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08-23-2010, 09:31 PM   #16
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QuoteOriginally posted by NicoleAu Quote
Argh, I get so confused reading about iso, aperture and shutter speeds I just can't seem to get a handle on it at all and it all makes me feel rather stupid. I've done insane amounts of googling and reading on the subject but it just doesn't seem to want to sink in. I fear I shall be on auto for the rest of my life
I believe you are over-thinking it.

Exposure requires a certain volume of light for the proper exposure.

Volume = length x height x width.

Think of the opening in the lens as the height and width. Shutter speed is the length.

A longer shutter speed means the opening in the lens can be smaller (bigger f-number).

A short shutter speed requires a larger opening (smaller f-number).

Remember the f-number is the denominator in a fraction. Bigger f-number, smaller fraction. That fraction is used to determine the diameter, more or less, of the aperture based on the focal length of the lens but you never need to worry about that part of it. Just remember a smaller f-number number lets in more light.

Everything being equal, the ISO sets the sensitivity of the sensor to light, and higher ISO number allows a smaller volume of light (smaller aperture or shorter shutter speed or both). Higher ISO can add "noise" or grain to the image.

08-23-2010, 09:36 PM   #17
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QuoteOriginally posted by NicoleAu Quote
Argh, I get so confused reading about iso, aperture and shutter speeds I just can't seem to get a handle on it at all and it all makes me feel rather stupid. I've done insane amounts of googling and reading on the subject but it just doesn't seem to want to sink in. I fear I shall be on auto for the rest of my life
Aperture is the opening of the diaphragm blades within your lens. It may help you to think of it this way.. If you shine a light into your eye, your pupils become very small so what you are looking at isn't so bright. When it gets darker, your pupils get larger so you can take in more light. Aperture works basically the same way except that you are controlling how much light you let into the camera for your photo. The smaller that opening, the more of your photo will be in reasonable focus (depth of field, DOF). The higher the aperture number (f11, f22, etc) the smaller the opening in the diaphragm. The smaller the number (f1.4, f2.8, etc) the larger the opening. Larger openings will result in less depth of field.

Shutter speed determines how long you let the light pass through the lens and aperture to the sensor. If you are taking a picture of a person running down the street for instance. A faster shutter speed will tend to freeze the action and allow you to get a sharper photo of the person. A slower speed (if you are not following the person with the camera) will result in a blurred runner in your photo. If your shutter speed is slow enough, you may not even See the runner in your photo.

ISO is the camera's sensitivity to light. The higher, the more sensitive. For most daytime conditions, you can set your ISO at 100 and leave it there. When to raise it depends on what you are taking a photo of and the amount of light available. Sunlight, ISO 100. A single Candle, you may want to go to ISO 1600 in order to get enough sensitivity to record something.

The way these tie together is this..

With a Fixed ISO (not automatic) you will have a range of shutter speeds and apertures (in combo) that are useful. Which one you choose to change, will depend on what you want to end up with. If you want a lot of the scene in focus, you would use a small aperture opening (higher number) and a lower shutter speed. If your intent is to freeze action, you may want to go to a more wide aperture and faster shutter speed. The time to change the ISO is when you A: Cannot open the aperture enough to get a clean shot (because the shutter speed is too slow) or B: you cannot slow the shutter enough for your chosen aperture.

ISO, Aperture, and Shutter speed can all be thought of as Stops or Steps. ISO 100 for example is step 1. A full stop faster is ISO 200. A full stop faster again is ISO 400 and so on. Where this is important to you is this. If your running person (from above) was moving too fast to get a properly exposed photo (aperture is wide open and you cannot use a fast enough shutter speed), you could raise the ISO in order to allow you to use a faster shutter speed.

Aperture steps are f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22. Those are Full stops. Our cameras can change them in either 1/3 or 1/2 steps. Changing the aperture one stop has exactly the same effect on exposure as changing the ISO one step. That is, if you are at ISO 200 and change to ISO 100, as far as exposure is concerned, it is the same as going from f8 to f11 (with ISO and shutter speed remaining the same).

Shutter speed full steps are 1 sec, 1/2 sec, 1/4 sec, 1/8 sec, etc up to 1/8000 sec (on the K7). Below 1 sec would be 2 sec, 4, sec, 8 sec down to 30 seconds (on our pentax cameras). Changing shutter speed, and keeping aperture and ISO constant, has exactly the same effect on Exposure. That is, ISO 100, f8, 1/250 sec for example, if you want to change the exposure one step, you would go to either 1/125 or 1/500 depending on what you are dealing with.

I've used step and stop interchangeably here and for my purposes, they are one and the same. Note that exposure has nothing to do with composition, DOF (aside from getting the desired one), or any of the rest. I am only referring to the amount of light that the camera is recording.

If you sit down, put your camera in Manual mode (M), and play a little bit with each of these settings, I promise you (as much as I can half a world away) that you'll get it. Pick a stationary object, well lit, and spend some time experimenting with each of the 3 settings but keep two constant for each round of your experiment. Pay attention to what the camera meter is showing you as you adjust each one. It may be confusing at first but once it comes, it'll be one of those slap the forehead with the hand moments.

Using your camera in an auto mode, allows you to adjust at least one of these settings while it adjusts the other two (If ISO is left on Auto). The green mode and the scene modes, if they are there, will adjust all 3 for you. There is nothing wrong with that but it doesn't do much to teach you about exposure. Once you have a handle on it, you'll stress about the choices it opens up just like the rest of us ..

Good luck..



Edit: For practicing, and learning what the meter does, I would suggest setting it to spot metering. You don't have to use it in practice but it will narrow in everything so that what you are pointing the center of the camera at, is what it is metering. Hint: Typically for proper exposure, on a light grayish area, you want the meter to be centered. For now, don't worry so much about that though, just learn to center the meter. It will at least demonstrate how each factor affects exposure.


Last edited by JeffJS; 08-24-2010 at 01:38 AM. Reason: Correct something in text.
08-23-2010, 09:50 PM   #18
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Simply put, light flows through the lens onto the film or sensor. The aperture sets how big is the hole. ISO sets how big is the bucket that holds the light; the sensitivity of film or sensor. Shutter speed is how long to let the light flow from lens onto film or sensor.

Like watering the lawn. Faucet valve is aperture; how much water. Sprayer handle is shutter speed; how long water flows. Size of the lawn is ISO; larger lawn needs more water. Obviously, watering the same size lawn with the faucet valve opened half-way will take longer than with faucet valve fully open. For identical exposure the lens set at f/8 takes a longer shutter speed than when lens is set at f/4; four times as long, in fact.
08-23-2010, 10:08 PM   #19
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We casually refer to increments of light as 'stops', after the f-stop aperture settings. To double the amount of light reaching a sensor, or to cut that light in half, is a one-stop change.

Let's say you're in P(rogram) mode. Very automatic there. You aim and shoot. The camera meters the light and sets the exposure. You chimp the picture -- too dark. Not enough light got to the sensor. Or it's too bright -- too much light got in. So you decide to re-shoot. What can you do?

* Spin the dial to change the EV setting, which lets in more or less light while leaving the other settings be. OR
* Change the ISO, which increases or decreases the sensor's sensitivity to light.

Let's say you've gone into uncharted territory, into M(anual) mode. You aim at a subject. You push the Green button, and the camera meters the light. You shoot and chimp and once again it's too dark or too light. You decide to re-shoot. What to do, what to do?

* Spin the dial to change the aperture setting slightly. OR
* Spin the dial to change the shutter speed slightly. OR
* Change the ISO.

Changing the aperture or shutter changes the amount of light hitting the sensor. And that's all. Well, not quite all. A faster shutter lets you shoot moving subjects. A wider aperture gives thinner DOF; a smaller aperture gives thicker, deeper DOF. Every photo is a problem you must solve: What are the best settings for any particular image? You don't really need to know the math. Just shoot, chimp, tweak, and shoot again. Eventually it'll become automatic.

A confession of my early days: I about grew up in my dad's small darkroom but I didn't REALLY learn photography until I got an early 135 camera. (That's 35mm film in cartridges, rather than loose spools like the first Leica.) It folded up; no rangefinder, no meter, like TOTALLY manual. I used a handheld light meter; and I eventually learned to judge light and distance, and automatically / subconsciously set the focus, aperture, shutter with my busy fingers. That took a few months.

The lesson: Practice, practice, practice.

08-24-2010, 12:36 AM   #20
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Thanks for taking the time to answer guys, it all sounds a little less scary, although I know I still haven't got it yet. I will do as suggested and play around with my camera some more, hopefully that will help. I think it all seems a bit mathematical to me and that's possibly why I'm having such trouble with it. Anyway, I will get it one day!
08-24-2010, 02:01 AM   #21
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QuoteOriginally posted by NicoleAu Quote
Thanks for taking the time to answer guys, it all sounds a little less scary, although I know I still haven't got it yet. I will do as suggested and play around with my camera some more, hopefully that will help. I think it all seems a bit mathematical to me and that's possibly why I'm having such trouble with it. Anyway, I will get it one day!
Yep, it's all based on mathematics but you don't really have to worry much about it. As long as you can multiply or divide by 2, you have the concept of the Stop. The only thing to decide now, is which of the three elements to adjust and how much.

We all said things differently but we all said basically the same thing. You were intelligent enough to buy a Pentax, you're intelligent enough to get exposure . That is, if you care about doing so (some don't and never do but still take great photos).

08-24-2010, 08:08 AM   #22
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QuoteOriginally posted by NicoleAu Quote
Argh, I get so confused reading about iso, aperture and shutter speeds I just can't seem to get a handle on it at all and it all makes me feel rather stupid. I've done insane amounts of googling and reading on the subject but it just doesn't seem to want to sink in.
I recommend putting Google aside for this one and visiting a library or bookstore to get an actual book. Lots of people like Bryan Peterson's "Understanding Exposure", but really, any basic book on photography should cover it.
08-25-2010, 05:49 AM   #23
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Let's make a big assumption here, that you are shooting hand held. For an 8 x 10 inch print the old rule of thumb is

Shutter speed = 1/focal length x 1.5

This gives relatively sharp and free from camera shake full format images. If you crop in, the shutter speed needs to be increased proportionally. This takes care of camera induced blur.

To freeze motion can take from 1/100 to 1/1000 or faster depending on the type of motion

Given these two limits you can shoot what ever you like

Note that while shake reduction can allow slower shutter speeds and eliminate shoe but this does nothing for subject motion

08-25-2010, 08:36 AM   #24
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QuoteOriginally posted by NicoleAu Quote
Argh, I get so confused reading about iso, aperture and shutter speeds I just can't seem to get a handle on it at all and it all makes me feel rather stupid. I've done insane amounts of googling and reading on the subject but it just doesn't seem to want to sink in. I fear I shall be on auto for the rest of my life

Hey man, I'm pretty new at dslr too, and although this site and its members are all super helpful, they do sometimes (and accidently) baffle the newbee with science.

To keep it simple, spend a couple of hours a day playing with your camera.
On the first day. shoot in auto and look at (all) the settings it decides to useand note the conditions (ie.. indoors or out, bright, overcast or damn dark).

On the second. Shoot all day in Av mode. Play about wih the apperture and make note of the shutter speed settings the camera decides on.

Day 3... Tv mode... Control the shutter speed today and let the camera sort the apperature. (this is a tripod day bigtime:-)... at least it was for me)

On every day, try to take the same shot 5 times using different iso settings for each. You'll soon work out what you need. Working out why can wait mate!!

My main issue is with framing! I get great shots but they're only really great after I've cut the edges off!! LOL!

I tend mostly to shoot in Av mode during the daytime and Tv after dark at the moment... But I'm still learning too:-)
08-25-2010, 08:52 AM   #25
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QuoteOriginally posted by Lowell Goudge Quote
Shutter speed = 1/focal length x 1.5
Even that ROT (rule of thumb) is flawed. In THE CAMERA, Ansel Adams tells of shooting a tree with a handheld 135/FF camera with a 50mm lens according to the 1/FL rule, but didn't get SHARP images until he'd gone from 1/50 to 1/250 second. That's 2+ stops. An APS-C cam needs another stop. Shake Reduction might give back those 2-4 stops under the right conditions. But for sharpness, a fast shutter (or tripod) is necessary.

Of course, if sharpness isn't the main criterion, just shoot and pray.

QuoteOriginally posted by DaveHolmes Quote
To keep it simple, spend a couple of hours a day playing with your camera.
...
You'll soon work out what you need. Working out why can wait mate!!
Great advise! Play with the camera, spin the dials, try different settings. See what works, what doesn't. Practice practice practice.
08-25-2010, 10:15 AM   #26
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QuoteOriginally posted by RioRico Quote
Even that ROT (rule of thumb) is flawed. In THE CAMERA, Ansel Adams tells of shooting a tree with a handheld 135/FF camera with a 50mm lens according to the 1/FL rule, but didn't get SHARP images until he'd gone from 1/50 to 1/250 second.
OK, but was he judging using 8x10" prints viewed from a typical distance, or perhaps larger prints viewed from extremely close? His standards for sharpness were probably higher than most people's. But anyhow, you're correct to observe that the old rule of thumb was never anything more than a broad generalization; it all comes down to what kind of standard of sharpness you use (as well as how steady your hands are!)
08-25-2010, 10:22 AM   #27
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Quite a bit of good advice here on exposure.

Only question I have is, in your original post you stated that you would always use an aperture setting of f/2.8. Is there a particular reason you would ALWAYS use f/2.8 or was it just an example in the OP? There are very good reasons for using f/2.8, but not for EVERY shot as you may want to play with the depth of field and the aperture is the mechanism you use to do so. By staying at 2.8 you're limiting your creativity.
08-25-2010, 10:32 AM   #28
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Good point. Realistically, you might find your camera doesn't have a fast enough shutter speed to avoid overexposure at f/2.8 in some situations, and in any case, the relatively shallow DOF and less-than-optimal sharpness that result from using that aperture wouldn't be what you'd want all the time.
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