Dumb lens question

[jukas]

I'm shopping for a macro lens and naturally I've been trying to justify the Canon 180 L to myself. I was looking at the specs on B&H when I noticed a magnification spec. On the Canon 180 macro it's listed as 1:1 and on my 70 - 200 2.8IS it's listed as 1:5.8 .

I hate to admit this but I'm not entirely clear on what that means. Does that mean my 70 - 200 lens is showing me the image 1/5th it's true size?

[Ronald S. Jr.]

well the 70-200 is no macro lens, that's for sure. When you compare a min. working distance of a few inches vs. a few feet, naturally they're gonna have a far different magnification.

[jukas]

well the 70-200 is no macro lens, that's for sure. When you compare a min. working distance of a few inches vs. a few feet, naturally they're gonna have a far different magnification.

Yeah I know the 70 - 200 isn't a macro lens. I guess what I'm not getting is how the 1:1 or 1:5.8 translates into real world results. I understand that 1:1 and 1:5.8 are different numbers but for some reason I'm having a hard time grasping what that actually *means*.

I'm sure it's an "Oh Duh" answer.

[Curtis N]

On the Canon 180 macro it's listed as 1:1 and on my 70 - 200 2.8IS it's listed as 1:5.8. I hate to admit this but I'm not entirely clear on what that means. Does that mean my 70 - 200 lens is showing me the image 1/5th it's true size?Actually closer to 1/6, but yes.

It's the ratio of the actual size of an object vs. the size projected onto the film/sensor, at its closest focusing distance. For example the sensor of a 1.6x crop camera is 15 x 22.5mm. So if you shoot a ruler at the closest focusing distance with a 1:1 macro lens, you'll see 22.5mm of the ruler on the image.

If you shoot a ruler with your 70-200 at the closest focusing distance, you'll see 130.5mm of the ruler on the image (22.5 x 5.8 ).

[Ronald S. Jr.]

The way I understand it...at maximum magnification, at minimum focusing distance, with 1:1 magnification, a subject that is 1cm long, for example, will appear 1 cm long. Someone wanna correct me?

[Ronald S. Jr.]

oh SURE! He beat me to it. AND gave a better example. PSH. :p

[Scottes]

1:5.8 means that the subject would be about 1/6th actual size on the sensor.

Your 20D's sensor is 15mm by 22.5mm. So if you used the 180mm Macro as it's closest focusing distance and shot something that was exactly 22.5mm long then that thing would completely fill the viewfinder on the long edge, perfectly. That's 1:1.

If you used the 70-200 at it's closest focusing distance and shot that same subject it would be only about 1/6th the size of the resulting picture.

[jukas]

Thanks Curtis, Ron and Scottes. That's exactly what I wanted to know

[jjonsalt]

1:1= 1 inch, cm, whatever, on film or sensor equals 1 inch, cs, whatever in real life. 1:5.8= 1 inch, cm, whatever, on film or sensor equals 5.8 inches, cm, whatever in real life.