DX vs FX: crop factor or no crop factor

Tam, the DX lenses are essentially optimized for the sensor. But the cropping is done at the sensor. So, yes, regardless of the focal length, it will still be cropped at when measured against a FF. This months Popular Photography has an excellent article on the subject.

That means I will never be able to experience the true view of wide angle until I get a FX body :(

On the same note, my assumption is the new Sigma 10-20mm F3.5 EX DC HSM (http://www.sigmaphoto.com/lenses/lenses_all_details.asp?id=3360&navigator=6) has the same effect: I'd get the 15-30mm view compared to a FX body, even though the lens is designed for small sensors?

Thanks for your input Mark.

An 18mm DX lens and an 18mm FX lens will look the same on a DX sensor. They will both look like a 27mm lens will look on an FX camera.

On an FX camera, an 18mm FX lens will look like an 18mm lens, and an 18mm DX lens will look like this (shot on film but it works the same), which I actually like:

I'm sure I'm not the first to ask this question: why the hell do they call it 18-135m, instead of 27-202.5mm then?

Thanks guys btw, that cleared it up.

Tam, it's all about sensor size, and the "industry" likes to compare any sensor that is not FF to the "effective" FF focal length.
So yes, you're correct...an 18mm focal length on a DX sensor, is the "equivalent" of 27mm on a FF.
This is one of the reasons why users of DX sensor cameras, such as myself, have 'ultra' wide-angle lenses, such as the 11-17 that I carry.
I HIGHLY recommend that you read the article I referenced above, as it will help your understanding of what is going on with focal lenghts of the different sized sensors.

Mark

They call it that because the focal length is 18-135mm. The field of view is a function of focal length and film/sensor size. Focal length is a physical characteristic of the lens.

Tam, Andew explained it the most simple. It's all about the sensor size. The focal length of the lens does not change if it's placed on a 4/3, DX or FX sensor camera. Only the output of your picture based on the crop-factor of the sensor.

Thanks a bunch guys. It has been very helpful.

If you use the same lens on different formats the field of view changes. The focal length does not change. Example: in DX a 33mm lens with give about the same 46 degree field of view (which is concidered a standard for as long as I can remember) as a 50mm gives in FX or film. In medium format 645 a 75mm lens gives about 46 degree field of view. In 6x6 its an 80mm which is also close in 6x7 format. I think a 150mm or 180mm is about normal for 4 inch by 5 inch format. All this is approx. depending on how the angle is measured but fairly close. IMHO its important to concider the prespective change that occurs when changing the focal length. If you want an ultra wide angle lens for DX look at the many zooms offered in the 10mm to 24mm range. You might have an easier time if you think about field of view. Greater than 64 degrees or so starts the wide angle range. I consider 90 degrees very wide.