Magnification - 105mm vs 100mm

[Mario Xavier]

I just took a picture of a cup with two lenses from the same position and the 100mm image shows a larger cup. Wouldn't a 24-105mm @ 105mm image of an object be larger/tighter than the 100mm version as far magnification goes?

[PhotomanJohn]

Mario - In a perfect world the lens labeled as being 105mm should give you slightly more magnification that the 100mm. There are two reasons why this is not always the case. First the effective focal length of a lens may not be exactly what the model number would lead you to believe. They tend to round the number and the difference between 100 and 105 is small. The second reason is that the effective focal length of many zooms changes with focus distance. The current Nikkor 70-200mm f/2.8 has an maximum actual focal length of around 135mm when set at its minimum focal distance.

So the bottom line is not to worry. I suspect both lenses are functioning as designed.

John

[Mario Xavier]

Thank you for the explanation!