I heard Canon 50Ds dont work well with a fish eye lens, any truth to this

[Moglex]

I'll leave it to someone else to answer now just in case we're talking at cross purposes and I'm spouting complete rubbish.

 

[Sachphotography]

I am probably the one who is wrong here but IDK. Like I said. I am not really usually worried about focal length numbers. They are just a reference. I frame my shots by what I see.

 

[Joves]

I am probably the one who is wrong here but IDK. Like I said. I am not really usually worried about focal length numbers. They are just a reference. I frame my shots by what I see.

If you buy a lens made for a cropped sensor then it is the true focal lenght. So a 10mm is a 10mm. If you buy a Film/Fullframe lens then yo tkae whatever your bodies crop is and, multiply the focal lengthX crop factor= Actual focal lenghth. So a 10.5mm film lens is 15.75mm on a body with a 1.5 crop.

 

[Moglex]

If you buy a lens made for a cropped sensor then it is the true focal lenght. So a 10mm is a 10mm. If you buy a Film/Fullframe lens then yo tkae whatever your bodies crop is and, multiply the focal lengthX crop factor= Actual focal lenghth. So a 10.5mm film lens is 15.75mm on a body with a 1.5 crop.

The underlined sentence is incorrect.

A lens has a focal length (or range of focal lengths) and that that is inherent to the lens. If a lens has a focal length of 20mm it will have that focal length whether on a crop sensor camera, a full frame camera, or sitting in its box!

What you can say is that if yo wanted to get the same field of view with a full frame camera as you do with a crop sensor camera with a 20mm lens mounted, then you would need to use a lens with a focal length of ~32mm.