Hello everyone, I`m currently considering purchasing ASI533 MM and planning to use it with Samyang 135 f/2 for Sony E mount. However, I'm confused with back focus issue and adapters for Sony E lenses. ZWO has such adapter (https://www.zwoastro.com/product/sony-adapter-for-asi-cameras/), but I can't find univocal information on whether it provides correct back focus length. For Sony E back focus length should be 18 mm.
Using of the ZWO adapter implies removing 11mm black ring from ASI camera and screwing camera directly into the adapter. The total thickness of the adapter is 11.5 m, the distance from the camera sensor to its front is 6.5 mm, which in theory adds up to the required 18 mm. But if to look at the adapter scheme, then out of 11.5 mm, 4 mm fall on the internal thread, which exactly corresponds to the thickness of the camera mount. That is, after screwing the camera into the adapter, if I understood the mounting mechanism correctly, for back focus length calculation, it is necessary to sum 6.5 mm from the sensor to the front of the camera with 7,5 mm (11,5 of total thickness — 4 mm of internal thread), which gives 14 mm in total, not required 18 mm.
Could you please explain where I am making mistakes in my calculations? Perhaps I misunderstand the mechanism of attaching the adapter to the ASI camera. I have not found information anywhere that any additional extenders would be required for such a bundle. Can anyone share the experience of using ZWO cameras with lenses for Sony E mount and the mentioned adapter? This was partially discussed here https://bbs.zwoastro.com/d/21059-back-space-issue-with-asi533mc-pro, but I did not find the answer to my question in this thread or in others.
