09-23-2018 02:54 PM - edited 09-23-2018 02:56 PM
I see it as a relic. If APS had taken over from 35mm film before the transisiton to digital, we would be saying that FF cameras have a 0.625 factor!
The only people who care are those that are used to a particular angle of view in 35 mm and want the same one in APS-C sized sensors.
Otherwise it just adds confusion.
I agree that it seems to have come from the dominance of the 35mm film format, just as the APS came from Kodak's Advanced Photo System film format, but was not so popular and, I believe, died out in the mid 1990's.
Still, almost any metric we consider is, to some extent, arbitrary. I have always wondered why, when the rest of the planet is using the metric system (much more condusive to digital computers), the USA has stuck, at a consumer level) with the imperial system. Especially given that at the time the metric system was developed the USA was breaking away from the UK and had strong ties to France. I realize that the cost was considered too high when it was finally mooted in the last century, but I will say that behind the customer interface much of industry has gone metric - especially in things like cars and of course science. I understood that issue of conversion between metric and imperial was the root cause of the error that was built into the original Hubble telescope and caused its optics issue.
The transition to metric has made certain imperial-based phrases somewhat perplexing to the metric generation. I was with a friend and his two teenage boys (here in NZ) and one of us said "give him an inch and he'll take a mile". The boys wanted that to be explained, but the direct translation: given them 25.4mm and the'll take 1.6093km just doesn't have the same appeal!
09-24-2018 12:36 PM
One thing this dialogue has done is made me consider how we really express, both in metrics and semantics the impact of the relationship between lens focal length, sensor size and FoV. It's not that the science is unclear, but often how that is translated into marketing, reviews (many reviewers use equivalence values without saying so), and general discussion. As one reviewer put it, "Actually explaining the changes in FoV between sensors by expressing them as Equivalent focal lengths doesn't do anyone any favours, even if it is a convenient or indicative metric".
Very sorry to read about your situation with your partner. A knee rehab and a house move must be "small stuff" in comparison to that. There's a quote by John Wheeler "Time is nature's way of keeping everything from happening at once." You've got a lot happening at the same time. I hope that my writing is respectful and sensitive. (I always try to be respectful ... I may not always succeed.)
I agree with you and I like your citation from the article.
Ultimately I think the good intention is that if a person used to shoot with a 35mm film camera, then they'd have an idea of what to expect using a particular focal length lens. Since lots of people shot with 35mm film cameras (especially if they have gray hair) the comparison often works. In reality it's only the angle of view or field of view that you care about -- and not the remaining properties of the "focal length". Then starts the confusion... if it's "like" shooting with a longer focal length, then all the rest of the properties of a different focal length must be included ... we've all seen arguments about even the focal ratio changes (it does not). Hence "expressing them as Equivalent focal lengths doesn't do anyone any favors."
Many years ago (so long ago that I don't remember exactly where I picked this up), someone or some article said that the sooner I start thinking in terms of "angle of view" (or field of view) instead "focal length", the better of I'd be.
As a somewhat new photographer at the time, I had to think about what that meant and why it should matter.
For any shot we could make a claim that for purposes of creativity, etc. there is a "best" spot for the photographer to be when they take that shot. We can't always be there. A sports photographer might like to be standing ON the field-of-play to get their shots, but they'll get thrown out of the venue if they try to do that during a game. Alas sometimes the zoom lens is a substitute for getting closer.
But that "best" spot to be is also the best spot because it uses an idea angle of view for your creative purposes. If you *can* position yourself in that "best spot", you're better off doing that then you are staying put in one location and using "zoom" as a tool to avoid having to move around.
Instaed of saying that "zoom" (or any change in focal length) is a substitute for being closer, I prefer to say that "zoom" is allowing you to change the angle of view, change the compression, and it also changes the depth of field. All these things change when you change true focal length. I sometimes step BACK (when I could be closer) and zoom in because I like what the longer focal length does for compression and depth of field. (My 70-200 is easily my most used lens. My 24-70 doesn't actually get much use. Shots that I used to take with the 24-70 ... are now often taken with my 70-200 and I just step back farther to get the shot.)
So yes... I completely agree with that quote about telling photographers about "equivalent focal length" isn't necessarily helpful. In any field, those who live and work in the industry have language and terminology that make sense to them ... but the face value of those words are confusing or misleading to others. This is one of those things.
09-24-2018 05:57 PM
Thank you for your kind thoughts and gracious comments. I thought your responses were business-like but not at all offensive. There has been a lot of stress for me lately and I know that it impacts one's ability to think well and express oneself effectively, so I am glad we all came out of what is a tricky discussion unscathed!
Being able to escape to the forum for a while and immerse myself in things photographic is a welcome relief right now. I just wish I could go out and do some more photography - that is, for me, a really relaxing activity.