I’m contributing this article to explain exposure for those beginning your exploration of photography. It is key to understand some very fundamental principles in order to produce an optimum quality image. One typical reference is constantly made to a time honored device, The Exposure Triangle. That seems to introduce a bit of confusion. Let’s simplify this entire concept with something with which almost everyone has, at least, a passing acquaintance, something that is dynamic in nature. However, before we start, let’s get a couple of definitions established. So we are all discussing the same concepts across the board, let’s set a couple of descriptions for the purpose of this article. These are not my arbitrarily made up definitions. They are definitions accepted throughout the photographic world.

Exposure
In photography, it’s how much light is allowed through an opening and for how long. That’s it. And, it’s that simple.

Photographic Exposure
This involves the above definition, but includes a light sensitive material (film or sensor) upon which the light coming through a lens, or pinhole, is allowed to fall.

It is understood that the reader of this article is familiar enough with the settings of their camera where it comes to ISO, Aperture, and Shutter Speed. The idea is to balance the amount of light with a duration to effectively expose the light sensitive material optimally. That is all we are trying to accomplish.

So, with balance being brought into the discussion, let’s imagine a scale, very much like the Scales of Justice. We have a beam from which is suspended two platforms, one from either end. The idea is that the ideal exposure will occur when the balance is perfectly level.

We have a set of weights that go on the left side of the balance, and only on the left side. These weights are labeled ISO. They are in values of 50, 100, 200, 400, 800, 1600, etc. Weights for the other side of the scale are labeled f/1.4, f/2.8, f/3.5, f/4.6, f/5.6, etc. and 1, 1/2, 1/4, 1/8, etc. The weights on this side are designed to be used together in some combination.

We now have all the tools to determine a means to associate the three weights. If the beam is perfectly horizontal, we have the correct settings for an optimum exposure. For example, let’s say we have a scene that requires a setting of f/11 at 1/125 of a second to balance an ISO of 100. If we choose to change the f/11 weight to f/5.6, we are either going to have to change the 1/125 weight to another value to make the scale balance again. In this case, the 1/125 weight would have to be replaced by one of value 1/500.

There is a one to one ratio in the manner in which the right hand weights work. As we saw in the above example, we changed the f/stop weight 2 units, f/11 -> f/8 ->f/5.6, we had to change the associated weight by two units, 1/125 -> 1/250 -> 1/500, as well.

If we change the left hand side of the scale, we are going to need to change one or both of the right hand scale to keep things in balance. It’s all that simple. Once this simple concept is understood one can see that exposure becomes a system management situation. Understanding the systems completely will aid in making consistently better exposures.

There are now two - the tried and true Tamron VC PZD - which has been around, for a while, now. Many have it, many have had good things to say about it. In fact, its only real fault seems to be its tendency to drop out to its maximum extension during use. Aggravating, but - to all intents and purposes - livable with. Pentax also has one. Is this the same lens, with the Pentax name on it? ... I think not, as users do not seem to be affected by the same plague. However, is it as good as the Tamron version? ... Or would the money be unwisely spent?

OK, The way to accomplish that test is this. Set the camera on manual. Meter on the paper and increase the exposure by two steps. Now focus on the edge of the paper. Keep the shutter release pressed 1/2 way, frame the entire piece of paper and push the shutter release.

The easier way is to look for the part of the menu system for your camera and switch off the "needs to be in focus to take the photo" selection. Then the camera will take the photo regardless of the image being in focus.

The third way is to purchase a device that will allow you to see dirt on your sensor. It's placed on the camera in place of the lens.
--Bob