Will a Sigma 15mm Fisheye Work on an XSI??

I am looking into getting a fisheye but I wanted to make sure it would work with my XSI before I purchase. I have heard something about needing a full frame mirror or something like that to be able to get 180 degrees.

It will work on your XSi, but because of the crop sensor of the camera, you won't get as pronounced of a fisheye effect.

it would work. you wont get much fish effect though.

get the sigma 10mm f/2.8 if you want a better fisheye for your camera.

Don't forget the Tokina 10-17....also made for crop cameras, with the flexibility of a zoom (and very good image quality). Great lens. Works on 1.3x cameras at 12.5mm and beyond, and on full frame at 15mm and beyond too, so it's very versatile.

wow thanks guys for the quick responses, what is the difference between the 10mm and 15mm besides the obvious? Why would the 10 be better than the 15?

The Sigma 10mm fisheye is designed for the XSi and will give you almost 180 degrees. The 15mm fisheye is not very wide, an UWA lens like the 10-22 is wider on an XSi.

Roughly the difference. I wish I still had my Tokina 10-17 FE. Awesome lens, I would post a more equal example.

10mm

yes it will work on an xsi.

I really like my sigma 15. It is a FF lens but I used it on my cropped cameras for years. On a 1.6x, the distortion is not as pronounced as it would be on full frame and you won't get 180 degree diagonal FOV. A straight line going across the middle of the frame will be straight, distortion gets heavier away from the center. Depending you what you shoot, distortion may appear anywhere from heavy to barely noticeable. Things shot close up will look pretty distorted. On FF every shot is heavily fishy. If you want super fishy images then get one made specifically for cropped cameras. Personally I find that the FF fisheyes are useful for more situations on a cropped camera than on FF, where the distortion is just too heavy many times.

That's the beauty of the 10-17...you can get that crazy, near 180 degree FOV at 10mm...and temper the distortion and get a near rectilinear UWA at 17mm. (17mm fisheye is roughly as wide as 12mm rectilinear...10mm fisheye is WAY wider than 10mm rectilinear.) On my 1DII, I get a full 180 degree shot at 12.5mm, and still get to temper the width a bit to 17mm.

Flyguytki wrote in post #7326706
I am looking into getting a fisheye but I wanted to make sure it would work with my XSI before I purchase. I have heard something about needing a full frame mirror or something like that to be able to get 180 degrees.

Just to make sure you understand what's going on:
A camera with a sensor just as big as a 35mm film has a so called full frame sensor.
Your XSI has a so called crop sensor in the APS-C format, which is 1,6 times smaller then a full frame sensor.

If you use any lens that was made for full frame on a crop sensor body, the photo you get is a cropped version of the image you'd get on the full frame one.
Also, when using for instance the Tokina 10-17 mm fish eye that was made for crop sensors on a full frame body, you'll get vignetting at 10 mm.

A 10 mm fish eye lens on a 1,6 x crop sensor gives the same effect as a 16 mm fish eye on full frame.
10 x 1,6 = 16.