uhoh7
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 First Sighting: A7rii Thin filter in action | |
MAubrey wrote:
I would expect that Steve is talking about the optical measurement of the glass. Physically measuring it is one thing, optically measuring its thickness is another thing.
From Roger at Lensrentals:
Our database for sensor-stack thickness remains incomplete (although I’m hoping for more contributions soon). Also remember that physical measurement of thickness and optical thickness may be different. If the glass used has a high index of refraction, it would have an optical effect greater than what is measured physically. For example, we might measure a physical thickness of 2mm on two different cameras, but if one has low-refractile glass and the other high-refractile glass, the optical measurement made might be 2mm and 2.5mm.
https://www.lensrentals.com/blog/2014/07/sensor-stack-thickness-part-iii-the-summary/
The variables are small. If you can identify the glass the numbers for calculating the precise optical depth fro any given thickness are right there. What is the biggest factor in optical depth? The thickness of the glass.
If you don't know the glass, you can easily determine the lowest probable Refractive Index. If the Sony had a hugely lower RI than Canikon it would be a big consideration. It's probably worse than Canikon. But even with the benefit of the doubt and a superior RI the thickness difference is overwhelming. So the whole "it's really the optical thickness and we can't know that" thing belies the facts on the ground which are obvious: we very likely already know all we need to know, and if somebody suspects otherwise, they should find out and report.
The deeply curious can pull the filter stack and use a refractometer. In fact I'm sure there are astro people who would have access to one. Or you could send out the filter stack. We might be too lazy to do so as it's a lot of work to verify the highly likely, but if somebody thinks it's telling a secret story, have at it. I'd love to see the Canikon and Sony filter stacks tested. I know where I'd put my money. 
I don't say that to bash Sony. I just know how cost conscious Sony is; and for that matter, Leica, who choose a very cheap IR cut for the M8, while Canikon had spent more, especially on the big top of the line DSLRs, which are reputed to have very thin and expensive IR cuts, but of course not on the cover glass, as Leica does, alone. The young designers of the A7 were very honest about their confidence in processor corrections related to the thickness of the filter stack, let alone the cover glass. The same would hold true for RI. No need to spend a fortune on super low RI if the processor is going to do alot of work, or so the thinking goes.
The RI for the UT is lower than I expected, less than v2 or M9 either IR cut, if I am not mistaken, and combined with it's thinness....well it would be very fun to just see one as a coverglass The Optical depth is of greater difference than the physical thickness vs either the V2, or a Stock camera, simply by the nature of the math.
For optical depth there are only two factors: RI and thickness.
But again:
There is alot of independant study on the glass over sensors
So if somebody feels this is a factor which somehow trumps the physical thickness with typical RI around 1.5, there are many people to correspond with, and contirbute something more than vague questions as a way to cast doubt on the meaning of physical thickness in this context. The actual results point to what is the simplest explanation: Sony is not using some secret glass with ultra low RI to reach a thin optical depth in comparison to Canikon. If anything their RI is very likely higher. It's not in their interest to be otherwise.
All of the Sony's and all of the Leicas (A7 and M) have their flavors, and the same for the mods we have seen. I shoot alot with the 75 Lux. A more bland room I can't imagine. But I almost wonder if the thinner glass lets in a bit more light.
I post this one just a bit bigger
Reflecting by unoh7, on Flickr
Like the A7s the A7.UT has a certain flavor. Which will be different on the ii, S, R and R2 And here the 75 Lux is doing it's job as a reportage lens. I only have to lug it to the room, at least 
F2 it's a totally sober recorder.
DSC01429 by unoh7, on Flickr
I'm very wary of "falling for" such a radically thin IR cut. But in faces it's starting to seduce me. 
M-Rokkor 40 in daylight, F/4:
DSC01226 by Charlie Webster, on Flickr
I think maybe the UT is a real character. Some quirks, but a certain uniqueness which is starting to grow on me.
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