Do premium lenses transmit more light than cheaper lenses at the same f-stop?
Asked 11/24/2010
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If two lenses have the same marked aperture, such as f/4, will a premium lens line like Canon L or Nikon’s pro lenses actually deliver more light to the sensor than a cheaper equivalent? For example, comparing Canon’s 100mm macro versions or lenses like the 24-105mm f/4L, is there any real exposure advantage, and could it ever amount to a full stop?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
15y ago
2 Answers
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No, it won't be anything like a full stop, but there is probably a small advantage.
Our friends over at DXO mark test transmission of lenses, though only wide open, and they don't have a pair of L non L lenses at the same speed. What the results do show is that the wider the max aperture the more transmission you lose compared to the theoretical f stop. So the 50 f/1.2L is about a fifth of a stop further away from the theoretical value wide open compared to the 50 f/1.8
Since manufacturers (of SLR lenses) don't release t-stop information the data is scarce so most photographers refer only to the f stop value when they talk about lens "speed". Cine lenses are often specified by t-stop as this is more important to film since you can't (easily) change the shutter speed.
Old answer:
You are right that the f/ number tells you how fast a lens is. The lenses designated "L" tend to be faster, but that's because of the lower f/ number, not the L!
Case in point, the EF 100 f/2.8L is not faster than the EF 100 f/2.8 as they have the same f/ number. However the EF 35 f/1.4L is a stop faster than the EF 35 f/2, because the f/ number is smaller.
The f/ number relates to how large the aperture is in relation to the focal length. f/2 means the aperture diameter is the focal length divided by 2. Wider aperture means you let in more light and get more background blur which is generally desirable.
Being a stop faster means you let in twice as much light, which means the area of the aperture is twice as big. Hence if you square the f/ numbers and one is twice the other one, the smaller one is a stop faster.
Originally by user1375. Source · Licensed CC BY-SA 4.0
user1375
15y ago
0
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Not by anything close to a full stop. At the same f-number, lenses are designed to pass roughly the same amount of light. Real-world transmission can differ slightly because some light is lost inside the lens, and that actual transmission is described by T-stop rather than F-stop.
In practice, the difference between lenses with the same f-stop is usually small—often only a fraction of a stop. More complex optical designs, especially zooms with many elements, may lose a bit more light than simpler lenses, but still not anywhere near a whole stop in normal cases.
So an L lens is not meaningfully “faster” than a non-L lens just because it’s an L lens. Premium lenses may offer other benefits like better sharpness wide open, contrast, autofocus, build, weather sealing, or image stabilization, but not an extra stop of exposure at the same marked aperture.
If exact transmission matters, cine lenses are often rated in T-stops; still-photo lenses usually are not.
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