What is the reason T stops isn’t mentioned anywhere?
I would like to know if my 400/4.5 is a actually 409mm T/4.12
So Why is Nikon doing 180mm Lenses?
- Thread starter NorthernFocus
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I would like to know if my 400/4.5 is a actually 409mm T/4.12
Unfortunately, focal length is usually shorter than stated (e.g. 380mm) and the maximum T stop value never lets more light than the F stop value suggests, it’s always less light due to the effect of things such as coatings and vignetting that affect actual light transmission.
Two different things. F stops are just an algebraic ratios. T actually measures transmission. It's relevant to video when you move among lenses (zooms aren't prevalent) and must have the same sensor illumination for post work. So T2.8 on a 24mm gives you the same expoaure and depth of field as T2.8 on 50mm (at any stop).
Irrelevant for stills since every frame stands on his own.
Oddly enough, if they were going to go 20mm in one direction or the other, I suspect most users of this optic would have preferred 20 mm of extra reach, i.e., 620 mm. But that might be me projecting what I would want onto others. Either way, looking forward to this lens.
In good quality glass, the difference is about 0.1 to 0.2 stops. In cheaper glass, more. It mostly has to do with the coatings on the glass.
It's irrelevant for stills since you don't have to match primes. It's critical for vid because you switch among primes in a single sequence and the look has to match. You often roll two bodies (one b-roll) and need to match the T.
I understand the reason for being open about Vids, but what is the reason this information isn’t available for Z glass? Isn’t the Z9 also for vids? Even if not, why not tell us?
They aren't cinema lenses. Sure, they can be used for it, but they miss all elements that make a lens specifically for cinema. Nikon doesn't make video cameras and the Zs cannot be adapted to any other system because of the radically shallow (and great) flange distance.
Cinema lenses are made in sets with identical filter thread, long focus throw, identical location and width for both focus and aperture rings, never AF, declicked aperture, etc. Zooms are rare because of the complexity making them parfocal.
For practical purposes, if you shoot your 1.2s side by side you can be assured that they have near-identical transmission characteristics, probably equivalent to something like T1.3.
Cameron T
Well-known member
Canon and Sony don't do it either, so this is just how the industry works. For stills, it's not a needed statistic for 99.999999% of people, and while I would like to know the exact numbers, as mentioned, it's very close. The worst difference I've seen anyone claim was a third of a stop for one of the older f mount primes (I think an older 500?).
SCoombs
Well-known member
T stops are not strictly necessary information for lenses used for stills in the way that it is for video work, but when comparing lenses for purchase decisions some people still wish to know because if one lens is a little better for transmission it can yield slightly better results as far as noise goes.
True in theory, but in practice, the difference between similarly-priced name-brand lenses is unlikely to be more than 0.1 stops. For FF or even APS-C sensors, that's a rounding error. For lenses with same specs for same mount with significant difference in price (eg Tamron 2.8 v Nikon 2.8), the difference to worry about is CA, distortion, edge sharpness, flare, AF speed, contrast, size and other factors related to IQ, not the small difference in light transmission.
It's likely just marketing, and history. F/1.2 sounds better than T 1.3, plus f-stops are a lot simpler and easier for more consumers to understand. And that's the way they've been describing it for decades.
It's quite something how many people don't really understand f-stops, and how many don't even understand the basics of f-stop's relation to aperture.
All fine and good to know that its not important to know for stills. But I’m curious… Why should this information be a secret? More people would appreciate knowing the actual T stop then trying to understand how coatings work.
No secret, just not measured and reported. Just like focus-throw angle isn't reported for stills lenses. For fun, take a look at the Tokina 11-20. It comes in both cine and stills versions (2.8 and 2.9).
Interesting insights to learn. Nikon themselves aren’t measuring it?
Question, what’s focus-throw?
(Maybe we should create its own thread for this kind of discussion)
I doubt they measure it since they don't sell into the cine marker.
Focus throw (measured in degrees) is the distance between MFD and infinity on the focus ring. In cine lenses, they are exceptionally long, 270-300 degrees for smooth focusing (which is done with an external device called follow-focus). Stills lenses have much shorter throw, but it isn't typically included in the specs.
It's no secret at all. It's just not advertised and marketed in most photography circles.
Here's a quick start on learning optics. I'll try to find a lesson where coatings and transmissibility are introduced later: Lenses - Stanford University Optics Class Lesson
Why a member of the Computer Science Department teaches it is a bit puzzling to me. When I took Basic Optics, over 40 years ago, it was taught by the Physics Department.
Lack of transparency in my view. I think they should provide that information, especially focal length, as well as how it changes with focus (focus breathing).
For me it's relevant for stills. There are lenses where the maximum T stop is different from the F stop by about 1 stop.
This means nearly doubling the image noise vs a lens that has its T stop value very close to its F stop value.
However, perhaps a lens with coatings that affect T stop may help improve other aspects of image quality so there may be a trade-off?
Modern lenses? Never seen/heard of it. How would you even know this?
I've seen simple tests where people compare the exposure or iso difference when using different lenses with the same settings input.
1 stop difference may be an extreme example (for example the Mitakon 50mm F0.95 is roughly T1.4) but for me even 1/3 of a stop can be significant and good to know when making buying decisions.
For me more information/clarity from manufacturers is always a positive, especially when photography is a world with many important nuances (in my view).
Even if the primary goal of a lens is to be used for stills, more photographers are using them for video too.
Mitakon is a toy lens, so no surprise. You'll have much bigger issues than 1/3 stop. But I am curious how it was tested. The only comparisons I've ever seen is the same lens (like a Tokina or a Canon) in both configurations.
I maintain that the difference in good lenses is minute and irrelevant in all stills application.
Noted.
