What makes a lens a macro lens?

[paulhillion]

I've always admired macro shots and so I've taken the plunge and ordered myself the Canon 100mm f2.8 Macro, should get it tomorrow:-)

My questions is this...what differences are there say between the EF-100mm f2 and the EF-100mm f2.8 Macro, what makes a lens a macro lens? And without wanting to sound a complete idiot - can I use the 100mm macro as a normal everyday type lens if need be, say for example out on the streets for candids etc?

Thanks.

[Scottes]

A true macro can achieve a magnification of 1:1. That is, an object is the same size on the sense as it actually is. That is, an 18mm long bug will take up 18mm of the sensor or film frame. It generally does this by being able to focus quite closely.

In the case of the Canon 100mm Macro it can do 1:1 and has a minimum focus distance of 5.9".

The Canon 100mm f/2 can only do 1:7.3 (an 18mm bug take up about 2.5mm on the sensor). This is mainly because the 100mm f/2 can only focus as close as 36".

Since the Macro can get so close it can "magnify" the subject more.


Yes, the Macro can be used for anything. Macros generally have excellent optics and are sharp and high in contrast. They don't make the greatest general-purpose lenses because they are often quite slow to autofocus.

[tim]

The 100m Macro's my sharpest lens. Because it's USM it's also very fast to focus, compared with my other lenses, though if you go from focusing at 6 inches to focusing on infinity it takes a short while - still not long though. I occasionally use it as a walk-around lens too.

[robertwgross]

Somebody correct me if I am wrong on this. It is conjecture.

I always thought that a macro lens had the equivalent of an extension tube built into the back end of it. That allows closer focus distance, and perhaps finer focussing. The apparent 1:1 magnification, or whatever, kind of falls out of the closer distance.

---Bob Gross---

[Scottes]

Bob I couldn't possibly consider saying that you're wrong under any circumstances.
:-)


I have to admit that the conjecture makes sense. However, it is possible to get close-focusing capabilities by the layout of the elements (more conjecture) but I'd still that the extension idea has merit. Granted, an internal "extension tube" would be part of the element layout design...

Alas, to have a better idea one would have to find the nodal point (not the exit pupil) between two lenses of similar length, one macro and one not. I personally have no idea how to find the true nodal point of a lens without the aid of a diagram from the manufacturer.

[Chazs]

Looks like there's quite a lot of glass difference, too. Bob looks correct as well. By the photo, the "extension" tube looks like it pushes out the furthest lens group. The macro certainly looks like a beefier lens.

http://home.wavecable.com/~stevensc/photos/100mm.jpg

CHUCK

[kb244]

A macro lens is basically a lens that can focus very close to a subject, typically 1:1 or higher. The longer the focal length, the more working distance you have for lifesize subjects. Something like a 180mm Macro lens would be good for trying to get pictures of wildlife at nearly life-size representation focusing in as close as you can get. I have a Sigma 105mm Macro f/2.8

The problem between getting a definite macro lens and using extension tubes are usability and quality.

Extension tubes depends greately on the lens you are already using, some lens may be better than others, but with most lens an extension tube will not give you lifesize (1:1), maybe half at best. Also when you slap an extension tube onto the camera, the lens is only setup for close focusing, if you wish to get up and shoot something at normal distance you have to take the extension tube out. Also depending on the body and lens there may be autofocusing issues with extension tubes.

A dedicated macro lens are generally going to be sharper ( and not talking those zoom lens with "macro" mode on them ), better quality in general. Also a macro lens can be used for focusing on subjects very close but at the same time used on subjects of normal distances where no swaping of an extension tube is required. And with a macro lens you are pretty much garanteed the focus and distance where as the extension tube its guesswork depending on which lens you are using.

I dont find the macro lens to be real beefy except maybe compared to my Canon 50mm f/1.8.

But do note in the post just above mine, the focusing distance between the 100mm Macro and non-macro is nearly 3 times closer than that of the non.

[ScottE]

Some manufacturers make a macro lens by simply writing "Macro" on the box. The lens may focus a little closer than some others, but most of us would not consider it to be a true macro lens.

A true macro lens is specifically designed for extreme close up photos. Some older macro lenses would only go to 1:2, but most will go to 1:1 magnification ratios. This is usually accomplished by making the lens barrel so that it can be extended much longer than a non-macro lens. Some more modern lenses use internal lens groupings to assist with this.

The "plane of focus" of most lenses is actually a segement of a sphere that is equal distances from the camera. For longer distances this does not matter, but for extreme close-ups the curvature of the plane of focus can be so severe thay you cannot get both the centre and the edges of a flat subject in focus. A true macro lens is corrected so that the plane of focus is flat at short distances.

A true macro lens is also extremely sharp since any deficiency of the lens becomes readily visible when working at very close ranges.

At macro distances depth of field is very shallow so it it often necessary to use very small apertures. Macro lenses will often have a minimum aperture of f/32 or even f/45 while non macro lenses seldom have to go smaller than f/22.

[ron chappel]

To clarify what has been said about 1:1 macro so far-
It used to be traditional that a macro lens could show true life size (1:1 ratio) on the film/sensor but for the last 20 years or so lens manufacturers have been putting the word macro on anything :(
One thing that close focussing normal lenses can't do is give deeper depth of field.Proper macro lenses are made to maximise DOF for a given aperture.
I'm not sure how much-i just read this recently and haven't had time to look into it properly

As for how they extend the focus...

Some cheap brand macro lenses use simple added extension to achieve close focussing.An example of this is the samyang/pheonix 100mm f3.5 macro lens.

Good brand macro lenses use more complicated optical formulas where, besides using the obvious added extension of the focussing group, they also move other lensgroups around to achieve very good performance at all focal distances.They usually have many more elements than normal lenses are heavier and have slower maximum apertures.

But as tim said,they are VERY sharp :D :D and can be used at all normal distances.
Some say they are TOO sharp to be used as portrait lenses and they are partly right-it depends on ones preferences.I prefered using the macro for portraits.Yes you do see every blemish and wrinkle but when you get a good pic,it's a great one!;) :D


By the way-you've bought the right one in my opinion.
The canon 100 macro is one of the better lenses ever built !
I had the non usm version but sold it because i simply didn't use it enough on digital:cry: