Noob question: macro vs zoom...

[jedirunner]

So I was reading this article: Canon MP-E 65 in which the author is trying to point out how getting a 5:1 magnification is different than zooming in. How is moving this lens from 1:1 magnification to 5:1 magnification different than zooming in on a normal zoom lens. I'm talking mechanics here ... what is mechanically different in a zoom lens from this macro lens with varying magnification?

I just need the mechanics explained a bit so I can understand where they're different.

Thanks for catering to less-than-novices. ;-)

Kevin

 

[analog.universe]

A zoom lens allows you to change the focal length, which translates to a change in field of view. The more you zoom in, the narrower the area that appears in the frame. The magnification at a given focal length depends on how close you can get subject to the lens (known as minimum focal distance). A macro lens is designed so that you can get your subject very close to the front of the lens. When 5:1 magnification is stated, that's a ratio relative to the sensor size. A 35mm sensor, at 5:1, means an object 7mm wide will fill the frame. (35/5) That 65 mm lens is fixed focal length. Meaning, it doesn't zoom, so you can never change it's field of view, you can just get it really really close to your subject.

 

[jedirunner]

A zoom lens allows you to change the focal length, which translates to a change in field of view. The more you zoom in, the narrower the area that appears in the frame. The magnification at a given focal length depends on how close you can get subject to the lens (known as minimum focal distance). A macro lens is designed so that you can get your subject very close to the front of the lens. When 5:1 magnification is stated, that's a ratio relative to the sensor size. A 35mm sensor, at 5:1, means an object 7mm wide will fill the frame. (35/5) That 65 mm lens is fixed focal length. Meaning, it doesn't zoom, so you can never change it's field of view, you can just get it really really close to your subject.

Thank you ... that helps.

One further question... that lens can change from 1:1 up to 5:1 ... I understand that the 5:1 is magnification and not related to a zoom lens' zoom ratio. However, is the actual mechanical process of moving from 1:1 to 5:1 (moving the lens further from the focal plane) different than what a zoom lens does when you twist the barrel? i.e.: on a zoom lens, aren't you also just moving the lens further form the focal plane? Or is there a different mechanical process to zooming on a normal zoom lens?

Thanks again,

Kevin

 

[Overread]

Much of the MPE is just moving the elements further and further from the camera body, however it also does some limited focal length reduction (at 5:1 its focal length is somewhere around 40mm and this reduction in focal length is common on many modern macro lenses as they approach their closest focusing distance).

 

[enzodm]

Zoom changes focal length by changing the geometry of optics inside. This lens does what focusing does, i.e., moves the whole lens, which maintains the same focal length (EDIT: except for what specified by Overread in the meantime). The more far the lens, the more close the minimum focus point. From this point of view, you can always obtain the same effect on any lens, beyond what provided by the lens focusing itself, by adding extension rings or mounting the lens on a bellows. Although a specific macro lens has also great resolution.

 

[jedirunner]

Zoom changes focal length by changing the geometry of optics inside. This lens does what focusing does, i.e., moves the whole lens, which maintains the same focal length (EDIT: except for what specified by Overread in the meantime). The more far the lens, the more close the minimum focus point. From this point of view, you can always obtain the same effect on any lens, beyond what provided by the lens focusing itself, by adding extension rings or mounting the lens on a bellows. Although a specific macro lens has also great resolution.

Excellent. Thank you. That actually makes perfect sense now. I don't think I could draw a picture for someone else explaining all of what happens, but it makes enough sense in my head.

Kevin