arneh wrote: Fred Miranda wrote: arneh wrote: Fred Miranda wrote: FE 20/1.8 G: It's almost a stop slower than the 24/1.4 GM
Do we know the T-stop of the 24 GM?
Bright lenses usually lose more light than slower lenses, so the actual light loss may be less than 2/3 stop. I'm guessing 1/3 to 1/2 stop difference is more likely.
I'm sure the 20/1.8G will be a great lens but you are stretching now!
Maybe I am. But that's why I was interested to hear if anyone actually know the T-stop of the 24. I admit I don't have much data for T-stops. But from looking at dxomark which do measure it, all of Sony's F1.4 lenses they have measured have T-stops of 1.5 or 1.6, while all Sony F1.8 lenses have a 1.8 T-stop.
So I'm not convinced the difference is "almost one stop" in light gathering ability.
Without being too pedantic (or maybe just a bit too pedantic ), you do realize that the difference you are noting could very well be rounding error. You do realize that and f number of 1.4 isn't exactly 1.4000, in fact if a lens with an f number of 1.4 is exactly one stop more than a lens of f/1.00000, then it's exact f number is 1.4142 (i.e., the square root of 2). Similarly a lens with an f number of 1.8, is unlikely to be exactly 1.8000, and if it is exactly a 2/3rds of a stop slower than f/1.4142 then it would be 1.7818. Of course all that extra precision is ridiculous because the manufacture of lenses aren't that precise. The one decimal point is probably as precise as the measurement can and needs to be. What that means is the difference in .1 may very well not be meaningful and could well be rounding error. So you should not make a big deal about 1.4 going to 1.5 and 1.8 not going to 1.9, that could simply be rounding and note in this case if there was greater precision even 1.41 is closer to 1.5 than 1.78 is to 1.9, so let's say both a 1.41 lens and a 1.78 lens lose 0.05 transmission that would round to 1.5 and 1.8 even though they lost similar amounts of light.
arneh wrote: Fred Miranda wrote: arneh wrote: Fred Miranda wrote: FE 20/1.8 G: It's almost a stop slower than the 24/1.4 GM
Do we know the T-stop of the 24 GM?
Bright lenses usually lose more light than slower lenses, so the actual light loss may be less than 2/3 stop. I'm guessing 1/3 to 1/2 stop difference is more likely.
I'm sure the 20/1.8G will be a great lens but you are stretching now!
Maybe I am. But that's why I was interested to hear if anyone actually know the T-stop of the 24. I admit I don't have much data for T-stops. But from looking at dxomark which do measure it, all of Sony's F1.4 lenses they have measured have T-stops of 1.5 or 1.6, while all Sony F1.8 lenses have a 1.8 T-stop.
So I'm not convinced the difference is "almost one stop" in light gathering ability.
Without being too pedantic (or maybe just a bit too pedantic ), you do realize that the difference you are noting could very well be rounding error. You do realize that and f number of 1.4 isn't exactly 1.4000, in fact if a lens with an f number of 1.4 is exactly one stop more than a lens of f/1.00000, then it's exact f number is 1.4142 (i.e., the square root of 2). Similarly a lens with an f number of 1.8, is unlikely to be exactly 1.8000, and if it is exactly a 2/3rds of a stop slower than f/1.4142 then it would be 1.7818. Of course all that extra precision is ridiculous because the manufacture of lenses aren't that precise. The one decimal point is probably as precise as the measurement can and needs to be. What that means is the difference in .1 may very well not be meaningful and could well be rounding error. So you should not make a big deal about 1.4 going to 1.5 and 1.8 not going to 1.9, that could simply be rounding and note in this case if there was greater precision even 1.41 is closer to 1.5 than 1.78 is to 1.9, so let's say both a 1.41 lens and a 1.78 lens lose 0.5 transmission that would round to 1.5 and 1.8 even though they lost similar amounts of light.
Mar 04, 2020 at 01:01 PM
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