What makes a Macro Lens a Macro Lens?

[sactown024]

I'm not really into macro but I know one day I will want to explore it. I was looking at lens last night and I notcied the Canon 100mm prime is considered a macro lens. What makes it a macro lens and is it still good for prime portriat lens?

 

[Dao]

I think ....

- Able to capture image at 1:1 life size
- Flat field.

There are people use macro lens (except the Canon MP-e 65) as portrait lens, the only draw back I can think of is the focus speed.

 

[Derrel]

Some macro lenses only go down to 1:2 or half life-size, and then have a dedicated extension tube that allows them to go to 1:1...but that is more of a design choice the designers and the manufacturer arrive at...

And yeah...a good FLAT field and minimal distortion are really important qualities as well.

As to the question of whether a prime lens macro design is also ,"still good for prime portrait lens?"...that answer is not so clear. In many cases, my answer is "No, it's not "good" as a portrait lens, but in a pinch, is can be used as one, often with some "issues". The issues are sometimes that the macro lens is difficult to achieve accurate focus with at portrait ranges and also that the lens might actually be sharper than desired. at distances of like 6,7,8,9,10,12,15 feet, MANY macro lenses have exceptionally hair-trigger focusing ring movement, and therefore even the SLIGHTEST mis-aiming of the AF bracket, or the slightest error or tolerance in the AF system will mean that the picture is simply NOT focused "right".

Macro lenses are optimized to focus best at very CLOSE distances; beyond about 1 meter, many of them have focus ring travels that move from that 1 meter range and out to Infinity is just a scant few degrees of focusing ring travel...so getting PERFECT focus is much more of a crapshoot when the real world factors are brought in. SPEED of focusing is also sometimes a problem with macro lenses, when the subject is active or moving.