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03-03-2012, 10:59 PM   #1
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Here's to a hopeful start

Hello,

I'm a student in VA, USA who just started developing interest in photography. I have zero knowledge so the past few days, all I've been doing is reading about camera mechanics and photography tips.

I've been given a Pentax K1000, a Pentax K100D, and an Argus A3 from my father. Currently I've taken more interest to film-cameras, so I think I will play with the K100D later.

For now, I will continue learning more about things like exposure, depth of field, and all these confusing terms... that's just how I like to start things, I guess.

I'll make sure to ask any questions here if I have any, if people here would be kind enough to assist me.

Thank you, and I hope this will be the start of a long, enjoyable hobby.

03-04-2012, 01:09 AM   #2
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Welcome to the forum and the world of photography in general.

It sounds like you're off to a good start and like most people here you'll probably end up enjoying it for the rest of your life. Feel free to ask any questions you have, this is a large and helpful community and there's usually someone out there with the answer to any question.
03-04-2012, 01:14 AM   #3
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Welcome to Pentax forums!
03-04-2012, 06:45 AM   #4
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Welcome!

Hello Sorashira, Welcome to the Pentax Forum!
Yes, there is a lot to learn and many of the terms are confusing. But the ones you mentioned, exposure and depth of field (DOF) are pretty simple, if you look at it in a purely mechanical way.
The correct exposure is a result of the amount of light that passes thru the lens and the amount of time it is allowed to pass. We control both.
The amount of LIGHT is controlled by the "F-Stop" or aperture ring on most older lenses. Lenses for digital cameras have eliminated this ring, but the function is still available through (usually) a dial on the camera body. These are numbers like f/2.0, f/2.8, f/4.0, etc.
The amount of TIME we allow the light to pass is controlled by the shutter speed. Again, this was set by a marked dial on top of film cameras, now it is controlled by a dial on the front or rear (top) of digital bodies. Again, same function, the selected speed is shown on the LCD or in the viewfinder. These numbers are 1/30s, 1/60s, 1/125s, etc.
Now we know that 1/60s is twice as fast as 1/30s, right? Or 1/1000s is twice as fast as 1/500s. This is important to remember, because if the shutter is only opening for half the time, only half as much light will reach the film or digital sensor.
Imagine you have a bucket of sand. You are going to pour the sand into another container, through a funnel. If the funnel has a large opening, the sand will pour quickly. Say it takes one minute to fill the second container.
Now, you try a smaller funnel. This one has a smaller opening, exactly 1/2 the size of the first one. How long does it take to fill the container?
Right! 2 minutes.
Light reaching the film or sensor works in exactly the say way. If we close the aperture (opening) by one f-stop (allowing 1/2 as much light in), we must double the shutter speed (time) to allow the same amount of light to pass.
1/30s at f/2.8 results in the same amount of light reaching the film/sensor as 1/60s at f/2.0.
1/1000s at f4.0 equals 1/500s at f5.6.
All a bunch of confusing numbers, I realize. But what's important to understand is that reducing the f-stop not only requires a longer shutter speed (smaller opening, more time, right?) but it has a profound effect on the photograph.
Depth of field. This means the "deeper" the focus.
This may be easier to see than explain. The smaller the f-stop opening, the more objects in front and behind the main subject are in focus.
To help you visualize this, here's a series of photos taken from the same location, with the same lens. Only the f-stop and shutter speed relationship are changed.
SMC Pentax-DA* 200mm F2.8 ED [IF] SDM Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database
Scroll to post # 10, by Matjazz.
Notice how, at f/2.8, only a small portion of the logs are in sharp focus. As we close the aperture (higher f-stop numbers), more detail in front and behind, come into sharp focus. More...
Depth of field.
Hope this helps,
Good luck!
Ron

03-04-2012, 10:26 AM   #5
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Thank you for all your welcomes!

To rbefly: I have a quick question: so what happens if the shutter speed is set to be super fast, and the aperture has a greater opening? (So lower f-stop #?) When you say it as a "profound effect" on the photograph, what kind of effects are they?

Thanks for your help.
03-04-2012, 06:03 PM   #6
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Depth Of Field

Hello Sorashira,
In the example you've given, which would be called a shallow (or narrow) depth of field, the object you focused on would be in sharp focus, but everything else would be blurred and out-of-focus (OOF). By "everything else" I mean anything that wasn't exactly as far away from the lens as the subject. Anything nearer or further away would be blurred and the further away it was, the more blurry it would be.
In the link I gave in my first post, the ends of the logs are sharp but everything else is an shapeless blob. This was shot "Wide Open" at f/2.8, the largest aperture setting that particular lens has. Although the shutter speed isn't provided, let's say it was 1/1000s.
Next the photographer stopped down the lens one full stop (or "click") to f/4.0.
This reduced the amount of LIGHT to the sensor/film by half, so he had to double the TIME, reducing the shutter speed to 1/500s. Half the light, twice the time. Same exposure value.
Next he stops down again, one full f-stop, to f/5.6. Again he has cut the light in half, so again he must double the shutter speed, to 1/250s. Half the light, twice the time.
Each time he stops down (higher f-stop number) more of the background comes into sharp focus.
By f/8.0, we begin to see the house in the background clearly, other details emerge. By f/11.0. the roof detail is clear and the reddish blobs appear as flowers.
But now he would be dealing with a slow shutter speed. Remember we started with f/2.8 at 1/1000s, right? So, the progression that allows the same amount of exposure is;
f/2.8 at 1/1000s
f/4.0 at 1/500s
f/5.6 at 1/250s
f8.0 at 1/125s
f/11.0 at 1/60s (roughly)
f/16.0 at 1/30s
Each would result in the same exposure value, the photo wouldn't be lighter or darker, all things being equal.
What would change is the depth of field. At f/2.8, it is very narrow and only the log ends are sharp. We have isolated the main subject and blurred everything else. This is commonly used in portraits and sports photography.
At f/11.0, almost everything near and far, is in focus. This is used in scenic photography, shots with objects at different distances from the lens, that are all important to the overall effect.
But the shutter speed is now so slow, we may have to brace or steady the camera. Usually a tripod would be used.
Another way to look at this effect is to notice what your eye does while looking at photos with different depth-of-field. At f2.8, we are drawn to the object in sharp focus, we are not distracted by anything else. It is a blur, literally.
At f/11.0, we look everywhere, usually the center first, then we scan everything else. Why? Because it's in focus. Our eye moves around the photo, taking in all the details, because the photographer chose to provide the details.
There's a lot more to this, I have simplified it as best I could to provide a reasonably clear example. Any good photography book could provide a better explanation.
hope this helps!
Ron
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