Help a newbie buy a lens

[redu]

I am a beginner into the technical side of photography and I have been having trouble figuring out which lens to buy, so I found this forum I thought there might be someone here who can help.

I have a Canon 400D and a Canon EF-S 18-55mm F3.5-5.6 and I am looking for a wide-angle lens with a large aperture. I need something around 20mm, but I am getting confused about the whole EF/EF-S thing.

Is 18-55mm on the EF-S the same as on a EF lens or are the numbers adjusted to the smaller sensor, so that it appear as 18-55mm would on a EF, or is it just the mount that is the only difference between Ef and EF-S?

So to get a circa 20mm on the 400D, what lens should I buy, considering I need an aperture of F1.4 or F1.8?

I have been thinking about the Sigma 20mm f/1.8 EX DG Aspherical RF, but that won't be a 20mm on the smaller sensor, right?

Thanks in advance, I really hope someone her can help!

 

[Big Mike]

Welcome to the forum.

The focal length of a lens is a constant...18mm is always 18mm, it doesn't change from one camera to another. However, the field of view changes if you go from a crop camera (like yours) to a full frame camera.

Now, EF-S lenses have a slightly different mount and a smaller image circle than EF lenses. EF-S lenses are for crop bodies only. EF lenses can be used on either crop or full frame bodies.

On you camera, the EF-S 18-55mm lens will give you about the same wide view as the EF 17-40mm F4 lens. The 20mm lens won't be as wide.

If you want a wider angle of view on your camera, you need to look at something like the EF-S 10-22mm. Another option is the Sigma 10-20mm. If you really need a wide aperture, then the Tonkina 11-16mm F2.8 is an option.

Do you really need F2.8 on such a wide lens though?

 

[AlexColeman]

If you are looking for something wide, you can check the Sigma 10-20.

 

[redu]

Do you really need F2.8 on such a wide lens though?

I dont know much, but why wouldn't I need a big aperture on a wide angle lens?

I am leaning towards the Sigma 20mm f1.8 because it has the big aperture, and I dont really need it to me a zoom, like the 10-20mm. But is there something I dont know about wide angle and big apertures?

Thanks

 

[LarryD]

Maybe we could help you better if you could tell us what you intend to use the lens for that you don't get with your 18-55.

A wide angle lens has a broader field of view and therefore has more light overall entering so a larger aperture is not always needed to get a decent exposure...

Wide angle lenses also tend to distort the image so if you want that effect, go wide.......otherwise, step back some more..

 

[weddingguy]

Probably the most expensive part of my equipment are the lenses that I bought that ended up not doing the job for me. I shoot Canon . . bought canon's cheaper lenses . . sold them and lost $$$ . . . bought Sigma . . sold them and lost $$$ . . bought Tamron . . sold them and lost $$$. Learned my lesson the hard way and bought Canon "L" glass. No matter how many cameras Canon dangles and talks me into buying I will always have the good glass! Best investment you can make, and much cheaper than trial and error!