Why does one lens give darker photos than another at the same settings?
Asked 4/20/2019
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2 answers
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Using a Nikon D500, I’ve noticed my AF-S DX Nikkor 16-80mm f/2.8-4E ED VR produces darker images than my AF-S DX Nikkor 18-105mm f/3.5-5.6G ED VR when I use the same ISO, aperture, shutter speed, and white balance on the same scene. The camera’s meter also reflects this difference, and I saw the same behavior on a Nikon D3200. At the same focal length, the difference looks to be around 1/2 to 2/3 stop. Is this just a T-stop/transmission difference, or could it indicate an aperture calibration problem? How should I interpret this?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
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Although the transmissivity of the lenses might explain this difference, part of it could also be due to the possibility that the 16-80's electronic aperture mechanism might be miscalibrated. I do not know if this lens's aperture mechanism has a greater or lesser tendency to be miscalibrated, but I assume the possibility is not zero.
I agree with you that the 16-80's T-stop should not be that much worse than the 18-105's. The difference in number of elements/groups is not huge, and if anything the pro lens should have better coatings. The difference in EV in your sample photos is something like 1/2 to 2/3 stop. That would indicate an unacceptably low T-stop for the pro lens.
If the lens is still under warranty, you could have Nikon take a look and adjust it, if necessary, for no charge.
Originally by user64358. Source · Licensed CC BY-SA 4.0
user64358
7y ago
0
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A small difference can come from lens transmission (T-stop), but 1/2–2/3 stop between these two lenses is larger than you’d normally expect from coatings/glass losses alone.
The more likely explanations are:
- the 16-80mm’s electronic aperture may be miscalibrated, or
- the 18-105mm’s mechanically controlled aperture may be exposing a bit brighter than nominal.
In other words, the lenses may not both be hitting the exact same real aperture even when both are set to f/8.
T-stops for still-photo lenses usually aren’t published, and f-stops are based on geometry, not actual light transmission. So two lenses set to the same f-number can still transmit slightly different amounts of light. But with these lenses, such a large gap would be unusual if transmission were the only cause.
Also check for obvious external causes such as different filters (UV, ND, polarizer) on the lenses.
If no filters are involved and the difference is repeatable on more than one camera body, it points to the lens rather than the camera. If the 16-80mm is under warranty, having Nikon inspect/calibrate it would be reasonable.
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