Explain to me MACRO

What I mean is I see a 50/1.8 is 75$ or so but the Canon 50/2.5 Macro is 240$ +. What I like to know is what is the difference there? What makes a lens a macro.

The minimum focus distance is the main difference. The 50 CM can get close enough to the subject that it will appear at 1/2 life size on the sensor. Put another way, you can fill the entire frame of a picture with something about the size of a quarter.

The 50/1.8 is not a macro and cannot focus close enough to anything to make it appear at more than about 1/5 life size on the sensor. This would mean filling the frame with something perhaps the size of a softball.

The other differences are more subtle, the 50CM has a very flat plane of focus so that it can be used to take pictures of documents (reproduction work) though flat scanners have made that a little needed use.

JeffreyG wrote in post #4561673
The minimum focus distance is the main difference. The 50 CM can get close enough to the subject that it will appear at 1/2 life size on the sensor. Put another way, you can fill the entire frame of a picture with something about the size of a quarter.

The 50/1.8 is not a macro and cannot focus close enough to anything to make it appear at more than about 1/5 life size on the sensor. This would mean filling the frame with something perhaps the size of a softball.

The other differences are more subtle, the 50CM has a very flat plane of focus so that it can be used to take pictures of documents (reproduction work) though flat scanners have made that a little needed use.

Good description...though I'd add that the term MACRO strictly applies to lenses whose image is LIFESIZE and this "macro" is only .5 LS...but for general closups it'll do...
Also...the "CM" has a metal mount like the 50/1.8 MKI and like that oldie, it has the old buzzy AF motor...the MKII has a plastic mount BUT the more modern, quiet motor, which some people claim is not as good as the older one...just quieter....When I got the CM I sold my MKI as I have the 35/2 (again with the buzzer) and that covers my need for low light shooting, and the CM is a VERY nice portrait lens and landscape lens (yes a bit longish, but great for longer landscape shots)...

The classic definition of Macro is an area where the image size is from 1/4 to 2x life size. In others words, the subject (that fills the frame) is from 4" x 6" down to 1/2" x 3/4". Smaller is another area of photography. Larger most lenses/cameras already do.

kitacanon wrote in post #4562333
Good description...though I'd add that the term MACRO strictly applies to lenses whose image is LIFESIZE and this "macro" is only .5 LS...but for general closups it'll do...
Also...the "CM" has a metal mount like the 50/1.8 MKI and like that oldie, it has the old buzzy AF motor...the MKII has a plastic mount BUT the more modern, quiet motor, which some people claim is not as good as the older one...just quieter....When I got the CM I sold my MKI as I have the 35/2 (again with the buzzer) and that covers my need for low light shooting, and the CM is a VERY nice portrait lens and landscape lens (yes a bit longish, but great for longer landscape shots)...

It's worth adding that the Life Size Converter was marketed to turn the 50CM into a true macro lens. The LSC also works with many other lenses (not to 1:1 though). It's basically an extension tube and T/C rolled into one.

Bob

Yes...should have mentioned the converter/tubes....