Originally posted by BigMackCam There's a big difference between disagreeing with folks, and accusing them of nefarious intentions. Let's avoid the latter of these.
Why does the word nefarious always remind me of Rocky and Bullwinkle?
But I have to agree with the basic information.... "trial and error" is being used as if it's somehow less valuable.
Scientific formulations are not even considered science until they are backed up with empirical data.
In other words theory (in this case equivalence" can only be substantiated through "trial and error". It might give bit of direction to your trial targets, but even that may prove unreliable in that you could be happy with a 40 on APS-c and unhappy with the only 60 you can find on FF. Equivalence does not reduce the need for trial and error, and it could save you time in that you know where to look, but it could cost you time in that what you find in that focal length doesn't create the look you want.
Anyone claiming you can do the theory without the empirical is selling you bill of goods.
After all the theoretcal constructs like equivalence you still have to go out and prove it with trials.
Given the difference in lens designs etc. it's pretty unlikely the suggestions provided by equivalence will lead to the best solutions to the problem.
After all, my FA 50 macro and the DFA* 50 1.4 produce very different results with the FA 50 macro being sharper edge to edge and the DFA 50 1.4 providing much smoother out of focus areas.
The FL is minor compared to the lens design.
Regardless of intent, one should not be intimating that equivalence will save time (that's not been proven), gives one a better understanding of different formats, that's also unsubstantiated, and it's limitations should be explained. It's not just equivalence at fault here. The only way to promote any shortcut, is to immediately point out it's limitations, especially for something like equivalence where all the claims made for it are debatable.
Most lens selections are made not using equivalence but by selecting something you might like from the categories. Ultra Wide angle, wide angle, standard, telephoto, aspherical, rectilinear, internal external focus, widest aperture and most important, what lens do you have now and why is it insufficient. Equivalence covers a little bit of that, but is in no way comprehensive, leaving us to debate over whether it actually saves any time or actually costs beginners time.
I personally wouldn't take anyone seriously one way or the other without some kind of hard evidence that what they say is true. Not even myself. Everything we have here about equivalence is that some people think it's a good thing, some people think it's misleading, and there's no actual evidence to say it's better or worse than any other method of picking out your next lens. In fact the only suggested use for it is is for the famous "beginner" shooting 2 formats (Is that even a thing.). Look at the criteria above and decide how useful it could possibly be. It just seems pretty insignificant to me. If others feel it's really important, that just means they approach things from a different mindset.
As long as you cover all the steps you need to in lens selection, spending the first 10 seconds of what should be hours of work determining which lens has the characteristics you want, the equivalence of the lens you want in a different format is probably neither here nor there.