Shutter Speed Range
The type of situation you are shooting in is going to help determine the photographic shutter speed that you decide upon. The shutter speed, along with the ISO and aperture, is one of the settings that is going to determine the overall light and character of your photographic image. The shutter speed is a recognition of how long the shutter stays open, and the fast the shutter speed indicates the quicker the shutter opens and closes to grab that image. There is a middle ground for what is an appropriate shutter speed so that you do not leave yourself open to the blur of slow shutter speeds or the dark images of high ones, and with this you can remain fairly versatile. The 1/1000 shutter speed is above that medium point and much more in the direction of other fast shutter speeds, but does not cross into one of the more extreme settings.
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When to Use the 1/1000
The 1/1000 shutter speed is in the higher end of available shutter speeds, and therefore its primary purpose is going to be to photograph objects that are moving relatively quickly. This could be things like fast cars and birds, but it is really going to depend on your specific situation and you will want to test out the shutter speed before you begin. If you are also shooting photos in a location with a large amount of natural light outside of your control then the 1/1000 shutter speed is a way of countering that since it darkens an image dramatically. This will allow you to avoid changing the aperture settings that may affect the depth of field, and especially the ISO settings that could change the amount of grain in your image. You will have to note that the 1/1000 shutter speed will allow for no motion blur in the image and all objects will look perfectly still, so you have to know that this is what you want out of your image ahead of time.
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The primary focus of the 1/1000 shutter speed is going to be fast moving objects outdoors in high intensity daylight, and you really do not have much use of this setting outside of this. If you do intend on going with the 1/1000 shutter speed then you will have to note that you are going to want to open the iris wide and shorten the depth of field. You will also want to try to redirect the amount of light hitting the primary subjects if possible, which may mean high intensity reflectors. Simple white cards are not going to be sufficient in this case and you will need foil based reflectors at the very least, though bringing in outdoor lights may really be the solution. It is going to be almost impossible to use the 1/1000 shutter speed in a nigh time situation even if there is artificial light.