We always think the use of a telephoto converter lens will bring the subject closer, and, as a result, the subject will appear larger in the image frame. Is this always the case? Well, the answer actually depends on the working distance, the distance between the subject and the front end of the lens. Unlike SLR/DSLR teleconverters that usually do not increase the working distance of a lens, the front-mounting afocal systems that are popular in the consumer level digital camera is a different story. When you mount a teleconverter to a lens, the working distance can be increased 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.
First, I measured the minimum working distance and got the following table in which the results are usually truncated to smaller integers:
|Converter||Minimum Working Distance|
|Canon TL-55 (1.4X)||127"|
|Olympus TCON-14B (1.45X)||145"|
|Minolta ACT-100 (1.5X)||152"|
|Olympus TCON-17 (1.7X)||207"|
|Sony VCL HGD1758 (1.7X)||207"|
As you can see, a higher power teleconverter implies a longer working distance. A 1.4X converter has a more than doubled minimum working distance than that of the on-camera lens, and that of a 1.7X teleconverter is more than tripled!
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. To show this, I take an image at the minimum working distance of each teleconverter. The subject is actually a book cover as shown below:
The drawing on the cover is about 14cm×7cm. The following shows the 30% crop of the original. Please ignore the image quality as there was no intention to address this issue. The purpose of this page is the relative size of the same subject taken by various teleconverters at their minimum working distances.
|FZ-10 On-Camera Lens|
|Sony VCL HGD1728|
From these images, we can immediately see that at the minimum working distance, the FZ-10 without any teleconverter generates the largest image, followed by the two 1.4X and 1.45X converters, followed by the 1.5X converter, and then the 1.7X converters. 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! See the table at the beginning of this page to determine the working distance.