Looking to go digital - what should I get?

[Don Simon]

Edit: Mike you beat me again! I'm going to search my room for hidden surveillance devices

10-20mm is 10-20mm whatever the size of the sensor or film area. Whatever kind of lens and whatever kind of camera body, the focal length is 10-20mm. The field of view however will be different depending on the size of the sensor or film.

To give an example, 50mm on a 35mm camera is a "standard" lens. On a dSLR with a sensor 1.5x smaller than a 35mmx24mm negative, the effective field of view with that same 50mm is that of a short telephoto which is "comparable" to 75mm with 35mm film. If there was a sensor 2x larger than the 35mm format, then the effective field of view of a 50mm lens would be wide, and comparable to 25mm with the 35mm format. This is why I prefer to use the word "comparable", because the field of view you get with a lens of a given focal length depends on the size of the area on which the image will be captured. As mentioned by others, the main reason this causes confusion is because people are used to certain focal lengths giving a certain field of view on certain formats, whether 35mm film or smaller sensor digitals. The more different formats you shoot the more it starts to make sense.

The upshot of this is that the images you get with a 10-20mm lens on a Rebel XT will not have the same field of view as those produced with a 10-20mm on a 5D. The sensor on a Rebel is 1.6x smaller than the sensor on a 5D, therefore if you liked the field of view you get with a 10-20mm lens on a Rebel, you would need a focal length around 1.6x larger (16-32mm) in order to get a comparable field of view on the 5D.

You are correct in saying that an EF-S lens, being designed for a smaller sensor, will produce vignetting on a larger sensor.

 

[sothoth]

Edit: Mike you beat me again! I'm going to search my room for hidden surveillance devices

10-20mm is 10-20mm whatever the size of the sensor or film area. Whatever kind of lens and whatever kind of camera body, the focal length is 10-20mm. The field of view however will be different depending on the size of the sensor or film.

To give an example, 50mm on a 35mm camera is a "standard" lens. On a dSLR with a sensor 1.5x smaller than a 35mmx24mm negative, the effective field of view with that same 50mm is that of a short telephoto which is "comparable" to 75mm with 35mm film. If there was a sensor 2x larger than the 35mm format, then the effective field of view of a 50mm lens would be wide, and comparable to 25mm with the 35mm format. This is why I prefer to use the word "comparable", because the field of view you get with a lens of a given focal length depends on the size of the area on which the image will be captured. As mentioned by others, the main reason this causes confusion is because people are used to certain focal lengths giving a certain field of view on certain formats, whether 35mm film or smaller sensor digitals. The more different formats you shoot the more it starts to make sense.

Actually what Zapod is saying is what I just said, that a 10-20mm LENS is the same lens whether it's on a small or large sensor but the images won't look the same if you take a picture with the same lens on an EF-S or EF sensor (they will have a different field of view). I was not suggesting that the lens somehow magically changes it's focal length depending on what camera you put it on. But the images collected by the sensor will look different on full sized or small sensors. Hence the crop factor. The crop factor isn't meaningless, it does effect how the images look. The other difference is that the EF-S sensors are closer to the back of the lens than the EF sensor when the lens is mounted, so Canon (at least initially) designed the EF-S lenses so they can't be physically mounted on a camera with a full frame sensor since the mirror movement could be physically hindered and damage the mirror.

I think we're all in agreement but I described this in terms that were different from yours (and vice-versa) so it was confusing.

 

[sothoth]

I think we're all in agreement but I described this in terms that were different from yours (and vice-versa) so it was confusing.

Butterflygirl probably stopped reading this several posts ago...

 

[Big Mike]

The sigma 10-20 is designed for an EF-S sensor, so if you use the lens on an EF-S camera, you'll truly be looking at 10-20, right? The images should have the same angle of view as a full sized sensor will have if they use an non EF 10-20mm lens (that's designed for a full size sensor). Is that not correct?

That is where you were not correct. I think you understand how it works...it just came out wrong.

 

[sothoth]

That is where you were not correct. I think you understand how it works...it just came out wrong.

Oops, it was indeed a typo there. :blushing:

This chart is what I studied before I understood this better. Its still very helpful if any brain farts should arise about how "apparent" focal lengths (angle of view) changes with different sensors:
http://www.usa.canon.com/app/pdf/lens/EFLensChart.pdf