Why canon don't make ef-s lenses with small aperture?

[JJR70D]

70D

[ScottyP]

Yes. You just have to convert the length in your head. The EF lenses all mount on crop bodies. Just line up the red dot instead of the white one. They COULD write the converted FOV equivalent on the lenses, but why?

And yes, I wish they DID make the Sigma 18-55 f/1.8 for full frame too!

[RexGig]

Why bother to calculate crop factor? Well, OK, when considering the acquisition of a new focal length, such as an ultra-wide, or long tele, one may need to calculate, but with a bit of experience, the shooter should know which lens, or which focal length, is right for framing a shot. Just knowing what is "normal" is a good place to start; 28mm to 35mm is "normal" on 1.6x APS-C cameras, and 35mm to 40mm is about "normal" on 1.3x APS-H cameras*. I use all three of Canon's sensor sizes, and am a horrible mathematician, so I remember what lenses are normal, and what are good for the various types of portraits. It requires no conscious thought, after a short time.

(Actually, "normal" for 1.6x may start a bit wider than 28mm, if only considering angle-of-view, but anything wider than 28mm requires extra care to mitigate perspective distortion, regardless of the sensor size, so 28mm is my idea of normal for 1.6x.)

*What is APS-H? The 1D-series, from the 1D to the 1D Mark IV, have 1.3X crop factors. The full-35mm-frame cameras, with integral vertical grips, before the 1D X, were the 1Ds-series.

[JJR70D]

Thanks again! And I know about that sigma lens
I'm here to learn nothing else! What you guys recommend For my 70d? I want to shoot indoor that's why I want a low f/# in a tie space. I guess that sigma is the best !!!!!

[ebiggs1]

" For my 70d? I want to shoot indoor that's why I want a low f/# in a tie space"

"I believe the EF-S 17-55 f/2.8 IS USM is the fastest EF-S lens?  It is nearly $900 bucks."  As I already pointed out to you.

Or the very good Sigma 18-35mm f/1.8 DC HSM Art Lens for Canon.  These are outstanding choices.  The Canon getting my preference of the two.

In addition the Sigma 17-50mm f/2.8 EX DC OS HSM

[JJR70D]

I'm thinking about getting a 5dm3 instead! !! That way I could use any lens! !!!

[jrhoffman75]

Actually, its the opposite. The 5D can only us EF lkenses. The 70D can use EF or EF-S. (but there is the crop factor)

[cicopo]

In actual fact the crop body can use the more common (EF mount) fast ultrawides & not be as noticeably effected by their softness in the corners & edges because it crops that area out.

[ebiggs1]

cicopo,

I don't think I totally agree with that.  You would have to do a lens by lens comparison. It depends on how many precieved megapixels each can put on the sensor.  I have seen cases where the EF-S lens actually put more precieved MPs on the sensor as the very expensive "L" lenses can.

[cicopo]

I think you've mis understood my remark. The crop body sensor doesn't need the extra diameter of an EF lens therefore light from the EF lenses outer area misses hitting the sensor.

[ebiggs1]

Of course that is a real possibility. But......

"... not be as noticeably effected by their softness in the corners & edges because it crops that area out."

The sharpness of the photo is determined by how many precieved MP that can be put on the sensor.  In a quite a few circumstances the EF-S lens put more.  Is that not what you meant?