Photography basics...

Jehu

Active member
It's quite common for someone to mention that they don't understand the functions on their camera. It would help to know that the basic functions haven't changed for over 100 years. I've prepared a few bare-bones lessons on the basics of photography. Here's the first one...

Photo lesson of the day: aperture

The first thing you need to understand about aperture is the logic behind the odd looking numbers that we call stops.

The aperture number is simply the relationship between the diameter of the aperture opening and the focal lenth of the lens. A 50mm lens with an aperture of 1 would have an opening of 50mm. Yes this lens does exist but it's not really affordable. A 50mm lens with an aperture of 2 would have an opening with a diameter of 25mm. You get the idea. So, why the odd numbers? consider a sequence of numbers:

1, 2, 4, 8, 16, 32, 64, 128 etc.

Let's say that represents units of area. A "stop" either doubles or halves the light allowed onto the frame (film or sensor).

Remember basic geometry? if you double the linear size of a shape then its area increases fourfold. If you don't understand the concept then take a simple square post-it note. It has an area of 1 square post-it. Now double the size (linear) and maintain the shape (square) you don't just put another post-it next to the first one. That makes a rectangle. You need to put three more with it to maintain the square. As you can see, the linear dimension doubled from one post-it to two post-its but the area quadrupled. If you triple the linear then you'll have nine times the original. 4x would be 16 square. etc...

If you double the diameter of a circle then you quadruple the area. It's the area of the opening that matters to your exposure value. An aperture stop means double (or half) the area so you need the square root to get the linear comparison.

Now take the square root of that series of numbers:
(just ignore the minor rounding errors)

1 = 1
2 = 1.4
4 = 2
8 = 2.8
16 = 4
32 = 5.6
64 = 8
128 = 11
256 = 16

Do these numbers look familiar to you? The old timers found out that marking the aperture ring of a lens this way would allow you to ignore focal length and reduce your light metering to the two basic functions of shutter speed and aperture.

That's about it. You only need to understand two things:

1. The"f-stop" is a the ratio of focal length to the aperture diameter.
2. A stop is double (or half) the area of the opening.

Any questions? Let me know.
 

69cj5

Active member
Ok, I get all the math. What does that have to do with taking a picture. :scratchhead:
 

Dirty Harry

Moderator
Staff member
Ok, I get all the math. What does that have to do with taking a picture. :scratchhead:

The proper amount of light is the key to a good photography. As Jehu said, the two most basic functions are shutter speed and aperture. A bigger area (wider aperature) will need to be open less time (faster shutter speed) than a small area, in order for the image to have the proper amount of light. In general a wider aperature (lower number) will freeze motion (like water, turning tires, or sports) and provide a shallower depth of field (where the subject is *hopefully* in focus and the background is soft).
 

Jehu

Active member
Ok, I get all the math. What does that have to do with taking a picture. :scratchhead:

Fair question...

If you consider all the factors that actually go into figuring correct exposure then it would be far too complicated for most photographers. The development of the f-stop system took about 50 years starting around the civil war era. Like, most early photography standards, Eastman Kodak adopted the f-stop system that we use today around the 1920's. That effectively standardized it. The f-stop system is a derivative of what was originally called "intensity factor". Without studying the history of the various methods of calculating correct exposure value, it's hard to appreciate the simplicity of the f-stop.

By the way, here's an outline of lessons to follow:

Reciprocity: The inverse relationship between shutter speed and aperture.

Shutter Priority: Manipulating shutter speed to control exposure and motion.

Aperture Priority: Manipulating f-stop to control depth of focus.
 

69cj5

Active member
Fair question...

If you consider all the factors that actually go into figuring correct exposure then it would be far too complicated for most photographers. The development of the f-stop system took about 50 years starting around the civil war era. Like, most early photography standards, Eastman Kodak adopted the f-stop system that we use today around the 1920's. That effectively standardized it. The f-stop system is a derivative of what was originally called "intensity factor". Without studying the history of the various methods of calculating correct exposure value, it's hard to appreciate the simplicity of the f-stop.

By the way, here's an outline of lessons to follow:

Reciprocity: The inverse relationship between shutter speed and aperture.

Shutter Priority: Manipulating shutter speed to control exposure and motion.

Aperture Priority: Manipulating f-stop to control depth of focus.



Ok, Say I am wanting to take a picture... I have this handy dandy email by my side, I look throught the lense, adjust focus, what f-stop do I pick??? How does one know what to use? For "correct exposure" that is...

Not trying to be difficult, but I have taken my fair share of photos, and just can't quite get the amazing photo that many on this board seem to be able to get. Would very much like to take it to the next level, but this does not seem to help me to know what apperature to use.
 

Jehu

Active member
Ok, Say I am wanting to take a picture... I have this handy dandy email by my side, I look throught the lense, adjust focus, what f-stop do I pick??? How does one know what to use? For "correct exposure" that is...

Not trying to be difficult, but I have taken my fair share of photos, and just can't quite get the amazing photo that many on this board seem to be able to get. Would very much like to take it to the next level, but this does not seem to help me to know what apperature to use.

Assuming your camera has the capabilities, here's a tip that you may like:

-Set your camera to aperture priority. That's where you control the aperture and the camera figures out the correct shutter speed to use.

-Now set your aperture to around f2 or as low a number as your camera allows.

-Set your flash to TTL metering. Do this even if you're outdoors. This is called fill-flash. You'll probably like the results. Try with and without the flash and you'll see what I mean.

Take portraits from around 4 to 8 feet from your subject. Try to keep the background elements at least 6 feet behind your subject.

Let me know how it goes.

edit:
If you control your ISO speed then you'll probably want to keep it low (ISO 100)
 

Inc

Moderator
Staff member
Like Harry said, it all comes down to light and the way that the camera uses f stops and shutter speed to produce an exposure you are looking for.

To figure out what f stop you want to use you need to know what kind of shot you want. Do you want the subject crisp and the background as soft as possible, or would you like everything in the frame to be in focus?

The lower the number f stop (wider aperture), f2 for example, the more the focused on subject should stand out from the background and even objects in the foreground. For landscapes a higher number f stop (narrower aperture), f22 for example, is usually used because you most likely want the entire scene to be in focus.

In manual shooting mode, most likely "M" on your camera's dial, a lot of cameras have an exposure meter built in to the eye piece and you can see a meter that tells if the shot will be under or over exposed. You adjust your f stop or shutter speed or both to get the right exposure you are looking for.
 

Jehu

Active member
That makes a pretty good rule of thumb Mike. Wider aperture to make your portrait subject pop. Narrower aperture for landscape type shots to get as much crisp focus as possible.
 

Inc

Moderator
Staff member
Yet another explanation. Really easy to understand and straight forward.

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