Canon EF-S Lenses

[kennygee]

Why did Canon bring out the EF-S lens?

Will it raise compatibility issues with my present range of EF lenses for future generations of Canon bodies?

Does the 1.6 'crop factor' still apply with these lenses?

[Adey Baker]

They're designed specifically for more recent digital cameras with the 1.6 crop factor-sized sensor and won't fit anything other than those models stated (at the moment, 300D, 350D and 20D) as they're a bit shorter at the back end.

The crop factor still applies.

As long as Canon keep making bodies with a similar-sized sensor they'll keep making these lenses and probably add a few more.

Independent lens makers' offerings with a similar sized image-circle will fit other bodies even full-framed ones although with those you'll get a circular image in the middle of the frame. Some of the zoom lenses can actually be used over some of their range with the 1.3 crop-factor 1D bodies without cut-off (tests in photo magazines will usually give the range possible)

[kennygee]

Adey,

Thanks for the reply.

To satisfy my curiosity, what is it about the EF-S fitting that makes them more suitable for DSLR's. How is the shorter back end an advantage? To put it another way, how are they more suitable than the EF fit?

[Leif]

Originally Posted by kennygee

Adey,

Thanks for the reply.

To satisfy my curiosity, what is it about the EF-S fitting that makes them more suitable for DSLR's. How is the shorter back end an advantage? To put it another way, how are they more suitable than the EF fit?

Basically the smaller image circle gives the optical designer more freedom. In principle they can get a higher quality image in part because the lens can be designed such that light rays are mostly perpendicular to the sensor as opposed to at an angle. This is best of for the sensor. The jargon term for this is telecentric. In addition the lens can in principle be smaller and lighter. However, in practice APS sensor compatible lenses do not seem to be smaller or lighter than full frame equivalents. And as to whether or not they are better on APS cameras than full frame lenses, well ... who knows.

Leif

[Adey Baker]

And I'd better clarify my 'shorter at the back' bit which on re-reading looks a bit 'wrong!' I meant to say a bit 'closer' to the sensor than a conventional lens so they would foul-up the mirror if you fit them to an incompatible camera.

Most telephoto lenses where the rear element is a fair way inside the lens body seem to be OK, giving a near-telecentric design as described by Leif, so it seems as if the biggest advantage is in the re-designing of shorter focal lengths.

I've got one of Canon's basic 28-80mm zooms which gives reasonable results on my EOS 50E body but the images on my 20D body are not very good other than 'snapshot' standard.

[kennygee]

Adey

Thanks very much for the clarification. I undestand now.

Your help is appreciated.

[Leif]

Originally Posted by Adey Baker

And I'd better clarify my 'shorter at the back' bit which on re-reading looks a bit 'wrong!' I meant to say a bit 'closer' to the sensor than a conventional lens so they would foul-up the mirror if you fit them to an incompatible camera.

Most telephoto lenses where the rear element is a fair way inside the lens body seem to be OK, giving a near-telecentric design as described by Leif, so it seems as if the biggest advantage is in the re-designing of shorter focal lengths.

I've got one of Canon's basic 28-80mm zooms which gives reasonable results on my EOS 50E body but the images on my 20D body are not very good other than 'snapshot' standard.

Yes, from what I've read the main improvements are to be expected for wide angle lenses for the reasons you've stated. Leif