Non USM lenses

[Rufus]

I see that these non-usm lenses are significantly cheaper than usm's. I realise that the usm provides quiet focusing, but I'm not sure why there is such a price difference.

What are the disadvantages of NON OSM lenses please?

Regards,

R.

UK

[chris maddock]

1) Noisy focussing, as you know.
2) Slower focussing.
3) No full-time Manual focus (i.e you can manually overide the AF without turning it off) There may be some USM lenses without this though, I think.
4) Many of them have rotating front elements - a pain if you want to use polarising filters.

Do also bear in mind that the presence or absence of USM focussing is often not the only reason for the price difference. The cheaper lenses are built "to a price" and often don't have such good optics or build quality.
One exception, however, to the former that I know of (and have one myself) is the Canon 50mm/f1.8. Optically it is a stunner for the price, however the physical design, focussing and general build are rather lacking.

KRs
Chris

[gregarpp]

There are other lenses in the same classification as the early 50mm/1.8 mk1

24mm/2.8
28mm/2.8
35mm/2.0

These are all great lenses, there is no reason not to purchase them.

[chris maddock]

gregarpp wrote:
There are other lenses in the same classification as the early 50mm/1.8 mk1




Sorry, I was referring to the 50/f1.8 Mk2.
As I understand it, the Mk1 is far superior in design/build quality, although the optics of the two versions are pretty much on a par.

KRs
Chris