All this theory about filt

#179623
AvatarAnonymous
Inactive

All this theory about filters is nice and all, but hardly of any practical value. Your question of which filter is more useful hasn’t been answered with any experience.

Whoever said a lens hood instead of a UV/haze filter to protect the lens is an idiot & we can ignore all his crap. A protective filter is essential for any kind of multi-element lens. Not only will it protect the lens glass from flying debris and such, but it also serves to protect the fragile multi-coatings all modern lenses use. You won’t be routinely cleaning your lens surface to remove finger smudges, rain & snow or dust & dirt, so there is virtually no chance you will scratch the surface of your front element. And it is far easier to clean a flat surface vs. the curved surface of that front element. Not to mention that in practice, lenses (and filters) are hardly ever struck hard enough to break, but it is not uncommon for them to be severely scratched. Once it has been scratched, the only option is replacement. And a filter’s price is a pittance compared to replacing a lens. So bravo that you are taking the right steps to protect your investment.

Now as for neutral density filters, their value for controlling depth of field directly corresponds to the size of the lens. I’m not going to get into the actual math used to determine depth of field. But provided you control focal length and camera distance, smaller diameter lenses have a great deal more depth of field. So in every situation, the 30mm lens on my HC20 will always have greater depth of field than the 58mm lens on my VX2100. Now if I want to decrease my depth of field to create a background or foreground blur, opening the iris my only option if I’m stuck at a particular distance/focal length. I can open the iris by increasing the shutter speed or decreasing the amount of light coming into the lens. The ND filters use the latter option, provided you can keep the shutter speed the same.

The smallest depth of field occurs when the lens is zoomed in to the max and you’re at the minimum focus distance. (Conversely, the maximum depth of field is when you are totally zoomed out and focus is set at about 2/3’s of the focus range.) Now depth of field is not centered around the focus point. Roughly 1/3 of the focused distance occurs to the front of the focus point, and 2/3’s of the depth of field occurs beyond the focus point. (On a non-zoom lens, you can see the dual effect of distance & F-stop with markings on the lens focusing barrel.) So to decrease your depth of field, you need to zoom in and open the iris. You can cause the iris to open by adding an ND filter or increasing the shutter speed. (By the way, to get your camcorder to use its fastest shutter speed in automatic modes, select the sports, or the little golfing guy, mode.) So which method is best? Neither, they both do exactly the same thing. And to reflect that, ND filters are available in densities that change the light value by F-stops. So an ND 1 filter decreases light by 1 F-stop, an ND 2 decreases light by 2 F-stops, and etc. Oddly enough, shutter speeds are also set to decrease or increase the amount of light getting to the pick-up chip by one F-stop between each shutter speed setting. So from 1/30 of a second to 1/60 of a second is a decrease of 1 F-stop, from 1/30 to 1/128 is two F-stops, and etc. So we can accurately state that increasing the shutter speed by one step (roughly 1/2 the amount of time) is an identical change as adding an ND 1 filter, increasing the shutter speed by two steps (roughly 1/4 the amount of exposure) is identical to using an ND 2 filter, and etc. (Isn’t math wonderful?!) I hope you’ve been able to follow me on this, ’cause now we are getting into actual situations.

Now if I’m using my smaller diameter lens and I want to decrease my depth of field, I have a variety of options. Generally the easiest way is to move closer & zoom in as much as possible. I can also increase my shutter speed or add an ND filter. Which method is more useful? Increasing the shutter speed is almost always the way to go. It is seldom the case that the lighting is so bright that the camcorder is less than 2 or 3 stops from its maximum speed. Unless you’re shooting in full sunlight on a beach or in snow (or a concrete parking lot.) So it isn’t often that an ND filter will be necessary due to already maxed out shutter speeds. The other consideration is just how much you would need to decrease the light volume to effect a noticeable change in the depth of field. Generally, it is going to take more than 2 F-stops to make a difference. And with my 30mm lens, I already have a rather large depth of field so even 4 stops may not be sufficient. And if I’m not fully zoomed in, the depth of field of the lens in daylight is already from 5′-10″ to infinity. I can decrease the depth of field more easily with my 58mm lens using an ND filter, but I still have to be fairly close for even full zoom to start blurring out the background. Lenses and exposure settings are designed with large depth’s of field in mind.

So to sum it all up, the most effective way to decrease depth of field is to move closer and zoom in more. Then a smaller decrease can be achieved by increasing the shutter speed and, generally speaking, the least additional decrease in depth of field can be achieved by adding ND filters. With the smaller diameter lenses, you’d need at least an ND 4 to get a noticeable change.

Now on the other hand, a polarizer does something that can’t be done any other way. The greatest use is in situations with reflected light as described above. You can easily see into shiny surfaces with a properly adjusted polarizer (water, windows & such) plus the polarizer can stop enough of the reflected light to dramatically improve contrast (and color saturation) on beaches, in snow, on concrete & streets, really a lot of situations. And I don’t know why our experts failed to mention that a polarizer is also about an ND 2 filter, no matter what its orientation. So the polarizer is a double duty filter, eliminating the need for an ND 2 or less filter.

So obviously a polarizer is the second most important filter. As I mentioned earlier, something to protect the front lens element is far and away the most important filter to have on any camera. And as far as actual field use goes, ND filters are far down the list. And I do know I have an ND 1 and an ND 2 filter built into my VX2100, as do the majority of prosumer & better video cameras. But they are there to decrease the light into cameras with larger lenses (which bring in more light to begin with) and help control overexposure problems. And when I need to decrease light levels even more, I just screw on my polarizer.

By the way, in order to get the deeper blue skies advertised for polarizers, You have to shoot when the sun is coming through the atmosphere at an angle. So you really won’t get the “polarizing effect” between 10 am and 2pm STANDARD time. But as I mentioned, you’ll always get the ND effect.

In conclusion (finally,) I highly recommend you get a polarizer along with the UV/haze, A1 skylight, or flat optical glass lens protector. Then you can clean the filter before every shoot and never worry that some errant dust or grit will be ground into your expensive camera lenses. And avoid using step down rings, mostly because they increase the force of any pressure on the filter’s edges and the camera’s filter threads, making it much much easier to damage both the camera and the filter itself.

Good luck and enjoy your new machine.

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