The teleconverter is a device that increases the focal length of a lens by a certain multiplier and turns it into a tele lens. Various power teleconverters are available such as 1.4X, 1.5X, 1.7X, 2X, 3X. Modern ones can support auto aperture, autofocus features. But we don’t need AF for macro.
If we have a 100mm lens and use it with a 2X teleconverter, we get a 200mm lens. In return, we sacrifice some of the aperture value and image quality.
Using a teleconverter with a tele lens (for example, for bird photography) is quite popular, but we have a chance to use it in macro photography. Whatever we use, a normal or reverse mounted lens, tubes, or bellows, we can add a teleconverter to the rear of this device and increase the magnification by the power of the teleconverter.
So why should we use teleconverter if we sacrifice image quality? Obviously I don’t prefer it anymore. This decision is directly related to the quality of the teleconverter. I have 3 different teleconverters that I can test, all three are 2X. That’s why I don’t use them often. Low-power teleconverters are able to achieve better results without distorting the quality, but those with 2X and above create a noticeable deterioration.
When to use a teleconverter
As the focal length of our lens increases, the teleconverter becomes a helper. Due to its two important features, we may prefer to use a teleconverter in a macro.
- You know we use a macro tube to force the lenses to a higher magnification. For example, the same (100mm) tube length is required to force a 100mm lens to double its magnification. Instead, we can create a more portable solution using a teleconverter.
- When we use a tube, our working distance is shortened. We’re much closer to the object and we scare live insects. Or they rather bite/sting us! The working distance does not change when we use a teleconverter. Only the magnification increases.
I will use the Pentax Rear Converter A 2X-S in the test and will try out a Tamron 90mm f2.8 macro lens and a reversed Rodagon WA 40mm enlarger lens.
I couldn’t find a suitable model in a cold and rainy weather and I chose a figurine with bird feathers on it. High contrast and sufficient detail on bird feather make it a good and challenging subject. The section with the red ring shows the area I used in the test photos.
Tamron 90mm with a teleconverter
The Tamron 90mm is an essential lens for me as a basic benchmarking tool. We will try Tamron again with the closest working distance and 1: 1 magnification value.
In the sample photos, I resized a part of the image to 200% to highligh the quality loss caused by teleconverter. With a more normal look, you’ll see that the situation is not that bad. I recommend you click and review the samples.
The Tamron 90mm, at f11 and 1:1 magnification gives a sharp and clear result, as we expect. There is minimal chromatic aberration. It can’t be seen unless you’re careful.
When using the Rear Converter A 2X-S, I set the Tamron 90 at f8 to compensate for the lost light and avoid the diffraction. I got 2X magnification but chromatic aberration has increased considerably. Especially the red halos have become apparent.
Reverse mounted Rodagon WA 40mm and teleconverter
There’s no special reason to choose this lens. I just used it here to test it a bit because it’s the latest lens I’ve got.
The Rodagon 40mm gives 2.6X magnification on a set of tubes. When we connect our teleconverter, the magnification will be doubled to 5.2X. Levels like 5X normally require special lenses. Wide-angle enlarger lenses, specialized macro lenses and microscope lenses provide sharper images. However, teleconverter can still be used with acceptable results.
Without using the teleconverter Rodagon 40mm has sharp results. As the magnification is higher than the previous test, we use the aperture at f8. Color degradation is minimal.
When I connected the teleconverter, I set the aperture to f5.6. CA appears in the same way as the previous test. However, considering that these are unprocessed photographs, we can say that the situation is acceptable.
Note: I did not post process the images except white balancing. You can achieve very good results and move the picture quality to higher levels by applying CA correction, contrast enhancement and sharpness filters. CA is no longer a serious problem in the computer environment. It is possible to fix it easily.
Note 2: If you get a lower-power teleconverter instead of 2X, you’ll have less chance of experiencing distortions. In teleconverters containing APO glass, you are less likely to encounter CA problems. You can add it to any type of macro gear as an additional magnifier.
Update July 02, 2015
Since the publication of the article, I had the opportunity to try different teleconverters. I currently have 6 of them. Two of them are 1.5X and one is 1.7X. As I expected, those with a low multiplier are more successful than 2X.
But when I look at my rate of using the teleconverter in macro, I see that it is almost “zero”. As my equipment evolved, the teleconverter was transformed into a tool that I used with my mirror lens only. It’s completely out of favor for the macro.
This is very natural. I have different lenses for different magnifications. For example, no one with a lens suitable for 5X, add a teleconverter to a 2.5X lens and use them together as 5X. It is always better to use the most suitable lens alone. In this case, the teleconverter option becomes more valuable for people with limited equipment.
Finally, I want to repeat the most powerful feature of the teleconverter. Sometimes the working distance in the macro is a serious problem. Teleconverter provides additional magnification without changing the working distance. There is no other tool that provides this.