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me@ invalid - 21 Dec 2004 16:40 GMT

Why do some these cameras only stop down to f-8?

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Gisle Hannemyr - 21 Dec 2004 17:12 GMT

> Why do some these cameras only stop down to f-8?

Refraction limits how much the lens can be stopped down before image
quality deteriorates. If a camera has a very small sensor, this
limit can be at f/8.

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- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
========================================================================
When you say you live in the real world, which one are you referring to?

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David J Taylor - 21 Dec 2004 17:33 GMT

>> Why do some these cameras only stop down to f-8?
>
> Refraction limits how much the lens can be stopped down before image
> quality deteriorates. If a camera has a very small sensor, this
> limit can be at f/8.

Diffraction.

David

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Gisle Hannemyr - 22 Dec 2004 04:55 GMT

>> Refraction limits how much the lens can be stopped down before
>> image quality deteriorates.

> Diffraction.

Of course. Thanks.

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AustinMN - 22 Dec 2004 06:35 GMT

> Why do some these cameras only stop down to f-8?

Diffraction "limiting: is a function of the absolute size of the aperture.
With a short lens, diffraction may begin to deteriorate the image by f/8.
I'd rather have the option to go into the diffraction limited region myself,
but the manufacturers seem to think they are smarter than us.

Austin

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Bart van der Wolf - 22 Dec 2004 16:21 GMT

>> Why do some these cameras only stop down to f-8?
>
[quoted text clipped - 3 lines]
> diffraction limited region myself, but the manufacturers seem to
> think they are smarter than us.

There is little to be gained beyond f/8.0 on these point and shoot
cameras. My G3 starts losing resolution beyond f/5.6, and it already
has more depth of field than I sometimes care for. Wider than f/3.5
will increase the chance of CA manifesting itself, so I usually shoot
on Aperture Value preselection for best quality.

Bart

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AustinMN - 22 Dec 2004 16:47 GMT

>>> Why do some these cameras only stop down to f-8?
>>
[quoted text clipped - 9 lines]
> increase the chance of CA manifesting itself, so I usually shoot on
> Aperture Value preselection for best quality.

How about exposure times? I shoot subjects that frequently call for 1
second or more exposure time. Being able to stop down one or two stops will
help me gain that. Admittedly, it's at the expense of image sharpness, but
why not let me decide which is important to me?

Austin

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Bart van der Wolf - 22 Dec 2004 19:08 GMT

SNIP

> How about exposure times? I shoot subjects that frequently call for
> 1 second or more exposure time. Being able to stop down one or two
> stops will help me gain that.

By closing down the aperture you change more than just the amount of
light that is used for the exposure time chosen. You might want
shallow DoF and long exposure time. You can use a Neutral Density
filter and still have maximum lens performance, assuming you are
already at the lowest ISO setting.

Bart

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Paul H. - 07 Mar 2005 17:03 GMT

> > Why do some these cameras only stop down to f-8?
>
> Diffraction "limiting: is a function of the absolute size of the aperture.
> With a short lens, diffraction may begin to deteriorate the image by f/8.
> I'd rather have the option to go into the diffraction limited region myself,
> but the manufacturers seem to think they are smarter than us.

I think it's fear of failure rather than contempt for people's intelligence:
one incompetent reviewer's opinion about "distorted" images, however unfair,
could result in low sales volume for a perfectly fine camera. Quibbling
over trivialities has been raised to an artform these days.

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