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Old Dec 30, 2009, 12:32 PM   #31
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Here's a shot from just about same distance/focal length. That first shot was at f2. This shot is f4:


With any kit lens, you're going to be at f5.6. To get an AF-S capable lens at 85-90mm that has at least f4 you're looking at some expensive lenses. You still have some options, just a lot less of them - with canon (or a nikon d90) you have all the OEM lenses plus all third party lenses. But the biggest thing is - that intro inexpensive 50mm 1.8 option for around $110.
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Old Dec 30, 2009, 1:03 PM   #32
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For example, these should all result in an image exposed the same way:

ISO 1600, f/2.8, 1/50 second
ISO 3200 f/2.8 , 1/100 second
ISO 6400 f/2.8, 1/200 second

If you're trying to used fixed settings for aperture and shutter speed when changing ISO speed, you're not understanding the basic concepts of how exposure works (which would explain your results, since the higher ISO speed image is obviously exposed brighter).
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Old Dec 30, 2009, 1:09 PM   #33
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Just wanted to show that the iso will expose higher if all things are equal.
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Old Dec 30, 2009, 1:22 PM   #34
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so it appears that bokeh portraits are out with the d5000 unless I'm willing to cough up several hundreds for a AF-S lens capable of f/1.8 to about f/4?

Kind of a bummer.
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Old Dec 30, 2009, 1:31 PM   #35
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That was the main issue I had with the d5000 lens issue. You can get a good prime lens for the t1i, for 100 buck that goes to f1.8. And it gives you allot of pleasing bokem imho.
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Old Dec 30, 2009, 1:39 PM   #36
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Quote:
Originally Posted by shoturtle View Post
Just wanted to show that the iso will expose higher if all things are equal.
All things are not supposed to be equal. ;-)

You use the appropriate aperture, shutter speed and ISO speed for the conditions you're shooting in, so that you always end up with a properly exposed image.

That's the entire concept for using a higher ISO speed with a digital camera (or higher ISO speed film). You are able to use a faster shutter speed for the same aperture and lighting when you increase ISO speed to get a properly exposed image. ;-)

Look at any good book on basic photography (and it doesn't need to be specific to digital as the same concepts apply to both film an digital) to get a better idea of how exposure works.

You have three main variables involved for proper exposure:

1. Lighting, usually measured in EV for Exposure Value
2. Aperture (measured as f/stop, which is a ratio between the diameter of the aperture iris and the focal length of the lens, with wider apertures (letting in more light) represented by lower f/stop numbers
3. ISO speed, which is how sensitive the film or sensor is to light (each time you double the ISO speed, you use shutter speeds twice as fast for the same aperture and lighting).

Your test methodology is very flawed, since you are obviously exposing the higher ISO speed images differently (i.e, probably using the same shutter speed and aperture for all ISO speeds tested, which is why your higher ISO speed images were brighter).
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Old Dec 30, 2009, 1:57 PM   #37
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Smiles, I know, but just wanted a quick example of different ISO. Just did not want to get too technical. When I was trying to explain the difference in iso with all the technical aspect to my brother. It got him confuse. When I show him the difference when all was equal the geezee moment happen. And he graps the concept of what the iso can allow you to do with fstop and timing. I guess I like explaining things from the most simple form then move up. Everyone is different some. I guess I think in simplified terms.
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Old Dec 30, 2009, 2:01 PM   #38
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John, you mention that you currently use 50mm and 85mm lenses. Do you find that for portraits such as the one of your son, that's the most appropriate focal range? I have 2 children myself and as I'm sure you know, it's quite difficult to get close and have them sit still (which I would have to do with MF), and am curious if I would really need to go beyond 100mm in a lens.

You really have me pondering over the lens restrictions now. Though, I'm not 100% I'll be able to swing the extra $100 for the T1i, and I like the pluses that the D5000 has over the XSi

Here's a link to some of the compositions I hope to be able to achieve. Aside from breaking the bank on compatible lenses for the D5000, is this type of subject isolation possible with some skill and the stock kit? http://fiveprime.org/hivemind/Tags/bokeh,d5000. It should be noted that I'm referring to traditional portraits, not close-up macro style photography where this effect seems easier to achieve. No one wants a roll of photos with closeups of my children's faces, lol.

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Old Dec 30, 2009, 2:09 PM   #39
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Smiles, I know, but just wanted a quick example of different ISO. Just did not want to get too technical...
The problem with your approach, is that you're telling members that you can get more detail using ISO 6400 instead of ISO 3200, using a higher ISO speed image that was exposed brighter as your "proof".

That's very wrong.

If you want the same exposure (for example, the same image brightness you got with the ISO 6400 photo when shooting at ISO 3200), you'll need to use shutter speeds twice as long for the same lighting and aperture at the lower ISO speed setting.

Then, guess which photo will have more detail and dynamic range? The ISO 3200 photo, as they'll both be exposed the same way.

The only time you'll get more detail with the higher ISO speed photo is if you're seeing a problem with blur from camera shake or subject movement. Then, a higher ISO speed is warranted. Again, each time you double the ISO speed, you can use shutter speeds twice as fast for the same aperture and lighting.

Lower ISO speeds are always going to be better, unless motion blur or blur from subject movement is a factor. Image brightness is a function of exposure, and you'll need to use different shutter speeds for different ISO speeds for the same exposure, when using a given aperture with the same lighting.
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Old Dec 30, 2009, 2:25 PM   #40
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I am not disagreeing with you. I just think there are different ways to explain the same things, as each person is different. I like to bring things to their simplest form. Then move forward form there, that has always been my instructing style when I was Army instructor, not in photography. But I think that there is merit in going to an equal example. When you look at the photos as is, which has more details that the naked eye can pick up?
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