20 votes

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

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). ...
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  • 140k
17 votes

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

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. ...
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  • 352
16 votes

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

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 ...
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  • 601
13 votes
Accepted

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

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....
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  • 1,749
8 votes

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

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 ...
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  • 540
7 votes
Accepted

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

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, ...
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5 votes

Can I use my camera to measure lens light transmission?

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 ...
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4 votes

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

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 ...
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  • 140k
4 votes

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

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 ...
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4 votes

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

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 ...
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  • 140k
4 votes

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

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 ...
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  • 4,835
3 votes
Accepted

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

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 ...
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  • 140k
2 votes

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

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 ...
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  • 21
2 votes

Can I use my camera to measure lens light transmission?

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-...
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  • 1,030
2 votes

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

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 ...
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  • 117k
2 votes

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

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 ...
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2 votes

What is the T Stop of a Human Eye?

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 ...
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  • 2,377
2 votes

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

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 ...
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  • 577
2 votes

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

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 ...
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  • 167k
2 votes

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

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 ...
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2 votes

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

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 ...
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  • 167k
1 vote

Transmission rate of vintage Petzval type lenses

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 ...
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1 vote

How can the EVF be brighter than the lens?

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 ...
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  • 3,374
1 vote

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

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 ...
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1 vote
Accepted

Transmission, Aperture, and Focal Length in Low Light Situations

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 ...
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  • 167k
1 vote

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

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 ...
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  • 1,174
1 vote

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

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 ...
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  • 2,377
1 vote

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

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 ...
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1 vote

What is the fastest T Stop available?

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 ...
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  • 2,377
1 vote

How do dedicated light meters account for light transmittance?

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 ...
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