- I've used the 1.4TC many times now and the results are very good. It is obviously well made/quality and the images have no noticeable loss in sharpness. Increases the f stop from my 200-600mm lens which has a constant f6.3 to a constant f9. I use this mainly for getting 'closer' to static or slow moving wildlife and am very happy with it. I'm finding that im leaving it on the long lens most of the time. There are auto focus limitations due to the reduction in f stop (on my A7R3) - so maintaining focus with all shots whilst panning birds in flight is more difficult (but by no means impossble.) Of course for static or slow moving subjects there is no problem at all and you can use manual focus (with peaking) if needed. Very pleased.