Is a 2x teleconverter useful?

August 17, 2017  •  Leave a Comment

I have a 70-200 2.8 Nikkor lens that I am quite happy with. On rare occasions, I want a longer focal length. (I am not generally a nature or wildlife photographer). After looking at the prices of 400mm FX lenses, I quickly decided a longer lens was not in the cards. So I decided I could make my 70-200 2.8 into a 140-400 5.6 with a TC-20E for less than $500. I expected some degradation of the image (as compared with a 400mm lens), but thought the results would probably be acceptable.  (Note:  I am shooting with a Nikon D800E, which gives me about 36 mpix.

I was initially pleased. At some point, however, I took a series of images with the TC-20E on my 70-200 at a focal length of 400mm. The subject was about 1/2 mile away over open water. The results were not as clear and sharp as I expected. So, I upgraded my technique to make sure the camera and lens remained rock steady during the exposure and experimented to find f/8 as an optimal aperture. Then I had an idea for a further experiment.

I photographed a distant subject, first with the converter for an effective focal length of 400mm, then without the converter at 200mm. In post processing, I cropped and upsampled (using Photoshop's default algorithm) the 200mm image so that it had the same angle of view as the 400mm image. I was surprised to find that the upsampled 200mm image had more sharpness, clarity and contrast than the 400mm image. I suppose that the upsampling algorithm does some sharpening on the way, so I applied the unsharp mask to the 400mm image to obtain similar results, at least in terms of sharpness. But I was not happy to achieve for several hundred dollars something that is merely similar to what I could have done in software.

I repeated the experiment on a D700 (12 mpix).  This time, the lack of sharpness was a bit less noticeable, but still present.

Conclusion:  Don't bother with the TC-20E if you're using a high megapixel camera.  If your camera has less resolution, you might make out better.

Tom


Comments

No comments posted.
Loading...

Archive
January February March April May June July August September October (1) November December (1)
January February March April May June July August September October November December
January February (1) March April May June July August September October November December
January February March April May June July August September October November December
January February March April May June (1) July (2) August (1) September (1) October November December