Images deleted as requested.

The aperture in a zoom does actually change inasmuch as the f value changes and the DOF changes. The actual physical dimension of the hole does not change of course, but that isn't what the "aperture" value is. The aperture is a ratio.

In photography we never refer to the actual physical dimension of the opening in the diaphragm, we always relate it to the focal length as the f value.

No, the aperture is fixed. However, because of the zooming the aperture of the Pentax 400-600mm does change.

In February there will be more new processors and video cards on the horizon, none of which are necessary for running Photoshop...

PMs stay in the Outbox until they are read by the recipient, after which they move to Sent Items.

SD cards are no good as a backup as the information on them is not permanent.

It depends on how well the zoom maintains focus over the range, so I would expect an average is about the best that can be achieved. Zoom lenses are fairly modest apertures, so hopefully Depth of Focus (at the sensor) will be enough to cover any residual error.

The manual says nothing about protecting the lens with a filter of any kind. It only says that if you use a polariser you should use the circular type rather than the linear type.

A polariser will lose 2 stops of light so is not useful for general use. Only use one when needed.

Generally, the use of filters to protect lenses is going out of favour. Why ruin the optical formula of a lens by adding unecessary glass in front of it? There have also been instances of filters breaking and scratching the front element.

To protect the lens, always use the lenshood and it is highly unlikely than anything amiss will happen to the front element. I would only use a protective filter possibly in areas of salt spray and a polariser when reflections need supressing.

I suspect you may have your metering set to spot mode, which will produce the effect you describe if the photographer is not aware of how it works.

Try centre weighted or matrix metering if this is the case.

Thanks Don, only sorry you didn't get a better response. Still, some interesting shots nonetheless.