Need explanation on "Extended Zoom" in Lumix FZ18

observed
I owned the camera over a year now, but have just learned to use it
recently (after reading the instruction manual)
I have some questions which I hope someone can provide answers in
"layman terms".
What is exactly the extended zoom feature in Lumix FZ18? Is this
still considered as "optical" zoom. I assume that this is not "digital
zoom" (because FZ18 still have 4x digital zoom on top of the 18x
optical.
It appears that this option has something to do with reducing the
resolution for the sake of getting more optical zoom feature. Could
someone explain in simple terms? How this affect the picture quality,
in particular if I usually only print photos to max 5"x7" sizes. Most
of the time it will be postcard size of 3.5"x5".
The manual said that the FZ 18 has a 18x optical zoom feature
(equivalent to 18mm to 504 mm). This is however based on picture size
equivalent to 8 MP (for 4:3 ratio). However, if I select the
resolution to only 5MP, I can zoom in to 23x. If I choose resolution
3MP, I can zoom into 28.7x.
8 MP is equivalent to 3264x2448 pixels, 5 MP is 2560x1920 pixels, and
3MP is 2048x1536 pixels (for aspect ratio 4:3).
What do you need to print 5"x7" size photo, 8"x10" and 11"x17"? Is
3MP good enough for 8"x10" photo? 5"x7"? I know that my computer is
only set to 1024x768 resolution.
If this is the case, I can just set my camera to 3MP and enjoy a 28.7x
zoom ( from 28 mm to 804mm)! I am still assuming this is NOT digital
zoom.
Could someone comment on this? Thanks

Is feature of "extended zoom" in Lumix is common for other long zoom
P&S cameras (such as Olympus SP570UZ, Fuji S8100fd, or Sony DSC H50)?
I do not recall that My Canon G7 has this feature (but I may be wrong,
as I also still have not looked in details into their instruction
manual).

I have an FZ50 which has a similar 'extended zoom'. I assume the FZ18 is
similar.

I have spent a significant amount of time experimenting with the
differences between 'extended zoom' and 'digital zoom' settings and
comparing notes with others on the dpreview panasonic group.

Firstly there is NO improvement in quality between either 'extra xoom'
method and cropping from the centre of the highest resolution image.

AIUI, the 'extended zoom' merely crops the centre of the higher
resolution image to a smaller resolution (which is why you can't use it
and retain the highest resolution).

The 'digital zoom', however, takes the centre cropped image and
interpolates pixels to 'fill it out' to the given resolution as defined.

I find extended zoom useful in nature photography (eg. birds in flight,
see: http://www.flickr.com/photos/watchman/2493800145/) where the
exposure is - I think - based upon what the camera sees, rather than the
whole area, and, of course, the EZ images take up less space on the
memory card.

Other than that, I can find no particular advantage in using it. Because
of the 'added processing' of 'digital zoom', I never use it!

I would suggest that in general the only advantage of either 'zoom'
facility is for those who have their images printed commercially and do
not wish to do any post processing of their own.

HIH

Mike

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--
Michael J Davis

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