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Posts: 3
Registered: ‎10-02-2015
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EF-S v EF Lens - Crop Factor (Image Conversion Factor)

[ Edited ]

Good evening,

 

Please excuse me if this is a dumb question.

 

If I use an EF-S lens on a camera with an APS-C sensor, does the sensor capture all that I see in the viewfinder i,e, with a ratio of 1:1?

 

Put another way; do EF-S lenses overcome the Image Conversion Factor  or Crop Factor that hapens with EF lenses on cameras with an APS-C sensor?

 

The Crop Factor means that what you see through the viewfinder is more than actually gets captured by the sensor by a ratio of 1:1.6.

 

I understand that the rear of the EF-S lens is closer to the mirror and, therefore the sensor, than the rear of the EF lens, which leads me to think that the image seen through the viewfinder with an EF-S lens is closer to that which will appear on the sensor than that of an EF lens.

 

Many thanks for any response that confirms or refutes my supposition, preferably with an explanation in simple terms.

 

Joe.

Esteemed Contributor
Posts: 3,999
Registered: ‎06-25-2014

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

You're overthinking it. Just remember that while a "normal" angle of view on a full-frame camera is about 24-70mm, on an APS-C camera it's about 17-55mm. In each case, anything longer is a telephoto lens; anything shorter is a wide-angle.

Bob
Boston, Massachusetts USA
Esteemed Contributor
Posts: 4,636
Registered: ‎11-13-2012

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

"If I use an EF-S lens on a camera with an APS-C sensor, does the sensor capture all that I see in the viewfinder i,e, with a ratio of 1:1?"

 

The answer is a qualified "Yes". There is a slight difference since the viewfinder shows about 95% (so you may capture a little more, but you never cut anything off.)

 

http://digital-photography-school.com/crop-factor-explained/

 

 

John Hoffman
Conway, NH

1D X, Rebel T5i, Many lenses, Pixma PRO-100, MX472
Honored Contributor
Posts: 5,933
Registered: ‎08-13-2015

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

[ Edited ]

jrjsmith wrote:

Good evening,

 

Please excuse me if this is a dumb question.

 

 

Joe.


My definition of dumb questions are the ones that you're too embarrassed to ask.  Everyone has to learn some day,  some way, and somehow.  Ask away.

 

Actually, it's my understanding that both sensor types occupy similar positions inside of their camera bodies.  Each one is centered in the exact same position at the center of the image projected by the lens.  With a full-size sensor, the diameter of the round image that is projected is only slightly larger than the sensor.

 

Meanwhile, an APS-C sensor does not cover as much area, and will only capture what is in the center [cropped] of the projected image, which is why a full frame will have a wider field of view with the same lens.  The net result is that the smaller sensor will seem to have more zoom, or focal length, compared to that same lens on a full frame body.

 

Why don't they just rate EF-S lenses with the equivalent focal length?  Because the focal length refers to a physical dimension inside of the lens.  The focal length specification is telling you about how the lens is made, not how it performs.  It is up to you to understand how a given lens will perform on your camera body, which really isn't all that complicated...just multiply the focal length by 1.6.

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VIP
Posts: 8,627
Registered: ‎12-07-2012

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

The 'S' in the name EF-S stands for short focus. This is of no concern to the user.  And the crop factor is also of no concern to the user.  The camera crops nothing.  It is a full frame in the sense of you get what you see in the view finder.

The term comes about because of old film camera that use 35mm film.  Somebody wanted to know how to compare the two.

 

People don't really consider there iphones as crop cameras but they are.  Just as much as a Canon Rebel is.  Nobody calls a medium format camera and enlargement camera!  But it would be if you used the same logic.  Forget it.

 

It is far better to think in terms of 'angle of view' (AOV).  This never changes no matter what camera you use.  Example ...  Any lens that give a 46 degree AOV is considered normal.  It makes no difference which camera you use.  This spec is included with every lens.  MM tells you what the lens is.  AOV tells you what it does.

A lot less stuff for 2018 but still a lot of Canon stuff. Along with, a lot of other stuff.
New Contributor
Posts: 3
Registered: ‎10-02-2015

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

Many thanks for the link.

New Contributor
Posts: 3
Registered: ‎10-02-2015

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

Thanks for the clarification and for setting my mind to rest about the image captured vs the viewfinder image.

 

Now, I need to brush up on the AOV.

VIP
Posts: 8,627
Registered: ‎12-07-2012

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

Try this one.

A lot less stuff for 2018 but still a lot of Canon stuff. Along with, a lot of other stuff.
New Contributor
Posts: 4
Registered: ‎01-22-2018

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

I'm new to this forum and this is exactly the info I was looking for.  Thanks to those that have contributed.  Well done.

 

I just want to make sure I understand it all completely.

 

I purchased a Canon 80D based on price and the dual pixel focus and such and the many recommendations I saw on Youtube.  I do all kinds of video and the 80D seemed like a good all-around choice.

 

Now I am getting into real estate videos and photos. For the interior shots (stills and video), I need something in the range of a 14 to 16MM wide angle lens.  My question...

 

Q.

Do I understand correctly that if it is an EF-S lens, whatever the focal length says on the lens will be what I see and if it is an EF lens, I need to mulitply the minimum focal llength by 1.6 to know th real focal length I will see?

 

So then, the EF-S 18 to 55 kit lens really will be 18mm and the EF 50 f1.8 STM that I just ordered will actually be an 80mm focal length (50 x 1.6 = 80).  Please confirm I have it correct...  whew.  

 

THANK YOU.

 

Esteemed Contributor
Posts: 4,636
Registered: ‎11-13-2012

Re: EF-S v EF Lens - Crop Factor (Image Conversion Factor)

Focal length is a physical property of a lens. A 50mm lens has a focal length of 50mm whether it’s on a full frame camera, a crop sensor camera or sitting on a table unmounted to a camera.

When on a crop sensor camera the field of view is changed and a 50mm lens has the field of view equivalent to an 80mm lens on a full frame camera.

EF and EF-S lenses are the same as far as this behavior goes.

If you want to shoot interiors you want a 10mm or so lens on the 80D.
John Hoffman
Conway, NH

1D X, Rebel T5i, Many lenses, Pixma PRO-100, MX472
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