Nikon zoom lens comparison. Some surprising results!

[brman]

I've just a 80-200 f/4.5n AI lens off ebay so thought I would do some very crude comparisons against my 18-200VR and 70-300VR lenses.

Given they weren't very scientific I would not take too much notice of the resolution results but they showed (all at roughly 200mm) the 80-200 to be pretty much the same as the 70-300 while the 18-200 was significantly worse. Maybe not a big surprise but I was pleased to find a 30 year old design matched a modern one.

The surprising thing was the focal lengths. Take a look at the following full pics, all the full frames and all taken on 200mm focal lengths (i.e. max on the 18-200 and 80-200 and the 200 mark on the 70-300).
1. 18-200VR

18-200VR full frame at 200mm by tobyjm, on Flickr

2. 70-300VR

70-300VR full frame at 200mm by tobyjm, on Flickr

3. 80-200 AI

80-200 full frame at 200mm by tobyjm, on Flickr

It is immediately obvious that the focal length of the 18-200 is way off compared to the other two. In fact, if I calculate it from the image size, object size and distance I get about 150 to 155mm. Over 20% less than the spec of 200mm!

Am I going mad or have Nikon really made a lens that is that far off the spec?

btw. this is an original VR version for the 18-200, not the later VR2 version.

Toby

 

[TomB]

I seem to remember reading that 18-200 really was actually only about 160 in reality, which would roughly match your findings.

 

[Meds]

Therefore why would they label it as 200mm?

 

[Kaolin]

This is focus breathing (link), the focal length varies with the subject distance, its smaller at closer distances. This does have the "advantage" of reducing the minimum focal distance. The 70-200 vrII shows strong focus breathing.

 

[brman]

This is focus breathing (link), the focal length varies with the subject distance, its smaller at closer distances. This does have the "advantage" of reducing the minimum focal distance. The 70-200 vrII shows strong focus breathing.

Ah, I knew about focus breathing but had no idea it could have such a dramatic affect.

Thanks
Toby

 

[brman]

for completeness I did a couple of quick checks this morning. At much larger distances (ie. close to but not quite infinity focus) there was much less difference in focal lengths. I reckon the 18-200 was still over 10% down on the other two but at least it was in the same ball park!

I guess I should stop over-analysing my lenses

Toby

 

[Gary Coyle]

Ah, I knew about focus breathing but had no idea it could have such a dramatic affect.

Thanks
Toby

The 70-200 VRII is only 135mm at shorter distances, i bought one and sold ASAP.