There is an invisible threshold we cross each time we travel. We board planes or trains or ferries as our normal selves – doctors, teachers, farmers, you name it – but, once at destination, this is no longer the case. To the community we’ve just flown into we’re something other than the people we are at home. We are transient members, here now and gone tomorrow, often unaware of the local customs and traditions. We don’t know the rules, fail to grasp the laws and sometimes even the languages don’t make too much sense. We can’t read street signs, miss non-verbal cues, fail to recognise the food.

This can be maddening, discouraging and often downright dangerous; but it also offers the chance for some exhilarating experiences. To be a traveller, in my opinion, is to receive a pass to live life beyond the constraints of our daily grind, to indulge in something one wouldn’t normally do. There are limits but I found that, within the constraints of law and common sense, a lot of my own self-imposed mental shackles fall off as soon as a plane has delivered me in a foreign land. I am an unburdened man, ready to reach with both hands to the unexpected, the happenstance and the random finds that are so common when travelling.

A quick getaway to Lisbon was, once again, proof of all that.

It’s uncommon, for me, to be dallying with photography in London. However remote, the chance of meeting someone I know – or to stumble again into something I’d photographed before – are enough of a trigger for my shyness to not bring my camera out on a walk. But no such qualms will trouble me in Lisbon, where little yellow trams are omnipresent.

I’ve since long held the belief that a proper city ought to have trams; the older and ricketier, the better. Portugal’s capital is a leader in this sense, for shoals of little metal boxes on wheel brave its hilly tracks at any time of the day, leaving a faint noise of electricity and the occasional bell ring in their wake. For many, they are a symbol of the city; for me, they are the perfect candidate for a panning shot.

Panning is a technique where the photographer shoots with a low shutter speed at a moving object. Done properly, the outcome is a picture where the background is blurred in motion, but the subject is frozen in the act of moving, captured in crisp detail. This, at least, is the theory and I’m sure there’s people out there who nail it every time. As for yours truly, well, it’s a bit like fishing with dynamite: carpet the whole lake with explosives and eventually a fish will come out.

It was the end of a long day of walking. So far my panning efforts had yielded plenty of blurred photos and a precious few bits of streetcars in motion, but the Holy Grail – a full tram – still eluded me. Then, we found the spot. A large junction, an intersection of cobbled streets just off the Parliament, with the perfect light and plenty of space. We stood under the advertisement of a politician promising all sorts of things in exchange for a vote at the forthcoming elections and waited.

A momentaneous drought in trams led me to some practice shots. A couple on the moped: a bit off-centre, but still passable.

Then, a late ‘70s Mercedes SL R107 tackled the junction. One of the coolest cars known to man.

There’s a sky-blue 350 SLC in my neighbourhood. Her owner is an elderly gentleman who once jokingly asked me to put up an offer forward if I liked her so much. Knowing full well that I could neither afford her nor keep her I actually took him seriously before I walked away, lest something stupid happened. Still, I can’t help but looking at that 350 every time we walk down Kingswood Road. There’s something in her simplicity - those straight lines, that long bonnet, the forward-leaning radiator grille – that makes her irresistible. In a world of boxy SUVs she’s as striking as a lynx on the prowl. And now her soft-top version was cruising past before our eyes.

I brought up my camera, aimed, pressed the button halfway down to put the car into focus and then went all the way. I arced as the Mercedes drove uphill, the camera shooting in rapid sequence. Then the shutter stopped, the innards of the camera whirred a bit and, finally, three photos appeared on the screen. Clic, clic, clic.

I’d all but forgotten the trams. Nothing, I thought, could top a decent panning of the R107… until the traffic lights changed and, up from the right, caught my eye. Something, if at all conceivable, even cooler than the R107.

It was her older sister. A Mercedes 250 SL California Coupé straight out the 1960s. When Janis Joplin was asking for a Merc, in my opinion this is the one the Almighty ought to have given her. Sofia Loren drove one and so did Peter Ustinov and Juan Manuel Fangio. And there she was, outside the Portuguese Parliament, shining in her black paintjob and matching rims. I quickly turned the camera on, changed a setting on the fly, pointed and shot a few frames.

Then, almost by accident, a tram cruised past.

We walked back to the hotel with a feeling of satisfaction. These seemingly mundane encounters are the perk of travelling to me. Unexpected finds, chance encounters, random surprises are what I treasure. Being invited to tea in Uzbekistan, spotting an orca in Iceland or an interesting conversation with a fellow passenger are all fond memories I find myself thinking back the most often. Seeing two of my favourite cars in Lisbon, while looking for something else, will certainly add to the collection – or so I thought on our way home.

A few days later, early one morning before work, I had to suppress a loud guffaw so not to wake up the entire household. I’d been editing the photos from my panning session, and I’d found these. Treasured memories indeed.