What's different about a macro lens?

clockworks · 2 Jan 2007 at 01:21

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?

Snapshot · 2 Jan 2007 at 07:01

clockworks said:
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)?

For a given focal length this is the same thing. Macro lenses come in a variety of focal lengths which give the option of different minimum working distances. The longer the focal length the greater the minimum working distance for a given magnification.

If they magnify more, is there a simple way to tell from the model/name of the lens what the extra magnification is?

The spec should say what the reproduction ratio is i.e. 1:1 is life-size, 1:2 is half life-size, etc.

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

Yes, they do because they reduce the working distance (in simple terms). They may not give good quality and the best ones aren't simple, single lenses.

SDK^ · 2 Jan 2007 at 08:43

Here is an example of a watch face taken using a Canon 100mm Macro lens, the magnification is lifesize 1:1. As you can see, the face easily fills the frame

clockworks · 2 Jan 2007 at 15:06

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?

SDK^ · 2 Jan 2007 at 15:30

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

clockworks · 2 Jan 2007 at 16:12

SDK^ said:
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?

SDK^ · 2 Jan 2007 at 16:31

clockworks said:
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?

Ideally you want a longer minimum life size focus distance - the further you are from your subject (Insects) the less chance you've got of scaring them away

The Canon 100mm Macro lens has a minimum distance of 32cm and sits in the middle of the Canons Macro lens range. The 60mm EF-S Macro lens has a shorter min focus distance (20cm) and the 180mm L Macro lens a longer one (48cm).

The Canon 70-200mm f/2.8L IS (standard zoom) has a max magnification of 0.17x with a min focus distance of 1.3 metres.

Bolerus · 2 Jan 2007 at 16:38

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)

clockworks · 2 Jan 2007 at 16:55

Bolerus said:
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.

Joe T · 2 Jan 2007 at 17:25

P&S cameras these days have pretty fantastic macro capabilities relatively speaking.

SDK^ · 2 Jan 2007 at 17:52

Point & Shoots with their small sensors have the advantage of greater depth of field which is one of the hurdles when using a DSLR. The downsizes are they are not true life size, the focus distance is unusable and image quality isn't on par with DSLR's.

Raymond Lin · 2 Jan 2007 at 17:58

some are ok

SDK^ · 2 Jan 2007 at 18:50

Depends what you're comparing it to

Geffen · 3 Jan 2007 at 09:53

Have you considered buying some extenstion tubes. These would allow your lenses to focus closure to an object. There not as good as a proper macro lense but should give you a better image then a magnifying lense.