While writing another article which contained reference to photographic exposure, a thought occurred to me, one that simplifies understanding the relationship between f-stop, shutter speed, and ISO.

For the purposes of this article, we are going to need some definitions. These are not made up definitions, they are scientific in nature.

Exposure -
Exposure = Intensity x Time

Intensity is how bright, time is how long.




That is pretty simple. We have the luminance of the scene that passes through the lens and the length of time the shutter is open. That’s it. We can regulate the intensity through the use of an iris, or f-stop. Shutter speed is regulated by the shutter speed settings on the camera. Because of the mathematical nature of exposure, these two quantities work together.

These two settings, f-stop and shutter speed, regulate the light passing through the lens. These are located on one side of the camera. On the other side of the camera, usually the back, we have a photo sensitive material.


Sensitivity -
Sensitivity is the degree of response to light, preferably for this discussion within the visible spectrum. This sensitivity is given a rating which is defined by the International Standards Organization (ISO). The greater the numerical value the more sensitive to light the material is. Again, this is pretty simple.


There are a few other related concepts that are important to keep in mind, but we won’t concern ourselves with those, in detail, at present. Those concepts are shutter speed determining how fast the image is captured. If one is trying to capture moving subjects a faster speed is advised. f-stop affects depth of field. The smaller the f-stop the larger the depth of field. Now that we’ve mentioned those, we can put them aside. We are concerned with the relationship of shutter speed and f-stop (exposure), and ISO (sensitivity).

Now, let’s see how the two subjects of our discussion interact with one another. I know we’ve all been exposed to the Exposure Triangle. So, now, let’s forget that we’ve ever seen it.

Again, we are concerned with two items on one side of the camera, and one item on the other. This is the system with which we are going to do some mental exercises.

We are going to imagine this system is a beam balance scale (see below for the illustration). The balance works such that when the weight on one side is equal to the weight on the other, the beam of the scale is horizontal, as shown below.

One the left side, just for a matter of choice, let’s put two weights. One weight is labelled f-stop, the other shutter speed. On the other side of the scale, we are going to put a weight labelled ISO.

The concept is that we have to keep the scale balanced. If we change the amount of weight labelled f-stop, we’re going to have to change the weight labelled shutter speed to maintain that balance. A smaller amount of f-stop requires a larger amount of shutter speed to maintain equilibrium. Conversely, a smaller amount of shutter speed is going to require a larger amount of f-stop.

Now, if we change the ISO side, we have to change either one or the other, or both f-stop and shutter speed to compensate. That is actually how simple the relationship is. It’s not complicated at all.

The additional matters that one needs to keep in mind are, as mentioned earlier, depth of field, stopping motion, etc. This is why taking a photograph becomes more of a system management exercise than just pointing a camera and clicking a shutter. There are trade offs to be made. You, as the photographer, manage these trade offs. And that is the essence of photographic exposure.
--Bob

I don't agree with you about speaker-receiver combo. If you don't have a receiver that it's out put frequency is matching with the speaker, it won't get the best out of it. for example, you speaker's response frequency range is between 50-40,000Hz. and your receiver only delivers 200-20,000Hz, then you will lose the sound of the extreme bass, and the high end of the sound. You will found the music from the speaker will be flat toned.
Same as camera lens combo, you need the best to match the best. That's difference between professional and consumer.

I'm thinking after vacation I'll start saving my money for a new lens I can use when taking pics in church w/out flash (I'm on the photography team), but it seems that I need a faster lens based on the results I've been getting. I took a bunch of shots today at our annual "horse trough Sunday" where people who've never been baptized can get it done by immersion. I had to up my ISO to 800 and decrease the exposure compensation so much to get a mediocre shutter speed (never made sense to me why you up exposure for a bright scene and lower it for a dark scene). I've seen 35-85mm prime 1.4s for anything from $150-$1500. I have a 1.5x crop Sony a77. Or maybe I need an a99.

Its taken me two years and lots of shots to finally get a northern flicker with its tongue fully extended. I thought some of you might like it, as I am sure many of you did not realize how long tongued they are. It's not a good photo, but at least I finally got one. They do it so fast and in most cases so rarely, it hard to see, let alone capture.

I also did another of him in a regular pose, and a kingfisher I got today after leaving the flicker.

Have the rest of a great week. Bill

I am an amateur photographer with an RX100m2 which I love...Here's the problem....

I'm told by some that I should master the art of taking pics with this camera FIRST before ever thinking of upgrading my camera but I'm a bit frustrated

I know the RX100 is a great camera and even a lot of professional photographers take this as their travel camera sometimes but when I take some pics I'm limited to a 3x zoom,aperture settings and a few other features...I've taken some phenomenal pics with this camera don't get me wrong...I just think I could take better pics and learn better without the limits of the camera

Am I whining for no reason?

Most of my time in photography has been spend pursuing sharpness and as a result I have had and sold a number of cameras and lenses over the years. Now however, I have the Nikon 610 and absolutely love the images. Couple it with my Nikon 300mm f/4 and I am in hog heaven sharpness. But at age 71 I find that weight is becoming a concern and the 610 and bird-seeking telles (also Sigma 150-600mm) are REALLY heavy. My question as I ponder the use of lighter mirrorless cameras is, am I foolish to think that, given my limited abilities that still achieves sharpness with the 610, that I can be happy with a smaller mirrorless camera?