Has anyone discovered the precise focal lengths of Sony’s compact G 40 and 50 mm f/2.5 lenses?Or even the exact ratio between the two? (Easier to determine without special testing.)I have the 40, which feels a lot closer to a 35 than a 50 to me (but the nominal values support that impression). I’m debating getting the 50 too – maybe swapping it for my 40 – or waiting for the long-rumoured Sigma 50 mm f/2. If the 40 is 42 mm and 50 is 48 mm or something like that, it would hardly be worth the effort to differentiate between these lenses.Anyone see a good reason to own both of these lenses?

I know the 40 G is noticeably tighter than the Canon EF 40mm F2.8 STM that I recently sold. It is not close to any 35mm I've had. I haven't tried the 50 G yet.

Both lenses exhibit significant focus breathing.  So "true" focal length would depend entirely on at what subject distance you focused.

SmokeAndMirrorless wrote:Both lenses exhibit significant focus breathing. So "true" focal length would depend entirely on at what subject distance you focused.Lenses that maintain their focal lengths with closer focus show breathing. Lenses without breathing must lose focal length with closer focus.

You could try to measure it yourself:Lay out a tape measure. Set up the IMAGE PLANE of your sensor 6 feet away from the tape measure and rotate the camera to measure the diagonal length of what you can capture on the tape measure. The camera sensor should be perpendicular and centered in front of the tape measure, at about the 39 inch mark. If you can see 78 inches of tape on, then that's a 40 mm field of view.https://www.pointsinfocus.com/tools/depth-of-field-and-equivalent-lens-calculator/#{%22c%22:[{%22f%22:13,%22av%22:%228%22,%22fl%22:40,%22d%22:1829,%22cm%22:%220%22}],%22m%22:0}

The Ryantist wrote:You could try to measure it yourself:Lay out a tape measure. Set up the IMAGE PLANE of your sensor 6 feet away from the tape measure and rotate the camera to measure the diagonal length of what you can capture on the tape measure. The camera sensor should be perpendicular and centered in front of the tape measure, at about the 39 inch mark. If you can see 78 inches of tape on,https://www.cameralabs.com/sony-fe-50mm-f2-5-g-review/ then that's a 40 mm field of view.Well, that would show you that "that's a 40mm field of view"--at 6 feet. Focal lengths are generally expressed based on the field of view at infinity.The fields of view commonly differ depending on focal distance, but the magnitude of the difference will vary from lens to lens. For these three recent Sony releases, the field of view decreases markedly as focal distance decreases. (That may or may not matter to the user. (For example, many people won't care, but that factor might be more important in videography or focus stacking.)"As you focus the [Sony 40mm f/2 G] lens closer, the field of view reduces noticeably." See ca. 10:45 in the review video:https://www.cameralabs.com/sony-fe-40mm-f2-5-g-review/You can see a similar degree of focus breathing for the 50mm lens at about 12:50:https://www.cameralabs.com/sony-fe-50mm-f2-5-g-review/Even the mighty 50/1.2 GM shows quite significant focus breathing at ca. 8:40 here:https://www.cameralabs.com/sony-fe-50mm-f1-2-gm-review/