The upside to A-mount popularity going down

Started 2 months ago | Discussions thread
QuietOC
QuietOC Veteran Member • Posts: 5,021
Re: Lens ROM data

ProfHankD wrote:

tbcass wrote:

QuietOC wrote:

ProfHankD wrote:

Quoting Rishi:

"Manufacturers of DSLR bodies and lenses do a lot of calibrations to make sure that this isn’t an issue, calibrating every AF point at the factory, writing look-up tables into lenses, and more."

As I said, using the wrong table is a big problem. Again, what does the Tamron ID as?

The A-mount Tamron 70-300 USD borrows the Lens ID of the Sony 70-300 G SSM.

Yes it does and because of that all the on sensor PDAF points of my A99ii work with that lens and work well I might add. It shows that Sony intentionally crippled that ability for 3rd party lenses.

Actually, all common lenses mounts are proprietary, and the lens ID was as much as Minolta originally thought would be needed from the lens ROM -- as discussed in the reference I gave before: Lens ROM data . Back then, ROM meant ROM, not flash, so you'd want the fancy info in the body so that it can be patched by firmware updates.

Anyway, that sounds like it's probably a good match. A lot of 3rd-party lenses basically designed to the specs the reverse engineered, and Tamron is one of the few known to have built lenses for Sony branding, so if this was made after 2006, good chance Tamron knew what they were doing rather than guessed....

So, I'm stumped by why a supposedly healthy A900 would be so far off on this. All I can guess is that something's s

The Tamron 70-300 USD optical design is very different from the Sony. They are both 70-300 zooms and that's about it. The Sony is designed to not have focus breathing, while the Tamron maintains its focal length with close focus. The Sony has rear focus while the Tamron focuses by moving much larger elements near the front of the lens.

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