Lens Specs - Enlargement Ratio

[FiestaRed]

Looking at lens specs a figure that baffles me is the Enlargement Ratio.

I've been looking at 300mm telephoto prime lenses, the Nikon specs quote 1:6.3 where the equivalent Sigma quotes 1:7.5.

Can anyone please explain in reasonably simple terms what the figures are and why the differences?

 

[Canon Bob]

The figures are a representation of image magnification at the closest focussing distance.
1:6.3 = 1/6.3 or 0.16x magnification
1:7.5 = 1/7.5 or 0.13x magnification

The implication is that the Nikon has a smaller minimum focus distance.

Bob

 

[FiestaRed]

Thanks for the help Bob.

Excuse the ignorance but how do you arrive at the 0.16x and 0.13x magnification figures?

 

[Lynton]

1 divided by 6.3 or 1 divided by 7.5

or reciprocals.......


what i don't get though is a magnification of 0.16 is pretty much a sixth of what is there????????????

 

[Canon Bob]

what i don't get though is a magnification of 0.16 is pretty much a sixth of what is there????????????

Don't forget that we're talking about the magnification at the closest focussing distance. Macro lenses achieve their high magnification by having the abilty to focus on a subject typically only 100mm or so from the front element.

Bob

 

[FiestaRed]

Many thanks for all the help.

 

[Blue Eagle]

Sorry to butt in but does this go back to 1:1 means the image of a 10mm object occupies 10mm on the sensor? and therefore these lenses give a 1.6mm image, of a 10mm object?

 

[Canon Bob]

1:1 is a simple ratio....10mm of subject covers 10mm of sensor. The only difference with the sensor size is how much of the subject fits on it, there is no additional magnification to be concerned with.

Bob