nimbushopper Loc: Tampa, FL

All good explanations! The simple way to look at it is that each time you open the aperture one fstop you are letting in twice the amount of light, and conversely, when you stop down one fstop you are letting in half the light.

warzone

When I took a digital photography class, the professor said the easiest way to remember is set the FStop according to how many things you want in focus. If you want 2 things in focus, set F2. If you want 8 things in focus, use F8. When the professor said that, it made it easier for me to understand. Later, when I became more skilled, I was able to understand the technical aspects of aperture.

Thomas902 Loc: Washington DC

"...I don't see a practical way to talk about T-stops when they are not given by the manufacturers..." While this may be true for still photographic optics DirtFarmer there is currently a paradigm shift toward Video... especially with the advent of mirrorless cameras which in terms of autofocus for video, mirrorless takes the lead. Because mirrorless cameras have phase-detection focus sensors while many DSLRs cannot use it with the mirror flipped up during video, DSLR video quality is often blurred during focus. DSLRs have to use the slower, contrast-detection focus method.

Nikon actually has tried to build a "Hybrid" mirrorless in the D780 which is Nikon's best DSLR for video... oversampled 4K with no crop, as well as 1080p video at 120 FPS. Not to mention 10-bit N-Log capabilities when shooting over HDMI... I believe the D6 matches this now... But holding up a DSLR camera at arms length is not what I consider a viable scenario... No EVF... a major deal breaker...

Please keep in mind the still photography has likely reached it's zenith... The rest of the world is moving toward video... Simply spending time of Facebook or IG will validate the aforementioned... a decade from now video likely will dominate... and camera vendors are scrambling to meet this anticipated demand...

But wait we are talking Aperture verses T-Stops DirtFarmer and Cine lenses.. which are far superior to currently Aperture oriented still camera lenses...

Why? Cine lenses allow far superior Light and "Aperture Control".

Unlike other lenses, cine lenses don’t just control the aperture. Cine lenses have iris rings with T-stop markings (as opposed to f-stops) that give you the exact measure of the amount of light that actually passes through the lens, instead of how wide the lens opening is.

This cine lens-only feature offers high-precision manual control over the exposure and allows you to maintain your exposure in every scene, regardless of the weather and ambient exposure. The iris ring is also click-less, so you can adjust the aperture much more smoothly and change the exposure without taking your audience out of the story.

However in my minds eye the huge difference is that Cine lenses are "Parfocal Lenses". These are lenses that are able to keep their focus locked on subjects even when you zoom in on a particular scene. With a non-parfocal lens, the simple act of zooming in or out may change your focus, requiring you to refocus your shot. And since zooming is an unavoidable part of cinematography, a cine lens will allow you to smoothly zoom in or out without losing focus. Something few if any "Aperture" lenses can accomplish...

Again cine lense take the lead in Precise Focus Control

One most important features of a cine lens is its ability to maintain focus on moving subjects or smoothly switch focus from one subject to the other. Moving subjects in a video scene are kept in focus by slowly rotating the focus ring and “following” the subject. This is a difficult feat with regular still lenses, as their focus rings have no hard stops and will require extreme precision on the user’s part to achieve proper focus while following a moving subject. On the other hand, a cine lens has a focus ring with clearly visible markings and hard stops at the beginning and at the end. This makes it much easier to get accurate and smoother focus pulls every time, even without the help of a follow focus system.

With all that said there are a rare collection of Superb Still Photography lenses that are very close to being Parfocal and are empowered with an extremely long focus throw... These optic gems are quietly being bought up by serious videographers... And folks like myself who cherish extremely long Focus Throw and Parfocal properties... My collection of AI and AI-S glass is constantly growing at a fraction of the cost of the current offerings of high end optics by Nikon and and third party vendors... Nikon created some of the finest optics in the nineteen eighties and they still shine like diamonds since they were built with precious of all metal (brass helicoils) and sans light robbing "anti glare" coatings...

Hope this helps the OP and others get a grasp on the world of Cine lenses...

Manglesphoto Loc: 70 miles south of St.Louis

Nah, they don't think!!!

wham121736 Loc: Long Island, New York

I think of the ‘f’ stop as a fraction where 1/1 is a fully open Aperture, f/2 is half the opening (1/2), f/4 is one quarter of the opening. Not exactly correct but a useful way of thinking about the subject.

fetzler Loc: North West PA

The explanation is pretty simple.

f = fl/d. f = the focal length fl= is the focal length of the lens. d= the diameter of the opening. If d is small the f is large. Aperture is the diameter of the opening which is usually expressed in f units.

if you have a lens with t stops a correction for light absorption by the lens elements has been made.

Abo

f10 = 1/10 of the focal length... the diameter of the aperture of a 50mm lens at f10 is 5mm...
at f8 the diameter of the aperture is 6.25mm... at f2; 4mm and so on.

At the risk of muddying the waters; if you've ever wondered why f8 is substantially more
than double the light of f16:

BebuLamar

Not wondered. I knew it's 4 times as large.

Abo

Long ago I shot a fox up its elementary aperture with my
Krupp 22 from Essen.

You couldn't see any wound, but
the fox stopped in its tracks... permanently.

Abo

havnt crunched the numbers but sounds right

kmarqu Loc: Houston

Abo

Anything wrong with?:
f10 = 1/10 of the focal length... the diameter of the aperture of a 50mm lens at f10 is 5mm...
at f8 the diameter of the aperture is 6.25mm... at f2; 4mm and so on.

CHG_CANON Loc: the Windy City

Life is like photography, when you try to use math to explain art, you're just boring everyone.

lamiaceae Loc: San Luis Obispo County, CA

I got over that in 1980.

jeweler53

I say I am "opening up one stop" when going from one stop to one stop larger. Just explain
that I am letting twice as much light in, if I am speaking to a lay person. If I am teaching a class it get more involved.

Does that answer the original question?