I don't normally visit this site these days, but a mate clued me in that something had come up on here that I knew a thing or two about and that I might want to set y'all straight.
This is not —categorically not—the optical formula of the old Canonet 45mm f/1.7. Firstly, anybody should be able to stop just by looking at the diagrams that the spacing of the front two groups is different, the relative scales and sizes of most of the elements are different (the second element in particular), and the rear three elements are also positoned further back and spaced slightly differently. Also, the Canonet 45mm f/1.7 is too big for a 43mm filter thread to be possible; the front element alone is approximately 40mm, which at the angle of view of anything under about 100mm means a 43mm surround would encroach on the image, even without an actual filter being there. From the photos of the new lens we can see that its front element is far smaller than this. Of course the fact one is a 50mm f/1.8 (likely around 51mm f/1.9 actual, same as the other Canon cheap 50s) while the other is a 45mm f/1.7 (actually 44.2mm f/1.72) should also clue you in that this is not the same formula.
Yes, it's six elements in five groups and yes they are in[ vaguely the same shapes and order, but that's different from being the same formula, which if you're being technically pedantic about it would actually mean they were literally 100% identical.
Second, as someone who owns several Canonets including three 45mm f/1.7 variations and as someone who has repaired said lenses several times, I can tell you not only are the "coatings, tolerances, etc" going to be different, but the very material of the elements will also be different. The 45mm Canonets, of all apertures, use thorium in two of the inner elements. (Second and fourth, to be specific.) That isn't used any more (though there are rumours that Zhongyi have been sneaking thoriated glass into a couple of their f/0.95 designs, I've not seen any actual evidence of that yet) and there is quite a difference in the results you get from thoriated glass vs modern materials. (Not necessarily better or worse results, of course, with such things being so subjective.) This is the main reason why the later models moved to a 40mm lens, as well as why so many FL lenses were quickly replaced with similarly slightly different focal lengths by the late 60s (the 58mm f/1.2 being replaced by a 55mm being the most famous example). Without thoriated glass on the table, some designs had to be entirely scrapped and getting satisfactory results at the same focal length and apertures without our radioactive friends was too hard, so different focal lengths were chosen which could more easily (and safely) be made to a high standard.
So while, again, it is the same number of elements in the same grouping and in a rough sense the same kind of shapes, the actual nuances of the design show that it's not the same formula (again, saying something is the same formula means something very specific, which this is not; don't throw the term around lightly if you're trying to show off) and beyond the most obvious advancements in build, the fundamental meterials will have the biggest affect on the resulting image quality.
FWIW, of course it's impossible to tell just how sharp, contrasty, flare-resistant or whatever else a lens may be just from looking at the optical formula, but I would anticipate the same kind of improvement from the STM to this RF as there was from the mkII to the STM. In other words, perfectly acceptable for the price point and for the purpose of a cheap(ish; this looks like quite a price hike for here in the UK) 50mm lens, but nothing special in any way. Slightly below-average wide open, dead average at f/2.8 and shockingly sharp at f/4, with totally average colour and contrast throughout and quite strong vignetting, is the trend that I would expect this lens to continue given the design is not trying anything radically new. (If I were a betting person I'd put a fiver on it being slightly sharper at f/2.8 but with at least a half stop more vignetting across the whole aperture range, but I tend to assume that about any lens which shrinks the front element and filter size...)
Anyway. The Canonet 45mm f/1.7, it ain't, and I highly doubt Canon spent a single second thinking about the Canonet when designing this. Stop trying to dig up some kind of 'gotcha' 'cause there's just nothing there.
This is not —categorically not—the optical formula of the old Canonet 45mm f/1.7. Firstly, anybody should be able to stop just by looking at the diagrams that the spacing of the front two groups is different, the relative scales and sizes of most of the elements are different (the second element in particular), and the rear three elements are also positoned further back and spaced slightly differently. Also, the Canonet 45mm f/1.7 is too big for a 43mm filter thread to be possible; the front element alone is approximately 40mm, which at the angle of view of anything under about 100mm means a 43mm surround would encroach on the image, even without an actual filter being there. From the photos of the new lens we can see that its front element is far smaller than this. Of course the fact one is a 50mm f/1.8 (likely around 51mm f/1.9 actual, same as the other Canon cheap 50s) while the other is a 45mm f/1.7 (actually 44.2mm f/1.72) should also clue you in that this is not the same formula.
Yes, it's six elements in five groups and yes they are in[ vaguely the same shapes and order, but that's different from being the same formula, which if you're being technically pedantic about it would actually mean they were literally 100% identical.
Second, as someone who owns several Canonets including three 45mm f/1.7 variations and as someone who has repaired said lenses several times, I can tell you not only are the "coatings, tolerances, etc" going to be different, but the very material of the elements will also be different. The 45mm Canonets, of all apertures, use thorium in two of the inner elements. (Second and fourth, to be specific.) That isn't used any more (though there are rumours that Zhongyi have been sneaking thoriated glass into a couple of their f/0.95 designs, I've not seen any actual evidence of that yet) and there is quite a difference in the results you get from thoriated glass vs modern materials. (Not necessarily better or worse results, of course, with such things being so subjective.) This is the main reason why the later models moved to a 40mm lens, as well as why so many FL lenses were quickly replaced with similarly slightly different focal lengths by the late 60s (the 58mm f/1.2 being replaced by a 55mm being the most famous example). Without thoriated glass on the table, some designs had to be entirely scrapped and getting satisfactory results at the same focal length and apertures without our radioactive friends was too hard, so different focal lengths were chosen which could more easily (and safely) be made to a high standard.
So while, again, it is the same number of elements in the same grouping and in a rough sense the same kind of shapes, the actual nuances of the design show that it's not the same formula (again, saying something is the same formula means something very specific, which this is not; don't throw the term around lightly if you're trying to show off) and beyond the most obvious advancements in build, the fundamental meterials will have the biggest affect on the resulting image quality.
FWIW, of course it's impossible to tell just how sharp, contrasty, flare-resistant or whatever else a lens may be just from looking at the optical formula, but I would anticipate the same kind of improvement from the STM to this RF as there was from the mkII to the STM. In other words, perfectly acceptable for the price point and for the purpose of a cheap(ish; this looks like quite a price hike for here in the UK) 50mm lens, but nothing special in any way. Slightly below-average wide open, dead average at f/2.8 and shockingly sharp at f/4, with totally average colour and contrast throughout and quite strong vignetting, is the trend that I would expect this lens to continue given the design is not trying anything radically new. (If I were a betting person I'd put a fiver on it being slightly sharper at f/2.8 but with at least a half stop more vignetting across the whole aperture range, but I tend to assume that about any lens which shrinks the front element and filter size...)
Anyway. The Canonet 45mm f/1.7, it ain't, and I highly doubt Canon spent a single second thinking about the Canonet when designing this. Stop trying to dig up some kind of 'gotcha' 'cause there's just nothing there.
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