Curtis Lowe thanks for your advice. I'm not sure what all the initials mean - is FF full frame? I haven't got my head around that yet. I seriously doubt I shall upgrade my camera for many years to come. Although I love photography, I am not terribly good at it. I don't know what the EF and EF-S lens mounts mean either. I shall take the advice to head to the Camera store to try and check out the two lenses. A friend who is rather more experienced in photography than me, says there wouldn't be much difference between the 10-20 and my 18-200 lens so I shouldn't bother buying the 10-20? Since I'm doing this big trip in May I'm keen to see if it is worth buying the 10-20. Some of the NP's I'm visiting are Canyonlands, Mesa Verdi, Arches, Sion, Bryce, Grand Canyon. Cannot wait.

I have a Canon 600D with a Canon 18-200mm lens. I am thinking of buying a Sigma 10-20mm lens for wide angle photography.

Two questions that I hope someone can help me with -

1. Can anyone advise if I will achieve a lot of difference between the 10mm and 18mm of these two lenses. In other words is it worth my buying the 10-20mm lens?

2. If I go ahead and buy the 10-20mm lens, is it worth paying the extra money to get the f3.5 or is the f4.5 sufficient for most occasions?

I'm doing a tour in May from Denver to Las Vegas via pretty much all of the National Parks enroute. I would really appreciate any advice on whether it would be worthwhile me buying the 10-20mm lens considering that I have the 18-200mm.

Many thanks in anticipation. If anyone had two photos of the same location showing the difference between the 10mm and 20mm that would be absolutely fantastic.

Nikon 10-24mm is a clear winner.

Sharpness is excellent even at the largest aperture, and images have bags of contrast, even when lighting conditions are flat and gloomy. The ring-type AF-S autofocus system is superbly fast, practically inaudible in operation and comes complete with full-time manual focus override.

Build quality is a good match for Nikon's top APS-C cameras, such as the D7000 and D300s, yet the lens still feels well balanced on lightweight bodies such as the D3100.

The only sticking point with the Nikon is that it's by far the most expensive lens in the group. For a more modest outlay, both Sigma 10-20mm lenses offer advanced features, but the older Sigma 10-20mm f/4-5.6 version is particularly good value.

The Tamron 10-24mm is the cheapest zoom lens in the group, but suffered from exposure inconsistencies in our tests and lacks the Sigma lenses' ring-type ultrasonic autofocus.

For maximum wide-angle coverage, the Sigma 8-16mm is a tempting proposition, but image quality isn't quite as good as with the two Sigma 10-20mm lenses. Another alternative is the Tokina 10-17mm fisheye lens, which gives the widest angle of view in the group.

But the fisheye effect is more of an oddity than something that will appeal on a regular basis. At the other end of the scale, the angle of view offered by the Samyang 14mm and Tokina 12-24mm lenses are disappointing, and the Samyang's distortion is pronounced, especially given that it's a prime lens rather than a zoom.

Best ultra wide-angle lens for Nikons

If you've got a bigger budget, the Nikon 10-24mm f/3.5-4.5G AF-S DX ED can't be beaten in terms of image quality.


GO BUY IT LADY!

I would strongly advise that there is a significant difference between 18mm and 10mm.
I think your friend is wrong.
I am primarily a landscape and seascape photographer.
If I had your camera and I could only choose 1 lens for landscape photography it would be either the 10-22mm Canon or the Sigma 10-20mm F/4.5-5.6.
I own this Sigma lens and use it on my Nikon D90. I already had the Nikon 18-200mm VRii.

The Sigma 10-20mm revitalised my photography. It is a brilliant landscape lens.
I wouldn't worry about paying the extra for the F/3.5.
You will take 99% of your shots at F/8 to F/22.

That is what these ultrawides are about - front to back sharpness and a strong foreground.
With this lens on your camera you can be in focus from 5 inches to infinity - so get low and close to a flower or a rock and put the Grand Canyon or a group of mesa behind it.
The slot canyons will love it.
With good light you will take the best pics you have ever taken.
It will blow the 18-200mm out of the water!!

Look into the Rokinon 8mm fisheye. Yes, there is distortion, but that can be fixed in post. I happen to like the distortion. The lens is fully manual. Landscapes are one of the subjects where "manual" doesn't hurt to bad, because nothing is moving. You can take your time. However, if you set theis lens to f/8 - f/11, and set the focus ring to just under 10ft, everything from 10 ft to infinity will be sharp. This lens is only $280. To my surprise, it is very sharp from f/5.6 on. I bought it as a "toy" to play with. I have actually sold prints taken with it. It has paid for itself many times over. Here is an example, I was practically standing on top of this thing.

I have a Canon 600D with a Canon 18-200mm lens. I am thinking of buying a Sigma 10-20mm lens for wide angle photography.

Two questions that I hope someone can help me with -

1. Can anyone advise if I will achieve a lot of difference between the 10mm and 18mm of these two lenses. In other words is it worth my buying the 10-20mm lens?

2. If I go ahead and buy the 10-20mm lens, is it worth paying the extra money to get the f3.5 or is the f4.5 sufficient for most occasions?

I'm doing a tour in May from Denver to Las Vegas via pretty much all of the National Parks enroute. I would really appreciate any advice on whether it would be worthwhile me buying the 10-20mm lens considering that I have the 18-200mm.

Many thanks in anticipation. If anyone had two photos of the same location showing the difference between the 10mm and 20mm that would be absolutely fantastic.