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Old Dec 1, 2004, 10:35 PM   #1
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hi everyone... i dunno where i should place this topic but maybe it's a newbie's question so i decided to put this here anyway...

when does one use EV compensation and ISO? i know those two things control proper exposure andthebrightness of a picture (correct me if i'm wrong) but i really don't know when and when not to use either. ISO does make an underexposed picture lighter but it adds noise. EV does lighten the picture. can't i just always use an EV +2 setting to all my indoor photos?are there drawbacks in always using EV compensation? my subject is usually my baby girl therefore i cannot use a slower shutter speed and the aperture is already wide open (f2.8 ).

also, i read in one site to use EV whenever you have a light or dark subject (-EV for black subjects and +EV forwhite subjects) to prevent loss of detail.

by the way, i'm not into using flash and the camera i'm using right now (A80) doesn't have contrast, brightness and saturation controls. i'm eyeing for a sony V1 though.

thanks!!!


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Old Dec 1, 2004, 11:45 PM   #2
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Well, you're a little off base on how it works, and I'm not the best at explaining things clearly, but I'll give it a shot.

ISO speed is not designed to brighten a photo. You increase ISO speed to increase the sensitivity of the sensor to light. Basically, it's just amplifying the signal from the CCD. This allows you to use faster shutter speeds. Each time you double the ISO speed, your shutter speeds can be twice as fast for the same EV (Exposure Value, which is how light is measured) and Aperture.

As you mentioned, you do see an increase in noise (due to the amplifcation of the signal, which also amplifies noise).

Now, if you saw a brighter image when using a higher ISO speed, then I'd guess you were in manual exposure mode, and had a shutter speed set too fast for proper exposure. Using manual exposure indoors in low light without a flash won't help you to get faster shutter speeds compared to Autoexposure (if you want properly exposed photos).

Your camera's autoexposure is going to select the largest available aperture in lower light anyway, so that the image is properly exposed. If you try to use manual exposure with a faster shutter speed than the camera's autoexposure is going to select, you'll end up with underexposed images (which is what it sounds like you're getting). The camera must leave the shutter open long enough for proper exposure.

Exposure Compensation (a.k.a., EV Compensation) is allowed to let you modify the brightness of the image. It's normally not available in manual exposure mode on most models (because you're controlling the exposure via aperture and shutter speed). With Autoexposure, if you want to expose the image brighter than the camera's metering thinks it should be exposed, you use a +EV setting. If you want to expose the image darker than the camera's metering thinks it should be exposed, you use a -EV setting.

The way this works, is when you set a +EV value with Exposure Compensation, the camera will use a larger aperture and/or a slower shutter speed than the autoexposure would normally use for proper exposure. If you use a -EV value with Exposure Compensation, the camera will use a smaller aperture and/or a faster shutter speed than the autoexposure would normally use for proper exposure.

So, in your example where you're already at f/2.8 (the largest aperture available on your model), and want a brighter image, the camera could only use a slower shutter speed to brighten the image in autoexposure modes.

Since you're trying to take photos indoors without a flash, my guess is that you're trying to figure out how to keep from getting motion blur without increasing ISO speed (to keep noise levels down), and thought that using EV Compensation may work.

Nope -- it won't. It's designed to help you modify exposure for subjects that the metering may not get right. For example, a backlit subject in shadows may require +EV Compensation for proper exposure (because the camera's default matrix metering is trying to insure that the majority of the scene is properly exposed, and this leaves your subject underexposed). The way it modifies exposure is by using a different aperture or shutter speed (just like you would do in manual exposure mode).

If you want to take photos indoors of a moving subject without a flash, you're going to need a model with a brighter lens and/or a the ability to shoot at higher ISO Speeds with lower noise.

For the time being, I'd suggest increasing your ISO speed (which is going to be noisy), staying at full wide angle (the maximum available aperture is f/2.8 and is only available at the wide angle lens setting), and using Noise Reduction tools to clean it up. Each time you double the ISO speed, the camera's autoexposure can use shutter speeds twice as fast, while still insuring proper exposure of the image. A tripod can also help (to reduce motion blur from camera shake).

Here is a good free tool to reduce noise: http://www.imagenomic.com

Very few current non-DSLR models will have a brighter lens (most models start out at f/2.8 ). One you could look at is the Canon G6 (it's lens starts out at f/2.0, which is twice as bright as f/2.8 ). So, you could use shutter speeds twice as fast as your A80 for any given ISO speed and lighting level and still get proper exposure.

But, what you really need for indoor shooting without a flash is a DSLR with a bright lens. If you're on a budget, look at the Canon Digital Rebel, and get a 50mm f/1.8 lens to go with it. It can shoot at much higher ISO speeds with lower noise compared to the non-DSLR models (because it's sensor is much larger, and requires less amplfication of it's signal for the same sensitivity to light).

Of course, there's always flash. ;-)




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Old Dec 2, 2004, 5:24 AM   #3
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thanks man!

geez... now i realized how much i really don't know and understand about photography. well i just started a few months ago and up to now i've beenguessing (really guessing :?) and changing and experimenting manual controls... i dunno why but i just wouldn'tuse auto mode.well, i'm still learning and i don't think a DSLR would fit my needs (and my budget) yet. i also like cameras that are just as big as the V1 or a P600.

any online courses in understanding the basics? thanks again...
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Old Dec 2, 2004, 7:02 AM   #4
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sago wrote:
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i also like cameras that are just as big as the V1 or a P600.
Just keep in mind that the lenses on these models are not any brighter (at least not at their wide angle setting) than the lens on your A80.

If you want to use a camera indoors without a flash or tripod, and are taking photos of a non-stationary subject, you'll need faster shutter speeds to prevent motion blur. So, you'll want a model with a brighter lens.

But, even with a brighter lens in a non-DSLR model, you'll have a difficult time getting some shots without unwanted noise from higher ISO speeds and/or motion blur from subject movement (you'll only be able to get shutter speeds up to a point at the ISO speeds available on non-DSLR models, so how much subject movement you have will be a limiting factor).

There are very few current non-DSLR models that have a lens brighter than f/2.8 at their wide angle setting. Some to look at (discontinued and new) with brighter lenses would be the Canon G series models (G2, G3, G5, G6), some of the Olympus Models (C-3040z, C-4040z, C-5050z), and some of the Sony models (Sony DSC-F707, DSC-F717).

Any of these models should allow shutter speeds at least twice as fast as your A80 for any given lighting condition and ISO speed (although the Canon models tend to be a little more sensitive than their rated ISO speed, so there may not be quite that much difference between your A80 and the non-Canon models).

Quote:
any online courses in understanding the basics? thanks again...
Forum Member Mikefellh posted a link to this site in another post a while back. I haven't read the lessons yet. But, it appears to be a comprehensive online course that may help.

http://209.196.177.41

You may also want to check out your local library for books on basic photography. The concepts will be the same for both film and digital (ASA/ISO speed, Aperture, Shutter Speed, etc.).

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