Every time I sit down to write something new to the blog I wonder if my content is depth enough or if it will be interesting to people?
I don’t know and I don’t have an answer to that question, I just do this because I like to share experience with other professionals and because I consider that taking better pictures we all make this craft a little bit better for everybody to enjoy.
The purpose of a blog is educational and for me is more of a social sharing type, somehow the writer tries to pass his knowledge or experience constantly and organized into easy to read articles, which allow readers to interpret the logic and thoughts of the writer, many sometimes what happens is that in the process of finding the right words to communicate thoughts thought itself ceases to be the most important content and is lost in unnecessary verbiage.
Topics about Photography that I plan to touch hereafter on photography are of an intermediate and advanced level, the content is not for people who are starting photography because I don’t explain in detail the process.
The task I chose for today is Depth Of Field (DOF)
Depth of field is the amount of distance between the nearest and farthest objects that appear in acceptably sharp focus in a photograph. A preferred selection Depth of field (“DOF”) in a focused subject in an image can be quite subjective.
How deep or shallow is the field will be a direct result of the selection a lens to take the shot, for example using a 70-200mm telephoto lens will be the best choice especially for these applications.
In order to achieve a shallow depth of field, we need maximum aperture, for example f/2.8 on a Canon 70-200mm lens shooting at 100mm to capture a portrait that is 20 yards away, light conditions are intensive sun light so let’s see what will happen:
Natural Light, the amount of light entering the lens forces me to go to a high shutter speed in order to maintain the shallow depth of field, if I need to use a flash to bring additional light to remove shadows from the harsh sun I am in troubles because my Sync speed won’t allow me to pass 1/160s to sync my cannon with the flash so what to do?
Neutral density filter ND
We have to limit the amount of light if we want to keep the aperture required for a shallow DOF , for this purpose was designed the ND filter.
In photography and optics, a neutral-density filter, or ND filter, is a filter that reduces or modifies the intensity of all wavelengths, or colors, of light equally, giving no changes in hue of color rendition. It can be a colorless (clear) or grey filter.
When it comes to labeling neutral density filters there are several customs.
The most popular is called a “Filter Factor”
By tradition exposure changes are given in an increment known as the f/stop. This method is based on making adjustable to the circular aperture that controls how much light can enter the camera. It copies our eye, the colored portion, that contracts in bright light and expands (dilates) in dim light. In our eye this wonderful control is called the Iris after the Greek goddess of the rainbow.
Many years ago it was deemed best if the camera’s aperture adjustment allows chances in increments of doubling or halving. Thus each f/stop change equate to a 2x change in light energy.
If 1 f/stop = 2x change then
2 f/stops = 4x change (two f/stops compensation)
3 f/stops = 8x change (three f/stops compensation)
4 f/stops = 16x change (four f/stops compensation)
This notation is called a “filter factor”.
Photo scientist are somewhat snotty, they use a different method based on advanced math. This method has advantages however it is somewhat difficult to follow. I will tell you about it because many neutral filters are sold using this notation. It is based on the 0.30 equals the number 2.
0.10 = 1/3 f/stop
0.20 = 2/3 f/stop
0.30 = 1 f/stop
0.60 = 2 f/stop
0.90 = 3 f/stop
1.20 = 4 f/stop
They lower the amount of light entering the lens, for example a filter NDx8 or 0.90 give us 3 f/Stops difference allowing us a low depth of field , imagine you set your aperture to f/8.0 in a sunny day following sunny 16, that shot will have all the details of the background but if you add an NDx8 you will drop your aperture to f/2.8 without changing the shutter speed allowing us to use them in conditions where sometimes flash the maximum speed of synchronization of our windows is no more than 1 / 250s for users of Nikon and 1/160 for users of Canon .
ND filter not only applies to any lens where you want to drop your subject illumination without affecting the quality of your colors and remember if you are a strobist, shutter speed is for your background light, aperture is for your subject illumination.