Calculating an Exposure

No light meter? No problem! Announcing, Light WTF, a mobile web app used to calculate your exposure. The site includes a general exposure calculator, as well as specialty calculators for Pinhole Exposures and Moonlight Exposures.

Please try them out and let me know any feedback. I find them quite useful when using old manual film cameras. They are just web pages, so you can visit from anywhere.

exposure-calculator screenshot

Exposure Value

The calculators are based off common Exposure Value tables which are still useful and good to learn. It helps to have an intuitive sense of the light of a scene and a good ballpark guess of an exposure.

The calculator can also be used with an existing reading. I’ll use a reading off a camera to give me an EV value of the scene. I’ll then lock the EV value and adjust for a desired effect, for example, if I want a long shutter speed.

Pinhole Exposures

The Pinhole Calculator is a bit simpler since usually the aperture and ISO is fixed when using a pinhole camera. You need need to select your scene light and get the exposure time.

Plus the pinhole calculator has apertures that go from f/32 up to f/384, which most general light meters, so makes it easy without having to do any calculations.

pinhole-calculator screenshot

Moonlight Exposures

The Moonlight Calculator is intended to be used when taking photographs of a scene primarily illuminated by the light of the moon. Your light source, the moon, is adjusted by the phase of the moon. You can then set your aperture and ISO to get an exposure.

You’ll notice if you’re not shooting at a full moon or right around a full moon, your exposures will get quite long to unpractical.

If you want to take a picture of the moon itself, it is an object in full sunlight, an EV value of 15. You can use the sunny 16 rule or the general exposure calculator to get a value.

moonlight-calculator screenshot


I’m not sure how useful but all of the code for the calculators is available as open source at I welcome any contributions or feel free to report issues there.

Uses noUiSlider for slider widget and wNumb for formatting, both by Refreshless.

You can follow me at marcuskaz on Instagram.