Planning to get another lens(es) Need some help!

[OldClicker]

IMO, a 70-200mm lens on a cropped sensor body is a 70-200mm lens. The lens doesn't change and there is no magic involved to make it longer. The cropped sensor only uses ½ the area of the image (as compared to a ‘35mm’ sensor) so there is less in the viewfinder, but it’s not closer. - Terry

[Photo-John]

IMO, a 70-200mm lens on a cropped sensor body is a 70-200mm lens. The lens doesn't change and there is no magic involved to make it longer. The cropped sensor only uses ½ the area of the image (as compared to a ‘35mm’ sensor) so there is less in the viewfinder, but it’s not closer. - Terry

Sorry I glossed over the focal length. The Canon APS-C sensor cameras like your 550D have a 1.6x crop factor. That effectively makes a 70-200mm lens into a 112-320mm zoom.

And to follow up on OldClicker's comment - technically, the lens is still a 70-200. The true focal length and optical properties aren't changed by what is essentially an in-camera crop. However, even though the optical properties are the same, I still consider that my lenses are "effectively" converted on an APS-C sensor camera. That crop counts for me and it's part of the reason I've chosen to commit to the smaller sensor Canon cameras.

[OldClicker]

Sorry I glossed over the focal length. The Canon APS-C sensor cameras like your 550D have a 1.6x crop factor. That effectively makes a 70-200mm lens into a 112-320mm zoom.

And to follow up on OldClicker's comment - technically, the lens is still a 70-200. The true focal length and optical properties aren't changed by what is essentially an in-camera crop. However, even though the optical properties are the same, I still consider that my lenses are "effectively" converted on an APS-C sensor camera. That crop counts for me and it's part of the reason I've chosen to commit to the smaller sensor Canon cameras.

And I can't help following up either. Talking about the 'effective focal length' as if something is actually different was the most confusing concept I encountered as a beginner two years ago until I figured out that chopping the center out of the image does nothing but make the image smaller. And I especially think it is wrong to suggest this as a reason for choosing one camera over another. - Terry

[Photo-John]

I understand, Terry. But maybe you need to see through my eyes. My camera choices are the Canon 7D, the EOS-1D Mk IV and the 5D Mk II. It's true I could crop 1D Mk IV or 5D Mk II images and get the same field of view. But what I can't do is ride my bike on 15 miles of technical terrain at 9000 feet of altitude with those cameras. And if I did, I'd have to carry a 300mm lens as well as those huge heavy cameras to get results comparable to what I get with my 7D and a 200mm lens. It's just not realistic or practical. My 7D also cost a lot less than either of those full frame cameras. So like I said, technically, you're absolutley right. But for practical purposes, I think the "digital conversion" is a legitimate factor. Especially if light weight, size and budget are worked into the equation.

[OldClicker]

I understand, Terry. But maybe you need to see through my eyes. My camera choices are the Canon 7D, the EOS-1D Mk IV and the 5D Mk II. It's true I could crop 1D Mk IV or 5D Mk II images and get the same field of view. But what I can't do is ride my bike on 15 miles of technical terrain at 9000 feet of altitude with those cameras. And if I did, I'd have to carry a 300mm lens as well as those huge heavy cameras to get results comparable to what I get with my 7D and a 200mm lens. It's just not realistic or practical. My 7D also cost a lot less than either of those full frame cameras. So like I said, technically, you're absolutley right. But for practical purposes, I think the "digital conversion" is a legitimate factor. Especially if light weight, size and budget are worked into the equation.

(Sorry about hijacking your thread. I did make some, I hope, useful comments earlier.)

Price, absolutely (and very important). Weight/size - Usually, but a 5D weighs less than the 7D. You can get the same shot on the full frame as you can on the APS with the 200mm lens - OR - you could always just use some tape to cover up 3/4 [EDIT - sorry, 1/2] of the area of a 100mm lens, get the same image and your kit would be lighter and cheaper yet.

I understand that the overall feature set of the 7D makes it a great choice for what you are doing, but I just cannot see equivilant focal length as a valid reason for choosing a camera.

Terry