Good morning everyone, and welcome back to my site. Thanks to those who have the patience to follow my posts. A warm welcome to those who are here for the first time. Subject of this post Extending Reach: Teleconverter Essentials
Doublers or teleconverters are accessories that multiply the focal length of a lens. Providing an economical way to achieve greater magnification without investing in expensive telephoto lenses.
While they offer an affordable solution for extending reach, they come with trade-offs such as potential loss of image quality, reduced aperture, and increased susceptibility to optical aberrations.
Despite these drawbacks, they remain a viable option for photographers seeking to expand their focal range on a budget.
Focal doublers – The term already suggests that these are tools capable of duplicating the focal length of something.
What ? Obviously a goal…
So we have already explained what it is and how to use it. They are additional lenses that are mounted between the camera body and the lens. Have the function of multiplying the focal length of the latter by a certain fixed value.
The term “duplicator” can in fact be misleading, given that there are certainly models that have a 2x multiplication factor, but also versions that are limited to lower values such as 1.6x and 1.4x.
Therefore the most correct definition is “teleconverters”, leaving that of “doubler” only to 2x. In English they are called teleconverters; some manufacturers also call them extenders.
In simple words, if we mount a 2x “teleconverter” behind (behind because it interposes between the camera body and the lens) on a 100mm it will “become” a 200mm.
Or rather, in the camera’s viewfinder we will see the framing of a 200mm and no longer that of the 100mm. In fact, it is not the lens that transforms, but the focal length of the multiplier+lens complex that changes.
If we had used a 1.6x multiplier we would have obtained the shot of a 160mm, with a 1.4x that of a 140mm.
PRO & CONS
Teleconverters look like Columbus’s egg. Here’s everyone wondering: “so, if it’s so easy to get to long focal lengths. Why are there still people who spend thousands of euros on a super telephoto?”
The answer lies in the fact that, like all things, these teleconverters, in addition to their advantages… Also have defects, and they are not small defects. They absorb light and introduce optical distortions into the image.
The theoretical part is valid for both modern teleconverters and “vintage” ones. The following refers to REAL tests conducted with a vintage lens and 2x doubler. Also vintage and of the same brand.
Decrease in brightness in teleconverters
The multiplication of the focal length of the lens behind which it is mounted does not happen by pure miracle…
What makes it possible, is a set of lenses (collected in groups like lenses) it’s inevitable that they absorb light. So all the multipliers “steal apertures” from the lens.
It means that the teleconverters absorb brightness, thus reducing the final brightness compared to the objective.
The absorption factor is measured and expressed by manufacturers in the form of “stops”. Or subtracted diaphragms, and is fixed as is the case for the multiplication factor.
Let’s take the vintage Tokina 2.0X RMC “focal doubler” as an example. Its focal multiplication factor is 2x, so using it in combination with a TOKINA 135mm – F2.8 we will obtain the framing of a 270mm.
On the other hand, it is characterized by a brightness absorption factor of 2 stops. It subtracts 2 “apertures” from the lens.
If the 135mm with which it is paired is an f2.8, the minimum brightness of the doubler + lens complex will be F5.6.
Consequently we will have to decrease the times by two stops to return to the correct exposure we had without mounting the duplicator.
If we had used teleconverters with a factor of less than two, for example 1.4x, the brightness drop would obviously have been smaller, let’s say roughly around 1 stop.
Deterioration of the optical quality of teleconverters
Teleconverters are made of lenses and each of them, although their final configuration is studied and optimised, introduces distortions and flaws into the image. Certainly the manufacturers have made giant strides in improving everything, but the problems remain and can be seen with the naked eye in the images.
The same photo taken with a 135mm+2x and a 300mm (quite similar focal lens) ruthlessly reveals the reason for the statement just made. Despite all the claims of the producers and certain optimistic reviewers, the difference in quality is there and can be seen with the naked eye.
In modern lenses, it must be recognized that modern software for “opening” RAW files, making the most of the information collected in the exif data by the on-board computers of the latest generation cameras and lenses, allow good recoveries of the drop in brightness at the corners of the image (vignetting ), but they certainly cannot rebuild the lost quality and definition.
With vintage lenses this is not possible as no EXIF is generated and consequently the only solution that I’ve personally adopted is to keep a small notebook and a pencil, with which I note down the data of the photographic shot. Empirical solution, but simple and easy, all things considered.
The problem of deterioration in optical quality is particularly highlighted if we use the images in large format print or for full-page or double-page editorial publications; if, however, we plan to use it only on the internet, multimedia supports or small format prints, this defect becomes less influential.
