lamiaceae wrote:
I'm pretty sure it is the light transmission or numbers of stops that falls off as an inverse square. At least the ones I've seen and used are like that. Virtually every "force" or "energy" in nature follows an inverse square rule. Note other repliers quotes of focal length differences as well. Say 400mm to 560mm with a 1.4x. But yes, an f/4 would then be f/5.6 or one stop. A 2x two stops (1/4 the light), a 3x three stops (1/8 the light). I have two older models that have conversion calculators built on. I'm pretty good with math. But this stuff confuses a lot of people, even professional photographers. See photo below.
I'm pretty sure it is the light transmission or nu... (
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I was not dealing with light transmission, only the degree of magnification. The loss of transmission due to an added element--which is what a tele converter functions as--is just another reason not to use them. I have only one converter left and I will use it this summer knowing it is a crapshoot whether it will give me what I want but I don't have the $$ for the longer lens. I will shoot both with and without.
The 3x I had I think I used for target practice.