4 replies to this topic

[Gabriel]

Hello, can someone help me pls in this question.

I have two nikon lenses 

1. 18-200mm 1:3.5-5.6GII ED DX

2. 55-200mm1:4-5.6G ED DX

Recently i made some test pictures whit the same setings same F number same shutter speed, same iso, and 200mm focal lenght but i noticed that the 55-200mm brings the subject more closer than the 18-200mm lens does is this normal or i should return it for service??

thanks for help

Attached Thumbnails

• 
• 

[Merco_61]

At what distance are the pictures taken? There are two factors that can work together in this case.

1. Nominal focal length vs actual f/l. Sometimes lenses are marked with a focal length that is rounded to the nearest larger nice and round number.
2. Focus Breathing. As you focus closer, the focal length becomes shorter because you move elements in the lens relative to each other. Bob Atkins has a good article about this on his site.

The 18-200 is well known as a focus breather, at the near focus limit it is more like a 135 than a 200. To compare tele lenses of different construction, use long distances, for example a moon shot instead of a closer range.

[Afterimage]

Merco mailed it right on the head. My guess is that the claimed focal length isn't the actual focal length of the lens. Sort of like how they round up engine displacements in cars. 

[Gabriel]

Thx for the answers, both pictures were taken from the same distance 9-12 m, well that was an interesting and a very good article, and i now know that at least my lens it is not broken...  have both lenses from.... 1 year or so... but never noticed this before. Now i know a new term "Focus Breathing" Thanks guys!!!

[Adam]

Moved to the lens forum