A new patent showing off some lens element coating to help with ghosting and other anomalies has appeared alongside optical formulas for what appears to be RF-S prime lenses.
Below are the three prime lens designs shown in the patent, we wouldn't be surprised for one of these to hit the market as a consumer product.
Canon RF-S 21mm f/1.8
- Focal length: 20.60mm
- F-value: 1.85
- Half angle of view: 46.4°
- Image height: 18.71mm
- Overall length: 84.87mm
- Back focus: 11.00mm
Canon RF-S 24mm f/1.8
- Focal length: 24,72mm
- F-value: 1.85
- Half angle of view: 41.2°
- Image height: 19.34mm
- Total length: 81.00mm
- Back focus: 11.00mm
Canon RF-S 28mm f/1.8
- Focal length: 28.60mm
- F-value: 1.85
- Half angle of view: 37,1°
- Image height: 20.15mm
- Total length: 81.00mm
- Back focus: 13.20mm
I thought that "RF-S" lenses would fit on normal RF mount, as well as on crop cameras, but that full-frame models would electronically recognise RF-S lenses, and crop the frame accordingly?
Or have I got it wrong?
They do also specifically mention that it fits on full frame cameras in crop mode. "This lens was designed with smaller APS-C sensors in mind, and when attached to a full frame EOS R camera, automatically enables the 1.6x crop mode. It offers 100% x 100% Dual Pixel CMOS AF coverage for APS-C sensors, and 80% x 80% Dual Pixel CMOS AF coverage for Full Frame sensors (in crop mode)."
I would imagine Canon most likely coming out with the 28mm (45mm equiv) but they could also spring for the 20mm (33mm equiv). Doubtful there's space for all 3 though.
While we are discussing technicalities, I would like to add that EF-S can be mounted on a full frame DSLR successfully if the mirror is in lock-up mode/silent shutter engaged. It would be good for video recording or one photo before you have to remove the lens to prevent the mirror slap damage.
IMHO, RF-S lenses will be made to suit the build/cost/etc level of the lower end R mount bodies so f1.8 seems to be different to that assumption.
I would be very surprised to see a RF-S lens that was L quality for instance. Has any EF-S lens been wider than f2.8?
Check half angle of view.
We checked this patent like a month ago and the 24mm design is the current RF24