I just purchased a Nikon D40 with the 18-55 mm AF lense and a 70-200 mm AF lense. I would like to get another telephoto lense and have read the Tamron 200-500 is a great lense. My question is will the Tamron's Auto Focus work on the D40 or will I have to manually focus the camera? Also, in Tamron's literature it says it works with an APS-C size digital SLR. What does that mean? Also, the focal length is equivalent to 760mm. What does that mean? I believe that you will have to manual focus, but you can get focus confirmation using the D40's rangefinder. I'm not sure if you can use this feature at full zoom, because the manual says, "If the lens has a maximum aperture of f/5.6 of faster, the viewfinder focus indicator can be used to confirm whether the portion of the subject in the selected focus area is in focus. After positioning the subject in the active focus area, press the shutter release button halfway and rotate the lens focusing ring until the in-focus indicator is displayed." Does this mean it won't work (confirmation beep) if you are at 500 mm where the maximum aperture is 6.3? I don't know. But, yes, you will have to focus manually.
Your camera has a Nikon DX sensor, which is close but slightly different than Canon's APS-C sensor. The lens factor (or crop factor) on the Canon is 1.6x and the Nikon is 1.5x, so this would be an "equivalent" of 300-750 and not 320-800 as it would on a Canon.
Tradition dictates that lens focal lengths are usually expressed in terms of "35 mm equivalent," where "35 mm" refers to a 35 mm film camera. This is because of the relation between the sensor size and the actual focal length of the lens and the resultant angle of view of the lens. Here is a mini-tutorial I made myself to compare focal lengths. This is NOT a lens test or a camera test! It is merely intended to show the difference between various focal lengths. The camera was a Nikon D200 and the lens was the Nikon 18-200 VR lens. There is further explanation on the image itself. It would help if you click on "All Sizes" above the image. This does not go higher than 200 mm (300 mm equivalent), because I don't have a super-zoom like the 200-500 that you are looking at, but it will give you a clue about comparing actual focal lengths to the 35 mm equivalent when using a Nikon DX sensor - as is found in the D40.
http://www.flickr.com/photos/7189769@N04... When it says its works for APS-C sensors it means its equalitant to a 35mm so it is 200-500mm on an APS-C sensor beacuse it was designed for APS-C sensors. I do not know anything about Tamron lens for Nikon. Sorry I cant help you therre |
