Westminster fountain at sunset

by Jorge Córdoba

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2
votes
2answers
1k views

How does lens-hoods for pancake lenses work? (Canon EF 40mm with ES-52)

Normally I use lens-hoods on every of my glasses (flairlight blocker, lens protection). Some days ago a bought the Canon EF 40mm STM (Pancake-Lens). So I look for the fitting lens-hood and found the ...
18
votes
5answers
874 views

Why do two lenses with the same F-number give different amount of light?

Why do the following two lenses provide different amount of light? In both images we have fixed focusing distance, distance to the object, ISO, shutter speed and F-number.
2
votes
2answers
316 views

Is there any practical way to measure the T-stop of a lens?

T-stop measures actual light transmission in a lens. Therefore, different f/2.8 lenses can have different T-stops. T-stops are usually only given for cine lenses. For photography lenses, is there any ...
8
votes
2answers
648 views

Do lenses with the same f-stop but different focal length gather the same amount of light? [duplicate]

I'm taking images of a light source in a scientific labratory, and I thought I had a good grasp on all these things, but now i'm second guessing myself after some results. The most important thing is ...
15
votes
2answers
830 views

Does a specific f number across all lenses denote same amount of light?

When we say a light source emits 1500 lumens of light, it does not really matter if the light source is incandescent, CFL, diode etc. Similarly, when I say f/1.8 can I assume that all lenses pass the ...