How to film a science experiment video with both iPhone cameras
A science experiment video has the same bones as a tutorial — something happening in front of the camera, and a face explaining or reacting to it — but the something is usually much smaller than a workbench, sometimes involves heat or an open flame, and the actual outcome — a colour change, a fizz, a spark — depends on the camera reading it accurately rather than flatteringly. Recording front and back at once still gets the demo and your reaction into one file from the first pour, so there is no separate reaction cut to line up against a screen-recorded demo afterwards.
What is specific to this subject: framing a small reaction instead of a wide surface, keeping the phone close enough to see it without putting the phone in the reaction, why the live filters are the wrong tool here even though they help elsewhere, and how to handle a reaction that plays out over longer than one take should run.
Frame the reaction, not the table it is sitting on
Most of what a workbench or a stovetop video shoots is a wide surface with things moving across it. A science demo is usually the opposite: one beaker, one petri dish, one small model, sitting still in one spot, with the actual result happening in a space a few centimetres across. Filling the frame with the whole table the way a cooking or workshop video would just makes the one thing that matters — the colour spreading through the liquid, the foam rising over the rim — small and hard to read.
DualCam’s lens picker lets the back camera use whichever lens actually fills the frame with the reaction: telephoto where your iPhone has one, to get close without moving the phone, or the standard wide lens with a bit of pinch-to-zoom if it does not. Decide this before you press record, because which lens the back camera is using is one of the things a multi-camera session locks in for that take — switching lenses mid-reaction means restarting rather than adjusting on the fly.
Keep the phone close enough to see it, far enough to survive it
Plenty of demos are genuinely safe to film from arm’s length — food colouring in water, a growing crystal, a simple circuit. Some are not: a vinegar-and-baking-soda eruption sprays further than it looks like it will, a flame needs real clearance, and anything that gives off smoke or steam will fog a lens or coat it in a film the way steam over a stovetop does. The zoom that solves the framing problem above solves this one too — pulling the phone back a step and using the telephoto or a pinch-zoomed wide lens buys distance from the mess without giving up the close framing the reaction needs.
A stand or a mount matters more here than in almost any other subject on this site, because a real experiment usually needs both of your hands — one to hold something steady, one to pour or strike a match — and a phone propped against a book or a stack of boxes leaves neither hand busy holding it. The countdown timer, set to 5 or 10 seconds, gives you time to finish setting up and be in position before recording actually starts, instead of fumbling with the screen while also trying to get the demo ready.
Colour is the result — leave the filter on None
DualCam’s six live filters — Vivid, Warm, Cool, Mono and Film, alongside None — are genuinely useful in other subjects on this site: Warm or Cool can nudge two mismatched light sources toward each other, and Mono removes a colour clash entirely. None of that is a good trade here, because in a demo where the entire point is a colour change — a pH indicator shifting from purple to pink, a flame changing colour with a different metal salt — a filter is changing the one piece of information the video exists to show. Shoot these in None and let the actual colour reach whoever is watching.
The front and back cameras still expose independently, so the reaction can read perfectly while your face sits duller beside it, or the other way round if the room light is stronger than whatever is happening in the container. Tap the frame with the reaction in it to make sure that side reads correctly — tap-to-focus carries exposure with it — and accept a dimmer face as the smaller loss. A viewer forgives your face being a little underlit far more easily than they forgive not being able to tell what colour the liquid actually turned.
One take per demo, not one file for the whole lesson
A dual-camera recording runs straight through from record to stop with nothing to pause it, and a video with several demos in it does not need to fight that limit — it needs to stop being one recording. Film the vinegar volcano, stop, reset the table, film the next one as its own take. Editing three short files together afterwards costs nothing that dual-camera recording changes; a normal video editor trims, joins and adds captions to a finished MP4 exactly the way it would to any other clip.
Some reactions also take longer to develop than a take should run — a crystal that needs hours to grow, or mould spreading over days, is not something to leave a phone recording through even if heat and storage allowed it, and at some point they would not. Film the setup and film the result as two short, separate takes instead, and let the actual waiting happen off camera the same way a recipe’s simmer time does.
Common follow-up questions
Should I use picture-in-picture or split screen for a science experiment video?
Picture-in-picture with the back camera filling the frame is the better default — the reaction needs to be as large and as readable as possible, and your face rides along in a small window. A split screen gives the reaction only half the canvas, which fights against framing something that is already small.
Why does my face look duller than the experiment in the video?
The front and back cameras set exposure independently, and here the reaction reading correctly matters more than your face doing the same, since the colour is usually the point. Tap the frame with the reaction in it and accept the trade — a slightly dim face is a smaller loss than a washed-out result.
Can I record while a reaction takes hours to finish, like a growing crystal?
Not as one continuous dual-camera take — there is no pause, and a recording that long would run into storage or heat limits regardless. Film the setup and film the finished result as two separate short takes and skip filming the wait itself.
Want to just do this?
DualCam records the iPhone front and back cameras at the same time and writes one finished MP4 while you shoot. Free, no account, no ads, nothing leaves the phone.