How do slimline adapters affect the focal point (stacked adapters)?

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mainoo Junior Member • Posts: 25
How do slimline adapters affect the focal point (stacked adapters)?

I have a plan to implement something I have seen done by others with apparent success but I have a nagging doubt and I'm hoping someone here can help me see clearly.

The idea is to shoot a load of manual lenses through a speed booster on a sony A6500. The speed booster is the Viltrox EF to E mount. All lenses will need to show an EF mount to the Viltrox and I'm hoping to use one of the many XXX to EF slimline adapters I see on Ebay. So the chain will be lens -> slimline adapter -> Viltrox -> A6500.

A subplot involves ensuring that the slimline adapters have a programmable chip attached so that I can enter the focal length of the lens and have automatic IBIS, but I digress.

The questions I have are as follows:

If I have understood correctly, the glass inside the Viltrox becomes the focal plane replacing the camera sensor - the magic done by the Viltrox is to bend that light such that it fits the smaller sensor in the camera. Is that more or less correct?

I understand that the Viltrox is playing the part of an EF mount camera with the correct flange distance from the mount point to the glass inside the Viltrox. Does the slimline adapter not throw that calculation out? I expect that there is a precisely calculated point where the rear of the lens joins the Viltrox (camera) mount from which the flange distance is measured. Does the introduction of a slimline adapter (no matter how slim) not change the focal point of the light that exits the lens?

Some of the lenses I plan to use in this system are Canon FD. I read about problems implementing the Canon FD to EF adapter. There was insufficient space to put in an adapter while still allowing infinity focus (something to do with the mirror box). Canon tried to solve this by implementing a special adapter which degraded IQ. Does the same problem not present when the Viltrox sits in place of the EF mount camera? Of course, this problem is avoided if I, instead, I go direct (skipping the Viltrox speed booster) to a mirrorless using an FD to E mount.

Thanks in advance.


Sony a6500
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