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Matt Grum wrote:
The only source I've seen for the thickness of the A7R filter stack is the LensRentals blog post which states it is approximately 3mm but is very difficult to measure. Sounds like it could actually be 2.5mm
It seems possible that the stacks are the same height across Sony sensors but slight differences in filter composition, AA filtration and pixel pitch give rise to the differences in rangefinder lens performance between the different A7 bodies.
Pretty sure they're just referring to the A7, A7R and A7s, which may well all have 2.5mm stacks.
where do we have these figures from?
When I spoke with maxmax, I think they said the A7s were 1.7mm, while an M9 is .8mm
dug up the conversation:
"Dan: (from maxmax)
Hi Charlie,
I have gotten some questions about this from others as well.
The Sony A7 ICF/AA stack is 1.75mm thick which is relatively thick. The lens flange to sensor distance is also short. If you think about the path of light exiting the lens as it goes to the sensor, it has to pass through the ICF/AA. If the light is going through the center, then the path is the shortest. As you move toward the sensor edges, the light has to travel at greater distance because the light is going through the ICF/AA at an angle. The effect is the same as if the ICF/AA stack changes thickness getting thicker towards the edges. The lens design and aperture also will affect this. A wide aperture longer lens will have less of a problem than a small aperture wide angle lens.
When we do an HR conversion, we remove the stock ICF/AA and replace it with a new ICF-Only having the exact same thickness. If you don't use the correct thickness, then you change the focal plane of the camera. So, our HR conversion AF will work correctly. Biggest downside on HR, and this changes depending on the camera ICF/AA design, is that the AA part of the stack is clear while the ICF has a teal tint. The new ICF-Only has a thicker ICF which shifts WB toward the cyan. Most just set a custom WB if it is an issue, but some don't like it. The thinner the ICF/AA stack, the less of a color shift.
To fix the A7, you would need to go with a thinner ICF. A thinner ICF is going to move the focal plane towards the lens. To get correct focus, you would need to move the sensor closer to the lens which is hard to do on the A7. You would have to either mill the sensor mounting points and modify the camera body sensor mounting points. Neither is an attractive option. Possible, but it would be a lot of work and easy to spend a lot of time trying to get it just right.
The Sony conversions are $550 because their bodies are all really hard to take apart."
He also said he could go ultra-thin, and install a .6mm cover.
"Dan:
Hi Charlie,
If I could put and a thin ICF and move the sensor closer to the lens, then the camera would focus. If put in a thinner ICF, then the camera will become near-sited. You would need to focus past infinity for focus or use one of those adapters that moves the lens back and forth. The thickness of the ICF/AA stack is the problem - you would still have the issue with a thinner ICF, but not as bad.
A quick check shows I have a 0.58mm ICF that I can cut to fit.
Most camera ICF/AA stack have a teal tint to the ICF layer. On a DLSR, typically, there is something like BG38 IR absorbing glass which has a teal tint and then vapor deposition coatings to help block IR as well. Since I put in a new ICF only that has the same thickness as the stock ICF/AA, the WB gets more teal. If I used 0.59mm, I don't think you would see much WB shift. There would be some shift somewhere because the stack is changing. Also, not sure if the Sony auto WB is off the sensor anyhow rather than a separate sensor like a typical DLSR."
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