Utter twaddle!!! She clearly needs to learn something about landscape photography before she teaches it......

You only have to read AP fairly regularly to realise that just as many fine landscape pictures are taken with medium and even long telephoto lenses.

Any ultra-zoom is a bit of an optical compromise but most of the modern ones are far better than they were even a few years ago, especially stopped down. The 10-20 may only be a 2x zoom but ultra wide angle zooms are very tricky things to design and use. IMO a 10-20mm lens is more likely to frustrate an inexperienced user than inspire them. It's all too easy to get vast acres of utterly dull foreground or sky while the meat of the picture is reduced to a minuscule dot in the background........

None to begin with... I have had my 10-20mm Sigma for over a year now and am only just getting to grips with what it can do, what it can't do and how to control, or use creatively, the distortions and convergence/divergence of verticals that are inherent in this kind of lens. It's not a lens I'd honestly recommend to a beginner.

Quality wise the Sigma is probably about the best you get in the price bracket though I imagine Tamrons 11-18 is pretty similar as is the Tokina 12-24 (though that's a little more expensive). The Nikkor lenses may well be a bit better but they are considerably more expensive......

This woman is clearly not fit to be teaching photography. She is meant to be teaching technique not peddling her own prejudices nor persuading herself that she's bought the 'right' camera by convincing others to do the same... BTW that's not to be inferred as any kind of anti-Canon comment as I have and use Canon digital cameras.

The camera 'to have' is the one you are comfortable using not the latest trendy model. Indeed the camera 'to have' amongst many of the real top landscape pro's is not digital at all but still uses that funny chemical stuff called film that comes in 5x4 inch sheets....... but I bet you don't fancy rushing out to buy one of those.......

If you want to improve image quality then by all means save for better lenses - and even today primes still have the edge though there are few that are really wide enough for APS format digitals - and buy yourself a good sturdy tripod, that will probably do more for your image quality than anything.

Personally I would write a letter to the institute that ran/runs the course suggesting that their instructors would do better to concentrate on basics and technique rather than trying to sell cameras and lenses...