It is sometimes overlooked, but another benefit of a TC is the close focus ability it permits a lens +TC combo when compared to a lens with the same focal length that has no TC attached.

Usually, a prime lens (non macro) has a close focus of about 8-10x it's focal length for the shorter tele's and maybe 6-10x focal length for longer tele's. This is a little Nikoncentric as I shoot Nikon, but the same applies to basically all DSLR's. If we look at Nikons prime lenses (and this is pretty much the same for all manufacturers lenses), a 50mm lens for example usually has a close focus of about 45-50cms, an 85mm is about 75-85cm, a 300 is about 230cm(AF) 220cm(MF), a 600mm is about 480cm(MF) and 500cm(AF).

However, if you use a 300mm f2.8 VRII and add the 2x TCIII, you have a 600mm lens that can focus down to what the 300 can focus to of 220cms but obstensibly with the magnification of the 600mm lens due to the TC, therefore doubling the recorded size of your subject matter compared to a bare 300 or a normal 600.

I do find it an annoyance in many situations that primes generally only focus down to this 8-10x their focal length for shorter tele lenses and 6-10x at the longer teles, especially lenses like the 85mm f1.4G, which can limit it's use. I do like the idea of Zeiss's 100 f2 Makro Planar which is more like a close focus 100mm prime than a macro lens.

Anyway, you can use a TC on some of these lenses to get a much better close focus ability. The benefit can be abserved when trying to shoot very small birds like wrens, pardalotes etc where a normal prime may not allow close enough focus for the bird to fill the frame and therefore a TC can help.

Here are some quick test shots of the Nikon 300 f2.8 VRII + 2x TCIII on my D7000 all taken at focus distances of about 2.5mts or thereabouts. All using a monopod as support. Bearing in mind that some were taken at f8 and at this close range the DOF is only about 4mm!! It makes basically no difference if I had used a macro lens as the DOF at that distance with the same magnification and aperture results in simlar DOF.

Focal Length 600 mm
Exposure Time 1/250 sec
Aperture f/10
ISO Equivalent 400



Focal Length 600 mm
Exposure Time 1/100 sec
Aperture f/8
ISO Equivalent 400



Crop of above:



Focal Length 600 mm
Exposure Time 1/100 sec
Aperture f/8
ISO Equivalent 400



Focal Length 600 mm
Exposure Time 1/400 sec
Aperture f/11
ISO Equivalent 400



Focal Length 600 mm
Exposure Time 1/125 sec
Aperture f/11
ISO Equivalent 400