Optical Zoom Equivalent, Very Confused!

[Daniel G]

I've got a question and I've been looking for answers on my own, but things just don't make sense to me. I have a Digital Rebel XTi with a 28-300mm lens. Obviously, that 300mm is the equivalent of a 100* optical zoom digital camera. However, when I searched the equivalent optical zoom of the Canon Powershot S3 IS (which is obviously equipped with a much smaller lens and is a much cheaper camera), I found it has over 400mm of optical zoom. This just doesn't sound right to me, especially considering the price of 400mm lens for an SLR is pretty steep. Is there a logical explanation to this? Why would my $400 lens have up to 300mm zoom and a smaller cheaper "Advanced Digital" camera have an equivalent zoom of over 400mm?

Edit: Straight from DCResource: F2.7-3.5, 12X optical zoom lens, equivalent to 36 - 432 mm. (For the Powershot S3 IS)

[John_Reed]

I've got a question and I've been looking for answers on my own, but things just don't make sense to me. I have a Digital Rebel XTi with a 28-300mm lens. Obviously, that 300mm is the equivalent of a 100* optical zoom digital camera. However, when I searched the equivalent optical zoom of the Canon Powershot S3 IS (which is obviously equipped with a much smaller lens and is a much cheaper camera), I found it has over 400mm of optical zoom. This just doesn't sound right to me, especially considering the price of 400mm lens for an SLR is pretty steep. Is there a logical explanation to this? Why would my $400 lens have up to 300mm zoom and a smaller cheaper "Advanced Digital" camera have an equivalent zoom of over 400mm?

Edit: Straight from DCResource: F2.7-3.5, 12X optical zoom lens, equivalent to 36 - 432 mm. (For the Powershot S3 IS)I say that because your camera has a 1.6X crop factor, so if you really have a 28 to 300mm lens, that works out to a 35mm equivalent of 44.8mm to 480mm zoom range. So right off the bat, your lens gives more zoom than the Canon S3, if your numbers are correct.

But the big reason why your lenses cost more than the S3's lens is that your sensor (the digital "film" inside the camera that's exposed by light while the shutter is open) is much bigger than the S3's sensor. Lenses scale with sensor size, and a lens that works as well for your large-sensor camera as the S3's lens with its small sensor must of necessity be much larger to get the equivalent zoom range and aperture capabilities. Larger = heavier, more expensive.

[AlexMonro]

The actual sensor size of the Rebel XTi is 22.2 x 14.8 mm, of the S3IS is 5.76 x 4.29mm. The actual focal length of the lens on the S3IS is 6 - 72mm, which gives a field of view on the tiny sensor equivalent to a 36 - 432mm lens on a full frame (36 x 24mm) 35mm camera. Your 28 - 300mm lens, as John says, gives a field of view equivalent to 44.8 - 480mm on a full frame 35mm camera.

It's the tiny sensors on compact cameras that make it possible to make affordable, lightweight lenses with huge zoom range and vast depth of field. The downside is that they have horrible noise at high ISO settings.

[Daniel G]

Thanks, I understand the answer to my question and a bit more, too!