I have a ND8 filter for my Panasonic DMC-FZ20 digicam which I often use to take pics on on clear days during the brightest part of the day. (10am to 3pm). As I understand it, the ND8 (neutral density 8) filter lowers the amount of light coming into the image sensor by the equivalent of 3 f-stops, which means that only 1/8th of the light hits the image sensor.

It has worked well for me for taking landscape pics, but I have been using it to take aviation pics for Airliners.net. I set the mode to Aperture control at f4 to throw out of focus the background because I'm usually just taking pics of small private jets passing about 50 feet in front of me.

The problem is that after doing some image processing on Paint Shop and uploading the photos to Airliners.net I've been getting rejected basically for grain/noise. I use the unsharp mask to sharpen the edges of the planes to the point just before I start getting jagged edges. I do some grain/noise removal, but still I get the grain rejection. Any body have any ideas to overcome this problem? How much of the problem is due to the ND8 filter?

Why would you use a neutral density filter when taking a action shot? The shutter speed would be too slow, especially at telephoto, and your camera is likely increasing the ISO to prevent blur (if you have it at auto ISO) and this might be what is causing the noise.

Also, 8 stops less light is not 1/8, it is 1/2 to the exponent of 8 or 1/256. 1/8 is actually only 3 stops.

At F4 and ISO 100, on a bright and sunny day, usually the shutter speed is 1/800. However with that neutral density filter, the shutter speed decreases to 1/3, far too low for any handheld photos without boosting the ISO, even with the 2-stop shutter advantage that the image stabilization of your camera provides.

The point fo a neutral density filter is to lower shutter speeds to the point that you create blur in your photo. If you don't want blur, then don't use the filter.

Providing some sample pics with EXIF info would be helpful.

@doady: Yes, I think you're right that the ND8 filter lowers the light by 3 f-stops, not 8. The 8 refers to the 7/8ths reduction in light.

Here's two photos that I have'nt done any image processing on. For both, I set the ISO speed at ISO-100 and had the camera chose the exposure time. For both pics I used the autofocus with the spot focus placed on the center of the plane.

http://img.photobucket.com/albums/v414/Nick_in_Atlanta/150400.jpg

^^EXIF details: Focal Length=33mm, Aperture=F/4, Exposure time=1/100 sec., ISO Speed= ISO-100.

http://img.photobucket.com/albums/v414/Nick_in_Atlanta/153805.jpg

^^EXIF details: Focal Length=38mm, Aperture=f/4, Exposure time=1/125 sec., ISO Speed= ISO-100.

Ah sorry about that, my mistake, so it is 3 f-stops. Personally, I think your photos are nice and properly exposed as is, and I don't see anything wrong with them. I don't see why the ND filter would cause noise, the problem probably lies in the sharpening.

What settings are you using for unsharp masking? I use a prosumer camera too, and I can tell you that photos from these cameras are usually already oversharpened to begin with, and you should be very careful with unsharp mask unless you have turned down the in-camera sharpness setting.

I set my camera to -2 sharpness so that images are not oversharpened and I can get better result with unsharp mask. If there is already noise or grain present in the photo to begin with, I raise the threshold setting of unsharp mask higher (I usually keep it at 0) to prevent it from sharpening the noise or grain.

BTW, an aperture of F4 on your camera still gives HUGE depth-of-field, equal to F24 on a 35mm film camera, so just keep that in mind when you want the background out-of-focus.

Anyways, I hope this has been helpful, I don't really know much, I hope someone else can answer you more definitively.