Tip & How-To about Canon PowerShot A520 Digital Camera

Explaining Camera Focus

Camera: Focus We've seen that a real image is formed by light moving through a convex lens. The nature of this real image varies depending on how the light travels through the lens. This light path depends on two major factors:

  • The angle of the light beam's entry into the lens
  • The structure of the lens
The angle of light entry changes when you move the object closer or farther away from the lens. You can see this in the diagram below. The light beams from the pencil point enter the lens at a sharper angle when the pencil is closer to the lens and a more obtuse angle when the pencil is farther away. But overall, the lens only bends the light beam to a certain total degree, no matter how it enters. Consequently, light beams that enter at a sharper angle will exit at a more obtuse angle, and vice versa. The total "bending angle" at any particular point on the lens remains constant.
As you can see, light beams from a closer point converge farther away from the lens than light beams from a point that's farther away. In other words, the real image of a closer object forms farther away from the lens than the real image from a more distant object. You can observe this phenomenon with a simple experiment. Light a candle in the dark, and hold a magnifying glass between it and the wall. You will see an upside down image of the candle on the wall. If the real image of the candle does not fall directly on the wall, it will appear somewhat blurry. The light beams from a particular point don't quite converge at this point. To focus the image, move the magnifying glass closer or farther away from the candle.
This is what you're doing when you turn the lens of a camera to focus it -- you're moving it closer or farther away from the film surface. As you move the lens, you can line up the focused real image of an object so it falls directly on the film surface. You now know that at any one point, a lens bends light beams to a certain total degree, no matter the light beam's angle of entry. This total "bending angle" is determined by the structure of the lens.




courtesy of HowStuffWorks.com

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1 Answer

my sony DSC H4 lens is stuck outside and it doesn go in .. the lens moves back and forth and is stuck ... the lens is also unable to focus.


Hi, Have you dropped your camera on the lens since I've seen that cause it before. If not then it's possible that the motor in the lens has gone. Either way it would be a costly repair which there's a 50/50 chance it would actually work again. Your best bet would be to get a new camera.

Jun 18, 2011 | Cameras

1 Answer

When I take a picture with my 18-55 on a d3100 I hear and see through my visor that the image moves and a sound like a click, many seconds after taking the picture. It seems like it's still open and closes way after. In some ocations when I'm checking the picture. My pictures seem moved when I zoom in to see the focus of the picture. is this normal?


Hi,

Giving the lens your using and depending on the shooting mode your in. I assume your shooting in a low light situation. The lens you have is not good for low light shooting because the F-stop is only 3.5 at widest, so minimal light gets in so the camera decides what speed to set it at to close the shutter. for example shooting in the school gym or church, the camera speed will be 1/20 second or even up to 1/2 second to get enough lighting into the sensor so the image is properly expose but for you to have a sharp image you will need to shoot on a tripod.

Without tripod and just handheld will create blurry images. I would suggest you bump up the ISO setting to minimum to 3200 or higher that way the camera speed will be higher and reduce handheld shakes that will create blurry images. But remember, increase ISO will increase in image grain.

That is why I suggest you invest into a 17-50mm F2.8 lens for low-lighting or 50mm f1.8 lens.

I hope this helps

Jet

Feb 23, 2011 | Nikon Nikkor 18-55mm f/3.5-5.6G ED AF-S DX...

1 Answer

how to mount Minolta AF 28-80/3.5-5.6 on pentax


Unfortunately, it is not possible to mount Minolta lenses on a Pentax K mount camera and retain either auto-focus, metering, or the ability to focus at infinity.
The reason for the loss of the ability to focus at infinity is because the distance from the mount to where the image forms on a Minolat lens is 43mm, whereas on a Pentax it is 46mm, so the Minolta lens glass would need to be 2mm into the body of the Pentax camera in order for the image to form on the sensor (i.e. have a clear image that is in focus).
The only solution to this is to purchase an adapter with an optical element such as this: http://photo-adapter-llc.amazonwebstore.com/Zykkor-Minolta-MD-Lens-to-Pentax/M/B004PB8142.htm?traffic_src=froogle&utm_medium=CSE&utm_source=froogle This will allow you to focus at infinity, however you will have to use stop down metering and manual focus, as the electrical contacts will not connect. Also, you can expect a slight loss of image quality when using an adapter.
I personally have a few Minolta lenses that I have wanted to use on my Pentax, so I understand your pain. It is a shame they don't work better.
Thank you for using FixYa!

Apr 18, 2010 | Pentax *ist DL Digital Camera

1 Answer

Camera Problem with Toshiba TLP 261


hi Document camera image is blurry: -The lens is dirty - Clean the lens with a blower or lens cleaner -The picture is out of focus - Focus the picture by turning the focus ring -The light is not on - Turn on the light check user manual for more details: http://www.fixya.com/BrowseManual.aspx?mnlid=5662&prdid=147420&__PAGED_=1 good luck

Mar 27, 2006 | Toshiba TLP 261 Multimedia Projector

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