How do handheld light meters deal with lens light transmission loss?

Asked 3/31/2012

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A camera’s built-in meter measures through the lens, so any transmission loss is already included. But a handheld incident or reflected light meter doesn’t know which lens is on the camera. How is this handled in practice? Do handheld meters assume an average transmission, use T-stops, or do photographers simply ignore the difference? If needed, is the usual solution to test each lens and dial in exposure compensation?

light-meter calibration lenses t-stops exposure

Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0

Photography Stack Exchange contributor

14y ago

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If not knowing the transmittance of your lenses is really bothering you, you could test them and see as this DPReview user did. Most of the lenses tested, about 25 Nikon lenses, averaged in the 80-90% light transmittance (telephoto lenses were less). Compensate accordingly. In the real world of photography, though, a safe assumption is that most don't worry about it.

Originally by user9509. Source · Licensed CC BY-SA 4.0

user9509

14y ago

AI Answer

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Handheld meters generally do not know your lens’s actual transmission. They work from scene light and the f-number you set, not the lens’s measured T-stop.

In practice, most photographers simply ignore lens transmission differences because many lenses are close enough that the error is small for still photography. Typical transmission is often around 80–90%, with some telephotos losing a bit more light. That can amount to a fraction of a stop.

If you need higher precision, the usual real-world solution is calibration or compensation:

test your camera/lens/meter combination,
determine how far off a given lens is,
then apply exposure compensation or calibrate the meter/camera workflow accordingly.

Some advanced meters support calibration procedures that effectively absorb lens transmission loss along with other system variables. Another practical approach is to look up measured transmission data for a lens and compensate manually.

So the short answer: standalone meters usually don’t directly account for individual lens transmittance unless you calibrate for it. For most still photography, people don’t worry much about it; for critical work, they test and compensate.

How do handheld light meters deal with lens light transmission loss?

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