I have searched the internet for an answer to this question, but all I get is conflicting answers so I thought I would go to the experts that have the experience. Will a larger diameter lens like a 300mm or a 500mm fixed lens let in more light at their widest opening (f/4) than a smaller diameter lens like a 50mm or a 105mm lens at f/2.8? It would seem to me that the larger diameter lens with its larger blade opening and larger barrel diameter would let more light pass than a lens with a smaller opening and smaller diameter barrel.

The reason I ask this question is to determine if it is worth the investment to get an f/4 300mm lens for indoor basketball or to stay with my 135mm f/1.8? As an experiment one day, I shot basketball with my 50mm Sigma Art lens at f/1.4 and the images were a lot brighter than they were with my 70-200, which is f/2.8. The lens diameters are almost the same, so this was not a good test at diameter vs light transmission. I expected the larger aperture would be brighter, as it was.

So I need answers from you guys that shoot a 300mm lens. Can you really get a lot more light onto the sensor with this larger lens, compared to when you shoot your smaller diameter lens?

Thanks

I have searched the internet for an answer to this question, but all I get is conflicting answers so I thought I would go to the experts that have the experience. Will a larger diameter lens like a 300mm or a 500mm fixed lens let in more light at their widest opening (f/4) than a smaller diameter lens like a 50mm or a 105mm lens at f/2.8? It would seem to me that the larger diameter lens with its larger blade opening and larger barrel diameter would let more light pass than a lens with a smaller opening and smaller diameter barrel.

The reason I ask this question is to determine if it is worth the investment to get an f/4 300mm lens for indoor basketball or to stay with my 135mm f/1.8? As an experiment one day, I shot basketball with my 50mm Sigma Art lens at f/1.4 and the images were a lot brighter than they were with my 70-200, which is f/2.8. The lens diameters are almost the same, so this was not a good test at diameter vs light transmission. I expected the larger aperture would be brighter, as it was.

So I need answers from you guys that shoot a 300mm lens. Can you really get a lot more light onto the sensor with this larger lens, compared to when you shoot your smaller diameter lens?

Thanks

Let’s make this easy.

The front element of a 300/2.8 most certainly tskes in more light than a 135/2.8.

It most certainly does not deliver more light to the film plane.

Imagine it this way, your eyes ... good or bad are your eyes.

Now, imagine you are looking into a flashlight 135 feet away that I’m holding.

Now if I move the exact flashlight 300 feet away.

The flashlight has the same brightness, but appears much dimmer because of the distance. To have the same apparent brightness I would need a much brighter flashlight at the farther distance.

That’s why distant stars appear to be much dimmer and than the Sun, even though many/most put out more light.

Basic Newtonian physics.

Your choice is important!

Assuming ‘enough’ light is the end goal, there may be two additional considerations. The light transmission (T stop) of lenses varies as by a considerable amount as it does with filters as well.

Depending on the brand/model of lens the difference could be 2/3 stop of light delivered to the sensor. If a filter (and they vary as well) is used then more light can be gained or lost.

Two ‘similar’ rigs with the same focal length and f stop can can easily vary by one stop of light at the sensor.

Has it occurred to you that the long telephoto with it's smaller field of view is gathering light that has been reflected from a much smaller area, thus less total light to play with. The size (area) of the the aperture of a telephoto thus has to be larger to let the same intensity of light in to the sensor. That's why, in theory at least, a given f stop (f stop is aperture diameter/focal length) will illuminate the sensor with the same intensity of light regardless of the focal length of the lens (everything else being equal) The front glass element of a lens has to be large enough to support a large aperture iris located right behind the front glass. At least that's how I think of it. Or thinking of it another way: 25 mm aperture /100 mm focal length =1/4 =100 mm aperture./ mm focal length (both are f/4)

Thanks for the diagrams and I do appreciate your support. But it still does not answer my question about the difference in light transmission between 2 different diameters and lengths of lenses at their wide open aperture. Will a 300 mm lens with its larger diameter wide open at f/4 transmit more light to the sensor than a smaller diameter 135 mm at f/1.8?

The best explanation so far was from an earlier UHH member that discussed the law of inverse squares when calculating light drop off. The distance that the light has to travel is roughly 12" in the 300 mm lens compared to 5" in the shorter lens. So the light has to travel an additional 7" of distance in the 300 mm lens. Now by the time the light reaches the sensor, the light in the 300 mm lens will have dropped off at least to at least ¼ to 1/5 of its original value that it was when it entered the lens opening. This concept I agree with and understand.

The whole purpose of this exercise was to determine if a 300 mm lens at f/4 would give me a better exposure in low light than my 135 mm at f/1.8 where the average ISO values are 18,000. An aperture of 1.8 has such a shallow DOF that the faces are sometimes not so sharp because my target hit the chest instead of the face on a moving gymnast.