security Camera - choosing The Best Lens (Focal Length)

This report assumes that you are choosing to buy a protection camera with a Fixed focal distance lens as opposed to a variable focal distance lens. variable focal distance cameras are becoming more commonly available. However, be aware that on midpoint cameras with a variable focal distance lens cost significantly more than those with fixed lenses. It costs more to build a good quality variable focal distance lens and it's also a challenge to weatherproof a varifocal camera for use outdoors due to the fact that the lens needs to turn to adjust the focal length. The large commercial watch cameras that have a zoom lens are usually housed in a weatherproof housing for outdoor use. This surely isn't a practical protection camera for the homeowner or small company owner though, due to its appearance and cost.

[b]Lens[/b]

Fixed lenses are commonly seen in the small, surely concealed weatherproof 'bullet' cameras that are sealed, and fairly inexpensive. Therefore, the fixed lens is still a mainstay of video watch systems for the normal consumer. choosing the best focal distance for your singular situation is important. You need to ask yourself these key questions: Is the camera just going to be used for a wide coverage (say to cover the parking lot at my company or my front yard) to monitor normal activity with slight detail? Is the camera going to be used to cover a exact narrow target area (say an entry way or doorway) where I want to recognize the face of the subject, and therefore need greater magnification?

Here are some steps that may be beneficial in determining the best focal distance protection camera:

Step 1: First, conclude the target distance - that is how far away your subject is likely to be. The idea here is to ascertain the target distance based on the situation. It's not an exact assessment, but choose a target distance that is representative of the area you want to cover. For example, if you want the protection camera to keep watch over your car parked in the driveway, choose a spot to mount the camera and then portion the distance from the camera to the far end of the car furthest from the camera. That way you're able to cover the car and the surrounding area that a perpetrator might have to cross in order to entrance your car. The idea is to choose an midpoint distance away from the camera that the perpetrator is likely to be.

Step 2: Next, conclude the width of the target area - that is the width of the area that you want the camera to cover. You want to choose a coverage area that is wide sufficient to capture the action, but not so wide that the magnification is diluted. Remember there is a trade off between coverage area and magnification, in that if you increase one you'll decrease the other (all other things being equal).

Step 3: conclude the Ccd chip format size of your camera. If you don't know this, then ask the vendor that you purchased it from. Good still, find out the Ccd format size Before you buy it. The Ccd sensor acts like the 'eye' of the camera. The lens of the camera focuses incoming light onto the Ccd chip which then converts it to a video signal using some very fancy circuitry. The focal distance is the distance from the lens to the covering of the Ccd sensor.

Step 4: Go to an online lens calculator (see website at bottom of this article).

Step 5: Enter the Ccd format size (Be Sure To choose The correct Ccd Size!), target distance and target area and click the 'Calculate' button to get the focal length.

Step 6: You'll consideration that it's probably some odd amount that does not match the acceptable focal lengths that are ready in the protection camera market. That's ok. The idea is to choose the focal distance that is closest to the one that you calculated. Some common acceptable focal lengths for protection cameras are 3.6 mm (wide angle), 6 mm, and 16 mm. If the focal distance that you calculated is is in between a acceptable size then you need to choose the one that you think is best for your singular application.

Here's where you need to make a decision as to either you want more magnification or greater coverage area. If you want more magnification then you would choose the longer focal length, if you want a wider coverage area then choose the smaller focal length.

For example, let's say that you have a 1/3 inch Ccd camera and your target distance is 25 ft. And your desired target width is 15 ft. Go to the lens calculator, enter the information, click 'calculate' and the reply is 8 mm. Possibly the type of watch camera that you want to buy doesn't come with an 8 mm lens as an option. You could use a 6 mm lens and it would most likely be fine since the 6 mm lens will surely cover a slightly wider area than the 8 mm. While the 6 mm lens does cover a wider area, you won't get quite as much magnification with it as you would with the 8 mm lens. Remember, there is a trade-off between magnification of information and coverage area!

If you want a Good opportunity of identifying your subject at a distance you might want to go with the stronger focal distance of say 16 mm to give you Good detail. Keep in mind though, the field of view will be narrower which entails a smaller coverage area. For a 1/3 inch Ccd, with the target distance at 25 ft., using a 16 mm lens gives you are coverage width of only 7.5 ft. This lens may help you get a subject's face in detail, but you may just miss him if he doesn't walk straight through the narrow target area! (This high magnification focal distance might be good for a doorway or entry that is a narrow target area is or if your target is at a greater distance).

What about the 'height' of the coverage area? For most watch cameras, the height of the coverage area is about 3/4 of the width (4 by 3 aspect ratio). So just multiply the width by 0.75 to gain the height of coverage area.

security Camera - choosing The Best Lens (Focal Length)

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Does Lens Focal length sway Depth Of Field?

For some time now I have been reading reports about this and trying to outline out how it should sway my digital photography.

[b]Lens[/b]

The basic interrogate is: Does a wide angle lens (smaller focal length) furnish more depth of field than a telephoto (longer focal length) lens?

This has been taught to us in the textbooks and the photo magazines for a long time and it appears that you get more depth of field with a wide angle lens than you do with a telephoto lens.

If you crusade the Internet for "depth of field", you will not look long until you come over many articles that say that using a wide angle lens does not increase depth of field.

Tests have been conducted by many, together with some of the photography magazines, that prove that depth of field is not dependent on the focal length of the lens being used.

This is a very technical issue and technically it is true. You can even conduct similar tests or experiments to verify it for yourself. However, from a practical standpoint what does this mean to me, the photographer?

All of the data that I have seen so far is based on the hypothesis that you keep the image size the same.

The test goes something like this: using a zoom lens, take a photograph of some subject using a telephoto or long focal length setting. Then zoon out to a wide angle or shorter focal length setting. You could also do this with interchangeable fixed focal length lenses, one telephoto lens and one wide angle lens.

Now, advance some section of the photograph taken with the wide angle setting so that the image in that section is the same size as the image in the selfsame section of the photograph taken with the telephoto setting.

Upon examining the resulting photographs, you will find the depth of field is approximately the same in each of the photographs. There is basically no difference. So, you have proven that technically zooming out to a wide angle focal length did not increase your depth of field.

But, let me ask you a question. Why do you zoom out or switch to a wide angle fixed focal length lens in the first place?

Suppose that you are standing out before some great mountain scene that is beautifully lit with sunrise colors. You zoom in to a telephoto setting and take a picture. Then you zoom out and take a photograph using a small focal length setting.

You want and expect to see more depth of field in the second photograph - all the way from the flower in the foreground to the sunlit mountain peeks. And that's what you appear to get.

Will it cross your mind that if you blow up a section of the second photograph that you will lose all that apparent depth of field? No, the greater depth of field still appears to be in the photograph taken with the wide angle focal length setting.

You zoomed out so that you could get a wider view and a larger depth of field or at least the perception of more depth of field. You also knew that the images would appear smaller.

Same for zooming in, you wanted to make the image appear larger and you also knew that there would be a perception of less depth of field.

From a practical point of view when you change focal lengths seldom if ever, will you zoom in or out with the idea in mind of keeping objects the same size.

Using different focal lengths, zooming in or out, gives the perception that depth of field changes. What you get with the wide angle lens appears to have more depth of field than what you get with the telephoto lens.

Technically this may not be the case.

But, what is all of your photography about? The main riposte is: what appears right to you. So, I say unless you are a stickler for technical correctness stick with the old time proven rule.

· If you want more depth of field, or you want it to appear that way, use a shorter focal length lens or zoom out.

· If you want less depth of field and a larger image of some part of the scene, zoom in to a longer focal length setting.

This will still give me the photographic results that I want. I have taken a gorgeous photograph of a mountain scene and my zone of sharpness appears great.

To me this technical revelation does not change the way I take my photographs. What about you?

After all, this is your art that you are creating. Don't let the pure technical explanation get in the way of you creating what you want to create.

Continue to pretend that a wide angle lens gives you greater depth of field than a telephoto lens. Your results will show it.

Does Lens Focal length sway Depth Of Field?

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