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


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.





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.

EOS 1DX and 1D Mk IV and less lenses then before!

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Thanks John. Not the answer that I was hoping for, but at least I understand it now and I will shop for a 10mm lens for my interior shots.

@photosbylorenz wrote:
Thanks John. Not the answer that I was hoping for, but at least I understand it now and I will shop for a 10mm lens for my interior shots.

There are two wide angle Canon zoom lenses made for EF-S mounts, a 10-18mm STM, and a 10-22mm USM.

"The right mouse button is your friend."

Perfect. Thank you!

Crop factor is a big joke.  It is a meaningless term invented to slap on certain sensors because they had to come up with something.It is nothing short of confusing to most people.  Even long time photographers think the crop sensor camera actually crops their image. People on all the photography forums will say so. It crops nothing!  All camera no matter what size sensor they have are FF in the sense that you get what you see in the viewfinder, nominally.


If you notice they don't call P&S cameras "really cropped sensor".  And they don't call medium format cameras "expando sensors".


Again if you have a 50mm lens and could put it on a P&S it would still be a 50mm lens.  Even putting it on the medium format or large format body, it is still a 50mm lens.


A better way to think about it is "angle-of-view".  There are charts that quickly tell you exactly what it is.  On your 'crop sensor' body you need a 18mm to 16mm for a WA angle of view.  A 14mm to 10mm is considered an ultra wide angle.



EOS 1DX and 1D Mk IV and less lenses then before!

I agree with Ernie that angle of view is a more comprehensible comparison vehicle than crop factor. But I think it's even easier to simply learn how a given lens behaves on each type of camera. I've found that the only times I've had to actually consider a len's "full-frame equivalence" is when I'm planning a shoot with both a FF and an APS-C camera, to make sure I don't have a coverage gap.

Philadelphia, Pennsylvania USA

Back in the day, when 35mm film was dominant in the market, for better or worse, the focal lenghts of the lenses for the 35mm system became the standard nomenclature for a particular angle of view.


Along came APS (Which I liked by the way, it was a good bridge to digital, with a first stab at film based "EXIF", but I digress). Since all the major manufacturers had interchangeable lens APS systems, there had to be a way to explain that the angle-of-view of a 50mm lens for APS was different than for 35mm and crop factor was born.


Since the first digital bodies had APS sized sensors, it was natural to keep 35mm focal lengths as the "standard" and use a crop factor to get a handle on the angle of view.


I think it is a handy way to understand the angle of view for a particular focal length. To answer the question above, it only matters for interchangeable lenses.

Thanks for the walk through memory lane. I think I got it now. 35 mm (24mm x 34mm) was dubbed a standard and hence dubbed "full frame". Anything other than a "full frame" size is just a different frame size and hence has a different angle of view. A way to express the angle of view is to compare it to to the standardized "full frame" via a ratio or multiple, such as 1.5, 1.6, 1.35, etc.

Thanks to everyone that responded. Very educational,
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