[Brightcolours]

@Brightcolors: I might be wrong, but I think the TC diminishes the DOF, so that f2.8 on a 100mm gives about the same DOF as f4 on the combination with the 1.4x TC...????


@popo: I have the Kenko 1.4x converter pro300 dgx, according to Kenko it fits on the Canon 100mm IS, I tried to find out if it also fits the Sigma 150mm OS, but I did not get any results.


I googled a bit more about IS and OS, I think both Sigma 150mm OS and Canon 100mm IS have tilt & shift corrections.


Thanks popo and Brightcolors!


Marie-Elise

The TC makes the f-value smaller. The f-value stands for focal length divided by that number = aperture diameter.

With a 100mm f2.8 you have a max. apparent aperture diameter of 100 / 2.8 = 35.7mm.

Adding a 1.4x TC changes the total focal length to: 100 x 1.4 = 140mm. The aperture diameter of the lens has not changed. Thef-value then will be: 140 / 35.7 = f3.92

 

So, your 100mm f2.8 lens changed into a 140mm f4 lens. Both in DOF and f-value. So, when you close down the Sigma 150mm to f5.6 for DOF purposes, and you close down the 100mm f2.8 + 1.4x TC combination to f4,  you get about the same DOF and light, due to the 1 stop difference the TC makes.

 

The Kenko TC will fit on the Sigma 150mm.