The typical use is when you have a dark foreground and a light sky. The use of this filter will balance out the density so that you get an acceptable image. I've tried to illustrate this below. You can get the same effect with a circular polarizer depending on the angle of light. It doesn't always provide the same results.

There are many filter systems available. Some people like the Conkin system which is a square filter that slides into a holder you place on your lens. I tend to buy B+W filters or Singh-Ray. Your camera will meter the view as normal but this is also dependent on how you have your metering set up.

[argyle]

The best way to figure out the number of stops that you'll need is to meter each part of the scene (shadows and highlights). The difference in stops is the strength of the GND that you'd need.

Personally, I use Hitech GND filters in a Lee holder. If you're in the USA, a good dealer for these types of filters is http://www.2filter.com They also sell starter kits consisting of a GND, filter holder, and the appropriate adapter ring depending on your lens diameter.

[fireman93514]

argyle is correct on figureing which GND to use. I think the imporant thing is to use a good quality filter. I like a good glass filter and use the sigh-ray GND.

[simmonsrandal]

The best way to figure out the number of stops that you'll need is to meter each part of the scene (shadows and highlights)..


Is there a general rule for buying them though. I don't won' to have to buy/carry filter for every possible scene. Sunsets for example, would a 4 stop filter be enough?

[argyle]

In general, most experts recommend starting with a 2-stop soft and a 3-stop hard filter. For very defined horizons (ocean, etc) a hard stop is recommended. For scenes that have uneven horizons (mountains, etc) a soft stop is recommended.

Once the sun has set and you're seeing primarily the colors, a normal hard stop filter would suffice. If you want to include the sun in the picture as it reaches the horizon, you will have a very bright area at the horizon that gradually fades a bit towards the top of the picture. For these, a 'reverse GND' would generally be needed. These are dark at the demarcation line and fade towards the top of the filter (reverse of a normal GND). I wouldn't worry about a reverse GND initially, though.

Here's a link for some help/uses for various filters:

http://www.bythom.com/filters.htm

[Perry Ge]

I have a 3-stop hard and a 2-stop soft, and that works for most situations - you can stack them after all.

As for uneven scenes - you don't have to insert the filters from the top, you can rotate the filter holders and insert them from all kinds of funky angles, and in these cases you'll want to be using soft of course.

[simmonsrandal]

thanks all

i was looking at the sigh-ray website and i only see the square gnd filters that go into some sort of mount.
Do they also make them that screw on the end of a lens?

[argyle]

thanks all

i was looking at the sigh-ray website and i only see the square gnd filters that go into some sort of mount.
Do they also make them that screw on the end of a lens?

I don't know if Singh-Ray makes round threaded GND's, but these wouldn't be recommended anyway. The square and rectangular filters allow you to adjust the filter up or down in order to get the demarcation line suited to your composition. With a round GND, the line is pretty much in the middle of the filter and you don't have the freedom to adjust the filter to your composition. My recommendation is to not spend your money on round GND's.

If you're on a bit of a budget, Hitech and Lee make very good GND's. The Hitechs are 4x5 and the Lee's are 4x6. The Lees cost a bit more than the Hitechs, but they're both made from the same type and grade of resin material. Try the 2filter.com website...they have GND kits that will get you started.