Why does my 24-105 have a different magnification (macro ratio) from a 105mm macro lens at same MFD?

Started 7 months ago | Questions thread
bclaff Forum Pro • Posts: 13,787
Distance in Optics
6

Monicaa wrote:

My Panasonic 24-105 f4 has a MFD of 0.3m. It gives me a magnification of 0.5x at 105mm, which I have confirmed by taking photos of objects with a known size. This is 0.3m from the sensor plane to the object, with a working distance of about 10cm.

However, a 105mm macro lens with the same MFD (for example the Sigma 105mm 2.8 has a MFD of ~0.3m also), produces a 1.0x magnification.

How does this work? Two lenses at the same focal length and focal distance achieve different macro reproduction ratios?

For more detailed information on Distance I suggest the Optics Primer - Distance article in the PhotonsToPhotos Optics Primer.

You'll find that something called the internodal distance (or hiatus) is important especially as close distances.

You can also see both lenses at the PhotonsToPhotos Optical Bench.

The Panasonic Lumix S 24-105mm F4 Macro OIS

Best viewed "original size"

And the Sigma Macro 105mm F2.8 EX DG OS HSM

Best viewed "original size"

The internodal distance is H'-H in the positions.
For the Panasonic it's -31.65mm and for the Sigma it's 9.68mm
Optically this is the chief reason for what you are observing.

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Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

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