100-400g-master focus

[Rod Williams]

I bought a (Supposed)very good used copy of a 100-400 GM lens from B&H around the beginning of 2020 for $2100.  It seems fine at 100 to 200mm. Somewhere closer to 400mm it seems to struggle, and if I ever try to capture something like a little bird, even relatively close, it seems like everything other than the bird is in focus. I have seen a few posts similar to this, but have not seen a remedy. I’m guessing this is not a lens that I can USB and update. Not sure if there is a technique to calibrate it. I was thinking about trading it back and grabbing a new 200-600 and giving up on this focal length altogether as this might not cause me to lose money. Does anyone know if this lens would be considered in-warranty at this time? Would Sony charge me $500 to look at it like they would my a7riii? The images I am getting at 400mm are universally unacceptable. So any opinions or recommendations are welcome. 

[Jeffreykmd]

I have had my 100-400 for almost 2 years. I have no issues with it focusing at 400. I have used it on an A7rii and A7riv. I would look at how your camera is set up ie focus setup. For Small distant objects, I use spot focus and choose what I want to focus on, or I manually focus. I do not know if your lens is in warranty. Lenses from Sony have a one year warranty. B and H usually gives some warranty on used equipment. You can check the firmware for the lens and see if it is the latest. If it is not the latest, it can be updated with your lens attached to your camera. Check the Sony website for the latest version and directions to do an update.

[Rod Williams]

Unfortunately my a7riii will not update to the latest firmware. I have tried all the various connection options and tried connecting it to different computers including macs and PCs. I think Sony will charge over $400 if I send it to them and then I will likely be without the camera for a month. I will try the lens on my a9ii again when I get it back. I went ahead and sent it to a Jersey shop that B&H referred me to. They are working on it for a hefty sum. Prior to sending it out, there didn’t seem to be a difference in 400mm focus on either camera. $2500 seems like a lot to pay to end up manually focusing. I wish I knew that before buying the lens. Thanks for your help. Clearly frustrated with all the cost and lack of results from these tools. Ultimately, it seems like the industry is more about making money than having reliable and superior products. These cameras should not be so impossible  to update and these ridiculously expensive g-master lenses should have a 5 year warranty.