What is this ring showing on my lens?

Started 7 months ago | Questions thread
John Sheehy Forum Pro • Posts: 24,758
Re: What is this ring showing on my lens?

Sagnet wrote:

Hi guys! Just bought the EOS 90D, which was an upgrade from my EOS 650D (Rebel T4i). I have some old lenses I'm planning to use with the 90D. One of them is a Sigma 50mm 1.4. However, when shooting with this wide open on the 90D, there is a circle showing. What is this? The aperture, or something else?

It only shows at 1.4, it goes away when stopped down to 1.6. It does not show on my 650D at 1.4. I find this strange, as both cameras are APS-C format.

The lens is masquerading as some Canon lens in the data it supplies to the camera, which needs different corrections, so in newer bodies that correct for lenses in their JPEGs, you need to disable whatever correction is causing the problem, a real pain in the neck if you switch lenses frequently or urgently.  You will have similar problems with "masquerading" with the IBIS in the R5 and R6; the wrong focal lengths are reported, and the shake corrections can be so wrong in some cases that IBIS causes far more blur than non-IBIS will give.  I have an old Sigma 12-24mm zoom that the R5 sees as an 85mm prime, and with IBIS, you can see the EVF swimming from the excess correction.

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