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RF 50mm f1.2 users (and probably EF version as well), do you use a protective filter on it?

Started Oct 13, 2020 | Questions thread
quiquae Senior Member • Posts: 2,265
Re: RF 50mm f1.2 users (and probably EF version as well), do you use a protective filter on it?

raytracer81 wrote:

I'm more concerned about dust getting into the gap around the extruding front element. But putting a filter brings another question, where does the air go when the front element extrudes? Will the air get suck into the lens?

If there is an airtight filter in place and you extrude the front element, then the air between the frontmost glass and the filter is compressed while the air in the interior of the lens is decompressed, resulting in a pressure differential that will cause an air flow from the front part into the interior through the gap around the front element until both sides reach the same pressure (equilibrium). There is no reason to breathe in air and dust from the outside because the total volume inside the lens barrel of the 50L is constant, regardless of the focus element position. (This makes the story different from the likes of 24-105L and 70-200L, which have extending barrels that require air to come in from the outside when zoomed out.)

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