VR 18 200 is really a 17 135

I just got my second VR 18 200. The first I returned because it was not very

sharp past 100mm.

 

The new one is sharp throughout its range but when set at 200mm it has the same

coverage as my VR 70 300 set at 135mm. I confirmed this with a fixed focal

length 180mm lens.

 

When set at 18mm the lens covers more than my 18mm f3.5 and when duplicating its

coverage with my Sigma 10 20 it looks to be a little less than 17mm.

 

Both tests were done at relatively short distances --- about 10 feet for the

long end and 3 feet for the 18mm setting.

 

Has anyone else run into this? This is a US lens purchased from Calumet and was

brand new when opened.

This has been discussed before and is normal. Focal lengths are measured at infinity.

It also has to do with the viewing angle of the lense. 18-135 is 76-12 degrees, while the 18-200 is 76-8 degrees. They even out at a further distance. And the 10-20 is a wide angle lense so there will me more in the picture and the same focul length.

<I>And the 10-20 is a wide angle lense so there will me more in the picture and the same

focul length</i><P>

 

Huh? Different fields of view at the same focal length on the same camera? This must be

some new kind of optical physics that I'm unfamiliar with.<P>

 

Kidding aside, as long as you are not dealing with optical oddities like fisheye lenses, field of

view (i.e., how much is in the picture) with a given camera depends on focal length and....

nothing else.

Internal focus changes the focal length. Consequently, the nominal focal length is specified when the lens is focused at infinity. The field of view of any lens changes with the focal distance, even one which focuses with a threaded helix only. Finally, the engraved focal length is nominal. For example, a nominal 50mm lens may be 52mm by design.

IMO, a Nikkor 18-200 VR is almost 99,9% a 18-200mm. But, really, a 18-200, anyway.

 

Regards.

I ran in to this years ago when the first super zooms came out, I had an internal focus Tamron 28 to 200, and at 10 to 20 feet distances, my Nikon 70-150E zoom was higher magnification than the 200 end of the Tamron (which even at infinity was more like a 180mm). I guess the term "rounding up" would apply.

Further results on the 18 200 at infinity - my tests indicate it is a 18 160 lens and sharp enough for amateur use but not up to professional standards.

 

It is really remarkable how good the lens is given its 11:1 zoom ratio but at enlargements of 11x14 and up, details are lacking throughout its focal length range at all f stops.

 

This is the second example I have tried, time to punt on super zooms.