Do You Really Need a Teleconverter?

Do You Really Need a Tele Converter?

We always believe that the use of a telephoto converter lens will bring the subject closer, and, as a result, the subject will appear larger in the image. Is this always true? The answer actually depends on the working distance, the distance between the subject and the front end of the lens, and the focal length being used. Normally, shorter working distance means higher magnification. However, unlike SLR/DSLR teleconverters that usually do not increase the working distance of a lens, the front-mounting afocal system that is popular in the consumer level digital camera is a different story. When you mount a teleconverter to a lens, the working distance can increase drastically. As the working distance increases, magnification reduces. Consequently, if a teleconverter reduces magnification to a degree that is less than the magnification you can get without the teleconverter, the use of a teleconverter becomes meaningless. This situation usually happens near the minimum working distance of the on-camera lens. Therefore, the intention of this page is to show you the differences.

Test Parameters

First, I measured the minimum working distance at 420mm as shown in the table below. See here for more details. All numbers are truncated to integers:

Converter Minimum Working Distance
FZ-30 56"
Canon TL-55 (1.4X) 102"
Olympus TCON-14B (1.45X) 112"
Minolta ACT-100 (1.5X) 122"
Nikon TC-E15ED (1.5X) 148"
Olympus TCON-17 (1.7X) 165"
Sony VCL HGD1758 (1.7X) 165"

As you can see, a higher power teleconverter implies a longer working distance. The working distance of a 1.4X converter is about twice as that of the on-camera lens, and that of a 1.7X teleconverter is almost tripled!

Test Results

What is the impact? It could be a surprise to you if you prefer to get close to your subject: no converter is better than adding a converter at close distance in terms of magnification. To show this, I took an image at the minimum working distance of each teleconverter. The subject is a book cover (actually, it is Authentication: From Passwords to Public Keys by Richard E. Smith). The following shows the 1/6 of the original. Please ignore the image quality as there is no intention to address this issue. The purpose of this page is to compare the relative size of the same subject taken by various teleconverters at their minimum working distances.

FZ-30 On-Camera Lens
Canon TL-55
Olympus TCON-14B
Minolta ACT-100
Nikon TC-E15ED
Olympus TCON-17
Sony VCL HGD1728

What Do We Learn?

From these images, we can immediately see that at the minimum working distance, the FZ-30 without any teleconverter generated the largest image, followed by the two 1.4X and 1.45X converters, followed by the Minolta 1.5X converter, and then the 1.7X converters. The Nikon TC-E15ED is a special case because the gap between its rear element is too far away from the camera lens, which might cause the unusually long minimum working distance. So, here is a conclusion: If you can get close, remove your teleconverter and use the on-camera lens. In this way, your subject will be larger on the image! Teleconverters are used for taking subjects at a distance. See the table at the beginning of this page to determine the working distance.