Blackmagic Forum

Hi,

I was thinking about modifying my BMCC to be able to shoot infrared.
The idea would be to remove the IR filter the camera comes with, but planning to substitute it with a clear glass custom made so that the sensor is protected.
Someone knows the exact size of the filter?

Secondly, once I customized the camera, if I put a good IR cut filter in front of the lens it should shoot basically like before, isn't it?

The infrared filter on the BMCC filter likely reduces infrared wavelengths but may not cut completely. The filter has been described as a "weak" infrared filter so it may just attenuate infrared but not eliminate infrared at any wavelength. This would have been a conscious decision to help ensure high quality skin tones that benefit from deep red wavelengths getting through to the sensor.

After you remove it because you want to record infrared wavelengths and cut visible light, when you resume normal shooting, you could use an IR Cut filter to eliminate infrared wavelengths or use IRND filters that attenuate infrared (like the built-in filter wheel in the Mini Pro) or use both depending upon your needs.


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No one?

I feel like Arya Stark in Game of Thrones when she was blind and called the "Girl Has No Name." Henceforth, I'll understand when you call me "No One."


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rick.lang wrote:I feel like Arya Stark in Game of Thrones when she was blind and called the "Girl Has No Name." Henceforth, I'll understand when you call me "No One."


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Sorry for that, should have been more polite.

My main interest was for the Filter Size. Thanks a lot for your answer.

Jean Paul, I was just having some fun! I know I didn't address your first question. I kinda like "no one."

I think BMD Support might answer your question about the dimensions if you call them. They'll need to talk to "Some One" in engineering.

"Knock, knock."
"Who's there?"
"No One. Some One, Let Me In!"


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Not only will you need the exact size but if you are not to upset the back focal distance you will need the correct combination of thickness and refractive index.

In zoom lenses I have already noticed that it doesn't keep the focus when zooming in and out (And haven't found ways to fix it) And usually I do not use the distance written on focus to track the focus, so it won't matter much.

Jean Paul Sneider wrote:.
Someone knows the exact size of the filter?

You may be able to get a replacement sensor cover glass from BMD if you ask through their service channel. You should then be able to work out the size.

It will be most important to make sure the thickness matches of whatever glass you replace it with. The collimation of a lens is GREATLY affected by any change of optical surfaces behind the lens.

It's held in place with a rubber o-ring, it's not difficult to replace if you know what you're doing.

The very big danger is not being able to do this in a super clean environment, anything less than a proper "clean room" and you're probably going to introduce dust to your sensor surface, or on the surface of your replacement glass.

JB

I am awareof the cleaniness problem. I would ask an optitian laboratory friend of mine to creat the needed glass.
Having a clear answer would have been better then reverse engeneer. I wrote to the support but no answer.

According to a video on youtube, the filter size is 37mm. If you plan on shooting IR in cinemaraw DNG, you'll have to find an r72 or r87 in that size and take the weak AA filter out. It is doable, I've done it but don't have my footage handy. Philip Bloom did it. He's got some footage you can check out.

I take that back, the production 4K is 30-37mm, the BMCC 2.5k is probably something more like 24-27mm

Im having problems with fungus in my BMCC's IR filter. Where I can buy a new one?