Avotius said:
hm....this makes me wonder what other lenses speeds are not as advertised
This kind of information is not readily available & it's generally accepted that the specs listed for a lens are approximations. In an M-mount 90mm lens, for example, measured focal lengths can be anywhere from the Leica 90/2 AA at 88 mm to the Konica 90/2.8 at 93mm. Same is true for 50mm lenses where a lens like the Leica Summilux is actually 53 mm long and for other focal lengths as well.
Here are some RF lens speeds that in Popular Photography's tests vary from what they are labeled:
Leica M
21/2.8 = 2.7
28/2 = f/2.1
35/1.4 - f/1.6
50/2 = f/1.9
50/1.4 = f/1.5
75/1.4 = f/1.6
Cosina/Voigtlander VM
12/5.6 = f/6.1
15/4.5 = f/f/4.1
25/4 = f/3.8
35/2.5 = f/2.7
35/1.7 = f/1.8
50/3.5 = f/3.7
50/1.5 = f/1.6
75/2.5 = f/2.7
Konica M-Hexanon
28/2.8 = f/2.9
Rollei
40/2.8 = f/3
The following lenses were measured as accurate for the maximum aperture listed:
Leica 35/1.4 ASPH, 50/2.8, 90/2 AA, 50/1.4, 90/4 Macro
CosinaVoigtlander VM 40/1.4
Konica M-Hexanon 50/2, 90/2.8
Rollei 80/2.8
None of this is a big deal, but it occasionally becomes significant as in the decision that ywenz is trying to make when the primary issue is speed. In this case, what appeared to be a full stop difference - more or less - turns out to be only a half stop.
Although they do a lot of good work otherwise, I do take issue with Cosina when I see such inaccuracy in their stated maximum apertures. This bothers me primarily because they label their lenses with non-standard maximum apertures, i.e. something other than full stops. To me at least, this gives the impression that they are not rounding off or approximating but are giving a more precise measurement than would normally be expected. When this turns out not to be the case & when the lenses are mostly slower than advertised - except for a couple of slow wide angles for which speed isn't much of a factor - I feel manipulated.
For example, why is Cosina clalling its 35, 50, & 75 lenses f/2.5? This is a maximum aperture I've never seen before. (It may be out there, but it's not common.) Why not call them f/2.8, which is what they're closer to than f/2.5? This would allow for proper comparison rather than mislead the consumer to think that he's getting a little more speed for his money. It's what any other company would do when the f-stops in question are f/2.7.
Maybe it's just me making too much of this because Cosina isn't really using this to hype their lenses, are they? Wait. You've seen the hype for the 29/1.9?
"Fastest 28 ever for 35 RF." Where's the spin doctor when you need him.?
😉 I have not seen a review of the 28 Ultron that reports the actual maximum aperture, so it may be f/1.9 or even f/1.8 for all I know. But given the pattern of errors on the slow side by Cosina, I have no confidence that this is really
"the fastest 28 ever". Why not just call it 28/2 & be done with it?
The reason for mislabeling these lenses seems to be quite clear. Marketing.
When I see such misleading information, it undermines my confidence in what's being sold to me by this company. I worry that the product is either misrepresented or that manufacture is sloppy.
In contrast, Leica specs are exceedingly accurate. Of the 11 lens reviews which I read & kept notes on, 5 of them were dead on & 4 more were +/- f/0.1. Only two was beyond that range. Of the 6 that varied from their spec, two were actually faster than advertised. No complaints in those cases. At least not from me. Same with Konica. Two were spot on & the one that varied was off by only f/0.1.
In the case of Cosina's Voigtlander lenses, 8 of 9 lenses tested were off their spec & 6 of the 8 were off by more than +/- f/0.1. Two of these lenses was faster than advertised. Oddly enough, in the case of the 25/4, it's one of the few labeled at full aperture. In this case they could have legitimately called it f/3.8. And in the case of the 15/4.5, it's labeled slower by using a non-standard aperture. They could have called it f/4 & there wouldn't have been much to complain about. The silver lining is that the fastest lenses were the most accurate - 40/1.4, 50/1.5, & 35/1.7 all within +/- f/0.1 or so.
It does seem that Cosina wanted to create a market niche for itself that would not put it in direct competition with Leica, so they setlled on this .5 thing, i.e. f/1.5, 2.5, 3.5, 4.5. IMHO, this just creates confusion & misrepresentation.l
