ND Filters and Exposure

mercphoto

Hey guys. I've been having a bit of trouble lately getting correct exposures from my 40D when using ND filters. Granted, I'm using a 2-stop filter stacked onto a 3-stop filter, so I'm cutting a ton of light from hitting the camera. And I'm wondering if that is part of the problem. The other potential problem is the subject matter: dark cars in bright sun. But I tried spot metering and didn't seem to help matters any.

The camera is wanting to underexpose the shot by 1 stop, sometimes 2 stops.

Is there some secret sauce I need to learn when it comes to using ND filters of that magnitude?

pathfinder

mercphoto wrote:

Hey guys. I've been having a bit of trouble lately getting correct exposures from my 40D when using ND filters. Granted, I'm using a 2-stop filter stacked onto a 3-stop filter, so I'm cutting a ton of light from hitting the camera. And I'm wondering if that is part of the problem. The other potential problem is the subject matter: dark cars in bright sun. But I tried spot metering and didn't seem to help matters any.

The camera is wanting to underexpose the shot by 1 stop, sometimes 2 stops.

Is there some secret sauce I need to learn when it comes to using ND filters of that magnitude?

Are you shooting in Av mode? I usually shoot in Av mode when using NDs, but I always check the histogram to verify that the exposure was satisfactory, as well, Bill. Once you see the histogram, you can adjust your exposure as needed, by shifting to manual mode, or using exposure compensation.

mercphoto

pathfinder wrote:

Are you shooting in Av mode? I usually shoot in Av mode when using NDs, but I always check the histogram to verify that the exposure was satisfactory, as well, Bill. Once you see the histogram, you can adjust your exposure as needed, by shifting to manual mode, or using exposure compensation.

I was using Tv mode as I needed to control shutter speed, and was using the ND's as a means of getting the shutter that low (1 sec, ISO 100, bright sun). Sounds as if I also just need to check the histogram as well and verify. I imagine when you cut that much light from the sensors that they lose some accuracy.

RogersDA

mercphoto wrote:

I was using Tv mode as I needed to control shutter speed, and was using the ND's as a means of getting the shutter that low (1 sec, ISO 100, bright sun). Sounds as if I also just need to check the histogram as well and verify. I imagine when you cut that much light from the sensors that they lose some accuracy.

Bill, I had that same problem when I was shooting manual with stacked 1.8 and 0.9 ND filters outdoors. I had to reshoot about 3 times (watching the histogram after each shot) until it was correct (which was about 2 to 3 stop increase over what the camera "thought" was a correct exposure).

jasonstone

pathfinder wrote:

Are you shooting in Av mode? I usually shoot in Av mode when using NDs

Any particular reason why?
I've got an ND8 filter that i want to play around with (have some ideas) but didn't even think that it would throw the metering system out

jhelms

mercphoto wrote:

Hey guys. I've been having a bit of trouble lately getting correct exposures from my 40D when using ND filters. Granted, I'm using a 2-stop filter stacked onto a 3-stop filter, so I'm cutting a ton of light from hitting the camera. And I'm wondering if that is part of the problem. The other potential problem is the subject matter: dark cars in bright sun. But I tried spot metering and didn't seem to help matters any.

The camera is wanting to underexpose the shot by 1 stop, sometimes 2 stops.

Is there some secret sauce I need to learn when it comes to using ND filters of that magnitude?

With dark cars under bright sun it sounds like a grad nd filter would help you out. Maybe use a polarizer, then the 3 stop ND then the ND grad.