When using long telephoto lenses we often want even more reach and the use of a teleconverter is often considered.

The question is always at what cost to the image quality and convenience.
Adding a teleconverter – from here on referred to as a TC – adds more glass to the lens and will as a result block some light.

The Fujinon XF TC1.4 that I will test here adds 7 extra lens elements to the 21 elements of the XF100-400/f4.5-5.6.
This will block 1 stop of light and make f5.6 become f8.0.

Adding lens elements will naturally have some detrimental effect on the overall image quality, but if the TC is well designed it may hardly be noticable.

So I want to explore how this TC affects the image quality when matched to the XF100-400mm.

Some will argue that it is best to use a test chart to measure these differences, but I don’t shoot test charts. I am interested in seeing what happens in real life scenarios.
So I will use a mostly static subject out in the park for these tests.

I mounted the Fujifilm X-T3 on a tripod – Gitzo GT4543 – and a 10 second timer used to trigger the shutter.
I attemted to keep the central fucus point on the same point of the sign that I used as the test subject.
However, when adding the TC the framing and leveling of the camera did change a little.
This shouldn’t make too much of a difference as the framing will change in any case when adding the TC.

All the full size images are sized to 6240 pixels wide as that is the normal frame size of the X-T3.
If any images were cropped slightly they would be resized when exporting out of Capture One Pro to become 6240 pixels wide again.

All images shot in RAW.
I have applied some basic processing to the images:
Capture One Pro is used throughout.
Basic Curve: Auto
Black and white point set to maximize contrast without clipping.
Sharpening applied: Amount: 400 – Radius 0.5

I shot 12 frames at differnet focal lengths between 100-400mm (140-560mm).
Then I matched the frames that came closest to each other.
I have cropped slightly into one of the images in the pair to better match the framing between them.

Test One

This series was shot at f8.0 as that is the widest aperture with the TC at 400mm.
This will potentially give the TC OFF images an advantage as the lens has been stopped down.
All images shot at iso 500

First the full frames.
TC OFF on the left – TC ON on the right:


Now lets look at the 100% crops from the centre.
The TC OFF is the left half – the TC ON is the right half:


Test Two

In this comparison I have shot the-TC OFF series at f5.6 and the TC ON series at f8.0.
This should even out the quality difference between shooting the lens wide open and stopping it down to f8.0
All images shot at iso 500
The TC OFF images are now shot at a higher shutter speed to match the exposure.

First the full images – TC OFF on the left – TC ON on the right:

Here are the 100% crops – TC OFF left half – TC ON right half:


At this point I will have to conclude that the image quality is very close.
There is a very slight softening with the TC on, but it is almost impossible to see the difference.
If you didn’t loose 1 stop of light you could just leave it on all the time.
The reputation of the XF-TC1.4 is well deserved. Very impressive.


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