This could only happen with a truly bad lens. Think about it. Imagine, just
for the sake of argument, that you bracket around f/8 by plus or minus one
stop. The light passing through the lens at f/11 produces one image. When
you open the lens to f/5.6, light passes through more lens, but it also
passes through the same glass as it did at f/11 and that portion of the lens
will focus at the same place as it did when set to f/11. The light passing
through the wider portion of the lens might focus a slightly larger or
smaller image, but then, it would be very unsharp.
On the other hand, I agree with the general rule of varying shutter speed
and not aperture. Why? Well, depth of field changes. This means that the out
of focus portions of the photo will look quite different.
Except where I can't lower shutter speed to get more light (hand holding,
action etc.), I prefer to set the aperture for the photo I want and vary the
shutter speed to control light. Most (maybe all?) cameras vary the shutter
speed when you modify exposure compensation.
Bottom line. The man is wrong. There is no change in image size. There is a
change in DOF and this could be critical, or even change the mood of an
image. It could be important even if you are just selecting one image,
especially with macro's and portraits or almost anything shot with a long
lens.
Regards,
Bob...
Democracy is two wolves and a lamb voting on what to have for lunch. Liberty
is a well-armed lamb contesting the vote!
From: "Shel Belinkoff" <[EMAIL PROTECTED]>
> Lewis Kemper, in an article in the current issue of Camera
> Arts magazine, states that when bracketing for critical use,
> such as registering different layers with different exposures
> in photo editing software, one should bracket by changing the
> shutter speed because if you varied the aperture the image
> sizes would vary slightly.
>
> Now this is the first time I've heard that changes in the
> aperture setting can change the size of an image. I suppose
> it's not important if you're only going to use one of the
> bracketed images, but I can see where it can be a problem in
> any sort of critical work, not only in photo editing software.
>
> So, how much change in image size can one expect bracketing
> in �-stop increments? How much might the image size change
> when going from wide open - say f/2.0 to f/8.0? Is the
> distance from the subject a factor, and, if so, how much of a
> factor? Is the change in image size effected by the focal
> length of the lens, and is it greater in longer or wider
> lenses? Has anyone here experienced this?
This message is from the Pentax-Discuss Mail List. To unsubscribe, visit
http://www.pdml.net and follow the directions.
Don't forget to visit the PUG at http://pug.komkon.org
