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New Contributor
Posts: 1
Registered: ‎05-03-2018

first prime lens 50mm ef1.8 stm - HELP

This feels like the dumbest question ever but I just got a 50mm ef1.8 STM lens for my Canon T6i.  Very excited to try it out but I'm not quite sure I'm attaching it correctly?  My kit lenses have a white guide dot that I align with the white dot on the camera body.  I'm not finding anything like that on this new lens.  


Respected Contributor
Posts: 1,198
Registered: ‎11-19-2017

Re: first prime lens 50mm ef1.8 stm - HELP


The lens has a red dot on the barrel right next to the AF/MF switch.  Use it for alighment and twist clockwise to lock.  The 50 is a fun lens.  You'll be very suprised how sharp the pictures you can take with it are. 



Bay Area - CA
~6D2 (f/w 1.0.4) ~16-35mm f2.8L II, 50 f1.8 STM, 85 prime USM, 70-200 f2.8L IS II ~70-300 USM II ~Sigma 24-70 f2.8 Art (f/w 2.02)
~Sigma 150-600 C + TC1401 1.4x (f/w 2.00) ~Speedlite 430 EX II ~DxO PhotoLab Elite ~Windows10 Pro1903 ~EVGA RTX 2080 FTW3 Ultra
Respected Contributor
Posts: 1,861
Registered: ‎12-02-2012

Re: first prime lens 50mm ef1.8 stm - HELP

[ Edited ]

You'll really love that lens. My first non-kit lens was the older 50mm f/1.8, before the STM focus and the rounded aperture blade yours has, but it nevertheless was a revelation.  The ability to create such a shallow DOF and the ability to shoot in low light without cranking the ISO up and ruining the image are just fantastic.  Congratulations and hope you enjoy.  


Be aware the nifty fifty can be something of a gateway drug, luring you into buying more and more non-kit lenses though. Smiley Wink



Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites

Why do so many people say "FER-tographer"? Do they take "fertographs"?
Posts: 11,664
Registered: ‎12-07-2012

Re: first prime lens 50mm ef1.8 stm - HELP

I don't have any ef-s lenses anymore but I seem to remember they had a white line up dot but ef lenses have the red dot.  Probably due to the inability of the ef-s lens to mount on a FF camera.


I have owned all the 50mil lenses has made.  I currently own the Canon EF 50mm f/1.2L USM Lens.  I simply love it.  There is nothing like it.  It is a unique lens.  However, my way of thinking over the years is, 50mil is a little troublesome to use.  It just doesn't fit most situations. Even more so on a Rebel or other cropper.  But when it does it is spectacular.

EOS 1DX and 1D Mk IV and several lenses!
Esteemed Contributor
Posts: 3,816
Registered: ‎06-11-2013

Re: first prime lens 50mm ef1.8 stm - HELP

See page 45 of your manual.


Your camera body can accept EITHER Canon EF or EF-S lenses.  


EF lenses have a red index dot on the top of the barrel and you align this to the red dot on your camera body's lens mount.

EF-S lenses have a white square ... which you align to the white square on your camera body's lens mount.


You might be wondering why there's a difference.


EF lenses project a larger image circle into the camera body to fill the arger size image sensor ... 36mm wide by 24mm tall (just about 43.3mm across when measured diagonally)


EF-S lenses are a bit smaller and made for cameras that have APS-C size image sensors.  The image sensor is roughly 22.5mm wide by 15mm tall (about 27mm across when measured diagonally).


As long as the image being projected into the camera body is large enough to fill the sensor with light... it would work.  This is why either EF or EF-S lenses can be used on YOUR camera body.


Cameras with full-frame size sensors (like the 1D series, 5D series, 6D series bodies) require EF lenses.  They cannot accept EF-S lenses.  But cameras with APS-C sensors (all Rebel series bodies, all mid-range series bodies (80D, 70D, 60D, 50D, etc.) as well as the 7D series bodies) can use EITHER the EF or EF-S lenses.




There's one more detail.  Once Canon started offering "mirrorless" cameras, they introduced new lenses for those camera bodies.  These lenses designed for "mirrorless" bodies (the Canon "EOS-M" series bodies) are called "EF-M" lenses.  Those lenses will NOT work with your camera.


There are a few specialty lenses including the tilt-shift series "TS-E" lenses and specialty macro-photo "MP-E" lens.  Those lenses can be used with any EOS camera body but they don't get the "EF" prefix because they are special manual-focus lenses.  The "EF" stands for "Electro-Focus" because all EF & EF-S lenses have built-in auto-focusing motors.  The specialty TS-E and MP-E lenses do NOT have auto-focus motors (they are many focus only) lenses.  But they are designed to mount to EOS camera body that can accept an EF lens.


Tim Campbell
5D III, 5D IV, 60Da
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