What's different about a macro lens?

[clockworks]

I've just been playing with some close-up shots with my Pentax K100D.
I was taking pictures of a couple of watches getting the image as large as I could. using the kit lens (18-55) and a Sigma 18-200.

I could actually get closer with the kit lens, because it has a shorter minimum focus distance, although I still couldn't get the dial to completely fill the picture.

This got me thinking about proper macro lenses - do they magnify the image more than a "normal" lens, or just allow you to get closer (shorter focus distance)?
If they magnify more, is there a simple way to tell from the model/name of the lens what the extra magnification is?

Do the simple filter-type add-on magnifying lenses actually work?

 

[clockworks]

Ok, that watch picture has got a lot closer than I could - with my lens, I still had the whole case and part of the lugs in shot (effective height of the image about 50mm). That was fully zoomed with the 18-55, as close as could get with auto-focus working.

When a macro lens quotes a magnification factor of 1:1, what does that actually relate to? Does it mean that 25mm of real-life will fill the frame (assuming that the CCD is 25mm across), and how does the zoomed position of the lens, as well as the distance of the object from the lens, factor into this?

To look at it a simpler way, what's the magnification factor of a "nomal" 18-55 lens?

 

[clockworks]

The 18-55 maximum magnification is : wide - 0.10x; tele - 0.28x

A macro lens that produces a life size images means that using a camera with a 35mm sensor a grain of rice measuring 10mm across is projected onto the sensor at the same size (10mm). Your 18-55 can only manage 2.8mm

So a 55mm macro lens with 1:1 magnification will give roughly the same effective image as a 200mm standard zoom lens, but the shorter lens (and, hopefully, shorter minimum focus distance) will allow me to get a lot closer?

 

[clockworks]

i have an olympus c-740

not a camera of dslr quality by any way of thinking

but, it has macro mode and Super macro mode (no idea what tha actual specs are on sm mode)

I can actually focus so close with the s-macro mode, that the lens is almost touching the item. I did one of a penny (after seeing somebody take a pic of a penny on here with a real camera and macro lens) and it wasnt bad at all.

If you are taking pictures that need that close a macro, it may well be an option for a fraction of the price of a real macro lens (not to mention the price of a dslr body)

Similar thing with my old Nikon 5700 - minimum focus distance was about 1cm. The only problem was that getting that close blocks out most of the light.

I'm really just playing around with my new toy, seeing what it's limits are. The difference between DSLRs and compacts was what got me thinking about this. I can't see myself blowing £300+ on a macro lens in the near future, though. Maybe I'll try a set of screw-on magnifying lenses - pretty cheap on eBay.

The next thing I need to buy is a decent tripod.