Possible dead pixel in sensor or dust in bmpcc og?

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petdarrow

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Possible dead pixel in sensor or dust in bmpcc og?

PostThu Mar 24, 2022 6:52 pm

Folks, I'm seeing something on my footage, I'm not sure if it's a dead pixel on the sensor or dust?

I tried carefully blowing some air with the sensor looking down but looks clean and still the same. I tried different lenses and still the same issue. I tried same lenses on a bmmmc and no issues.

Thoughts? Thanks.

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petdarrow

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostFri Mar 25, 2022 1:47 am

Just wanted to post some additional details on the sensor and the possible dust/pixel issue. I plan to get one of those sensor cleaning swabs to clean the IR-cut filter from outside. Anyone has done this before? Thanks

zoomed image with close aperture and opened it until zebras appeared (taken against a studio light with a diffuser)
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soohyun

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostSat Mar 26, 2022 1:51 am

If the blue-green IR Cut filter really is the problem, there are replacements sold on eBay from Chinese optics vendors; just search "BMPCC IR Cut" and you'll find it, costs about $30. There are AR-coated variations of it that cost more, $40, but are recommended as some users have complained of fungal growth on their original glass, and the coating is claimed to prevent it.

Replacing it is really easy; just pry out the rubber ring, pull out the original glass, place in the new, then re-place rubber ring. I've done it multiple times by now, alternating between the RAWLITE and the original. Keep in mind, though, that I've noticed a slight blue color shift with the eBay ones; correct it in post.
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petdarrow

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostSat Mar 26, 2022 3:08 am

@soohyun, Thanks for your reply. If I need to replace the IR-cut, would you say that both, the non-coated and coated give a slight blue color shift or just the coated one? Also, I've been thinking about the RAWLITE, however, I've heard that sharpness is reduced, have you noticed this too? and do you see some sharpness being reduced on the ebay ones?

I'm still curious if it's simply a dust spec, it's pretty much the only spot I see. For instance, if you see the first picture I posted of the sensor, it has something that looks like a dust spec in the upper 1/3 of the sensor. I'll try one of those sensor cleaning swabs and see if it helps.
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Uli Plank

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostSat Mar 26, 2022 7:53 am

Other than the cheaper replacements, the RAWlite is a true OLPF, an anti-aliasing filter.
It has to reduce resolution to some degree to fight moiré. But I can confirm that these OLPFs achieve a very good balance between loss and improvement.
Of course, it’ll be more obvious with the already limited number of photocells compared to newer models.
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Brad Hurley

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostSat Mar 26, 2022 2:05 pm

petdarrow wrote:@soohyun,Also, I've been thinking about the RAWLITE, however, I've heard that sharpness is reduced, have you noticed this too? and do you see some sharpness being reduced on the ebay ones?


My understanding from a post by Dmitry Shijan last year is that Hans redesigned the OG BMPCC Rawlite filter last year (or maybe it was the year before) to reduce its impact on sharpness. I have Rawlites in my two Micro Cinema Cameras and am contemplating getting one for my original Pocket as well; I would get the new one rather than the older ones (which are likely what you're seeing on eBay).
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soohyun

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostSat Mar 26, 2022 6:00 pm

petdarrow wrote:@soohyun, Thanks for your reply. If I need to replace the IR-cut, would you say that both, the non-coated and coated give a slight blue color shift or just the coated one?

I have only the coated one installed, but I would assume the color shift would appear on both. It's that the eBay replacement glasses have a very slightly stronger IR filtration compared to the original, which results in some reds being filtered, hence the blue-green shift. Irony is that the IR cut is still insufficient; a separate IR Cut filter will be needed for say, shooting in sunlight with NDs.

The RAWLITE has IR cut as well, and is stronger, removing the need for a separate filter, but still introduces the color shift; that is inherently optics, nothing to be done about that. In fact, RAWLITE markets that as a boost to dynamic range, as the reds typically clip first out of any color on the BMPCC, and the reds are attenuated.

Brad Hurley wrote:
petdarrow wrote:@soohyun,Also, I've been thinking about the RAWLITE, however, I've heard that sharpness is reduced, have you noticed this too? and do you see some sharpness being reduced on the ebay ones?


My understanding from a post by Dmitry Shijan last year is that Hans redesigned the OG BMPCC Rawlite filter last year (or maybe it was the year before) to reduce its impact on sharpness.

This is very true. Dunno if Dmitry is still around, but there have been several revisions to the RAWLITE for its filtration strength. The latest, I believe, is the strongest one, but that should be confirmed with Hans.

Personally, I don't use the RAWLITE much; I have the latest (I think) and the strongest one, but I found the loss in sharpness a bit too great for my tastes. It's a 1080p camera; it needs all the sharpness it can get. That said, the moire is quite severe on this camera, and the RAWLITE is very effective at removing it, but I use the camera mostly for close-ups anyway, which are usually less prone to moire.
Soohyun Kim

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Steve Fishwick

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostSat Mar 26, 2022 9:36 pm

soohyun wrote:Personally, I don't use the RAWLITE much; I have the latest (I think) and the strongest one, but I found the loss in sharpness a bit too great for my tastes. It's a 1080p camera; it needs all the sharpness it can get. That said, the moire is quite severe on this camera, and the RAWLITE is very effective at removing it, but I use the camera mostly for close-ups anyway, which are usually less prone to moire.


For any OLPF to be effective, particularly in reducing colour aliasing, it has to filter out high frequencies at and above the sensor's resolution capabilities - no such perfect OLPF exists - they always eat into actual rez. Unfortunately in the case of CFA bayered single sensors, where the colour resolution is half that of luminance, this inevitably will result in a compounded loss of sharpness, whatever you do. Nonetheless an OLPF in many CFA bayer sensor cameras can still make sense if you always shoot at full sensor size and the maximum output resolution and down sample in post correctly (or the camera down samples elegantly). Shooting in 1080 resolutions only makes sense these days, in these cameras, if workflow, time and delivery demand it. There are also other ways to reduce aliasing in a more adaptive and flexible way, if you need to use varying resolution and sensor crops too.
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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostWed Dec 07, 2022 12:10 pm

Hi petdarrow

Did the cleaning of the sensor work? was it dust? I'm getting faint black out of focus specs on mine every time I stop down.

Let me know.
Thx.
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robert Hart

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Re: Possible dead pixel in sensor or dust in bmpcc og?

PostThu Dec 08, 2022 5:17 pm

I suspect that you have a spot on the IR filter or on the sensor cover glass. I would expect a spot on the cover glass would be more sharply defined. The spot will become more obvious with tighter iris setting and become very soft at the widest iris setting.

If you want to get a better view of a dust mote or spot on a cover glass, take the lens off. Make a large pin hole in a piece of cardboard, place that against the flange face of the mount then shine a bright torch at the pinhole. You should find that you can move the bright disk around the image with the torch moving or moving the cardboard.

The spot should become well defined and you may also discover others you had not noticed.

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