Not a Sony user, but often crop lenses don't work on full frame because the image circle isn't large enough. I would guess that is what they meant. If it does mount (which I think it would), you would have to crop heavily and end up back at a crop sized image.
Thanks to both of you.As Molly said, if you mount them on the full frame camera you'll just end up with an APS-C camera. But the Sony should automatically handle the cropping for you, so they'll perform exactly as well on the A7 as they do on the APS-C cameras. The big downside is you'll lose resolution, and so the A7 III with an APS-C lens is only a 10MP camera.
That said, there's no reason you couldn't use the APS-C lenses until you get around to buying full frame lenses gradually. And then you can use the full frame lenses just fine on all of the Sony APS-C cameras.
I see others have already mentioned APS-C mode (AKA: "Super 35 Mode") on the A7 III. My philosophy at the time I was buying my A7R IV was that I was buying a full-frame camera, why would I want to buy and use APS-C lenses on it? I was starting out from scratch with Sony at that point and so didn't have any lenses, either FF or APS-C so it was an easy decision to just purchase only FF lenses for the camera as I was going along. Other people are in different situations.
Sony, with this APS-C mode on its FF cameras, makes it easier for those who already have an APS-C camera and lenses to move up to a FF camera without losing the ability to use their APS-C lenses. Pretty cool!
All that aside, the A7 III was one of Sony's most popular and best-selling cameras. It's a little gem and only has recently been replaced by the new A7 IV. Definitely if your friend is willing to sell for a reasonable price it would be a purchase well worth considering. As time goes on, yes, you could then begin adding FF lenses to what you've currently got, and they would work on both cameras, too. It's very handy at times to have two different cameras.....
Not yet...in my hands, but when I will 🙃The a7iii is a great camera, enjoy.
To recap, the only issue should be a smaller photo but still in the 10 mb+ size?Yeah I agree with Kenoh, I borrowed my brother's APC lens for a moon shot and the A7III just automatically adjusted without having that tube effect.
Everything else should be good to go, it is one of the reasons a lot of people have been switching to Sony because E-Mount lenses basically just work with the Sony Cameras. When I borrowed my brother's zoom (I don't remember which model) APS-C I didn't have to do anything extra. His lens is also a manual zoom btw so I couldn't test like power zoom.To recap, the only issue should be a smaller photo but still in the 10 mb+ size?
And everything else from the Full frame camera should work?
Thanks for the extra infos. I 'm not a video photographer. I tried few slow-motion video with the zoom but without a tripod it's complicated = moves-jumps a lot because it's difficult to keep camera and zoom steady just handheldEverything else should be good to go, it is one of the reasons a lot of people have been switching to Sony because E-Mount lenses basically just work with the Sony Cameras. When I borrowed my brother's zoom (I don't remember which model) APS-C I didn't have to do anything extra. His lens is also a manual zoom btw so I couldn't test like power zoom.
Do keep in mind (as you probably already know) 10mb to work with will possibly be difficult depending on what kind of photography you want to do or if you plan to use the APS-C lenses for video too. I know the A7III technically records in 6k and downsamples to 4k (if shooting 4k) and I am not sure how the video will look.
I guess it's better not to sell my a6400 and keep both , following all what you wrote.In the old days when DSLRs were reigning in the world of digital photography, a lot of times people who went on frequent shooting excursions, especially if those included wildlife, would have both an APS-C camera and a full-frame camera. The APS-C took on the duties of shooting with the long prime FF lenses because of the so-called "crop" factor, while the FF camera body and a wholly different FF lens would be used for shooting other things while waiting for wildlife to show up.
cthompson94 points out something which really is important, which is the resolution available when shooting with a FF camera in APS-C mode. This can be very problematic when shooting in low-light conditions, when shooting something with the expectation of needing to crop afterward, etc. The image quality and resolution shot with an APS-C camera and either a FF or APS-C lens will be higher than shooting the same image with a FF camera using an APS-C lens in APS-C mode, which drops down the resolution. Shooting a FF camera with a FF lens will get you the highest resolution and best quality.
There are ways around this, such as software programs with AI and resolution-boosting/pixel extrapolation features, but this still is not the same as utilizing the resolution of the camera's sensor in the first place.