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1020 Jul 2, 2005 8:00 AM

Please explain to me how the aperature works, and why you would want to change the settings. When would you use certain settings? THANKS:|

Nagasaki Jul 2, 2005 8:59 AM

The aperture is the size on the hole that lets the light into the lens. Each F stop of aperture lets in half or twice as much light as the next one. The F numbers are a unusual series of numbers where the larger the number the less light is allowed through. The shutter speeds on the camera also change in steps which either half or double the exposure time so let in half or twice as much light for each step.

As to why you'd want to change it there are two reasons. There are a large number of aperture and shutter combinations that will correctly expose any shot. A larger aperture gives a faster shutter speed allowing you to stop action. On the other hand a small aperture slows the shutter speed and allows you to introduce deliberate motion or blur, for example when shooting moving water.

The aperture also has an effect on the depth of field. This is the depth front to back that appears in focus. A large aperture say f2 F2.8 F4 will give a shallow depth of field go for throwing the background out of focus in portraits. A small aperture F11 F16 F22 gives a large depth of field where everything is in focus, good for landscapes.

1020 Jul 2, 2005 10:38 AM

thank you for the explanation...now another question. I am getting a new camera so that I can get better wildlife shots. A couple of years ago we went to Yellowstone, saw some awesome wildlife. However, when I got the pictures the grizzlies and moose were mere dots. SO we are getting a 12x zoom, either Sony H1 or Canon S2, can't decide. Anyway it has auto program for the aperature/shutter. I was told we could manually set the aperature and the setting would auto adjust. WOuld I want to change the aperature for shooting wildlife at a distance?

Tom Rogers Jul 2, 2005 3:27 PM

The only way an unsharp picture looks good is if it looks like it was done on purpose. Something slightly out of focus looks like you goofed. Under ideal conditions, use F stops to control depth of field,but do not sacrifice sharpness for the ideal goal. It is best to use a tripod in order to not have to use wider F stops in order to gain shutter speed.

eric s Jul 2, 2005 7:35 PM

I have several thoughts on what you ask. Some are beyond what you're looking for, but I think you'll find it useful.

First off, get something with a good lens. I've heard about too many people with small cameras with limited zoom lenses walk right up to wild animals at places like Yellowstone. They don't realize that it really is a wild animal and they are risking their lives. We want to you live long enough to come back here and post shots from that vacation! It sounds like you're trying to get a good zoom... so thanks! But I just had to say this, as this problem happens way to often.

The next thing is about the "12x" description of those two cameras. That is really almost completely meaningless information. Its really marketing jargon that has little meaning in reality. Here is why. By "12x" they are describing the ratio of the short end of the zoom to the long end of the zoom. What really matters is the "35mm equivalent" description of the lens. With that info, you can actually compare lenses. Let me give you an example. A 50mm lens produces the same image as the human eye. A 100mm lens makes everything twice as big. And so on. With this info, you can say "a 200mm lens will make things 4 times as big" and that actually means something to you. But 12x just says the ration of the short end of the zoom to the long end of the zoom. For example,
a 10mm to 120mm lens is a 12x zoom.
a 20mm to 240mm lens is a 12x zoom.

Now both of those will say "12x zoom" on the camera box, but they are completely different cameras. The first has a very wid angle lens (amazingly wide, actually) but offers only slightly more than twice the magnification than the human eye. The second camera starts at 20mm, which is fairly wide (wider than anything I have) but goes out to 240mm, which is almost 5 times the magnification of the human eye. Huge difference, huh?

So lets look at those cameras. Interesting... I think both use the same lens. They are both:

36mm - 432mm

That makes them around 8.5 times the magnification of the human eye. That should work very well for wild animals. Now, unfortunalyte 36mm isn't very wide angle, so you might have trouble capturing really big landscapes... but you can always take multiple pictures and combine them on your computer.

So purely on lens reasons, there is basically no difference between the two cameras. You'll have to pick on things like battery life, quality of picture, usability (don't forget that one. I suggest going to a store and actually handling the cameras to see how they feel in your hands.)

Now, on to your question. For animals at a really lon distance, you might want to change the aperture. This would let you get a larger depth of field, which might let you get the mother bear and her cubs all within the depth of field.

Most of the higher end cameras let you set a mode where you change either the aperture or shutter speed and the camera automatically adjusts the other one. I bet both those cameras do that (but you should read the reviews to be sure!)

Does that help?

Eric

experimental_pilot Jul 4, 2005 12:15 AM

I was just going to post this :-)

So for shooting moving aircraft it is better to use a larger aperture? higher number?
and for shutter speeds what is faster 1/30 or 1/1000?

Also what is ISO? how does a 100 or 400 setting affect a photo?




Thanks

Carrots Jul 4, 2005 1:58 AM

I just got a Canon S2, and I THINK that it 12x zoom is from 35 mm equivalent. I thought 12x zoom would be HUGE, but its not so long a zoom as you might think. If you want a closeup of a lions face at 100m, think again. I dont even think the lion will fill the whole frame at 100m.

1/1000 is the faster shutterspeed. It is a 1000th of a second, as opposed to a 30th of a second.

I would think that if you shoot aircraft during the day, your shutterspeed would be fast enough no matter what aperature you use. And it might be difficult to focus on the aircraft, so using a small aperature (large number) would be best.

pagerboy Jul 4, 2005 5:39 PM

Depends on which way the plane is going. I've taken plane pics with 1/1000, 1/500 and fromf2.8 to f6.3.

Some were landing, flying by, real high, low. I use auto most of the time.

eric s Jul 4, 2005 7:53 PM

experimental_pilot

The real question is what you are trying to achieve. If you want to stop a plane in flight, that requires some a bit of shutter speed. 1/30th won't do it. On the other hand, if you really stop the plane in flight, it will look artificial (like its hanging in space and not flying.) The smaller apertures will give you more depth of field, which might make it easier to get the plane in focus (but reduce the shutter speed.)

I guess I would suggest trying it different ways and see which works well for you. The harder part will be to pan with the plane and keeping it in the field of view. :)

Carrots,
I don't believe you understood what I said. "12x" isn't a question of 35mm or any other system of measure. It will always be "12x". But 12x is almost completely meaningless. What matters (at least should matter to you) is how much wide angle the lens has and how much telephoto it has. The only way to figure that out (and compair two cameras) is to translate the actual focal length into a "35mm" equivalent. Then you can compare it to what your eye see and what the different cameras say.

The Canon S2 is 36-432mm in 35mm equivalent. That means it a bit less than 1/2 as wide as the human eye, and almost 9 times more powerful than the human eye.

But nothing, even the most expensive lenses (and I have one, the Canon 600mm f4) won't take large pictures of a lion at 100m. Nothing will, even small portable telescopes.

Eric

Carrots Jul 5, 2005 1:43 AM

I understood that, yes. I think my use of the word "equivalent" was wrong. What I meant was that the widest angle is 35mm. Thus 12x35 = 420mm. Which is wider than if it had a widest of say 20mm. Like you explained earlier in the post.

And yes, I greatly overestimated zoom. (before I had an optical zoom camera)

Nagasaki Jul 5, 2005 4:20 AM

eric s wrote:
Quote:

The larger aperture will give you more depth of field, which might make it easier to get the plane in focus.


A larger aperture (smaller F number) will give less depth of field and a faster shuuter speed. A small aperture (large F number) will give a greater depth of field but a slower shutter speed.

eric s Jul 5, 2005 11:01 AM

Thanks for the correction... I know that, but clearly the info got flipped somwhere in the process of writing that... let me go correct what I said so I won't confuse anyone in the future.

Eric

1020 Jul 6, 2005 8:52 AM

Eric...thank you so much for answering my questions. I think I have a better understanding. This is how I see it, tell me if I am right. If I am looking for better depth in my zoom shots I should choose a higher f number, which is a smaller aperature. This will slow my shutter speed and in turn my pictures will not be as clear, without a tripod. Now, both of these cameras (S2 and H1) have image stabilization, won't that work? AND...I understand for outdoor use you should use lower ISOfilm, which totally goes against what I always thought. I tought the higher # the better picture. Sooo...do I need to use different ISO film if I change the aperature to a higher number? I hope you understand what I am asking....I think I do!:?

geriatric Jul 6, 2005 9:27 AM

Hi

If you have microsoft excel spread sheet installed on your pcI will send you my full DOF chart.



Carrots Jul 6, 2005 9:59 AM

When taking photo's outside in daylight, the IS should be able to compensate for whatever the new shutterspeed at the smaller apperature would be. IS is no mirracle worker however. 12x zoom (432mm) indoors with reasonably dim lighting is a bit much for my shaky 25 year old hands and IS. For longer exposures (say 4s at night) with no zoom also leaves me with blurry results.

On the ISO question, I have never changed any settings on a film camera, but if it works the same as digital, then you would'nt necessarily need to change the ISO setting. On the S2's aperature priority mode, the camera automatically makes the shutterspeed longer when the apperature is smaller. It leaves the ISO as is.

The higher the ISO, the more noise will be on the image (on film I think itsgrain). But it will also be brighter.

Carrots Jul 6, 2005 10:18 AM

IS does helps in most cases. If you shoot outdoors in the day, IS should compensate for any reduction in shutter speed that the smaller aperature would cause. Although IS doesnt help my shaky 25 year old hands indoors (reasonably lit)with 12x zoom without a flash. Also without zoom, shutterspeeds of more than a second is also too much for me.

On your ISO question. I have never changed any settings on a film camera, but it should work the same as withdigital. On the S2s aperature priority mode, it only compensates for the smaller aperature by making the shutterspeed slower. It leaves the ISO unchanged.

Using a larger ISO makes the photo's brighter, but also increases the noise on digital, and I think the grain on film.

If Im wrong in anyway, sorry, and please correct me.

rjseeney Jul 6, 2005 10:37 AM

Higher iso's do not make a picture brighter. ISO refers to light sensitivity. Higher ISO's are more sensitive to light, allowing you to achieve faster shutter speeds at lower light levels. This is useful for indoor or low light shots where you don't want to lose flash, or where you want to freeze motion. The trade off is higher noise levels, which limits the quality of your prints and sharpness. You probably would not be able to print a decent 8x10 at iso's above 200 on most consumer level digicams.

eric s Jul 6, 2005 11:45 AM

1020
Glad to help. Part of why I come here so often is because I like helping people... it's in my nature. Thanks for showing your appreciation

I agree with rjseeney.

There is 1 "proper" exposure for a given scene that a camera will pick (I'm ignoring doing something special like emphasise a backlit scene when the camera would try to correct for that.)

But how that exposure is achieved is where the photographer and their skill (and intent) take over.

Let me give you a quick bit of background.

Say the proper exposure for a scene is:
f2 1/250 ISO100

All those settings are interrelated in the same why (nice of the inventors of this stuff, huh?) The rule is simple, it's all based around halfing or doubling. Changing 1 f-stop up (smaller aperture) halfs the shutter speed. Change 1 f-stop down (larger aperture) doubles the shutter speed. raise the iso (from 100 to 200) doubles the shutter speed. Teduce the ISO (from 100 to 50) halfs the shutter speed.

So all of these combinations produce the same exposure (But not the same picture!)
f2 1/125 ISO50
f2 1/250 ISO100 (more ISO = more shutter speed)
f2.8 1/125 ISO100 (smaller aperture = less shutter speed)
f2 1/500 ISO200 (more ISO = more shutter speed)
f2.8 1/250 ISO200 (smaller aperture + more ISO = same shutter)
f4 1/125 ISO200 (2x smaller aperture + some more ISO = slightly less shutter)
f4 1/250 ISO400 (2x smaller aperture + double the ISO = same shutter)

(if I've made a mistake, someone please correct me.)

But its the use of the side effects that help divide the snapshot shooter from the photographer. Maybe you want more DOF so you choose f4, maybe you want to isolate the subject from the background so you choose f2. Maybe you need to stop motion, so you pick the higher shutter speed, or maybe you want motion blur.

And you have to always weigh the noise that higher ISOs produce (which as said above obscures details and produces a less sharp image.)

As you said, if you increase the fstop (i.e. use a smaller aperture) you get a larger Depth Of Field, but a lower shutter speed. The problem will be how to use this when photographing planes. They are large objects (so larger DOF is good) but they are farther away (when flying.) If you go with a high shutter speed, you'll loose the motion blur, which can look bad. But panning with a plane to get the motion blur but keep them steady in the picture is hard. It takes practice.

My suggestion is to try taking the pictures with various settings and see what works for you. And don't expect perfection right away... shooting any moving object is not easy.

You are right, you can use higher ISOs to give you higher shutter speeds, but that raises the digital noise, which reduces overall sharpness. In other words, there is no free lunch!

Eric

1020 Jul 6, 2005 1:46 PM

Thank you for your response, but I am not the "plane shooter", I am shooting wildlife. Can you help me more with that?

eric s Jul 6, 2005 7:16 PM

Sorry.

With wildlife, you almost always want to stop the action. A blury animal almost always means you throw out the picture.

For big things, it gets tricker (the bears and moose you list.) They have such a large body you'll have trouble getting them entirely in focus. Luckly they also don't move a lot. You have two choices. Don't try to get them all in focus (you'd need a really big DOF) or try to do it. Just change your position so they are more wide then deep. DOF is infinitely wide, but the aperture controls how "deep" the DOF is. If you shoot the moose from the side, it will be easier to get it entirely in focus than from more straight on. Obviously, it's a better shot if the moose faces you, so that will make them a bit wider... but still skinny compared to more stright on.

Always, always, always get the eyes in focus. The shot won't work if the eyes are not in focus.

I'd suggest somewhere inbetween. Use a larger aperture to get some DOF... try shooting around f8 or so (that is where you'll optically be the best as well... probably, it's a safe generalization.) and then figure out which ISO value gets you a fast enough shutter speed without introducing too much noise. So take some test shots. See how much noise the different ISO values get you. BTW, this is one of the reasons that DSLRs are popular. They produce much cleaner images at higher ISOs that the P&S cameras (it has to do with the physical sensor size in the camera, but other things as well.) So while I can shoot at ISO400 and be generally happy with it (I prefer 200) you probably can't shoot at ISO400.

Another thing to look into is the programs neatimage or noise ninja. Both are noise reduction packages that you can train to learn what the noise "patter" is of your camera and then they will remove the noise without (in theory) removing detail from the image. They work well, and might save some images you otherwise wouldn't have shot. That might let you shoot at a slightly higher ISO.

Eric

experimental_pilot Jul 6, 2005 7:41 PM

Thank you all for the replies!!! Its really helpfull!!! Im going to experiment now :-)
and sorry 1020 for stealing your thread.


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