Originally posted by Kunzite
True normals are ~22mm on 4/3, ~28mm on APS-C, ~44mm on 135; usually you'd round upwards to 25, 30 and 50mm.
Using equivalence, you came up with the answer. Good job. Now, I forget - what's wrong with equivalence again?
Quote: Moving the goalposts, I see... :
ABSOLUTELY NOT. Just following through with the thought, which you really, really don't want to do for some reason.
Quote:
#1. ...and your "question" really is: "if I make up a scenario which require the partial use of "equivalence", what will you do?".
It's not made up at all, it's something someone might ask if they wanted to maximize their system without changing formats - could they re-create something a larger format could give them without changing formats, without having to buy into a new system? Or could they get "close enough"? Knowledge of equivalence answers that.
Quote: #2. Lens giving you noise? Oh, boy...
You didn't actually read Joseph James' paper, did you?
Oh, yes. Yes I did. And I am glad that you're starting to skim it now, we're making progress!
Even if you cherry pick a phrase here and there and then misapply it... that's still a form of progress.
Quote: "The most controversial visual property of equivalent images is that people incorrectly assume that Equivalence is based on equal noise. Equivalence is based on the five principles listed above, which do not include noise, nor any other elements of IQ."
Equivalence is not based on equal noise, but as Joseph James
patiently goes on to explain to you**, the total shot noise is tied to the Total Amount of Light that falls on the sensor (Total Light = Exposure * Sensor Area.) The total amount of light is tied to the linear aperture of the lens (entrance pupil,) and for the same AOV, distance to subject and F-stop we will have a larger entrance pupil being used on the larger sensor combo.
For example, say we're working with normalish FLs and your m43 stalker is asking you about a lens to match the noise performance on an FF sensor,
which cranks you up even more than if he asked about aps-c! :
50mm f/1.4 FF = 50 / 1.4 = 35.7mm linear aperture
25mm f/1.4 m43 = 25 / 1.4 = 17.8mm linear aperture
OK, so you have to answer him, because he asked nicely: "That 25mm f/1.4 won't match it, if that's what you're after. You would need about a 25mm f/0.7, if read-noise and sensor QE are about the same."
Your m43 stalker goes away dejected... But clear-headed. He will not bother shelling out $1200 for that VL 25mm f/0.95 MF prime.... he hates MF anyway, and if he's going for 'close-enough' he at least wants AF. You saved him money, which he can put toward another purchase which more closely matches what he's really after. You did a good deed, Kunzite, congrats!
** "
For the same AOV, lenses for larger sensor systems often have larger aperture diameters which gather more light than smaller sensor systems, and thus deliver less noisy images even if the sensor for the larger sensor system is less efficient "
-JJ
.