The Nikkor 200-400mm f/4G VR is a very versatile and sharp lens and those that own it or previously used it know that is a great choice for close action photography, such as photographing bears in Alaska. I recently saw a comment by a photographer, who claimed that the lens gets even sharper if its front protective filter is removed. Both the Nikkor 200-400mm f/4G VR and its newer VR II version have a removable front protective element, as well as a 52mm drop-in filter that most other super telephoto lenses have. While I was testing my 200-400mm f/4G VR in my Imatest lab, I decided to compare the performance of the lens with and without the front protective and the 52mm drop-in filter to see if the above claims were true or not. It turned out to be an interesting study. I apologize for the geeky nature of this article!
I measured the performance of the lens for this study at 200mm, so let’s take a look at how the lens performs with and without the filters:
The results on the left represent the performance of the lens with both the protective and the 52mm drop-in filters in place. Look at what happened when I removed the front protective filter in the second result set “No Front” – the image became blurry and I could actually even see this blur on the camera Live View. Looks like the front element actually does affect the way light rays bend inside the lens: removing the front filter actually slightly changes the focal plane. After I re-acquired focus again without the filter in place, the image sharpness went back to normal, as seen from the third result set “No Front RF (Re-Focus)”. If we compare the first and the third result sets, that’s basically what happens in reality with and without the front protective filter. Although there is a very slight difference in numbers, those are within the error threshold. And even if they weren’t, you would never be able to tell the two apart with your eyes!
The fourth result set was an interesting one. Without changing anything, I simply removed the 52mm drop in filter. To my surprise, I could immediately see the Live View image turn from sharp to complete blur, as seen from the crop below:
Whoa! Now that’s interesting. It turns out that the 52mm drop-in filter severely moves the focal plane. So it is not just sitting there for nothing!
The last test was to see if I could obtain proper focus without the filter. The fifth result set called “No Drop-in RF (Re-Focus)” shows that I could. And if you compare the result with the first and the third result sets, it is actually pretty similar again.
Conclusion
The above study shows us that one should not be removing protective and drop-in filters from super telephoto lenses like the Nikkor 200-400mm f/4G, as they are clearly there for a reason. While removing the front filter does not do much aside from exposing the fragile and expensive front element, removing the drop-in filter drastically moves the focal plane, which might result in all kinds of focus problems and inconsistencies. The photographer who indicated that his lens was sharper without a filter most likely had focusing issues, or his testing methodology had some flaws.
I am heading out to the mountains for our fall workshops tomorrow, but once I come back, I am planning to finally review the Nikkor 200-400mm f/4G VR, along with a few other cameras and lenses. I apologize for the wait!