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Old Jul 24, 2007, 10:52 AM   #1
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Hi,

I'm new to digital photography and want to ask experienced members of this forum
something about ISO-settings.

I've been looking at sample pictures of many digicams and have noticed that the image quality of most cameras is very good at low ISO-settings, say 100 or 200. At ISO 400 and above seemingly only pictures of DSLRs are still excellent.

My question now ist the following: Is it not possible to always shoot pictures at ISO
100 or 200? Please explain that to me.

Thanks!!


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Old Jul 24, 2007, 11:13 AM   #2
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ISO was originally a photographic film's sensitivity to light or, equivalently, today's digital sensors' sensitivity to light.

Lower ISO (lower sensitivity) calls for longer exposures (and/or more light) while higher ISO speed ratings allow for shooting the same scene with shorter exposures or in lower light conditions. P&S cameras are often poor performers in low light as they generally do not offer as broad a range of ISO settings.

In most dSLR's, ISO is one of several easily set options. But while this trade-off allows cameras to shoot in lower light situations by using a higher ISO, the higher the ISO (in general) the more noise in the resulting digital image.

There is far more to learn about the interrelationships of ISO, aperature (f-stop), and shutter speed. You might try finding a good, beginning book on photography to learn more.

But, to answer your question very simply"Is it not possible to always shoot pictures at ISO 100 or 200?". Sure ... if you are willing to take photos where everything stands still for many seconds or minutes while a low light photo is being taken due to the camera's low light sensitivity (low ISO settings). If things do not stand still under lower light conditions, movement blur will occur. Again, read a good intro photography book to get started!

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Old Jul 24, 2007, 11:48 AM   #3
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Hello and greetings to West Virginia (USA),

For beginners like me it's nice to have experts like you out there.

Well, the field of digital photography is a huge one, at least from my point of view, and it would probably be a good idea, as you suggested, to buy a book and start studying.

Thanks for your comprehensive information and good luck to you and your family.

xer2004

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Old Jul 24, 2007, 12:40 PM   #4
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Try "Rick Sammon's Complete Guide to Digital Photography 2.0". He covers a lot of what you want in a friendly style.
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Old Jul 24, 2007, 1:58 PM   #5
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And, of course, there are MANY places online. A student of mine mentioned liking these two, but there are many, many more free online tutorials:

http://www.shortcourses.com/
http://www.ashotapart.com/tutorials.html
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Old Jul 24, 2007, 7:21 PM   #6
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Reading is good, and it doesn't much matter if the book is addressed to digital photography or chemical in terms of f/stop, shutter speed, ISO, composition, focus, and many other issues. The most important single book for digital is your camera's manual.

Spend some time in your local library looking through books, and in particular at books by the masters with lots of photos and notes on how they were taken.
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Old Jul 24, 2007, 7:56 PM   #7
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Hi, Henry, Bob Nichol & Bill Drew!

I got your messages and I'm grateful to you all.

As a 57-year-old newbie I feel that there're many people in this forum who are extremely understanding and helpful. They don't laugh at you.

Once again, thank you very much indeed!!!

xer2004
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Old Jul 24, 2007, 9:47 PM   #8
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xer2004 wrote:
Quote:
My question now ist the following: Is it not possible to always shoot pictures at ISO
100 or 200? Please explain that to me.
Sometimes it's not possible to shoot pictures at ISO 3200 either, unless you want motion blur. or photos that are not properly exposed). Any model is going to have some limitations in some conditions.

Your lens (how bright it is), lighting and ISO speed all impact the shutter speed a camera will need for proper exposure.

In some lighting, depending on the available apertures with the lens you're using, you may need to use a higher ISO speed to keep your shutter speeds fast enough to prevent blur from camera shake and/or blur from subject movement.

This exposure calculator can give you a better idea of the relationship between them (note that film speed in the calculator is the same thing as ISO speed).

http://www.robert-barrett.com/photo/...alculator.html

You have to look at the lens you're using to see the largest available aperture (represented by the smallest available f/stop number) for the focal length you're using (how far you're zoomed in if it's a zoom lens).

Most lenses lose light as you zoom in more (so, instead of having f/2.8 available, you may only have a widest aperture of f/5.6)

The aperture scale (in one stop increments) goes f/1.0, f/1.4, f/2.0, f/2.8, f/4.0, f/5.6, f/8.0, f/11, f/16, f/22, etc. With each one stop move to a smaller aperture (represented by larger f/stop numbers), you will need shutter speeds twice as long for proper exposure for the same lighting and ISO speed.

Basically, your camera's lens has an aperture iris that works like the pupils in your eyes), and you want to open it up more (larger apertures, represented by smaller f/stop numbers) if you need to expose an image faster for the same lighting and ISO speed (which is how sensitive the camera's film or sensor is to light).

You may need to expose it faster (using a faster shutter speed) to reduce motion blur from subject movement or blur from camera shake at times, and ISO speed helps with that (each time you double the ISO speed, the camera can expose the image twice as fast for the same lighting and aperture setting).

For low light sports (and night sports under the lights falls into that category), you'll probably want a lens that can maintain f/2.8 throughout it's focal range at a mininum (indoor sports may require an even brighter lens), using a camera capable of shooting at higher ISO speeds (i.e., ISO 1600 or faster) for a higher percentage of keepers without blur.

You may find many condtions requiring both a bright lens and a camera capable of shooting at higher ISO speeds, unless you can use a flash and stay within the rated flash range, if you want a reasonable percentage of keepers without blur from subject movement (and/or blur from camera shake if you can't use a tripod).

For example, here's a snapshot from some of the youngsters on stage at a dance recital my great niece (my younger sister's daughter's daughter) was in a couple of months back (she's the one holding the instructor's hand).

Note the blurred hands and more from movement? It's even a tad underexposed (shutter speeds would have been even slower for a brighter exposure). This one was taken at ISO 1600 at f/2.5 with a 100mm f/2 lens, and my shutter speed was 1/160 second, which resulted in a bit of motion blur in some shots. If I had tried to use ISO 400 at that same Aperture (f/2.5), there would have been a lot more blur, since it would have taken 4 times as long to expose it in that lighting (or 8 times as long at ISO 200).



Now, if you can catch them when they're not moving as much, your percentage of keepers without blur will go up, and you can sometimes get away with using lower ISO speeds.

But, this was pretty good stage lighting, too. So, in darker conditions, you may find that nothing is going to work unless you can use a flash (and stay within the rated flash range), even if you have a brighter lens and higher available ISO speeds.

Take this snapshot for an example of how it can be difficult to avoid blur indoors without a flash if your subjects are moving very fast. See the blurred foot movement and more? Even though I was shooting at ISO 3200 with a 135mm f/2.8 at it's widest available aperture of f/2.8, I still got some motion blur at 1/400 second in a number of the shots. It would have taken 8 times as long to expose this shot using ISO 400 at the same aperture setting (or 16 times as long if you tried to use ISO 200).




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Old Jul 24, 2007, 10:10 PM   #9
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Hello, JimC!

I'm grateful to you for your very extensive report regarding ISO.

Now I see many things clearer than I did before.

Good luck to you!!

xer2004
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Old Jul 25, 2007, 2:21 AM   #10
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Very informative posts....Off topic question maybe but what exactly is Exposure Values and what are they used for? Most digital cameras I have seen have them preset at 0 and you have the option to go positive or negative...Not sure what the benefit or use of this is....Any clarification?
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