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-   -   Exposure Compensation vs. Neutral Density Filter (

calr May 31, 2004 11:53 PM

If I use -1.0 EV exposure compensation, is it the same as using a ND2 neutral density filter. -2.0 EV vs ND4? I suspect that at some point the relationship is not linear.

marokero Jun 1, 2004 12:23 AM

Using an ND filter you're reducing the ammount of light that gets to the sensor, where compensation is done in hardware to underexpose by a certain ammount. You may try to compare shooting with and without an ND filter, but my guess is that shooting with a filter will produce noisier images.

calr Jun 1, 2004 11:17 AM

I guess my real question was, is exposure compensation a good substitute for a ND filter? I currently have no ND filters that fit any of my lenses. While shooting on the Southern Oregon coast this past weekend, I had to use some negative compensation for some very bright scenes. It occurred to me that this was basically an electronic ND filter.

Does anyone agree with me? If not, where is my logic flawed?

photosbyvito Jun 1, 2004 2:19 PM

hmm....i have to read my manual again to learn how to compensate exposure! i'd love to be able to "fake" an ND filter!!

calr Jun 1, 2004 3:25 PM

Been thinkin' on it some! It occurs to me that exposure compensation may only affect the apperture opening on the lens. I say this because my last two film cameras (Nikon F100 and Nikon N70) both had exposure compensation available but no CCD to adjust.

There are times when I want to use a slow shutter on a bright day to create the "fuzzy" water effect on a waterfall or fountain. If f32 is the smallest the aperture can go and I am overexposing at the shutter speed I want to use, will the exposure compensation help or is it limited by the f32 also?

We need some digicam engineers to pipe in on this one.

In the meantime, I think I'll try an experiment. I will find a bright sunlit scene, select shutter priority, set the shutter to the setting that causes the "HI" warning to show. At this point the aperture should be at minimum (largest f-stop). Then I will dial in -1.0 EV compensation and see if it has any effect on the aperture or the image. This should tell me if the compensation affects the CCD or just the aperture.

photosbyvito Jun 1, 2004 4:51 PM

well...if it effects the arperture you wouldn't be able to negatively compensate at your smallest arperture....unless the camera manufacturer lies to you when they say it doesn't go smaller than that (f8.0 for me!)

JimC Jun 1, 2004 6:52 PM

EV Compensation controls exposure via shutter speed in most cameras (provided the aperture is already stopped down to it's smallest opening).

So, if you use a - EV setting, the camera is simply selecting a faster shutter speed. This will also result in underexposed photos (if the correct aperture/shutter speed would have been selected by the camera without EV Compensation).

Likewise, the use of +EV Compensation will result in overexposed photos (because the camera is picking a slower shutter speed than needed for proper exposure, based on it's metering).

You can easily test this by using a tripod, flash off, and taking photos in the same conditions with different amounts of EV Compensation (faster shutter speeds and underexposed images with - EV Compensation; slower shutter speeds and overexposed images with+ EV Compensation).

In contrast, use of an ND filter actually reduces the amount of light getting through to the sensor. This allows the camera's autoexposure algorithmsto select a smaller aperture and/or slower shutter speeds than possible without the ND filter, while still insuring proper exposure of the image.

Unfortunately, there is no "magic setting" to simulate the use of a Neutral Density Filter.

The closest you can get, is using the Camera's ISO sensitivity (setting the camera to the lowest ISO setting to allow slower shutter speeds for the same conditions). However, you'll probably find that the camera is already using it's lowest sensitivity anyway in any conditions that you would want to use a ND filter.

It's too bad that we can't set the ISO Sensivity lower than 50-100 in most cameras.

ohenry Jun 1, 2004 7:27 PM

Yes, JimC pointed out, you're speaking of two different operations. EV changes the exposure setting whereas a ND filter will reduce the amount of light reaching the sensor yet still maintain the metered settings set by the auto exposure meter.

Consider the case where you're using manual exposure. To underexpose a picture by setting your manual meter to -1EV will result in that underexposed setting of -1EV (Now that may be the right exposure, but it's not the metered exposure). Place a filter in the way and you reduce the amount of light that the meter will sense and thus it will result in larger aperature/slower shutter, but you could still underexpose by setting to -1EV (if that makes sense).

In any case, ND filters and EV compensation do not do the same thing.

calr Jun 1, 2004 7:33 PM

Thanks, JimC. I figured that was the way it worked. Since Nikon first introduced exposure compensation on their film cameras, it was logical that they would use the same method on their digital models. I guess if I want my fuzzy water, I'v got to go buy a ND2(and maybe ND4) in 62mm and 82mm sizes.

OHenry, I understood the effect of compensation but was not sure if it did it in the lens or in the CCD. Thanks for your input.

photosbyvito Jun 1, 2004 10:57 PM

calr.....i'll take any ND filters you got for 58mm!!!


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