Originally posted by FHPhotographer Try rephrasing it... " "oh, I have a 77mm, if I shoot this subject at 12 feet I may have the best chance of the optimum image quality." No absolutes, just gut feeling and experience on what subject distance works for that lens.
I certain respect the desire to collect this information. I going to try one more time to explain why I am skeptical, but I am still interested to see if numbers come in that make a believer out of me.
First, I can't imagine thinking along the lines you just laid out. Why would I choose the 77 - or any lens, for that matter - if I didn't already know what distance I wanted to be at? I choose my position first - either because of the perspective I want, or just practical considerations like I can't get any closer because there is a barbed wire fence in the way, or if I moved any further away then there would be too many other people between me and my subject. Then, based on where I am relative to the subject, I decide what sort of angle of view I want - how much of the scene I want to encompass in my composition. That pretty much decides for me what focal length I want, and then that pretty much decides for me what lens I'm going to use.
I can't imagine getting the lens on the camera then saying, "I'm in the perfect position for the perspective I want, and I'm getting just the composition I want, but gee, I've got some data that says this lens would perform 0.3% better if I were to move 20 feet closer - so what if that ruins my perspective and composition".
That is, whatever tiny differences there might be, I can't imagine any real life situation where that would trump the more fundamental desire to want to get the perspective and composition I want. That stuff is important. Miniscule - as I beleive they will prove to be - differences in lens performance at different distances won't be nearly so important except in the most extreme cases.
The situation where I *do* think this information might be useful would be in deciding between buying two lenses of a given focal length. If I know I'm buying a lens for a particular purpose - say, concert photography, where I'm often working at around 10-15 feet - and I have a general idea of what focal length I want for that distance - say, somewhere around 80mm - then I might be interested to know if, of the various lenses that exist somewhere around that focal length, if one of them performs better than the others in the 10-15 foot range. Or, for that matter, if I happen to already own two lenses of a similar focal length, to decide which one to put on the camera in a given situation if I find myself wanting to shoot at that focal length.
Unfortunately, that information would be hard to get from this sort of poll. The best lens at 10-15 feet might turn out to be the 77, but it might be the case that the 77 does *even better* at a distance of 6-7 feet. So someone says that the 77 is better at 6-7 than it is at 10-15. The 85/2 might be at its best at 10-15 feet, but still be way behind the 77. So I'd really want to see different lenses of similar focal lengths compared *with each other* and *at a variety of different subject distances*, not have different subject distances compared for a single lens. And even then, frankly, I'm still not sure this would trump the more obvious considerations like price, maximum aperture, overall quality, etc. In other words, I suspect we're talking about collecting a lot of information to measure something that barely matters.
Like I said, I'm willing to be proved wrong by incoming data that shows sopme clear and significant trends, but so forth, obviously, I'm underwhelmed...