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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 15 Nov 2010 (Monday) 23:01
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T2.8 vs F2.8 [film/video lenses vs photography lenses]

 
StructuredAmazing
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Nov 15, 2010 23:01 |  #1

T2.8 vs F2.8 [film/video lenses vs photography lenses]

whats the difference? do the letters just signify what they are?
like T2.8 and F2.8, do they both gather the same amount of light?


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phreeky
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Nov 15, 2010 23:11 |  #2

My understanding is that the F-stop is the theoretical/true aperture, and the T-stop instead takes all light loss (i.e. from optical elements) into account. A T-stop is the figure you want to use for exact exposure information.




  
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JeffreyG
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Nov 16, 2010 05:38 |  #3

F-stop is the ratio of the aperture to the focal length. T-stop is the same and includes an offset to account for the amount of light lost in the lens due to transmission losses.

Modern camera lenses have coatings that make losses so small that T-stops are not needed practically any more.


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alemerson
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Nov 16, 2010 12:36 |  #4

http://www.cinema5d.co​m/news/?p=2575 (external link)


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JPM ­ Photography
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Nov 16, 2010 13:28 |  #5

http://en.wikipedia.or​g/wiki/F-number#T-stops (external link)

maybe this will help some.


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RaZe42
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Nov 16, 2010 13:58 |  #6

DxOmark has the t-stops of the lenses they've tested listed. Some people are quite skeptical towards DxO, but things like that should be quite easy to measure, so the results should be reliable. eg the 24-205 f/4 is T5.1, the 24-70 f/2.8 is T3.4.


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JeffreyG
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Nov 16, 2010 16:00 |  #7

RaZe42 wrote in post #11295361 (external link)
DxOmark has the t-stops of the lenses they've tested listed. Some people are quite skeptical towards DxO, but things like that should be quite easy to measure, so the results should be reliable. eg the 24-205 f/4 is T5.1, the 24-70 f/2.8 is T3.4.

How do they account for vignetting? Are they measuring the T-stop at the center of the frame or as an average value?


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phreeky
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Nov 16, 2010 16:10 |  #8

JeffreyG wrote in post #11296093 (external link)
How do they account for vignetting? Are they measuring the T-stop at the center of the frame or as an average value?

It SHOULD be across the frame. I have seen another website that had the T-stop of a bunch of lenses but cannot remember what it was.




  
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T2.8 vs F2.8 [film/video lenses vs photography lenses]
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