20

Because in cinema, it's common to change lenses within a shoot while preserving identical exposure. This is rarely important in still photography (and even less so with the flexibility of digital). You might say But t-stops are more accurate, allowing me to be more precise! — and that's basically right, but the main thing is that precision is overrated in ...


17

To add to mattdm's great answer: In addition to the added exposure precision, which is not important to photography, T-Stops are LESS precise in other ways which ARE important to still photography. F-stop is the literal proportion of the aperture to focal length. T-stop adjusts this for exposure, but this raw value is important to depth of field. Depth of ...


16

F-Stops matter most when you care about knowing your composition and depth of field, T-Stops matter most when you care about knowing your exposure. Photographers want to control composition first and adjust exposure as needed. Cinematographers need to control exposure first and then compose as needed. The critical difference with photography is that we can ...


13

If you look at filter #209 you'll see "Reduces light 1 stop (Transmission = 51%)". That is what you expect to see. Filter #210 reduces light 2 stops and has transmission of 24%. Again, what you expect. So what is the matter with filters 207 and 208? They are COLOR filters not neutral. They a) reduce light, and b) reduce it differently in different ...


8

There's nothing here to grasp. T-stop is the same thing as f-stop, except the manufacturer or a third party has physically tested the lens to find how much light it transmits, rather than making a theoretical calculation based on the size of the exit pupil, which is where the f-stop measurements come from. When a manufacturer specifies T-stops on their lens,...


7

It IS part of the exposure calculation in fully professional cinematography; these folks prefer lenses marked in T-stops. A full F-stop is actually a factor of two (or one half) in light transmitted, while the typical transmission losses of a lens are in the range of an eight to a quarter stop. This makes transmission nearly irrelevant to correct exposure, ...


5

In a nutshell: no, you cannot use your camera to accurately measure light transmission. The problem is with the way your ISO control works on a digital camera. ISO is not a generic "amplify signal by X amount"; it is designed as a compensation adjustment to match the exposure index of the equivalent film stock. Therefore ISO 100 with one lens is not the same ...


4

Assuming I understand what you're saying, the answer is no. Or, depending on how you look at it, yes, but. The optics you use to squeeze that full-frame image into the smaller size are effectively reducing the focal length of the lens. Let's say that your crop sensor is ⅔ the (linear) size of your larger sensor, like the difference between APC-S and full-...


4

About the notations used for filters: Notations based on tradition of 19th century scientist. T = Transmission (always as a percent) O = Opacity (always as decimal fraction) D = Density (always as logarithmic value) T as percentage O as decimal fraction (avoids confusion). D as log base 10 (because scientists of that era had no computers or calculators)....


4

This is because the filters you are looking at on that page are color filters in addition to neutral density filters. The ND portion is as described at How to read ND filter description? and as you expect: 0.3 has (around) 50% transmission, 0.6 25%, and 0.9 12.5%. From further down that table: #209: .3 Neutral Density — Reduces light 1 stop (Transmission = ...


4

First, what is not required for such measurement? calibrated light source (because transmission is about relative, not absolute intensity) calibrated light meter (because, again, transmission is about comparing light intensity, not measuring absolute values) We will, however, need a reliable constant intensity light source and an image sensor that reports ...


3

You can look at DxOMark's Lens Ratings, and particularly the Optical Metric Scores, which include a T stop measurement. I don't put too much stock in DxOMark's overall numbers (which don't have much practical impact for real use), but if you're interested in this particular thing, here's a way to tell. Manufacturers do not typically give this number, so the ...


2

Maybe a more practical way to determine the T-Stop of a lens?: Arrange a uniformly lit white surface big enough to cover the FOV of a lens. Use your camera with fixed shutter speed (M-Mode), ISO, WB etcerera to make an exposure of the surface without a lens. Put the lens on the same camera with the same settings, and make a second exposure of the surface. ...


2

As has been said, for most lenses you can find the T-stop measured on dxomark, depending on the camera used. For example find the 70-200 VRI Nikkor here: http://www.dxomark.com/Lenses/Nikon/AF-S-VR-Zoom-Nikkor-70-200mm-f-2.8G-IF-ED-mounted-on-Nikon-D300__440 To answer your question more specifically, you can either compare the histograms for full image ...


2

You're right that transmission contributes to the light gathering ability of a lens. To compare like for like you need to look at the T-stop, which is a measured value of total light transmission (on a log scale similar to the f-stop). Manufactures rarely specify the T-stop of photographic lenses (as opposed to cine lenses) but you can find values on some ...


2

The modern camera lens is an array of individual glass lenses. Some cemented together, others air-spaced. Each lens element has two polished surfaces that act to reflect away some of the exposing light. The recipes used to make the optical glass are diverse. Surface reflection is the cause of considerable light loss. Worst, much of this reflected light will ...


2

Your eye can be treated exactly like a camera lens, and its maximum f/# really is around f/2.2 or so. The cornea has an index of refraction of around 1.33, so the fresnel reflections are around 2% or so. The reflections off of other surfaces are very small because of minimal index breaks. T# = F# / T_avg over some bandwidth, so we have f/2.1 / 0.98. The T/...


2

Speaking about noise. Noise is random, so when taking a picture with high iso you get some random noise that lowers the "quality" of the shot. While filming the noise in each shot is different, you get some pixels of noise in one shot of the video and then in the next one the noise is on other pixels. The overall effect is that you perceive less noise than ...


2

Even two $10K+ cinema lenses with the same T-stop rating does not guarantee the center of the frame will be the same brightness or the edges of the frame will be the same brightness even when both are used with the same camera - only that the TOTAL amount of light collected by the lens when pointed at a constant light field (a featureless scene with constant ...


2

If it is a quality cinema lens with T-rating/stops rather than F-rating/stops it should include vignetting characteristics. To determine T-rating lens manufacturers use an integrating sphere which is not image/camera based. It measures the total collected light from a known light source after it passes through a lens. T-stop is a relative measure/percentage ...


2

Sometimes it is. But for most photographic purposes, it doesn't make that much of a difference. In special cases when it does, it usually is part of the calculation. Even a highly complex zoom lens with many elements, such as the Canon EF 24-70mm f/2.8L II with 18 elements in 13 groups is T2.8 at 24mm, T2.9 at 35mm and 50mm, and T3.1 at 70mm. At worst, the ...


1

As a rule of thumb, loss is generally assumed to be about 4% per glass to air interface in uncoated lenses. So you will have a transmission of 0.96 per interface. A true petzval lens has six glass to air interfaces and two cemented glass-glass interfaces. Likely, the cemented interfaces do not make a major contribution to loss unless the cement hasd become ...


1

You basically already told yourself. The EVF or electronic view finder is not limited to use the visible light as seen by the lens. It takes the sensor data which can be amplified to give you a brighter image. Most mirrorless cameras have two modes: Simulate the exposure - this will lead to the evf show whatever the exposure settings will yield as image. ...


1

Besides the fact that lenses are not perfectly transparent, there are umpteen more negative factors that impede any instrument from proclaiming the “correct” exposure. Naming a just a few: activity of the developing process, color of the ambient light, medium sensitivity to ambient light, variability of the ISO of the medium, inaccuracy of shutter speed, ...


1

Brightness in terms of exposure is always about light per unit area. If you are using both lenses on an APS-C camera the larger size of the image circle projected by the 14mm lens is totally irrelevant. T-stops are similar to f-stops: the lower the number the brighter the lens. A lens with a transmission of T3.4 is dimmer, by about one stop, than a lens ...


1

Just to add to the other answers, I want to address: I wanted to quickly understand how they were managing to get such a good picture in relatively low light. They had a long depth of field on a very large sound stage; one I'd equate to maybe f6 - f8 or more, yet they appeared to be able to pull in a lot of light for such a small apparent aperture. The ...


1

The F/# is a geometrical property. It describes, in a way, the apex angle of the cone of light that forms an image of a point. To a first approximation, this also determines the exposure since you are collapsing light from some area onto a point. However, because both reflection (mirrors) and transmission (lenses) are imperfect, some light is absorbed, ...


1

The f-stop is calculated by dividing the focal length by the working diameter of the lens. As an example: The focal length is 200mm and the working diameter is 25mm; then 200 divided by 25 = 8 thus the f-number of this combination is written as f/8. The f/ is an abbreviation for "focal ratio". The f-number (focal ratio) is universal; meaning any lens ...


1

Depends what you want? Photolithography lenses are sitting around f/0.6 consistently these days and they have almost perfect transmission, so t/0.65 or so. You can buy microscope objectives faster than f/0.4 these days as well, though they require immersion oil to function. These systems again have very fast t/#s. In the consumer marketplace? t/1.2 is ...


1

Like you this bothered me as well. Depending on the lens, the exposure was always underexposed to some degree. I use a Sekonic L-758DR, but in the end I don't calibrate using the provided software and tests required. My gear is Nikon. Effectively their camera calibration procedure takes lens transmission loss into account, along with many other variables ...


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