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| Exposure; Per Bam's request | |
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| Topic Started: Nov 19 2007, 12:49 PM (175 Views) | |
| kman627 | Nov 19 2007, 12:49 PM Post #1 |
Film Junkie
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Since Bam requested some ISO and shutter speed info, I thought I'd just go over the basics of exposure here. There are three things that determine the proper exposure of a photograph.
 N is the aperture T is the shutter speed While this is certainly not neccecary for making a good photograph, it's good to know how it all works. Your camera is doing all of this very quickly and without your knowledge. It will instantly give you the proper exposure it has determines in the process and equation. Now I'll talk about ISO's ISO stands for The International Standards Organization, which is organization the ensures conformity and uniformity of products. This insures that every manufacturer's ISO values are equal. So your exposure at ISO 50 on a Canon will be equivilant to ISO 50 on a Nikon and so on. The most common ISO's are are follows:
The lower the number, the less exposure or less sensitivity there will be. They are also reffered to as stops, so you would say that "ISO 100 is four stops slower than ISO 1600" and thus giving you four times less exposure. ISO 1600 is four time more sensitive for example. Another consideration of ISOs is noise/grain. The higher the ISO, the more grain/noise your going to see. This is because the greater sensitivity is more apt to expose random bit of light that will be present on the sensor. For film, the the silver halides are larger the faster the film, thus making the grain more apparent. You may hear someone say "I pushed it to 1600" This means that the film was say ISO 400, but it was developed three times as long to conpensate for the underexposure. The same can be done digitally, especially when shooting RAW. If you just don't have enough light, you can underexpose by one stop or more and try to bring out the image in processing. What you sacrifice in pushing is more contrast, and less shadow detail. Shutter Speeds The shutter is what controls the amount of time the image is exposed. It is also measures in stops, also including half and third stops depending on the camera. Using one half or third stops can ensure more precise exposure. The following are common shutter speeds, measures in full stops:
1. If working handheld, the slowest shutter speed you should use should be equivilant to your focal length. Ie. if you're using a 50mm lens, you should stay at or above 1/60s to avoid blue induced by camera shake. And if you're shooting with a non-full frame DSLR, keep in mind your 1.5 or 1.6x conversion factor. So for a 50mm on a 1.6 crop body you've got an equivilant 80mm lens, so be careful if shooting handheld under 1/125 and consider a tripod or a higher ISO or larger aperture. 2. Another consideration of shutter speed is how you want to portray motion. We'll use the waterfall example. If you want to stop the motion of the waterfall, then you'll want as fast a shutter speed as possible without underexposing. If you want to give it that silky motion look, go with as slow a shutter speed as possible, but use a tripod. If you wanted to shoot a person walking and freeze them in their tracks, then go for something 1/125s or faster, and below that if you want to imply the motion of their walking. Make sense? Here's an example of a 1/5000s shutter speed:  Apertures The aperture is a diaphram the contracts or expands with the purpose of allowing more of less light to enter the camera. Just like the shutter speed, it controls the amount of light reaching the sensor/film. The way apertures are number can be confusing for the beginner, but soon becomes second nature. Here are the apertures, listed in full stops from the largest, to the smallest:
Here's a good image showing what the actual diaphragm blades look like at each given aperture:  The most important thing to remember is that the larger the number, the smaller the actual opening is/less light is entering the camera. So f/1 would be a very large aperture, and f/22 would be a very small one. Yes it's backwards, but that's the way it is. These are also reffered to as "Stops" . So here again you would say that for example f/2.8 is three stops faster that f/8, and likewise f/8 is three stops slower than f/2.8. When you buy a lens, you'll notice that it gives you an aperture value. For example you might buy a 70-300mm f/4.5-5.6. This means that at the short end (70mm) your maximum aperture is f/4.5 and at the long end (300mm) your maximum aperture will be redudes to f/5.6. The more expensive the zoom lens, the larger apertures you'll have available and you can have a constant maximum aperture. For example you could get a canon 70-200mm 2.8L. This lens ahs a max aperture of 2.8 at all focal lengths. You'll also see what are called prime lenses or fixed focal length lenses. While these cannot zoom, the advantage is that fewer mechanics and optics are needed to do this, thus allowing for larger apertures possible. This is where you'll see much faster lenses down in the f/1.0 to f/2 range. The advantage of these is thir ability to accept a large amount of light. Another important consideration of the aperture is the depth of field. As I've taught here before, the larger the aperture, the less depth of field possible and visa vera. While a lens at f/1.4 can capture a lot of light, it is also subject to a limited amount of depth. As you can see here, I was able to expose his face with just a small amount of light, but very little of the field is sharp because I shot it at f/1.4.  Just opposite, this was made with a pinhole at f/235. While it's not super sharp because it has no lens, you can see that the apparent sharpness is equal through out the entire field. Such a tiny aperture will give infinite depth of field. You don't need something as small as f/235, f/16 or 22 will usually do perfectly.  Putting it all together All three of these elements are taken into consideration when your camera takes a meter reading. Where you come into play is determining what element of the frame you want to meter for. Determine what element needs the best exposure and what elements you might be able to correct in post processing. Remember when all three of these elements are put together, the become an exposure. Remember that these can be changed around and still be equal. For example, say you've got the following exposure:
Hopefully this has been informative and not too long winded (you all know I have a tendency to give way more information than needed), but the more I give you the more option you have to take what you want and discard the rest. If there's any questions or anything I missed, don't hesitate to let me know. |
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| gretchensteele | Nov 19 2007, 07:37 PM Post #2 |
Admin
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THis was not long winded nor was it way too much info..you have missed your calling. You are an excellent teacher..I've been tryinng to explain all that to Bam and mine just comes out all deranged...but you have made it crystal clear... Thank you again for sharing your wealth of knowledge and sharing it well. |
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| kman627 | Nov 19 2007, 09:29 PM Post #3 |
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Film Junkie
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My pleasure! I do enjoy it and have given a lot of consideration as a profession. Thanks! |
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| bambam203 | Nov 20 2007, 11:04 AM Post #4 |
BAM
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Awww Kman your too nice........yes, that helped alot!!!!! I missed this post the first day you posted it........ I think I understood about 75% lol......:D  I have to wait and read this stuff late at night when the kiddos are in bed or else I would only understand about 15% lol...Thanks again! |
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| mhcityplanner | Nov 27 2007, 09:32 PM Post #5 |
Acceptance
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KMan ... very nicely presented, thanks for the info |
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| minnielee1 | Nov 28 2007, 12:47 AM Post #6 |
 
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wow!!! That's info. that i really need to learn. I read through it, and I think i need to print it out, so i can re-read it , play with my camera, and learn a little more about this topic instead of "just winging" and not paying attention to these details!!! Thank you for explaining this to us!!! |
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| bambam203 | Nov 28 2007, 02:07 AM Post #7 |
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BAM
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Oh that's a good idea print it out......duh.......lol seems like I know what I am doing for like 2 days and then forget again.........I def need to print..... Can't wait for the next lesson from mr. k........he's the man......lol |
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| genarae | Nov 28 2007, 03:11 AM Post #8 |
GenaRae
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I love this! Kyle always knows what he's talking about and if doesn't he finds the answer! If I wasn't married and he wasn't I'd track him down! 
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