I finally got a little time (and sunshine) to head out to the local nature center to fiddle around with my 600mm VR lens and try it with the TC-20E III. When you are using long lenses, tripods are absolutely mandatory; hand-holding is not at all feasible (well, maybe if you pump iron like Ah-nold).
I started off with my normal combo for small birds: 600mm + TC-14E. This gives an effective 840mm focal length on my FX Nikon D3s. The TC-14E only costs one stop of light, so my lens behaves as though it were f/5.6 instead of f/4 when it is wide-open. I’ve used this combination several times in the past, and it works really well. I get sharp images and AF performance is still very fast and accurate.
I then decided to experiment with the TC-20E III, effectively doubling my focal length to 1200mm, but costing me two full f-stops of light. That means my lens now is f/8 wide-open. To ensure that camera shake would be minimized, I used the auto-ISO feature on the D3s and set the minimum shutter speed to 1/1000s. I also utilized VR in “tripod mode” to hopefully offset small camera vibrations. When you have that much focal length, it can be quite a challenge to get sharp shots of distant objects– even the tiniest camera movements are translated into large image shifts.
I was able to get very nice results shooting small birds from 25 feet away. I was pleased with the image sharpness in my “keepers,” and I got very good results at f/11 and f/13. I wanted to stop down from wide open to not only improve image quality, but also eke out a little more depth of field. Birds are notoriously hard to get critical focus on; their breast feathers stick out and tend to be what the AF grabs onto, leaving the head and eye slightly soft in the background.
Autofocus performance with this combo is hit or miss. I found that pre-focusing and then engaging the AF system with the AF-ON button was the best method for me. Initial acquisition of the target was otherwise a very slow process as the lens racked back and forth through the focus range.
In all, I was very pleased with the images I got with the 600 + TC-20E III. However, I’ll probably stick with the TC-14E in most circumstances where I want optimal AF performance. I won’t be afraid to use the TC-20E III if I need to; the image quality is quite good– surprising for a 2x TC!