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Questions tagged [light-transmission]

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8 votes
4 answers
7k 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 ...
3 votes
2 answers
44 views

Transmission rate of vintage Petzval type lenses

Is anyone aware of a transmission rate test for vintage lenses, such as 1800's Petzval lenses?
2 votes
1 answer
223 views

How can the EVF be brighter than the lens?

When I use my mirrorless camera, an Olympus OM-D EM1 Mark II, in a dark room, the EVF shows the room as though it is fully lit, but the lens does not have the same brightness. It's as though the EVF ...
20 votes
3 answers
3k views

Why are DSLR lenses measured in F stops instead of T stops?

I understand the difference between f-stop and t-stop, but why are cinema lenses measured in one, and dSLR lenses measured in another?
0 votes
3 answers
148 views

Why isn't glass transparency part of the exposure calculation? [duplicate]

The F number is a ratio calculated purely from the focal length of the lens and the size of the aperture. Any light meter talks in terms of F, Shutter, and ISO. Different glass, or just different ...
4 votes
2 answers
161 views

Does the T-number account for lens vignetting, or only for glass/coating transmission?

Surprsingly I could not find information on this. Many lenses have vignetting profiles available. Vignetting changes if you use a cropped sensor, or, in case of zoom lenses, can change with zoom. ...
2 votes
2 answers
348 views

Transmission, Aperture, and Focal Length in Low Light Situations

I've been looking for an affordable lens I can use for nighttime shooting, including astrophotography. The two lenses I have found that seem best suited for this are the Samyang 16mm f/2 and the ...
1 vote
3 answers
260 views

Can a larger format lens provide more light to a crop sensor for a given f-stop?

Having recently spent some time fighting for light with a high-speed camera having a CS mount and a sensor area under .1 inches2, I was wondering if the f rules apply to cropped sensors? For example: ...
8 votes
5 answers
1k views

Do top-of-the-line lenses transmit more light at the same f-stop?

We usually refer to the F number to compare how fast is a lenses with another one. I understand that the optic quality should help as well — so would a L series in Canon (or whatever is the equivalent ...
4 votes
5 answers
597 views

F-stop vs T-Stop - how do I quickly grasp a videographers view of the world?

I'm aware this is flirting with video rather than photography, but the question really relates to how each world can be understood by the other. Very briefly - I am an amateur photographer who ...
0 votes
3 answers
185 views

Why does my one lens have different exposure (t-stop) than my other lens?

I have been comparing my Pentax Takumar 28mm f3.5 lens (via an adapter) to my Canon 18-55mm 3.5-5.6 IS lens. When I have them both set to the exact same f-stop, the exposure meter of the camera is a ...
7 votes
2 answers
596 views

What is the T Stop of a Human Eye?

I was reading that the maximum F number of a human eye, if treated the same way as a camera lens, would have an F number of 2.1, but basically since the eye cannot be treated the same way as a camera ...
6 votes
3 answers
1k views

Why does Rosco's filter page show that 33% transmission is 1 stop rather than 50%?

I was taught that each stop halves/doubles the light throughput. So one stop up is double as much light, one stop down is half as much light. Now, according to this Rosco table: https://www.rosco.com/...
3 votes
2 answers
950 views

Can I use my camera to measure lens light transmission?

I want to compare and quantify the light transmission of various lenses (with some custom modifiers). So I have a target setup with constant illumination, and a camera body for them ready to shoot ...
5 votes
2 answers
343 views

How do dedicated light meters account for light transmittance?

Dedicated light meters seem to be well-regarded for their versatility and accuracy of metering. What puzzles me about them is how can they account for the different light transmittance of different ...
3 votes
2 answers
510 views

How to compare the speed of lenses taking transmission into account?

When comparing the speed of two lenses, you almost exclusively hear about the maximum aperture. This of course makes sense, since at a certain lighting condition, a larger aperture in general allows a ...
19 votes
2 answers
4k 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 ...
1 vote
1 answer
438 views

What is the fastest T Stop available?

What is the widest T Stop possible We are having f stops of below even 0.7 NASA lenses What will be the T stop of such lenses with f stop below ONE?
32 votes
2 answers
27k views

What is T-number / T-stop?

Usually, when discussing aperture of a lens, F-stop and F-number are used for quantifying. But some photographers, and especially videographers, also mention T-stop. The concept and numbering used (e....