When I was 15, I bought my first Single Lens Reflex (SLR) camera, a Fujica ST-605n. At the time, I thought it was the coolest thing I’d ever held in my hands.

The camera arrived one July day with a light, small 50mm f/2.2 lens mounted on its even-in-1978-archaic screw threads. It was a decent lens, particularly since the camera and lens together cost, as I recall, $127. It focussed smoothly and the viewfinder was bright, so I was off and running in the game of SLR photography.

As I explored the potential of the 50mm, I also found that I wanted something telephoto. I looked on from afar at the spectacular telephoto lenses of the day (in the era before zooms) advertised in photography magazines and reviewed by Herb Keppler, an equipment reviewer for Popular Photography Magazine who influenced an entire generation of photographers, including me.

I found a bargain on a no-name 3x teleconverter from Cambridge Camera Exchange, which from that day to this remains one of the biggest rip-off stores in the business. In fact, when I ordered the converter over the phone, they forgot to ask me for what camera I was ordering, so a week later I got an envelope in the mail with the corner of a sheet of yellow legal pad torn off with the words “what mount?” handwritten on it.

I finally did receive the converter and immediately mounted it behind my 50mm. Wow! 150mm! The viewfinder was impressive, but the image quality was not. It was essentially junk.

So what is a teleconverter? “Teleconverter” is photography nomenclature for “telephoto focal length converter,” and uses optics placed between the camera and the lens to multiply the focal length of the lens by the number on the teleconverter. A 1.4x teleconverter multiplies your focal length by 1.4 times; a 200mm lens becomes a 280mm lens with a 1.4x converter, and so on. Also not inconsequential is the fact that you lose an f-stop for each increment of teleconversion. When your 200mm f/2.8 lens becomes a 280mm, for example, the maximum aperture is then f/4. With a 2x converter, a 200mm f/2.8 becomes a 400mm f/5.6. You can do the math yourself to see why: f/stop = focal length divided by aperture diameter.

So that leaves the obvious question: why would I use a teleconverter? For the most part, the only teleconverter I recommend is a 1.4x converter, and ever then I only recommend very good – and very expensive – ones. Using a teleconverter usually compromises a lens to begin with, and with a cheap one, things just fall apart. Some lenses, like the legendary Nikkor 300mm f/2.0 of 1985 vintage, have their own dedicated teleconverters.

When do I use a teleconverter? When the longest lens I have, which is usually a 300mm, isn’t giving me the reach I need, and the subject is too tiny in the frame to be effectively enlarged, I’ll use a teleconverter. A good example comes from March 1996 when a train derailed and caught fire. With unknown and possible toxic chemicals on the trail, fire department personnel wisely kept us back a quarter of a mile.

A dedicated telephoto or supertelephoto lens is always going to be my first choice, but a teleconverter is a decent option when I occasionally need to really reach out.