On a film set, the Martini shot is the last shot setup of the day because the next shot would be out of a glass at the bar. Well let’s make that a literal Martini shot.
The first step is to figure out the scale between the martini glass and the talent. After sitting with the martini glass and doing some mental visualizations, I eventually decided on 1/8th scale.
I needed to make the glass eight times bigger or the talent eight times smaller. This means whatever distance I have the martini glass, I had to have the talent 8 times further away.
Before I broke out the cameras, I created a handy spreadsheet to calculate angle of view and mathematically prepare for the shoot. You can open up the spreadsheet and use it for your own lab later in this course.
Object A is my Martini Glass with is 7.5 inches tall. Object B would be how tall I wanted the martini glass after I blow it up. Since I have a scale of 8, that value would be 60 inches or 5 feet. My studio has about a good 30 to 35 feet to work with so I set my talent at a distance of 20 feet from my lens - or 240 inches. Reversing the scale, one eighth of 240 inches is 30 inches and that’s where I’ll put my martini glass.At this distance the martini would cover about 15 degrees of my vertical field of view. Now onto selecting the right lens -I found that a 70mm lens on my full frame Canon 5D mk II would give me a 20 degrees of vertical angle - just enough to cover the subject with room to spare.
But… and here’s the real frustrating thing: If I shot 70mm even at f22: if I focused at 11 feet - the talent would be in focus but my martini glass would be out of focus. If I focused on the martini glass, then my depth of field would still only be half a foot even at f22 - and that’s not to mention we lose sharpness at this really small apertures.
So the 70mm is out. Using my depth of field calculator I tried a bunch of focal lengths until I found that a 30mm lens shooting f/18 and focusing to 4.5 feet would give me a near depth of field limit of 2.5 feet and far limit of 26 feet - perfect.
But my vertical field of view with that lens would be 43 degrees - almost three times the field of view of my martini glass and model - so I would have to crop in. If I crop in, I should use a smaller circle of confusion - lets say I crop in 2x. My Circle of confusion is now 0.015 and now my depth of field is shallower!
So back to shooting a wider lens. Eventually I find that a 20mm at f18 will do the trick. Cropping an image is acceptable for a photo with high resolution to begin with but not so much for motion picture especially if I’m starting with HD. But what if instead of cropping in, I used a crop sensor?
Redoing the numbers for my Blackmagic Cinema Camera values I find that 18mm at f/13 will cover the distance. Now at 27 degrees vertical which would comfortably frame my martini glass plus one extra stop which means less diffraction and less light needed on the set.
The numbers I gave you here are my final results - I did plug in a lot of different values to see what worked… but the amazing thing is I could pretty much visualize everything on paper and avoid the scary pitfall of not having the right lens combination on on set. Keep in mind though that although we can calculate depth of field precisely, whether something appears sharp or not is still rather subjective - there is some tolerance for error. Now it’s a matter of executing the plan.
I measured the martini glass and scaled up the proportion to make a posing rig for the model to rest on out of steel square pipe. At first I tried just putting this triangular posing rig on the floor but I ran into a problem. In order to sell the effect, I have to have the both front and back rims of the martini glass in line with the lens. I do have a cheater martini glass which I was able to cut in half but that won’t hold liquid obviously. I needed to raise my posing rig but by how much? Well the answer came from good old basic geometry class again.
If I know the height of my martini glass and I know the distance to the camera - this is just a similar triangles problem - so I welded on an additional base with 14” of height and micro adjusted with some square wood I had laying around. For padding on the 1 inch square pipe I went with pipe insulation which is pretty much the same thing as a pool noodle but in black.
Now to light this monstrosity. Shooting at f11 and higher meant I needed a ton of light. For the foreground martini glass, this wasn’t so hard. I just put a couple LEDs and a 500 watt tungsten fixture with CTB gel - I kept everything daylight balanced because I knew I would use strobes for photos. By keeping the lights really close, by the distance rule we can maximize their illumination effect. Lighting the talent in the background would prove to be a little trickier. For shooting still images, I fired off two strobes. But for motion picture I needed to bust out the big guns, a 2000 watt light with a daylight blue gel. I kept this close and flagged them out of view using strips of material near the camera.
And that is it, a martini shot created in camera with forced perspective based on some simple mathematics.
Now what I just walked through took a lot of math and planning to get just right. Obviously you can eyeball the effect and come away with pretty decent results. I shot these changing up the perspective on the fly.
But the math does matter if you’re working with miniatures and want to stay consistent from shot to shot.
Of course all this work begs the question - wouldn’t it be easier to just greenscreen the thing and do it in post? Well maybe- if you’re careful you can achieve results that are as good or even better without having the challenges of shooting with deep focus. For instance, because of the distance, we’re not seeing the talent inside the liquid, such a thing would be a trivial fix if we shot it on greenscreen. Now I won’t say this effect can’t be duplicated in a composite but there is something fun and exciting about getting it in camera. Every special effect shot you encounter will need it’s own tailored solution. So give forced perspective a serious try. Even if you never use it again, the discipline of understanding perspective, lenses, and focus will prove to be a strong foundation in your quest to making something great.