I'm about to buy a wide prime lens for my 7D. here are the 3 lens I'm considering,

1.Nikon Super Wide Angle AF Nikkor 20mm f/2.8D Autofocus (or the Manual Focus Lens. I heard that the manual version of this lens is sturdier but a little more expensive.)
2.Canon Super Wide Angle EF 20mm f/2.8 USM Autofocus
3. Sigma Wide Angle 24mm f/1.8 EX Aspherical DG DF Macro Autofocus

I already have the Zeiss 50mm 1.4 and I love the glass so i'm leaning a little towards the nikon cause I think optically it would be similar. (I'm aware that the 20mm when cropped would be about a 32mm) The problem with both the nikon and the canon at least for me is the 62mm filter size. I have two ND Fader's neither one would fit on both cameras but would work with the sigma which has a 77mm filter size. The ND faders were expensive so I would save some money with the Sigma.The sigma is a 24mm not as wide as the canon and nikon but that's not a big deal. Optically I have no idea how the sigma compares with the nikon or canon. All 3 are in the same price range between $450-520 so price is not an issue for me. I have one other question about all 3 lenses. Is there a switch on the lens to disable AF? Almost forgot to mention I bought my 7D primarily for filming. Any suggestions or input would be appreciated.

You can buy a step-down ring - 77 to 62mm for about $8 on ebay - I have 2 or 3 of these. They are a permanent fixture on all my lenses below 72mm anyway. Then you can get the Canon lens!

Hey Kaj, thought it's only 4mm, the difference in frame between a 24mm and a 20mm is very significant (at least full frame). With the crop sensor, I'd try and get as wide as I could, so I'd skip the 24mm and go with the Canon or Nikon, and use the step down rings that Jon suggested.

Best of both worlds.

Consider this:
Tokina 11-16mm f/2.8 AT-X 116 Pro DX Autofocus ATX116PRODXC -

or this:
Tamron 17-50mm f/2.8 XR Di II LD Lens for Can AF016C700 - B&H

Best would be:
Canon Super Wide Angle EF 14mm f/2.8L II USM 2045B002 - B&H

They are truly wide.

Consider this:
Tokina 11-16mm f/2.8 AT-X 116 Pro DX Autofocus ATX116PRODXC - (http://www.bhphotovideo.com/c/product/554035-REG/Tokina_ATX116PRODXC_11_16mm_f_2_8_AT_X_116.html)

or this:
Tamron 17-50mm f/2.8 XR Di II LD Lens for Can AF016C700 - B&H (http://www.bhphotovideo.com/c/product/423714-REG/Tamron_AF016C700_17_50mm_f_2_8_XR_Di.html)

Best would be:
Canon Super Wide Angle EF 14mm f/2.8L II USM 2045B002 - B&H (http://www.bhphotovideo.com/c/product/519474-GREY/Canon_2045B002_Super_Wide_Angle_EF.html)

They are truly wide.

I have the canon super wide on my wish list but not for this year. The tokina is hard to get around here.
i'm looking for prime lens but thanks.

You can buy a step-down ring - 77 to 62mm for about $8 on ebay - I have 2 or 3 of these. They are a permanent fixture on all my lenses below 72mm anyway. Then you can get the Canon lens!

is the step down a piece of glass that attaches to the ND fader or an adapter ring?

Hey Kaj, thought it's only 4mm, the difference in frame between a 24mm and a 20mm is very significant (at least full frame). With the crop sensor, I'd try and get as wide as I could, so I'd skip the 24mm and go with the Canon or Nikon, and use the step down rings that Jon suggested.

Best of both worlds.
I'll stop over at B&H tomorrow and try both the canon and nikon to see the difference. Thanks!

You can buy a step-down ring - 77 to 62mm for about $8 on ebay - I have 2 or 3 of these. They are a permanent fixture on all my lenses below 72mm anyway. Then you can get the Canon lens!
Found it nice!
step-down ring - 77 to 62mm (http://www.bhphotovideo.com/c/search?Ntt=step-down+ring+-+77+to+62mm&N=0&InitialSearch=yes)

Why not the Sigma 20/1,8? I love this lens, and it is fast... The thread is 82mm so you may need a new ND filter. What I like about this lens is the big focusring... You should check it out

cheers

didn't know they had a 20mm i'll check it out. thanks!