[toni-a]

Transmittance or T stop is very important mainly for lenses desiggned to be used in low light, you might pay plenty of extra $$$$ for a f1.2 lens over f1.4 lens for low light performance to discover that both are equal or worst the f1.4 lens has a lower T value and thus transmits more light 
can the transmittance be measured her in our tests ?? 
DXO is doing it so it is feasible

[JJ_SO]

T-Stop means transmission stop. And the other word is transmittance. See https://en.wikipedia.org/wiki/F-number#T-stop

So, one answer could be "people don't even know how to spell it", but OL is not a site specifically for cine lenses and what would you gain by knowing T-stops?

[Brightcolours]

Transmittance or T stop is very important mainly for lenses desiggned to be used in low light, you might pay plenty of extra $$$$ for a f1.2 lens over f1.4 lens for low light performance to discover that both are equal or worst the f1.4 lens has a lower T value and thus transmits more light 
can the transmittance be measured her in our tests ?? 
DXO is doing it so it is feasible

No, DXO is NOT doing it. DXO claims they do, but that is nonsense.
Their published T-stop values are just nonsense, and do not take into account the extra amplification a camera applies because of the F-stop used. Do I need to give examples, or will you accept me just telling you it is nonsense?

It is NOT doable with most lenses using cameras, and even if the lens would allow what you have to do, you still have to have very specific knowledge about what the camera is up to to kinda measure T-stops.

How would you go about measuring T-stops? In the middle of the frame you get a lot more light than in borders, let alone corners. So... What and how to measure it? And how to defeat the camera's manipulation? And how to distract the light lost by the sensor microlenses?

[davidmanze]

Transmittance or T stop is very important mainly for lenses desiggned to be used in low light, you might pay plenty of extra $$$$ for a f1.2 lens over f1.4 lens for low light performance to discover that both are equal or worst the f1.4 lens has a lower T value and thus transmits more light 
can the transmittance be measured her in our tests ?? 
DXO is doing it so it is feasible

No, DXO is NOT doing it. DXO claims they do, but that is nonsense.
Their published T-stop values are just nonsense, and do not take into account the extra amplification a camera applies because of the F-stop used. Do I need to give examples, or will you accept me just telling you it is nonsense?

      No, go on BC explain it !!

[Brightcolours]

Transmittance or T stop is very important mainly for lenses desiggned to be used in low light, you might pay plenty of extra $$$$ for a f1.2 lens over f1.4 lens for low light performance to discover that both are equal or worst the f1.4 lens has a lower T value and thus transmits more light 
can the transmittance be measured her in our tests ?? 
DXO is doing it so it is feasible

No, DXO is NOT doing it. DXO claims they do, but that is nonsense.
Their published T-stop values are just nonsense, and do not take into account the extra amplification a camera applies because of the F-stop used. Do I need to give examples, or will you accept me just telling you it is nonsense?

      No, go on BC explain it !!

What is the no to? To "Do I need to give examples"?

[davidmanze]

Transmittance or T stop is very important mainly for lenses desiggned to be used in low light, you might pay plenty of extra $$$$ for a f1.2 lens over f1.4 lens for low light performance to discover that both are equal or worst the f1.4 lens has a lower T value and thus transmits more light 
can the transmittance be measured her in our tests ?? 
DXO is doing it so it is feasible

No, DXO is NOT doing it. DXO claims they do, but that is nonsense.
Their published T-stop values are just nonsense, and do not take into account the extra amplification a camera applies because of the F-stop used. Do I need to give examples, or will you accept me just telling you it is nonsense?

      No, go on BC explain it !!

What is the no to? To "Do I need to give examples"?

will you accept me just telling you it is nonsense?

[Brightcolours]

Transmittance or T stop is very important mainly for lenses desiggned to be used in low light, you might pay plenty of extra $$$$ for a f1.2 lens over f1.4 lens for low light performance to discover that both are equal or worst the f1.4 lens has a lower T value and thus transmits more light 
can the transmittance be measured her in our tests ?? 
DXO is doing it so it is feasible

No, DXO is NOT doing it. DXO claims they do, but that is nonsense.
Their published T-stop values are just nonsense, and do not take into account the extra amplification a camera applies because of the F-stop used. Do I need to give examples, or will you accept me just telling you it is nonsense?

      No, go on BC explain it !!

What is the no to? To "Do I need to give examples"?

will you accept me just telling you it is nonsense?

What is nonsense that you tell of?

[popo]

Their published T-stop values are just nonsense, and do not take into account the extra amplification a camera applies because of the F-stop used.

Surely T-stop is by definition only the optical component. Anything the sensor does to adjust for it doesn't matter.

It is NOT doable with most lenses using cameras, and even if the lens would allow what you have to do, you still have to have very specific knowledge about what the camera is up to to kinda measure T-stops.

The simple solution is not to have any electrical coupling between the camera and lens. The camera can't adjust the output if you don't know where that light is coming from.

How would you go about measuring T-stops? In the middle of the frame you get a lot more light than in borders, let alone corners.

I don't know if there is an industry definition, but some kind of peak or center-average might make sense.

And how to distract the light lost by the sensor microlenses?

That should not be counted as it is not part of the objective. You can have a separate sensor efficiency measure if you really want.

[Brightcolours]

https://www.dxomark.com/Lenses/Sigma/Sigma-35mm-F14-DG-HSM-A-Nikon-mounted-on-Nikon-D800E__814
https://www.dxomark.com/Lenses/Sigma/Sigma-35mm-F14-DG-HSM-A-Sony-mounted-on-Sony-SLT-Alpha-99-II__1120
https://www.dxomark.com/leica-apo-summicron-sl-35mm-f2-asph-lens-review/
https://www.dxomark.com/sony-fe-85mm-f1-8-lens-review-excellent-choice/
https://www.dxomark.com/sony-fe-50mm-f-2-8-macro-lens-review/

---

Their published T-stop values are just nonsense, and do not take into account the extra amplification a camera applies because of the F-stop used.

Surely T-stop is by definition only the optical component. Anything the sensor does to adjust for it doesn't matter.

It is NOT doable with most lenses using cameras, and even if the lens would allow what you have to do, you still have to have very specific knowledge about what the camera is up to to kinda measure T-stops.

The simple solution is not to have any electrical coupling between the camera and lens. The camera can't adjust the output if you don't know where that light is coming from.

How would you go about measuring T-stops? In the middle of the frame you get a lot more light than in borders, let alone corners.

I don't know if there is an industry definition, but some kind of peak or center-average might make sense.

And how to distract the light lost by the sensor microlenses?

That should not be counted as it is not part of the objective. You can have a separate sensor efficiency measure if you really want.

So how do you propose to measure T-stop? Without a sensor?

And many brands have the aperture closed when not connected.

[popo]

So how do you propose to measure T-stop? Without a sensor?

It doesn't have to be a camera sensor although I don't see any major problem with using one. Any suitable light detector could be used.

And many brands have the aperture closed when not connected.

If that happens, then for sure some way around would have to be found. I recall EF lenses can be forced to a given aperture by using DoF preview and disconnecting the lens in that state for example. I don't know how other lenses might react to similar.