T vs F stop of Cine Lenses

[Rory Hinds]

Hi there

Please could someone tell me how T stops of Cine lenses works compared to F Stop?

If I have a T2.3 what does it equal to in F Stops?

Thanks
Rory

[Brian Drysdale]

Originally Posted by Rory Hinds

Hi there

Please could someone tell me how T stops of Cine lenses works compared to F Stop?

If I have a T2.3 what does it equal to in F Stops?

Thanks
Rory

A T stop is the f stop with the lens transmission losses factored in. You can lose up to a stop with some of the older zoom lenses from the 1960s. More modern zoom lenses tend to lose around a 1/3 stop or even less because of the improvements in lens coatings.

What T 2.3 will be as an f stop will depend on much light a particular lens will lose due to internal reflection etc. A zoom lens will lose more than a prime lens.

You use the f stop for working out your depth of field and the T stop for exposure. Professional cine lenses are marked in T stops.

[Don Donatello]

F stop is a mathmatical equation and does NOT measure the amount of light coming out teh back end of the lens that hits the film plane ... T stop is the measurement of the light that hits the film plane ...

[Rory Hinds]

Hi guys

Thanks for the response.

So I still don't really understand the T stop reading.

I understand F Stops and am used to working with them so can easily distinguish between say F1.2 and F2.4 but I can figure out much slower a T2.3 lens be compared to T1.3.

I can see it would be T1 difference, but what is that like 1 F stop?

Thanks
Rory

[Brian Drysdale]

A stop difference is the same in both. Both run in the same progression (1, 1.4, 2, 2.8 etc)

http://en.wikipedia.org/wiki/F-stop

Because you're changing lenses on film cameras you have to know that if you set an exposure of a certain stop on a fixed focal length lens, it'll not change when you put on a zoom which has a lot more elements (with the increased light loss).

You want exactly the same exposure on the film. With the Transmission or T stop you don't have to work out how much extra exposure you need to give when using zoom compared to the prime lens to achieve the accurate exposure on the film.

T stop = f stop + (transmission loss in lens measured in stops)

[Rory Hinds]

Hey Brian

thanks for the info.

So a T2.3 will be alot slower than a T1.3.

I'm looking at purchasing a set of lenses and of course want T1.3 but the cost is alot higher than T2.3 lenses.

I'm trying to figure out how much of a difference this will make and if the T2.3 will still do the job for me or should I hold out and save for T1.3's.

Many thanks
Rory

[Don Donatello]

80% of the time i rented ziess 2.1's over the hi speed 1.3's ..when using 35mm i usually light sets for T 2.8-4 ... for 16mm i try to get at least a T2-2.5

[Rory Hinds]

Hi Don

Why would you have 2.1 over 1.3's? Is it that you shoot mainly daylight or brighly light subjects and the 2.1 would have a better sweet spot?

I'm thinking I really want a set of 1.3's as I mainly enjoy night scenes and really trying to shoot with available light. But hey this trend could change.

Would you recommend going for cheaper 2.1 or 2.3 over a set of 1.3's?

Kind regards
Rory

[Don Donatello]

i have only ever shot one shot at 1.3 and that was 16mm using a 25mm lens dolly in on tight med shot to C/U = that was 1st shot production , 1st time working with new AC and he did pull focus excellent - after that shot he asked for more F stop so i gave him T2 on all interiors on that film..

i shoot wide night street scenes at T2 ( wide open with 2.1) when using 1.3's .. i try to lay in 3ft candles general fill and a few key area's if there are none but i find if stores have lights on and there are street lights T2 will do it ...
i always use a little filtering on 1.3's = could be 1/8-1/2 =ultra con ,double fog, low con ..with 2.1's i'll shoot with no filter = so i find for my taste i prefer a little less contrast/dirtering on the 1.3's ... once i hit T 2.5 then i go with 1/2 to 1 filters

either set i try to keep 5.6 as max f stop ( use ND filters to keep it there)

also i get 6 to 7 2.1 primes vs. 5 to 6 1.3 primes for less $$ ...

i rent the lens ... so depending on the project i can go with either set and/or both sets and/or mix the sets but most of time 2.1 full set ( to 135mm)...

i do have RED 103 reserved .. when it comes time to BUY ??
well i have few months to think about it ...
i'll be starting off with a S16 zoom lens .. and i'll be using 35mm nikon/canon still lens with PL adaptor to F or canon mt ( older manual lens not EFs ) ..
at some point i may add used zeiss lens ?? 2.1 or 1.3 's ??
depends on price and the set ...

you might test out both sets to see if the $$$$ difference is worth it ?

[Greg Lowry]

Rory,

There's nothing wrong with asking questions to fill in knowledge gaps, but it is rather surprising that you work for MINE in London and don't know an f-stop from a T-stop. That's about as fundamental as it gets. It's frankly hard to believe that you're a working pro. In any event, I suggest that you do some serious reading on the subject of cinematography. There are many excellent books available.

Greg

[Don Donatello]

i know many persons shooting and getting paid 1000-1500 day ( including betaSP camera) that would find F/T stops difficult to explain ..i find that most persons that have a video background have not had to deal with t stop vs f stop .. infact i find most just turn on lights ,move the f stop ring till they have the zebra settings the way they want ( looks good on monitor) and don't know what the current f stop is actually set to .. where as in general film background persons i find tend to light for a F stop ( use a light meter) and prefer to shoot at a favorite f stop ... either way will work ...

[Rory Hinds]

Thanks Brian & Don

Understanding T stop vs F stop is clear now.

"It's frankly hard to believe that you're a working pro." -
Greg, I sometimse wake up and think the same thing, yet go on and create amazing images for my clients who all seem to think we are pro's, so I must be doing something right :-)

Knowledge is power.
Sharing knowlege is just nice :-)

[Steve Gibby]

Donatello is correct in saying that those with television and video backgrounds haven't had to deal with the difference between F stops and T stops. I think it's important to remember, in a convergent media world, where lenses and techniques of cinematography, and electronics of videography are converging, not to be cine-centric in our approach to the concept of acquiring images. Are videographers less "professional" than cinematographers just because they haven't had to deal with T stops and other requirements of the cinema world? (Tape measures, hand held light meters, mechanical shutters, etc.) Definitely not.

I shoot both styles, so in a way I'm a poster child for convergence. Am I any less of a professional when I shoot TV/video/ENG-style than when I shoot cine-style? Absolutely not! I just have to use different techniques and equipment to get images that satisfy the needs of the project. For those of you that are entirely film and cine-centric in you backgrounds, here's a short primer on how TV/video shooters in an ENG-style production environment deal with light and focus.

Because of continuous multiple focal length needs, 1/2" and 2/3" lenses are generally zooms. They have switches top and bottom to enable quick changes from manual to auto operation for servos and iris. You have to know when to switch from manual to auto lens modes to be effective. Focus is always manual on 1/2" and 2/3" lenses, but aperture can be switched between auto and manual. In some run 'n gun environments, with 1/3" chip camcorders, all lens operation is auto. Depending on the camera make, it can still be quite effective. Other times it is partial auto/partial manual. Other times it is all manual - focus, aperture, white balance. We're talking a real fast moving environment, where you either capture the story or you don't - no focus pullers, tape measures, lighting tweaks, etc. You rack focus and judge DOF quickly. And then move on to the next shot. Good principles of shot composition: framing, lighting, focus, DOF, action follow, etc., still apply, as in cine-style shooting, but you're usually on your own to get the images very quickly. After shooting that way, you may then need to go full manual with the lens, and shoot cine-style b-roll and creative shots with shallow DOF, soft light etc. The best ENG-style shooters also have cine-style skills. It's unbelievably challenging at times.

So, back to ENG-style light (and color) management. Most often you're using available light that changes rapidly - but your footage still needs to be exposed correctly. Professional ENG-style cameras usually have three channels of white balance (plus black balance): Preset, A, and B. If you don't have time to do a custom white balance you need to use Preset, which is very accurate in most modern ENG cameras. If you're constantly going indoors and outdoors, you'll probably do a custom white balance on A & B, and simply switch between them when you change from interior to exterior lighting. Modern ENG-style lens/camera combinations are quite accurate on auto iris modes. Most shooters also use zebra pattern to quickly judge the light level of the brightest objects in the frame. In manual iris mode the zebra is your lifeline for getting correct exposure. When there is time to do so, many ENG-style shooters will put the lens on auto iris, frame up the shot to see what F stop the camera/lens want for exposure, switch over to manual iris on the lens, check the zebra level, back down the iris about ½ stop, and shoot the shot. Same thing on the next setup, and on and on. HD is especially critical not to overexpose. I routinely shoot precisely exposed HD and SD footage using the above procedures - footage that wins Emmy Awards and scores of other national awards.

My experience shooting ENG-style really helps me when I shoot cine-style, and conversely, my experience shooting cine-style really helps me when I shoot ENG-style. I’m already used to quite often working alone, but I merely have to switch to my cine-style knowledge base. Quite often my cine-style shooting is actually a melding of cine-style and ENG-style.

I’m quit comfortable with someone on this board not knowing what a T stop is. After all, this is DV Info (as in Digital Video). With media convergence, a lot of guys are going to arrive here with TV/video backgrounds. Conversely, many will arrive with cinema/film backgrounds. They’re both equally valid mediums of expression. Though cinematography is the older art, I don’t feel that makes videographers less professional. I’m a true convergence shooter who respects the nuances, knowledge, challenges, and professionalism of each discipline.

Respect leads to collaboration - which fosters progress in art.

[Patomakarn Nitanontawat]

Well said Mr. Gibby.

[Charles Papert]

I personally find the term "pro" or "professional" bandied around far too much as a dividing line in the sand. All that means, by definition, is that one is paid for whatever occupation the term is being applied to. (we all like a roll in the hay, but consider which of us are called "pros" in that particular arena...!)

I have met TV news cameraman who may have garnered awards and been on the job for years who wouldn't know a T-stop from an F-stop; I also know folks who I work with in the film industry who know FAR less or even nothing about the barely arcane terminology of the video world; there's quite a few 17 year olds on this board that could school these Hollywood veterans on the intricacies of compression, file formats and the like. (Whether they like it or not, most of them are having to learn as HD is pushing film out slowly but inexorably).

I think that certain basics of optics and image making are universal, format-agnostic and should be learned as a core knowledge base. I can well see that someone who has only dealt with video zooms would not have necessarily come across a T-stop marking, but such things are becoming more relevant in the video world when "film-style" techniques are observed. For instance, if one is shooting at a T4.3 and wants to apply a "skinny shutter", perhaps a 1/120th of a second, they would need to know how much to compensate the aperture to match the footage shot at 1/48th.

Convergence really is the name of the game these days!