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My Mamiya ZD Back featured a user removable IR absorption filter which I removed and replaced with Schott WG280 clear glass of the same thickness. I made two filters and sent one to Mamiya for evaluation and they subsquently offered a factory clear glass filter option. The clear glass allowed required the use of filters on the camera lens but permitted full spectrum photography. Since your DM22 Back doesn't have an easily removed IR filter, I suggest you contact Graham regarding his source for his conversion.
A flat layer of glass having a different index of refraction as air will move the plane of focus when introduced between a lens and a sensor.I don`t really understand why you need a glass in front of it?.. Other then protecting the sensor offcourse. But different focus because of it, I don`t get. The sensor is placed the same place with or without glass.
That should do it. It does assume that both filter glass types have the same refractive index; they will probably be close enough that it hardly matters.Ah. Forgot about that. So if I put a 720nm filter in front of the sensor with same thicknes, that would fix it.
Three surfaces? (front & back of filter, front of sensor cover-glass).With the removable filter system on the ZD Back I have trouble keeping all four glass surfaces dust free.