A little Monday morning humor

[pcasciola]

I was browsing J&R's site, and I came across an EF-S 10-22mm, allegedly for a Digital Elph or a 20D. Now, I've seen the Digital Rebel called a lot of bad things in my day, but NEVER a Digital Elph. :lol:

http://www.jr.com/JRProductPage.process?Product=4008477

[photography By Evangelos]

LOL :D Good one!




Angelo 8)

[cmM]

LMAO!!!!
Digital Elph :P

[thomascanty]

Hey, I have a Digital Elph (S330)! How do I make that lens work with it? :lol:

[booggerg]

Wow the crop factor still applies to EFS? :lol:

"Equivalent to a 16-35mm zoom"

[Jon]

Wow the crop factor still applies to EFS? :lol:

"Equivalent to a 16-35mm zoom"

Yeah. Focal length is an absolute metric. a 10 m lens will always have a focal length of 10 mm. "Crop factor" really relates the sensor sizes of the respective cameras (linear 24 mm/15 mm = 1.6x). The angle of coverage of a 10 mm lens on a D30/D60/DR/10D/20D is, because of the smaller sensor, equivalent to the angle of coverage of a 16 mm. lens on a full-frame 35 mm SLR.

[booggerg]

I thought the EFS series lenses are made for 1.6x crop factor cams. So the 10mm ought really be a 10mm.

[Persian-Rice]

Wouldnt a 20D be called the elph? they feel like a big P&S........

[Jon]

I thought the EFS series lenses are made for 1.6x crop factor cams. So the 10mm ought really be a 10mm.

They're made for the 15 x 22.5 mm sensor of the "1.6x crop factor" cameras. They can't cover a full 24 x 36 mm frame/sensor. They still have a real focal length of 10 mm, unlike the PowerShot P/S line where they advertise a "35 mm equivalent" focal length. But they're no different in coverage than a full-frame 10 mm. lens would be on a DR/20D. A picture taken with the new 17-85 EF-S at 17 mm will look identical in coverage to one taken by a 17-40 EF L at 17 mm, or Drisley's new love, the 17 mm Tokina prime on a DR or 20D. It doesn't matter that the one is EF-S and the other two are EF (full frame).

[booggerg]

I do'nt understand, I thought these lenses are made for 1.6x sensors, so shouldn't they focus their image onto a smaller size? So you'd be getting the full 10mm field of view instead of a 16mm field of view. So setting the EFS 10-20mm to 17mm on a 20D, you'd get the identical field of view as a 17-40mm L set to 17mm on a 1DS. Correct?

[Jon]

No. Focal length is an absolute measure of the distance between the optical center (nodal point) of the lens and the point at which a light source at infinity will focus. So a 10 mm lens will focus the light from the sun 10 mm from the optical center of the lens. A 16 mm. lens will focus it at 16 mm. from the optical center of the lens. And a 100 mm lens will focus it at 100 mm from the optical center of the lens. It has no bearing on how large an area a lens is able to illuminate (cover).

"Nodal point" isn't the same as the middle of the SLR lens, they play some tricks in the design of modern lenses to get something called "retrofocus", where the nodal point of a complex lens is physically outside the lens proper. You'll see focal length most easily with a simple magnifying glass, a close-up lens, or a pair of reading glasses (the reading glasses' "diopter" is 1/focal length in meters) in the sun.

The lenses being "designed" for different sensor sizes means that they can provide uniform illumination across (cover) a different amount of the sensor area. So "designed for 1.6x sensors" just means that the lens is only designed to "cover", or illuminate the 15 x 22.5 mm area of the DR/20D's sensor. It doesn't mean that it bends the light more than another lens would, to give you a larger angle of view. If it could bend the light more than the other lens, it'd actually have a different focal length. This coverage is sort of backwards vignetting (where a lens hood or filter gets included in the picture, so you get dark corners) if you like.

A 16 mm. lens designed for a DR/20D's smaller sensor will not even pretend to be able to cover (project the image on) a larger sensor area. If you were to put it on a standard 35 mm Eos, you'd see a circle in the center of the frame with black around the edges where the lens can't "cover". A 16 mm lens designed for a 35 mm camera will be able to "cover" the whole 35 mm frame evenly, with no blacking out at the corners.

But if you put either of them on a 20D or DR, they'd take exactly the same picture. And that picture would include exactly what you would see if you used a 25.6 mm (1.6x, remember) lens on a full-frame 35 mm camera at the same place. If you were able to put that 16 mm (1.6x crop) lens on an Eos full-frame camera, take a picture, change to a full-frame 16 mm lens on the same camera and take another picture, then superimpose the two images, they'd match perfectly.