Back to Back: The Making of the “Back to the Future” Sequels

With the runaway success of the first instalment, there was no way that Universal Pictures weren’t going to make another Back to the Future, with or without creators Bob Gale and Robert Zemeckis. So after confirming that Michael J. Fox and Christopher Lloyd were willing to reprise their roles as Marty McFly and Doc Emmett Brown, the producer and director got together to thrash out story ideas.

They knew from the fan mail which had been pouring in that they had to pick up the saga where they had left off: with Doc, Marty and his girlfriend Jennifer zooming into the future to do “something about your kids!” They soon hit upon the idea of an almanac of sport results being taken from 2015 into the past by Marty’s nemesis Biff Tannen (Thomas F. Wilson), resulting in a “Biff-horrific” alternate 1985 which Marty and Doc must undo by journeying into the past themselves.

Gale’s first draft of the sequel, written up while Zemeckis was away in England shooting Who Framed Roger Rabbit?, had Biff giving the almanac to his younger self in 1967. Marty would don bell-bottom trousers and love beads to blend into the hippy culture, meet his older siblings as very young children and his mother Lorraine as an anti-war protestor, and endanger his own existence again by preventing his parents going on the second honeymoon during which he was conceived.

Upon returning from England and reading the draft, Zemeckis had two main notes: add a fourth act set in the Wild West, and how about 1955 again instead of 1967? “We could actually do what the audience really, really wants, which is to go back and revisit the movie they just saw,” Zemeckis later explained. “That is the thing that excited me most, this idea of seeing the same movie from a different angle.”

Adding the Wild West act ballooned the script to over two-and-a-half hours with an estimated budget of $60 million, far more than Universal wanted to spend. So Gale revised the screenplay, expanding it further with a neat point in the middle where it could be split in half. As two films, each budgeted at $35 million but shot back-to-back over 11 months, the project was much more appealing to the studio. However, it was still a bold and unusual move for Universal to green-light two sequels simultaneously, something that it’s easy to forget in these days of long-form movie franchises planned out years in advance.

A sticking point was Crispin Glover. As Marty’s father George McFly he had been a difficult actor to work with on the first film, and now he was demanding more than a ten-fold pay increase to appear in the sequels. “Crispin… asked for the same money that Michael J. Fox was receiving, as well as script approval and director approval,” according to Gale. He gave Glover’s agent two weeks to come back with a more realistic offer, but it didn’t come. Glover would not be reprising his role.

Jeffrey Weissman in prosthetic make-up as George McFly

Gale accordingly made George dead in the Biff-horrific 1985, and Zemeckis employed several tricks to accomplish his other scenes. These included the reuse of footage from Part I, and hanging cheap replacement actor Jeffrey Weissman upside-down in a futuristic back brace throughout the 2015 scenes. Life casts of Glover’s face taken for the ageing effects in Part I were even used to produce prosthetic make-up appliances for Weissman so that he would resemble Glover more closely. “Oh, Crispin ain’t going to like this,” Fox reportedly remarked, and he was right. Glover would go on to successfully sue the production for using his likeness without permission, with the case triggering new Screen Actors Guild rules about likeness rights.

Make-up was a huge part of the second film, since all the main actors had to portray their characters at at least two different ages, and some played other members of the family too. A 3am start in the make-up chair was not unusual, the prosthetics became hot and uncomfortable during the long working days, and the chemicals used in their application and removal burnt the actors’ skin. “It was a true psychological challenge to retain enough concentration to approach the character correctly and maintain the performance,” said Wilson at the time.

Filming began in February 1989 with the ’55 scenes. To save time and money, only one side of the Hill Valley set – still standing on the Universal backlot – was dressed for this period. The company then shot on stage for a few weeks before returning to the backlot in March, by which time production designer Rick Carter and his team had transformed the set into a gangland nightmare to represent Biff-horrific 1985. In May the company revisited the Hill Valley set once more to record the 2015 scenes.

When the real 2015 rolled around, many were quick to compare the film’s vision of the future to reality, but Gale always knew that he would fail if he tried to make genuine predictions. “We decided that the only way to deal with it was to make it optimistic, and have a good time with it.” Microwave meals had begun to compete with home cooking in the ‘80s, so Gale invented a leap forward with the pizza-inflating food hydrator. Kids watched too much TV, so he envisaged a future in which this was taken to a ridiculous extreme, with Marty Jr. watching six channels simultaneously – not a million miles from today’s device-filled reality.

While the opening instalment of the trilogy had been relatively light on visual effects, Part II required everything from groundbreaking split-screens to flying cars and hoverboards. This last employed a range of techniques mostly involving Fox, Wilson and three other actors, plus five operators, hanging from cranes by wires. While every effort was made to hide these wires from camera – even to the extent of designing the set with a lot of camouflaging vertical lines – the film went down in VFX history as one of the first uses of digital wire removal.

But perhaps the most complex effect in the film was a seemingly innocuous dinner scene in which Marty, Marty Jr. and Marlene McFly all share a pizza. The complication was that all three roles were played by Michael J. Fox. To photograph the scene and numerous others in which cast members portrayed old and young versions of themselves, visual effects wizards Industrial Light & Magic developed a system called VistaGlide. 

Based on the motion control rigs that had been used to shoot spaceships for Star Wars, the VistaGlide camera was mounted on a computer-controlled dolly. For the dinner scene, Fox was first filmed as old Marty by a human camera operator, with the VistaGlide recording its movements. Once Fox had switched to his Marty Jr. or Marlene costume and make-up, the rig could automatically repeat the camerawork while piping Fox’s earlier dialogue to a hidden earpiece so that he could speak to himself. Later the three elements were painstakingly and seamlessly assembled using hand-drawn masks and an analogue device called an optical printer.

The technically challenging Part II shoot came to an end on August 1st, 1989, as the team captured the last pieces of the rain-drenched scene in which Marty receives a 70-year-old letter telling him that Doc is living in the Old West. Four weeks later, the whole cast and crew were following Doc’s example as they began filming Part III.

In order to have open country visible beyond the edges of 1885’s Hill Valley, the filmmakers opted to leave the Universal backlot and build a set 350 miles north in Sonora, California. The town – which had appeared in classic westerns like High Noon and Pale Rider – was chosen for its extant railway line and its genuine 19th century steam locomotive which would form a pivotal part of the plot.

Joining the cast was Mary Steenburgen as Doc’s love interest Clara. Initially unsure about the role, she was persuaded to take it by her children who were fans of the original film. “I confess to having been infatuated with her, and I think it was mutual,” LLoyd later admitted of his co-star. Though the pair never got involved, Part III’s romantic subplot did provide the veteran of over 30 films with his first on-screen kiss.

By all accounts, an enjoyable time was had by the whole cast and crew in the fresh air and open spaces of Sonora. Fox, who had simultaneously been working on Family Ties during the first two films, finally had the time to relax between scenes, even leading fishing trips to a nearby lake. 

The set acquired the nickname “Club Hill Valley” as a volleyball court, mini golf and shooting range were constructed. “We had a great caterer,” recalled director of photography Dean Cundey, “but everybody would rush their meal so that they could get off to spend the rest of their lunch hour in their favourite activity.”

There was one person who was not relaxed, however: Robert Zemeckis. Part II was due for release on November 20th, about halfway through the shoot for Part III. While filming the action-packed climax in which the steam train propels the DeLorean to 88mph, the director was simultaneously supervising the sound mix for the previous instalment. After wrapping at the railway line, Zemeckis would fly to Burbank and eat his dinner on the dubbing stage while giving the sound team notes. He’d then sleep at the Sheraton Universal and get up at 4:30am to fly back to Sonora. 

The train sequence had plenty of other challenges. Multiple DeLoreans had been employed in the making of the trilogy so far, including a lightweight fibreglass version that was lifted on cables or hoisted on a forklift for Part II’s flying scenes, and two off-road versions housing Volkswagen racing engines for Part III’s desert work. Another was now outfitted with railway wheels by physical effects designer Michael Lantieri. “One of the scariest things to do was the DeLorean doing the wheelie in front of the train,” he noted in 2015. “We had cables and had it hooked to the front of the train… A big cylinder would raise the front of the car.”

The film’s insurance company was unhappy about the risks of putting Michael J. Fox inside a car that could potentially derail and be crushed by the train, so whenever it was not possible to use a stunt double the action was played out in reverse; the locomotive would pull the DeLorean, and the footage would subsequently be run backwards.

The makers of Mission: Impossible 7 recently drove a full-scale mock-up of a steam locomotive off an unfinished bridge, but Back to the Future’s team opted to accomplish a very similar stunt in miniature. A quarter-scale locomotive was constructed along with a matching DeLorean, and propelled to its doom at 20mph with six cameras covering the action. Marty, of course, has returned safely to 1985 moments earlier.

Part III wrapped on January 12th, 1990 and was released on May 25th, just six months after Part II. Although each instalment made less money than its predecessor, the trilogy as a whole grossed almost $1 billion around the world, about ten times its total production cost. The franchise spawned a theme park ride, an animated series, comics and most recently a West End musical.

But what about Part IV? Thomas F. Wilson is a stand-up comedian as well as an actor, and on YouTube you can find a track of his called “Biff’s Questions Song” which humorously answers the most common queries he gets from fans. The penultimate chorus reveals all: “Do you all hang out together? No we don’t / How’s Crispin Glover? Never talk to him / Back to the Future IV? Not happening / Stop asking me the question!”

Back to Back: The Making of the “Back to the Future” Sequels

Back in Time: The Making of “Back to the Future”

Spaceman from Pluto is a 1985 sci-fi comedy starring Eric Stoltz and Christopher Lloyd. Lloyd plays Professor Brown, an eccentric scientist with a pet chimp, who builds a time machine out of an old fridge. Stoltz portrays a teenage video pirate, Marty McFly, who is accidentally sent back to the 1950s in the machine. After almost wiping himself from existence by endangering his parents’ first meeting, Marty returns to his own time using the power generated by an atomic bomb test in the Nevada desert.

Fortunately this movie was released in some alternate version of history. In our timeline it went through a number of changes in writing and production to become the blockbuster classic Back to the Future.

For co-writer and producer Bob Gale it all started when he came across his father’s highschool yearbook and realised that, had he and his father been peers, they would never have been friends. Spotting the comedy potential in the concept of a teenager going to school with his parents, Gale sat down with co-writer and director Robert Zemeckis to develop a script. 

The pair knew they needed a time machine and decided that it would be created by a backyard inventor rather than some government organisation. “I can’t really put my finger on when I stumbled on the idea of time travel,” said Gale in 2002, “whether it was from watching The Twilight Zone, reading Superman comics, or when the H.G. Wells Time Machine – the George Pal movie – came out, but I do remember being totally fascinated by that film.”

Writer-director Robert Zemeckis & writer-producer Bob Gale

Getting Back to the Future made proved challenging. Most of the studios that Gale and Zemeckis approached found the script too sweet and innocent compared with the typical R-rated teen movies of the time. Disney, on the other hand, felt that the mother-falls-for-son plot was too taboo. 

Making matters worse was the duo’s less than spectacular track record. Their first two feature films, I Wanna Hold Your Hand and Used Cars, were both box office flops. They even had the dubious honour of writing the least successful film of Steven Spielberg’s directorial career so far, 1941.

Everything changed when Michael Douglas hired Zemeckis to direct 1984’s Romancing the Stone. The adventure romp was a hit and suddenly everyone in the notoriously fickle Hollywood wanted Back to the Future. Spielberg, who had always loved the script, signed on as executive producer and – after a false start at Columbia – the movie was green-lit by Universal Pictures.

Studio president Sid Sheinberg requested a number of script changes. Professor Brown became “Doc” and his chimp became a dog. Marty’s video piracy (which would have explained his possession of the camcorder with which he films the time machine’s test run) was written out, as the studio were understandably unwilling to promote the revenue-slashing crime.

Sheinberg also hated the title Back to the Future and wanted it changed to Spaceman from Pluto, a reference to the comic clutched by the Peabody children after the DeLorean crashes into their barn on arriving in 1955. Zemeckis and Gale turned to Spielberg to help them dodge this title without offending Sheinberg; his solution was to send a memo saying what a big laugh they all got out of Sheinberg’s joke. The studio president never mentioned it again.

The title Back to the Future was retained, but the barn scene did prompt another change. By this point the writers had realised that an immobile fridge was not dramatic or practical as a time machine, and were searching for a suitable vehicle for Doc to build it into. They chose the slick, stainless steel DeLorean with its futuristic gull-wing doors so that the Peabody family could mistake it for a UFO.

Budget concerns drove the elimination of the A-bomb scene. Shooting on location and building the miniatures of the bomb and its test tower were estimated to cost $1 million. Switching the power source to a lightning bolt not only saved this money by keeping all the action in Hill Valley, it enhanced the time metaphor represented by the clock tower as well as giving Doc an active part in the climax rather than being stuck in a blast bunker with a walkie-talkie.

The filmmakers’ first choice for the role of Marty McFly was Michael J. Fox, the 23-year-old star of sitcom Family Ties. But that show’s creator, Gary David Goldberg, refused to even let Fox see the Back to the Future script, fearing the actor would love it and resent Goldberg for not releasing him from his Family Ties commitment.

A disappointed Zemeckis accordingly began screen-testing other actors, eventually narrowing the choice down to C. Thomas Howell (best known for the coming-of-age drama The Outsiders) and Eric Stoltz (who had appeared in Fast Times at Ridgemont High and The Wild Life). It seems that Sid Sheinberg was Stoltz’s most vocal advocate. Gale recalled the studio president declaring: “I’m so convinced that Eric is going to be great in this part, if it doesn’t work out you can recast it and start all over again.”

No-one expected that to actually happen.

Filming began on November 26th, 1984. The logistics of transforming a real town into Hill Valley in both 1955 and 1985 were daunting, so instead production designer Lawrence G. Paull adapted the town square set on Universal Studios’ backlot, which had originally been built for the 1948 film noir An Act of Murder.

Special effects supervisor Kevin Pike had taken three DeLoreans and, working to concept art by the legendary Ron Cobb amongst others, fitted them with a variety of aircraft surplus parts and other junk to create the iconic time machine. The “Mr. Fusion” generator added to the vehicle in the final scene started life as a coffee grinder.

Cast in the role of Doc Brown was Christopher Lloyd, whose prior roles included a Klingon commander in Star Trek III: The Search for Spock, a psychiatric patient in One Flew Over the Cuckoo’s Nest and five years in the sitcom Taxi. In another alternate timeline he wasn’t involved in Back to the Future either, having binned the script in favour of a stage role in New York; it was his wife who made him reconsider.

Basing the character on the conductor Leopold Stokowski, Lloyd made the Doc larger than life. Eric Stoltz had a very different approach, a method approach, focusing on the serious aspect of Marty’s out-of-time predicament and apparently ignoring the fact that he was starring in a comedy. “Eric didn’t get it,” camera assistant Clyde E. Bryan remembered in 2015. “Eric didn’t understand the physical, pratfall type of humour that Bob [Zemeckis] was looking for.”

By the sixth week of filming, almost halfway through the schedule, Zemeckis knew he had a huge problem. After conferring with Gale and his fellow producer Neil Canton, the director asked Spielberg to come to the editing suite and watch the 45-minute rough cut of everything that had been shot so far. All the filmmakers agreed that Stoltz had to go.

Unwilling to have Universal shut down the film and suffer the attendant negative press, Zemeckis kept filming with Stoltz for another week, with most of the cast and crew unaware of the situation. Meanwhile, behind the scenes, Canton worked out exactly how much reshoots would cost ($4 million) while Zemeckis and Gale went back to Goldberg at Family Ties, begging him to let Michael J. Fox take the role. Goldberg agreed on condition that the TV show would take priority. Fox himself claims to have merely weighed the script in his hand before agreeing to do it.

During the lunch break on Thursday, January 10th, 1985, halfway through filming the DeLorean’s test run in the car park of the Twin Pines Mall, Zemeckis called Stoltz into his trailer and broke the bad news. By the following Monday, Michael J. Fox was Marty McFly.

The young actor’s schedule was exhausting. He would wake at 9am, work on Family Ties from 10am to 6:30pm, get driven to Universal and shoot Back to the Future until 2:30am. Any scenes that required Marty in daylight had to be filmed at weekends.

Nonetheless, Fox somehow managed to squeeze in guitar lessons in preparation for Marty’s performance at the Enchantment Under the Sea Dance. He already had some experience with the instrument, but was determined to learn to play “Johnny B. Goode” note for note so that he could finger-sync perfectly to the pre-recorded track. Marty’s singing voice was provided by Mark Campbell, while the energetic choreography of his performance incorporated the signature moves of Pete Townshend, Jimi Hendrix and Eric Clapton as well as Chuck Berry.

The scene is one of the most memorable in the movie, but Zemeckis and Gale were very worried about it during editing. “It’s the only scene that doesn’t advance story or character, and we didn’t know how that was going to play,” said Gale. A preview screening in San Jose removed any doubts; the audience loved “Johnny B. Goode” and everything else about the movie.

After a second preview, this time with Sid Sheinberg in attendance, Universal realised they were onto a winner and moved the film’s release date up to the July 4th weekend, paying through the nose to accelerate post-production.

“I want it to be violent,” Zemeckis told the animators creating the effect of the DeLorean breaking the time barrier, “something akin to a Neanderthal sitting on the hood of the car, chipping away at the fabric of time in front of him.” The hand-drawn cell animation combined with built-in lighting on the car and actual fire trails that had been captured on location, plus additional pyrotechnics overlaid after the fact, created the signature effect.

Meanwhile, Alan Silvestri assembled the largest orchestra in Universal’s history to record Back to the Future’s iconic score, and a tie-in single was provided by Huey Lewis and the News. The latter took a couple of attempts to get right; Lewis’ first submission was a minor-key track that didn’t work at all, according to Zemeckis. It was only after the filmmaker showed Lewis the skateboarding scene that he understood the upbeat mood required and composed “The Power of Love”.

Fox was away filming a Family Ties special in England when Back to the Future was released. He was surprised to get a call from his agent telling him that it was the biggest film in America. It spent 12 weeks at the top of the US box office charts and quickly became part of popular culture, with even Presidents Reagan and Bush Senior giving speeches about taking the country “back to the future”. To date it has grossed almost $400 million.

Summing up the film’s appeal in 2002, Gale offered: “There’s something very special about this story that everyone can identify with, the idea of trying to imagine what your parents were like when they were kids – that just touches everybody.”

When Back to the Future was released on VHS in May 1986, fans noticed a small change from the theatrical version. There as expected was the DeLorean’s lift-off and departure to the future – originally intended by Zemeckis and Gale simply as a joke on which to end the story. But now, sandwiched between that final scene and the end credits, was a caption.

The caption read: “To be continued…”

Back in Time: The Making of “Back to the Future”

“Harvey Greenfield is Running Late”: June 2022 Pick-ups

Last summer I lensed Harvey Greenfield is Running Late, a hilarious comedy feature starring Paul Richards, based on his acclaimed one-man play, soon to have its 100th performance. We had a 14-day window in Paul’s schedule for the shoot, during which we captured two thirds of the film – less than we’d hoped, but still a remarkable achievement given the resources we had and the production value we achieved. This summer we shoot the rest.

 

Day 15

Ten months on, we returned to the house from days 11 and 12. It’s on the verge of being sold, and this was our last chance to mop up the outstanding material here.

We eased into it gradually with simple inserts, recreating the look and lighting in the kitchen using Fifi’s camera notes, clips from the assembly edit, and this blog (yes, it’s not just for you, dear reader). At times like this I wish I recorded even more information – intensity and colour temperature readings for every source would be extremely useful, but is that really practical?

After traumatising Paul with a reshoot of a scene in which he gets slapped (accidentally for real the first time around) we popped outside to get a shot of him on the street, filmed through a car windscreen. Last year we captured the first monologue of the film as a oner, but with hindsight director Jonnie Howard decided it needed breaking up; this windscreen shot is one of several that he has added to illustrate the things Harvey monologues about. Proving that there are no easy shots, it took me an embarrassingly long time to eliminate annoying reflections in the glass by covering shiny parts of the dashboard with matt black tape and putting a polarising filter in the matte box.

Next we moved to the back garden for one of the film’s most complicated shots. It starts off as a two-shot of Harvey and Alice (Liz Barker) in a nighttime interior setting then – via a low-tech, Michel Gondry-style transition – becomes a single of Harvey in a daytime exterior. Gaffer Stephen Allwright and spark Jeremy Dawson built a dark box out of flags and bolton, parts of which had to swing away to let in the natural light during the transition. A light had to be panned off and a reflector swung in too, while production designer Amanda Stekly and her helpers performed their own magic with the set. By the time we got it in the can we were losing the light, but the result was well worth it.

The dusk gave us just the look we needed for a quick scene in the bedroom, then we were into full nighttime scenes. I climbed into the wardrobe to get the right camera angle – we were without our beloved 14mm lens this time around, so the locations felt a little tighter!

Later we had to recreate the lighting of the aforementioned oner, so we could shoot coverage, again with extensive reference to the camera notes, rushes and R3D metadata, this blog, and on-set photos captured on my phone. Last year we dialled a custom cyan colour into the Astera tubes and I really wish I had noted the XY or HSL numbers so that we could have dialled those into the Rayzr MC 200 that was replacing them for the pick-ups. Instead we had to judge it by eye.

It was now about midnight and we still had an important sequence in the kitchen and living room to shoot; we ultimately captured it in two set-ups and an insert. This day’s filming had seen the most extreme examples of the colour scheme I planned last year: orangey-red colours to represent Harvey’s stress, and cooler, greenish shades for calmer moments. By the end of the night it was starting to look like The Neon Demon and I was wondering if I had gone too far. I guess I will find out when it’s all cut together.

 

Day 16

A pleasant cycle ride through Cambridge and out across a meadow brought me to the brand-new village of Eddington and the impressive Storey’s Field Centre where we would be filming the office of Harvey’s boss, Bryan (Alan Hay). First up was a fantastic shot of Harvey huffing and puffing up a spiral staircase in the centre’s main hall. The high-tech building had its lights and two layers of blinds controlled electronically, and Stephen was able to completely reshape the natural light in the huge wide shot and even put a glorious streak of light on the staircase just by pressing a few buttons. If only every location was equipped so.

A smaller, but still obscenely spacious, hall served as Bryan’s office. French windows faced east into a beautiful courtyard garden. High windows on the opposite side of the room featured motorised blinds again, which sadly would not stop halfway, forcing us to close them completely to control the light. An overhang above the French windows, combined with the high walls of the courtyard, meant that very little natural light now entered the room. For a key, Stephen constructed a book-light by pointing an Aputure 600D up into a tilted frame of Ultrabounce and then hanging some diffusion (half grid, I think) off the top edge. We added a tungsten fresnel on a boom to give some orange, stress-themed hair-light to characters in the middle of the room.

The first shot was effectively the POV of a dartboard, so we stuck three darts to the matte box with Blu Tack. Sharp points and oily substances – exactly the things you want right next to your lens! – but it looked great.

The next couple of shots featured co-writer Raymond Howard’s baby daughter. One was a contra-zoom, captured on the 18-35mm which I zoomed manually off the barrel while pushing in on the Tango ProSup slider. The other required me to brandish the handheld camera right in baby’s face for a very long time until she eventually cried.

Then it was onto the big scene. This featured Bryan referring to a PowerPoint presentation, which meant a lighting transition as the screen came down and the projector fired up. For Harvey’s angle, with his back to the projector, we boomed an Aputure 300D behind him to simulate the projection beam, and sat a pocket LED light on the matte box to represent the bounce off the screen; these faded up as the 600D book-light and tungsten hair-light dimmed down. For Bryan’s angle the real projection light wasn’t doing enough on his face, so we “extended” the practical lamp on his desk with a small tungsten fresnel. For the wide shot we could get away with re-angling the practical so that it cast a dramatic, Citizen Kane-esque shadow from Bryan up onto the screen.

All in all, the day’s work added a huge amount of scale and humour to the movie. It was lovely to see and work with everyone again for the weekend. Next month most of us will be back for eight more days of running late.

“Harvey Greenfield is Running Late”: June 2022 Pick-ups

What is a Diopter in Cinematography?

If you’re a fan of early Steven Spielberg films, you’ve probably heard of split diopter shots (also spelt “dioptre” in the UK). Brian de Palma used them a lot too, and Robert Wise’s Star Trek: The Motion Picture is absolutely riddled with them.

A split diopter allows half the image to be focused at one distance and half at another. Shallow depth of field is sought after by many filmmakers today, but it wasn’t always so popular. Sometimes a director or DP wanted both characters in a deep two-shot simultaneously in focus, and slow film stock and/or lenses meant that it wasn’t possible to just stop down the iris.

So what is a split diopter (a.k.a. split-field diopter)? It’s a convex lens of a semi-circular shape that can be slotted into your matte box. Light passing through this lens is converged so that it focuses closer, while light passing through the empty half of course goes unaltered to the main lens.

Bog-standard diopters are available too, with no missing half, enabling the entire image to be focused closer than normal. (In stills photography they are sometimes called close-up lenses or macro filters.) These are especially useful with anamorphic and zoom lenses, which tend to have greater close-focus distances than spherical primes. There’s no stop loss, so you don’t have to compensate with more light.

I carried a set of diopters with me on Hamlet and we used them for a couple of shots with the vintage Cooke Cinetal 25-250mm zoom (CF: 5’6″) when I was shooting quite tight and quite close to the talent.

So that’s what the physical object is. But a diopter is also a unit of measurement. A typical set of physical diopters (full or split) contains ½, 1, 2 and 3 strengths. What do those numbers mean?

A diopter is defined as a reciprocal metre, or 1 over the focal length. It’s the same unit used to define prescriptions for glasses. The important thing in cinematography is what effect a diopter of a given strength has on your minimum and maximum focus distances. Apps like pCAM Pro will work these out for you, but let’s do the maths ourselves because it’s my blog and I said so.

The formula for minimum focal distance is

where

  • x is the normal minimum focus of the lens (in metres),
  • x’ is the new minimum focus,
  • and d is the strength of the diopter.

Let’s take my Cooke Cinetal as an example. The 5’6″ close focus in metres is 1.68, so with a number 1 diopter…

… or with a number 3 diopter…

Diopters can be stacked; simply add the strengths together and then drop that number into the formula, so in the above case we’d have a total of 4 diopters (diopters the units, not diopters the objects!) which would produce a close focus of 0.22m. Keep the strongest diopter closest to the camera when stacking.

You have to be careful that you don’t reduce your maximum focal distance too much and find you can’t hold focus on a character as they move away. Your new maximum focal distance y’ (when the main lens is set to infinity) is

So that would be 1m with a number 1 diopter! Pretty restrictive, huh? A number 3 diopter gives you a maximum focal distance of 0.33m, even worse! I remember having to cheat Ian McKellen (CLANG!!!) a little closer to camera when we did a diopter shot on Hamlet, so that we could pull focus to him from a foreground actor’s hands.

If you bear that caveat in mind, however, a set of diopters is a very useful thing to have with you.

What is a Diopter in Cinematography?