40-150 PRO focus breathing?

CrisPhoto wrote:

whumber wrote:

Anders W wrote:

whumber wrote:

Anders W wrote:

Arctra wrote:

...

It's very easy to calculate the focus breathing from the lens specs. The 40-150 PRO has a max reproduction ratio of 0.21 (at 150 mm obviously) and a minimum focus distance of 0.7 meters. The focal length, F, at that reproduction ratio, R, and focus distance, D, is calculated as

F = D/(1/R + R + 2) = 700/(1/0.21 + 0.21 + 2) = 100 mm

so yes, certainly some focus breathing going on, just as one might expect.

...

I took Anders formula, the manufacturers specs and checked it against reality. I put the camera on a tripod, took two folding rulers: one as subject to get the FOV in mm and the other to get the distance as well as the working distance.

Here is my excel sheet:

Spec values against real values and AndersW's formula (effective focal length)

I think the 40-150 PRO does quite well.

The 12-40 was a nice surprise, it does equally well. But the working distance is 8x smaller. Not good for butterflies and such ...

The PanaLeica has a lot of focus breathing but at least the result is as crispy as the PRO lenses, despite the bad numbers it is very usable for close up.

And the small 40-150/5.6 was very disappointing. Two years ago I used it for close up and macro, how much better would the PRO lenses have been

This is the thing the table does not tell: with the PL14-150 as the only exception the non-PRO lenses give up IQ very dramatically if you go closer. Sharpness and contrast is going down the drain ...

Hi Christof,

Thanks for that. Quite an ambitious little exercise. Much appreciated.

Note, however, that the figures for the 75-300 are not right. This lens manages a focus distance of 0.9 meters only at 75 mm. At any other focal length, the minimum focus distance, is 1.5 meters. At 300 mm, which is where it manages a reproduction ratio of 0.18, its effective focal length is 194 mm, not 116 mm. And are you sure its MTF-values too are going down the drain at close distance? I haven't really tried to test it but ...