Optical Pass Filters

[XDCAM]

Looking for a cheap source of Optical Pass Filters (Blue Filter) for 4/3 Analogue Betacam,s(BVW 300p/ 400p /7p .Is their anyway of repairing these (Milky) please ?Does anybody have this problem too ?

[old_tv_nut]

I don't know the answer, but can you provide more details of what you are looking for? Where is this in the optical chain? On the sensor? Do you mean optical lowpass filter? An optical lowpass filter does not have any inherent color, but I'm guessing one used in this camera could have an additional color filtering function, like infrared suppression, and be blue in color.

A Google search led to a Facebook page, but I am not a member of Facebook. You might try there.

[dtvmcdonald]

www.edmundoptics.com

No longer cheap like 50 years ago, but they have the stuff. Oh do they have it.

[XDCAM]

Yes I mean the optical lowpass filter .All my Sony Cameras have this problem .If you remove this all the focus range goes out .This is the Glass in front of the CCD Block .

[old_tv_nut]

OK, that's what I guessed. The only problem now is, I can offer no help at all on actually finding one. Hope someone else here can.

[BrianSummers]

It does seem to be a problem for the whole of Sony's camera range for that period, most have this problem or will have soon. All I can suggest is to try and find a filter from a different make of camera that may not have the time related problem of the Sony filters.

The term we use to describe it is a Bi-refringent filter. The CCD chip is in effect an optical sampling device and, like the sampling in an analogue to digital converter, must be preceded by a low pass filter.

You could put some plain glass in there to try to keep the optical path length the same and put up with the aliasing that you might see from fine detail. I would be interested to know if this approach might work?

[old_tv_nut]

If it's also blue-colored, I think it's also an infrared-cut filter. Necessary with a CCD, which has response into the near IR much too far to get proper color without a filter.

[wiseguy]

I have 3 of those cameras with the filter problem, looks like a greasy finger print almost, but I think its a chemical reaction problem in the layers of the glass itself..BVP-270, BVP-370 AND a BVP-360, could not get one from a Panasonic to fit

[XDCAM]

I think if we can find a way of getting a piece Glass cut the same size that will work .

[wiseguy]

it is a I.R cut filter and that's the problem matching specs up, I remember being in a Sony Broadcast School years ago for one series of these camera just after the BVP-270 came out and half a day was about the optical block and the Filters, I remember him saying that you could remove the i.r cut filter and test i.r remotes for fun that way.

[dauberich]

Hi.
I guess it is exactly this piece of glass that is the problem, isn't it: http://www.flickr.com/photos/1090701...7639123625524/

Well, here is what I did:
I searched the bay for a similar camera, you can see it as number 5 in the row. It is only a still camerabody that is even more useless then any SD video body as e.g. the 950 would be. So you should get it for much less than the glass with a real camcorder or camera body "around" it.

In my case, I payed 20€ for a DKC 5000, that looks very similar to a DXC 950 (pic no.4, where I "parked" the glass before I got the 5000). Of course that attempt does not need to work (no offer or stupid offerer with stupid ideas about what a SD 4:3 camera still is worth) but it can work.
Fact is the glass does fit on my 1/2" Camera (http://www.flickr.com/photos/1090701...2435/lightbox/ and it also works perfect. I'm sure they used the same stuff for still and video cams - at least with the 1/2" DXCs and the DKCs, as in these days even still cams did not have more pixels than a videocamera had.
So I guess even the lowpass characteristic (..if they did put that on the IR- filter at all) was the same.

I hope you find one..

Best, Stefan

[XDCAM]

Thanks for the info & welcome to the Group .

[J Ballard]

Yes, it is the IR cut filter, and due to its thickness, it may be the 1/4 wave polarization filter also. And/or an optical low pass filter to reduce aliasing.

Wayne is right-IR cut is needed for CCDs, and manufacurers would frequently play games with how much red to cut. I recall once Sony sending me 3 filter designs, each with a different amount of penertration into the red region. They were chasing another Japanese company who had the highest marker share at the time.

IR drives CCD camera designers nuts, so it must be reduced before it hits the imager.

Let me know if you find a source, as I have seen Sony cameras with the problem that you describe.

One bit of caution-the thickness of the filter package must be exactly the same as the original, or you might run out of back focus adjustment range on the lens.

Regards,

JB

[old_tv_nut]

The early professional CCD cameras had strong infrared (and deep red) cut filters to match plumbicons, which had notoriously poor deep red response. None of these cameras could see the red phosphor of a CRT properly.

A local news show had stacks of monitors plus a CRT rear projector as background on the set. All the monitors needed color correction gels to reduce the green and blue output. The rear projo was actually two units with their images superimposed, so that there was enough output when the green and blue were attenuated and both red tubes were running full blast. [Edit - the pictures looked very pink to the eye, but neutral to the cameras).

These days, camera manufacturers are experimenting with extending the red response again, beyond what the eye can see, for a better match to the old film responses when doing digital cinema.