Mount Adapter EF-EOS R vignettes terribly

[clifff27]

Canon RP camera with adapter.  Sigma 18-200 vignettes terribly so that picture is an oval surrounded by black.  If shooting at 200 it is fine, but anything less vignettes.  Same with Tamron.  Is this to be expected?  If so the adapter is useless...Thanks

[clifff27]

thank you..all is well...just need to save for a full frame lens...

[ebiggs1]

I believe the DC name is Sigma’s note for crop sensor cameras. DN is for mirrorless.
I can’t remember mounting a DC on my FF body so I don’t know if it will.

[Waddizzle]

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@ebiggs1 wrote:
I believe the DC name is Sigma’s note for crop sensor cameras. DN is for mirrorless.
I can’t remember mounting a DC on my FF body so I don’t know if it will.

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Canon uses a red dot for EF lens mounts, and a white square for EF-S lens mounts.  Sigma uses neither.  Sigma uses a white dot that aligns with Canon's red dot on a camera body.  All of their lenses are made this way.

[Waddizzle]

Sigma 18-200mm.  Notice the white dot, which aligns with the Canon red dot.

Why spend the extra money to make two diffferent mounts, when using just one gets the job done?

[ebiggs1]

"Why spend the extra money to make two diffferent mounts, when using just one gets the job done?"

Perhaps so, however, Sigma does indicate which camera model their lenses are designed for. DG is for full frame while DC is for the cropper series. DN is their new designation for mirrorless. Example my 120-300mm F2.8 DG OS HSM Sport is designed as a FF lens. Indicated by the "DG" in its name. Although it will mount on a cropper and perform flawlessly.

I have not, or at least I can't ever remember doing so, mounted a DC lens on any of my FF cameras. I would hope that people would realize it is not the best idea and specifically why Sigma makes the name different for each line. I actually don't ever think I have owned any EF-S/DC lenses at all.  I have used a very few but I don't remember owning any. They are just not built well enough to satisfy my requirements.

[jrhoffman75]

Only Canon lenses have an EF-S mount. All third party lenses use the EF mount, but if they are designed for the APS-C bodies they will usually vignette at the wider focal lengths. 

[hothrt]

Today I was shooting birds and the vignetting is horrible even at 200mm.

Canon EOS R6 with the basic adapter and the Canon EF 70-200 

[p4pictures]

This problem is caused by the Sigma lens. Several of the lenses from Sigma / Tamron and other independent makers were designed for APS-C crop sensor cameras and sold as such. However the manufacturer didn't make the lens tell the camera that it was an APS-C lens, Canon EF-S lenses do tell the camera that they are APS-C lenses. 

As such, the EOS RP with mount adapter sees a lens, doesn't get info from the lens that it is a crop lens so the camera shoots as a full-frame camera. The result is vignetting / circular images to some effect. I wrote about that here on my blog https://www.p4pictures.com/2019/06/eos-r-crop-lenses-aps-c/ 

Canon EF-S lenses fitted to the adapter do tell the camera they are crop lenses, and so the camera automatically selects the 1.6x crop mode and it cannot be deselected.