["Followup-To:" header set to rec.photo.digital.slr-systems.]
2Bdecided wrote:
On 18 Jan, 16:45, Paul Furman wrote:

Do you really need zoom for family photos though?

It seemed very useful, but I don't know. The idea of changing lenses
worries me - I'd break something.

Unless you are in the habit of dropping your Ixus, you won't.
It's _build_ to be used.

The reason I ask is a
fixed length fast 'prime' lens is really ideal for kids & indoor family
shooting: you can shoot without any flash at all and capture the
ambiance much better and you can get a faster shutter speed for
herky-jerky little kids.

This is something I'm interested in. Let's say a given amount of light
(indoors, night, normal-ish lighting) meant the zoom lens needed ISO
1600 and 1/100th. I have no idea what aperture.

The zoom lens would probably have ca. f/4 (short end) or f/5.6
(towards long end) as fastest aperture.

The result would be
noisy, of course. What ISO could I come down to with a fast fixed
length lens, still at 1/100th, for a comparably bright picture, with
hopefully much less noise?

If the lens is f/2.0 or better (e.g. Canon 50mm f/1.8, ~ USD100
IIRC, optically sound but all plastics), ISO 400 or ISO 200.

If the lens is f1.4 or better (e.g. Canon 50mm f/1.4, Sigma
30mm f/1.4, ...), ISO 200 or ISO 100.

-Wolfgang