What’s Your Preference?

Zoohouse · #1 (**permalink**) 12-18-2009, 12:49 AM

I am still a little confused about something.

Do I need to still worry about the crop factor when I use a EF-S lens or is a EF-S 50mm going to give me the same view as a EF 50mm?

I am getting the impression that a EF-S 50mm lens still crops the image as if it were shot with a 80mm... If this is the case, what's the point of the EF-S series? Just cheaper because it uses less glass?

Thanks

firebox40dash5 · #2 (**permalink**) 12-18-2009, 01:05 AM

Quote:

Originally Posted by Zoohouse

I am getting the impression that a EF-S 50mm lens still crops the image as if it were shot with a 80mm... If this is the case, what's the point of the EF-S series? Just cheaper because it uses less glass?

Correct- focal length is focal length, whether it's full-frame or crop-frame. A 50mm EF-S lens and a regular old 50mm lens would give you the same image on a crop-frame camera. Lenses like Canon's EF-S and Nikon's DX series are smaller/lighter/cheaper because they only have to project an image circle big enough to cover the smaller sensor, not a full-frame sensor or 35mm film.

acedrew · #3 (**permalink**) 12-18-2009, 01:06 AM

Pretty much, they can also typically be smaller and lighter than their full-frame counter parts. Some EF-S lenses simply don't have equivalents in the FF world, like the Canon EF-S 17-85mm Zoom. You need to understand what Focal Length is before any of the crop factors make sense, the focal length really has nothing to do with the crop-factor, they're completely seperate. A 50mm lens is a 50mm lens no matter what size sensor is used. The crop factor is just a convenient estimate of the approx field of view achieved based on a standard photogrpaher's already know (35mm Full Frame Equivs)

PS. one benefit of using FF lenses on crop sensors, is that most lenses designed for FF have no noticeable vignette when used with a crop sensor.

Andrew Rodgers
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inkista · #4 (**permalink**) 12-18-2009, 01:18 AM

Look at it this way:

Same lens, but the inner frame is what a crop body image will be, the larger image is what the full frame image would be. The focal length itself doesn't change (i.e., you're not zooming in any more) across formats, it's just the amount of coverage the sensor can see that changes, and how large the image circle from the lens has to be to cover the whole sensor.

If an EF-S lens of the same focal length had been used for the shot above, the crop image would remain the same, but the full-frame image would have black corners, and you'd probably see the edges of the image circle from the lens within the edges of the frame. This is why EF-S lenses have an extra "bumper" flange on the back so that they physically cannot be mounted onto full-frame/film cameras.

Zoohouse · #5 (**permalink**) 12-18-2009, 08:36 PM

Ok so if I want the same view of a 50mm I need to buy a 30mm... Got it...

Amazon.com: Sigma 30mm f/1.4 EX DC HSM Lens for Canon Digital SLR Cameras: Camera & Photo

inkista · #6 (**permalink**) 12-19-2009, 12:47 AM

Quote:

Originally Posted by acedrew

Some EF-S lenses simply don't have equivalents in the FF world, like the Canon EF-S 17-85mm Zoom. ...

Bad example. That one was made to be the crop-body equivalent of the EF 28-135 IS USM. Exactly. (17-85)*1.6 = 27.2-135. Maybe you meant the EF-S 17-55 f/2.8 IS USM, instead?

And yes, to get the equivalent FoV of a 50mm on a full-frame body, you'd need a 30mm lens on a crop body. However. That doesn't mean a 50mm lens is useless on a crop. It equates to an 85mm, just as an 85mm equates to a 135; and a 135 equates to a 200. All of these are traditional prime focal lengths, and all are useful on both formats.

There's also another definition of normal, which is the lens with the focal length that equates to the diagonal length of the image plane (film or sensor). In the case of a Canon 1.6x crop sensor, that comes to about 27mm. In practice, a 28-35mm lens is probably going to get you the field of view that would be considered "normal" on a crop.

But because this is just the field of view we're talking about, and not the focal length, it won't actually be "normal" in terms of magnification. If you put a 50mm lens on your camera, and have both eyes open, the unaided view matches the view through the viewfinder. That can only be done with a 50mm lens. This is one of the reasons that 50mm was such a prevalent focal length throughout the film era--what the lens sees matches what you see without the camera.