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raw_toe Feb 9, 2005 11:06 AM

Ok, help me here. I have a Canon A95. One of my friends says that even though you can select an aperture, there is no PHYSICAL aperture that stops down prior to taking the pic. He says that it takes pics at a wide open aperture then the image processor adjusts the image to fit the selected aperture. Is this true?

Meryl Arbing Feb 9, 2005 11:30 AM

There are some effects related to physical aperture that are purely optical and cannot be replicated in post processing. For example, Depth of field is related to three variables: aperture, focal length and distance to the subject. If there was no physical aperture then the camera would have to have some algorithm to recognise and separate the foreground, subject and background and apply different degrees ofsharpness (blurr, focus)to simulate DoF. It is much easier to do it optically!

Also, if there was no physcial aperture then there would be no diffraction effects when the aperture becomes very small (less than 1mm across in the case of the Sony V3 at f8 and wide angle) but the effects are there.

And, if there was no aperture to control light, then there would be many situations where highlights would be irretreivably lost due to overexposure and shadow detail lost due to underexposure. Once optical detail is lost, no post processing will recover it since the data has already been recorded and you can't go back and pick-up more detail.

BillDrew Feb 9, 2005 3:53 PM

Not having a physically variable aperature might be true for digicams that cost less than $50 at full retail (Barbie Cam), but it is not true otherwise.

steve Feb 9, 2005 4:12 PM

Some digicams have a two-step aperture diaphram rather than a real multi-blade diaphram. It is simply two different size holes on a rotating plate that is mounted behind the lens. It offers a maximum aperture for indoor or dim lighting and a minimum aperture for use outdoors in the bright sunlight.

The more expensive digital cameras employ a real aperture diaphram as is found in most 35mm SLR lenses and offers a range of variablef/stops and more realistic depth of field due to the way thediaphrambladescombine toform anon-round aperture opening. It's all optical physics and rocket science to most ;)

Meryl Arbing Feb 9, 2005 4:56 PM

I had an old box camera that did slid a little piece of tin with two holes in it across the lens opening and that was your aperture...looks like we have come full cricle!

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