The Milky Way on Film
Why long exposures work differently on film than on digital – and how to get a picture of the Milky Way anyway.
On digital, the Milky Way is almost a standard subject: 20 seconds, ISO 3200, done. On film it’s a real challenge – and that’s exactly what makes it appealing.
When and where
- From the northern hemisphere the bright core of the Milky Way is visible from about March to October, best from June to August in the late evening.
- From Barcelona it never gets high: at just over 41° north, the galactic centre only reaches about 20° above the southern horizon. A clear view south matters.
- New moon and a truly dark place – see Dark places around Barcelona.
The problem: reciprocity failure
In very long exposures, film becomes less sensitive than its ISO rating suggests. This reciprocity failure (or Schwarzschild effect) means that when the meter says 30 seconds, the film needs considerably longer.
Ilford publishes a formula for it: corrected time = metered timep. For HP5 Plus, p is about 1.31, so a metered 30 seconds becomes roughly 86 seconds. Other manufacturers publish tables – check the data sheet of your film.
Slide films such as Fujichrome Provia 100F are famous for needing hardly any correction up to about two minutes – but at ISO 100 they’re slow.
What that means in practice
A rough calculation: on digital, ISO 3200, f/2.8 and 20 seconds is a typical starting point. With ISO 400 film you’re three stops short – that’s 160 seconds, and with reciprocity correction more like 10 to 13 minutes. By then the stars have long turned into trails.
That leaves three routes:
- Embrace star trails: expose long and let the Earth’s rotation draw. That’s not a mistake but a style of its own.
- Tracking: a small astronomical mount (star tracker) turns the camera with the sky. Then even 10 minutes with pinpoint stars are possible – the foreground blurs instead.
- Fast film and a fast lens: Ilford Delta 3200 or pushed HP5 on an f/2 or faster lens cut the time considerably.
Gear
- A camera with Bulb mode and a locking cable release.
- A sturdy tripod – with minute-long exposures every vibration counts.
- A wide angle between 20 and 35 mm.
- A red light, spare batteries and a lot of patience.
At the lab
Tell the lab there are night shots on the roll – and whether you pushed. Very thin negatives are otherwise easily missed when cutting, just like with the moon on film.
The first Milky Way negative is usually disappointingly thin. The third gets better. And at some point you hold a picture of light that travelled for tens of thousands of years – on a strip of film.