Camera/Lens interaction

slat · Feb 22, 2025

If you have a fully manual aps-c (EF-S) lens and use it on a full frame mirrorless will the camera still recognize it as an aps-c lens and go into crop mode?
If it doesn't recognize it will it have make a smaller image on the full frame mirrorless like it would on a DSLR or is the difference in camera design negate this?

wfooshee · Feb 22, 2025

You'll need a mount adapter, as neither EF nor EF-S lenses will mount to a mirrorless camera. If the EF-S lens is fully manual, like some of the Rokinons out there, then the camera has no idea that it's a crop-sensor lens. If it's a prime, it will not cover the sensor's field of view, and if it's a zoom, there may be a point toward the wider zoom range where it actually will cover the entire sensor. The camera won't meter since it has no control of the aperture, so exposure is completely manual, and EXIF data about the lens will be blank.

Thiophilos · Feb 22, 2025

wfooshee said:
You'll need a mount adapter, as neither EF nor EF-S lenses will mount to a mirrorless camera. If the EF-S lens is fully manual, like some of the Rokinons out there, then the camera has no idea that it's a crop-sensor lens. If it's a prime, it will not cover the sensor's field of view, and if it's a zoom, there may be a point toward the wider zoom range where it actually will cover the entire sensor. The camera won't meter since it has no control of the aperture, so exposure is completely manual, and EXIF data about the lens will be blank.

That's a pretty good description of how the system will behave.

If you have a Canon EF-S normal zoom mounted with the RF-EF adapter, the camera will automatically switch to crop (1.6x) mode. The viewfinder will be filled with the lens's image.

slat · Feb 23, 2025

Yes it is a Rokinon lens and I knew I would need an adapter just wasn't sure what kind of field of view it might give on a mirrorless vs DSLR.
I thought if there was a difference in the sensor position that it might work ok on the mirrorless.
Thank you for the responses.

Golem · Feb 24, 2025

wfooshee said:
You'll need a mount adapter, as neither EF nor EF-S lenses will mount to a mirrorless camera. If the EF-S lens is fully manual, like some of the Rokinons out there, then the camera has no idea that it's a crop-sensor lens. If it's a prime, it will not cover the sensor's field of view, and if it's a zoom, there may be a point toward the wider zoom range where it actually will cover the entire sensor. The camera won't meter since it has no control of the aperture, so exposure is completely manual, and EXIF data about the lens will be blank.

I intentionally do the mismatch on occasion, and by my observations its not the wider angles of the zoom that nearly fill the whole FF sensor, but the mid and longer FLs of the zoom that do that pretty well. At the wide end the image looks very small on the FF format, but by mid to longer it fills up quite nicely. My 10 to 24 APSC is pretty much full frame from 15 to 24mm.

wfooshee · Feb 24, 2025

Yeah, I did say that backwards, sorry. It's the longer end of the zoom that fills the sensor, and i have a 10-24 that seems the same... at 15 and longer it's usable on full frame.

greybeard · Feb 25, 2025

Depends on the camera. Some automatically go into APS-C mode while some do not. If it doesn't then the APS-C lens won't cover the entire sensor and will only give you a circle image in the center of the frame. Some APS-C zoom lenses will cover the FF sensor at the medium to telephoto settings.

RacePhoto · Feb 27, 2025

You mean the full frame camera, with a manual EF lens on an R to EF adapter, will actually sense that it's a crop camera lens, and adjust to crop mode? That's pretty interesting technology. I would have thought that since it's manual, the camera has no way to know what's out front, and it would stay in full frame mode and make a smaller image from what's available, and being projected onto the sensor.