Home · Register · Software · Software · Join Upload & Sell

Moderated by: Fred Miranda
Username  

  New fredmiranda.com Mobile Site
  New Feature: SMS Notification alert
  New Feature: Buy & Sell Watchlist
  

FM Forums | Canon Forum | Join Upload & Sell

1
       2       3       end
  

T-Stops vs F-Stops and Ev Difference: School Me
  
 
Paul Mo
Offline
• • • • •
Upload & Sell: Off
p.1 #1 · p.1 #1 · T-Stops vs F-Stops and Ev Difference: School Me


Hi.

DxO rates the T-Stop of the EF 35mm f1.4L at 1.7

DxO rates the T-Stop of the EF 35mm f2.0 IS at 2.0

DxO rates the T-Stop of the EF 35mm f1.4L II also at 1.7

What would the Ev (if that is the correct term) difference be between the 1.7 and 2.0 = 1/3rd of a stop, is that correct?

And would that show up in reality? 1.7 and 2.0 seems very close.

I am currently considering buying another fast 35. While the 35 1.4L II looks amazing - truly fantastic - money is not limitless as I'd also like to reacquire a 16-35 f2.8L II (for practicality's sake) alongside that new 'fast' 35.

I hope that makes sense.

Cheers.




Sep 01, 2017 at 09:41 AM
RobDickinson
Offline
• • • •
Upload & Sell: Off
p.1 #2 · p.1 #2 · T-Stops vs F-Stops and Ev Difference: School Me


For stills photography its no real relevance.

Its for movie shooting where you want the exact same exposure between lenses



Sep 01, 2017 at 09:58 AM
Paul Mo
Offline
• • • • •
Upload & Sell: Off
p.1 #3 · p.1 #3 · T-Stops vs F-Stops and Ev Difference: School Me


But what about in terms of overall light transmission? Isn't the DxO data showing only a 1/3rd of a stop difference between the f1.4's and the f2.0?


Sep 01, 2017 at 10:00 AM
JohnBrose
Offline
• • • •
Upload & Sell: Off
p.1 #4 · p.1 #4 · T-Stops vs F-Stops and Ev Difference: School Me


My understanding is that the T-stop designation is used more in video and stands for light transmission where as f-stop is used in photography as a measure of the aperture or opening of the lens in relation to focal length. They are typically pretty close. I'm sure wikipedia has more of an explanation. I would just suggest buying the lens that works for you depending on the look you want and your budget.


Sep 01, 2017 at 10:05 AM
Paul Mo
Offline
• • • • •
Upload & Sell: Off
p.1 #5 · p.1 #5 · T-Stops vs F-Stops and Ev Difference: School Me


JohnBrose wrote:
My understanding is that the T-stop designation is used more in video and stands for light transmission where as f-stop is used in photography as a measure of the aperture or opening of the lens in relation to focal length...


Thanks, and I understand that. My question lies more in the post prior to yours - the actual light transmitted to the sensor by both 1.4 and f2.0 models varies only by 1/3rd of a stop, does it not?



Sep 01, 2017 at 10:14 AM
jcolwell
Online
• • • • • • •
Upload & Sell: On
p.1 #6 · p.1 #6 · T-Stops vs F-Stops and Ev Difference: School Me


Basically, T-stop is derived from direct measurement of light coming through the lens, while F-stop represents the potential amount of light that can enter the lens, based on geometry; i.e. aperture diameter (as seen through the entrance pupil) and focal length.

F-stop f/1.7 is one-half stop faster than f/2 (i.e. one-half EV).

Two f-stop tables are attached, below. The first simply shows the sequence of f-stop values for full stops, half-stops, and third-stops, from f/1.0 to f/4.0. The second f-stop table shows the relationship between 'n' (the power) and SQRT(2), on which the sequence of f-stops is based. The square-root (SQRT) of two is important, as that represents the change in aperture diameter when the aperture area is increased; doubling the area (one-stop increase in EV) corresponds to increasing the diameter by SQRT(2) = 1.41...

Note that, for some obscure reason, not all f-stop values are "rounded-up" or "rounded-down" following normal practice. For example, we see "f/5.6", not "f/5.7", and "f/22", not "f/23". Maybe numbers ending with even numerals were considered to be more socially-acceptable than those ending with odd numerals, which is odd.



© jcolwell 2017


F-stop values from f/1.0 to f/4.0, for full stops, half-stops, and third-stops.





© jcolwell 2017


F-stop table for full stops, half-stops, and third-stops.




Sep 01, 2017 at 10:53 AM
Paul Mo
Offline
• • • • •
Upload & Sell: Off
p.1 #7 · p.1 #7 · T-Stops vs F-Stops and Ev Difference: School Me


Thanks Jim. So the 1.4 lenses in question are actually on average 1/2 a stop faster than the f2.0? Sorry if I seem dense about this.


Sep 01, 2017 at 11:01 AM
jcolwell
Online
• • • • • • •
Upload & Sell: On
p.1 #8 · p.1 #8 · T-Stops vs F-Stops and Ev Difference: School Me


Hi Paul.

You're welcome.

F-stop f/1.4 is one full stop faster than f/2. IOW, in the lefthand box of the second table, going from n = 1 to n = 2, corresponds to a full stop (one EV), with f-stop going from f/1.4 to f/2 (assuming shutter speed and ISO remain the same).

One confusing aspect is that, when you're talking about changing EV, is that shutter speed and ISO both change 'directly', but f-stop changes by SQRT(2). IOW, to increase exposure by one EV, you can (i) reduce shutter speed by 1/2 (i.e. twice the time), (ii) double ISO (e.g. 100 to 200), or you can increase f-stop by SQRT(2). In reality, increasing the aperture diameter by SQRT(2) doubles the area of the opening, and so it fits the pattern, but SQRT(something) is not a normal part of everybody's daily diet.



Sep 01, 2017 at 11:16 AM
charlyw
Offline
• • •
Upload & Sell: Off
p.1 #9 · p.1 #9 · T-Stops vs F-Stops and Ev Difference: School Me


t-stop only applies to the image brightness, f-stop applies to both DOF and image brightness (all else being constant)...

So forget about the t-stop it only matters if you need to have different lenses behave the same regarding image brightness under constant lighting conditions - and that thus only applies to video. And the DxO ratings are partly incorrect as there isn't a lens in existence that doesn't have a worse t-stop with regard to it's f-stop (because the f-stop is an upper limit to the t-stop and every single lens surface in the lens reduces transmission as there isn't a perfect coating in existence yet - and probably never will)...



Sep 01, 2017 at 11:27 AM
dmacmillan
Online
• • • • •
Upload & Sell: On
p.1 #10 · p.1 #10 · T-Stops vs F-Stops and Ev Difference: School Me


When I worked in TV, I used to shoot sound on film with an Auricon 16mm camera. I also shot with a Bolex Rex. The Auricon had the famous Angenieux 12-120 zoom with a reflex viewfinder that used a semi-reflecting prism. The Bolex had a built-in split viewfinder as well. This bled of about 1/3 of the light passing through the lens to the viewfinder.

The lenses were marked in T stops instead of f-stops. This allowed you to set to a number (f5.6) that indicated how much light would reach the film if there was no viewfinder bleeding off light.

Imagine trying to shoot using that kind of viewfinder. The lens is stopped down to begin with, then you're only seeing a fraction of the light transmitted by the lens. It's as bad or worse as looking at a 4x5 ground glass with the lens stopped down.



Sep 01, 2017 at 12:56 PM
 

Search in Used Dept. 

        


Paul Mo
Offline
• • • • •
Upload & Sell: Off
p.1 #11 · p.1 #11 · T-Stops vs F-Stops and Ev Difference: School Me


Read and noted - thanks.


Sep 01, 2017 at 01:02 PM
jcolwell
Online
• • • • • • •
Upload & Sell: On
p.1 #12 · p.1 #12 · T-Stops vs F-Stops and Ev Difference: School Me


Hi Paul,

Looks like we're both a bit confused. My reply about being a half-stop different was based on this question from the OP,

Paul Mo wrote:
...What would the Ev (if that is the correct term) difference be between the 1.7 and 2.0 = 1/3rd of a stop, is that correct?


(f/1.7 to f/2 is one-half stop)

...but your specific question after my first post was about f/1.4...

Paul Mo wrote:
Thanks Jim. So the 1.4 lenses in question are actually on average 1/2 a stop faster than the f2.0? Sorry if I seem dense about this.


(f/1.4 to f/2 is one full stop)

As long as we're both equally confused, it should work out fine.



Sep 01, 2017 at 01:20 PM
stevesanacore
Offline
• •
Upload & Sell: On
p.1 #13 · p.1 #13 · T-Stops vs F-Stops and Ev Difference: School Me


I also started my career with Bolex Rex V with The 12-120 and the 35mm Arri 2C, (remember those?). I think the real reason for T-Stops was in the days of film and light meters. I used to shoot reversal and not negative film in 16mm, which means exposure had to be perfect. The T-Stops were used instead of F-Stops so exposure was more accurate. Of course it was also used for consistency between lenses. I see no purpose for them in still work. When I shoot with a 1.2 or 1.4 lens these days, it's for shallow focus and not for more light. IMO the great performance of todays sensors allows the use of slower lenses without any penalty in quality. I went from the 16-35 2.8II to the f4 IS version and never missed that extra stop.

My 2 cents.



Sep 01, 2017 at 01:40 PM
dmacmillan
Online
• • • • •
Upload & Sell: On
p.1 #14 · p.1 #14 · T-Stops vs F-Stops and Ev Difference: School Me


stevesanacore wrote:
I also started my career with Bolex Rex V with The 12-120 and the 35mm Arri 2C, (remember those?).

Yes, I got to shoot a little footage with the 2C and the Arri 16 BL. I also shot some footage with the Éclair NPR. The NPR weighed about 18 pounds IIRC. It would wear you out! Remember the old Spectra light meters?



Sep 01, 2017 at 02:03 PM
mb126
Online
• • •
Upload & Sell: Off
p.1 #15 · p.1 #15 · T-Stops vs F-Stops and Ev Difference: School Me


To the OP-- in practice it amounts to about a half stop of light transmission. However, that half stop is not the reason you would buy the 35L II. ISO 6400 being what it is on modern FF sensors, it's really hard to come up with scenarios where ISO 6400 and f/2 won't get the job done.

Buy the 35L II for the overall build, clarity, sharpness, DOF control, and rendering.

Buy the 35 IS for the smaller size, cost savings, and valuable IS.

In all honesty the 35L II is probably my favorite lens ever (it's a close call with the 200 f/1.8 and the 135 APO). But I'm a wedding guy and ~50% of the images I deliver from every shoot are with that lens and I shoot it almost exclusively between f/1.4 and f/2.

It's very possible that the cost would not be worth it to you.
As an example, you can easily buy the 35IS and 16-35 IS for the cost of the 35L II. For 95% of people that will be the smarter choice.



Sep 01, 2017 at 02:25 PM
stevesanacore
Offline
• •
Upload & Sell: On
p.1 #16 · p.1 #16 · T-Stops vs F-Stops and Ev Difference: School Me


dmacmillan wrote:
Yes, I got to shoot a little footage with the 2C and the Arri 16 BL. I also shot some footage with the Éclair NPR. The NPR weighed about 18 pounds IIRC. It would wear you out! Remember the old Spectra light meters?


Yes, shot with the NPR and the ACL which was tiny in comparison. The NPR was insane to hand hold which it was designed for! Also shot with Arri S, M, 35BL, Panaflex etc. I was a union AC in NYC for a few years. Used a Spectra but never purchased one, I had all the Minolta meters, (still do but haven't used them in years).



Sep 01, 2017 at 03:26 PM
snapsy
Online
• • • • •
Upload & Sell: On
p.1 #17 · p.1 #17 · T-Stops vs F-Stops and Ev Difference: School Me


It has some practical implications for photography. For example, I shoot with a pair of 5D's, one with a 24-105L f/4 and the other a 70-200 f/4. The t-stop of the 24-105L is noticeably higher (less transmission) than my 70-200, which causes me to have to constantly change the careful ETTR metering I did of a scene when I switch back and forth between the cameras as I shoot the same scene with different focal lengths.


Sep 01, 2017 at 03:33 PM
jcolwell
Online
• • • • • • •
Upload & Sell: On
p.1 #18 · p.1 #18 · T-Stops vs F-Stops and Ev Difference: School Me


stevesanacore wrote:
... I went from the 16-35 2.8II to the f4 IS version and never missed that extra stop.


Same here. I also went from the 24-70/2.8L II to the 24-70/4L IS.



Sep 01, 2017 at 04:17 PM
whumber
Offline
• •
Upload & Sell: On
p.1 #19 · p.1 #19 · T-Stops vs F-Stops and Ev Difference: School Me


Paul Mo wrote:
Hi.

DxO rates the T-Stop of the EF 35mm f1.4L at 1.7

DxO rates the T-Stop of the EF 35mm f2.0 IS at 2.0

DxO rates the T-Stop of the EF 35mm f1.4L II also at 1.7

What would the Ev (if that is the correct term) difference be between the 1.7 and 2.0 = 1/3rd of a stop, is that correct?

And would that show up in reality? 1.7 and 2.0 seems very close.

I am currently considering buying another fast 35. While the 35 1.4L II looks amazing - truly fantastic - money is not limitless as I'd also like to reacquire a
...Show more

I'd take DxO's transmission measurements with a grain of salt. They almost never line up with the ratings given by OEMs to the Cinema versions of a given lens and the same lens will vary wildly by camera body.



Sep 01, 2017 at 04:24 PM
stevesanacore
Offline
• •
Upload & Sell: On
p.1 #20 · p.1 #20 · T-Stops vs F-Stops and Ev Difference: School Me


snapsy wrote:
It has some practical implications for photography. For example, I shoot with a pair of 5D's, one with a 24-105L f/4 and the other a 70-200 f/4. The t-stop of the 24-105L is noticeably higher (less transmission) than my 70-200, which causes me to have to constantly change the careful ETTR metering I did of a scene when I switch back and forth between the cameras as I shoot the same scene with different focal lengths.


I'm sure every lens is a bit different, but you'll see the result on the histogram for precise exposure anyway. Wouldn't it be nice if you could switch between F stops and T stops in the menu settings?




Sep 01, 2017 at 05:08 PM
1
       2       3       end






FM Forums | Canon Forum | Join Upload & Sell

1
       2       3       end
    
 

You are not logged in. Login or Register

Username     Reset password