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Photography Question 
Christopher Budny
BetterPhoto Member Since: 10/3/2005
chrisbudny.com
 

What else did the ND filter do for me?


Hi folks... I recently shot an image, Wilson's Tomb, that I'm very happy with. It was a deliberate exercise to improve upon an older, similar photo. I feel, in hindsight, that the earlier photo, Light Lives Here, has the colors blown out too much. I decided that for the reshoot, I'd try a neutral density filter (thinking it might help control the intense morning sunlight streaming through the stained glass onto the neutral walls. I don't have much experience with the NDF, but thought it couldn't hurt ;)

So my question is, what else if anything, did this resulting longer exposure do for the image, in terms of the way the details throughout the scene were captured by the camera? And, if no other benefits to the overall image appearance were realized with the NDF, could I have achieved the same look without the NDF? Assuming I kept the f/6.3 for the same depth of field, I'd have to have a much shorter exposure time---but could I just adjust the exposure compensation setting to arrive at the same image? I suspect maybe my camera's +2.0 / -2.0 exposure compensation range might not be sufficient to cut the light as much as the NDF did? (I don't have any specs on how strong exactly, the NDF is.)
I should have thought of this question at the time, and done some hands-on test shots to compare...! Any answers on the "benefits of ND filters creating longer (daytime) exposures" would be great!


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1/9/2007 1:08:35 PM

 
Bob Fately   Christopher, the only "advantage" of an ND filter insofar as giving you a longer exposure would be when there is movement within the frame, and you want to purposefully have some motion blur in the shot. For the still-life you took (very nice shot, by the way) it really makes no difference, since all an ND does is reduce the light in all sections of the image area equally.

This light reduction can alwo have its place in brightly lit situations where you want to minize depth of field - but have "run out" of shutter speed. That is, if even at ISO 100 and 1/4000th second you have to use f8 to get proper exposure (at the beach, say) but you want to use f2.8 to limit DOF, the ND filter is the way to go.


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1/9/2007 1:23:28 PM

 
Christopher Budny
BetterPhoto Member Since: 10/3/2005
chrisbudny.com
  Thanks Bob, for the reply... I recall reading that the NDF's were helpful in some motion shots (such as helping to creating the silky-effect waterfall without blown-out highlights.) Just curious if anything else was going on in the image as a result, such as color saturation changes, etc. (I suspect too, that increased noise could become an unwanted side effect of those longer exposures.)
I'll definitely entertain myself on my next sunny visit, trying to recreate the Wilson's Tomb shot without using the NDF ;)


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1/9/2007 4:11:32 PM

 
Bob Fately   Sure, Chris, just know that the silky effects to which you refer are only the result of the slower shutter speed made possible by the filter - had the reflections off the water been too bright in comparison to the rest of the scene then they would have blown out anyway. In other words, the filter darkens everything the same amount, and blowout is what happens when the differential between brightest and darkest areas is too great for the chip to handle (that's called the dynamic range).

As for increased noise; while this is certainly possible if you must increase the ISO rating of the chip, it's unlikely that a slightly longer exposure duration will cause noise to appear at low (i.e. - 100-200) settings.Noise is the result of the photosites' being set so sensitively that they pick up random photons - usually heat related - and record them as if they were part of the image. At low ISO settings this should not be an issue.

Of course, astronomers chill their CCD imagers with liquid nitrogen to prevent noise, but then again they expose on the order of hours.


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1/9/2007 4:41:05 PM

 
Andy 
BetterPhoto Member Since: 5/28/2002
  Hi Christopher, I like your Wilson's Tomb picture very much. I like the color and the reflection of the marble floor.

Anyway, Bob is right. In this case you really do not need the ND filter. All you need to do is cut down the exposure time (if you want to keep the same aperture value and depth-of-field). Besides using a ND filter for motion shots, another usage is if you want to use a larger aperture. For example, you want to take a picture of someone under bright sun light with your f/2.8 lens and the fastest shutter speed is 1/2000 second and let just say you have a 400 speed film in the camera (I know you use a digital). You want to main subject crystal clear but anything else out of focus. The sunny 16 rules says that you have to shoot at f/16 with shutter speed 1/500 sec. If you want to shoot at f/2.8 (5 stops different), the shutter speed has to be 1/16000, which is way over the limit of your camera. One way to do is set the max. shutter speed to 1/2000 sec (2 stops) and put on a 3 stop ND. Then you can shoot at f/2.8.

Hope this makes sense to you.


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1/10/2007 9:01:19 AM

 
Christopher Budny
BetterPhoto Member Since: 10/3/2005
chrisbudny.com
  Yup! Thanks, Andy... I'll have to see if I can dig up the packaging from my ND, to see just how many stops it is knocking down.


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1/10/2007 10:18:59 AM

 
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