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Blackmagic Pocket Cinema Camera 4K

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1 hour ago, Kisaha said:

Have you heard about this "sensor thickness" before? It is the first time that I heard about it.

 

It is referred to as sensor stack ...

https://petapixel.com/2014/06/10/sensor-stack-thickness-matter/

It is why many Leica M wide angle lenses perform so poorly on Sony A7 cameras ... 

Here is a link to a video by Filippo Chiesa ... BMPCC4K and Speedbooster

... read his comments on AC and glow .... may be related to the stack thickness.

I assume that if you use a SB it should be designed for the camera in question ... otherwise you lose the benefits of the great glass you

have mounted ... the Metabones smart adapter without glass avoids the problem but you lose speed and boost in angle of view.

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52 minutes ago, docmoore said:

It is referred to as sensor stack ...

https://petapixel.com/2014/06/10/sensor-stack-thickness-matter/

It is why many Leica M wide angle lenses perform so poorly on Sony A7 cameras ... 

Thank you very much for the info. This seems like a pretty significant issue.

In short, for everyone using old film lenses, Samyang/Rokinons, and a lot of different primes (you have to know the exit pupil location of that particuliar lens, which you can't, except you have an optical bench or the manufacturer states it), you are gaining a lot with this specialized speedbooster.

If you shoot mostly zooms and teles, not so much..

Depending the sensor stack and the lenses exit pupil location, the difference can be (with 1 as max, and 0.85 as an hypothetical perfect lens) 80% worst! Now, in real life both are very difficult to happen, but I see a lot of combos that can take this number to 30% loss, or something (I am not sure if I can read the table right, maybe this number is too pessimistic).

I can tell from the data that APS-C and FF are near 2-2.5mm sensor stacking. For some reason, most m43 are 4-4.5mm, so Metabones doesn't lie, BM cameras with m43 mount need different Speedboosters. 

That's all in theory of course, but there is not only smoke..

I wonder what those extra layers do on the other m43 cameras and if the BM P4K sensor can still be considered the same as the GH5S..

As I see it, one more specialized item to rise the total P4K cost.

 

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I missed reading this in the description for the new speed boosters the first time:

"...the optics have been re-designed to optimize for the filter stack thickness of 2.4mm found in Blackmagic cameras rather than the 4mm of a standard Micro Four Thirds."

Wow...That filter stack thickness is much less than standard M4/3. But, apparently the old Black Magic 2.5K camera had a 2.5mm stack thickness. So, Black Magic is doing this for some specific reason. I wonder the reason...

So, it looks like there really is a reason for a new Speed Booster unique to the P4K. Now, I really want to see one so that I can compare them side by side. According to the petapixel article, a thickness difference like that could have a large impact on image quality when using the booster with adapted lenses.

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43 minutes ago, drm said:

I missed reading this in the description for the new speed boosters the first time:

"...the optics have been re-designed to optimize for the filter stack thickness of 2.4mm found in Blackmagic cameras rather than the 4mm of a standard Micro Four Thirds."

Wow...That filter stack thickness is much less than standard M4/3. But, apparently the old Black Magic 2.5K camera had a 2.5mm stack thickness. So, Black Magic is doing this for some specific reason. I wonder the reason...

So, it looks like there really is a reason for a new Speed Booster unique to the P4K. Now, I really want to see one so that I can compare them side by side. According to the petapixel article, a thickness difference like that could have a large impact on image quality when using the booster with adapted lenses.

maybe bm have shares in metabones ...🙄

can you really call it a standard micro four thirds mount if the filter stack is thinner and it affects mounted optics ? surely with or without a speed booster, optics wouldn't be focusing to the correct point no matter what lens was on it, which would make it bm's fault or is my thinking flawed ? the fact is that the lenses i fit on the front seem to focus ok makes me think its not the issue some people say it is. Metabones might be exaggerating the situation slightly hoping  people might teeter over the edge into buying a newer and greater adapter. How many percent better is unclear at this point, if its 10-20 percent well that would be worth splashing out on if its only a few percent better i'd stick with buying a cheaper used adapter. Thats my thinking anyway. Until someone can do a definitive side by side test we won't know. Maybe andrew could approach metabones about a  test unit for blogging purposes if its really that good, andrew  could sell heaps of these for metabones thats a win/win right ?

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41 minutes ago, webrunner5 said:

Kind of a bit outdated article, but I think you get the point. Should help with wide angle lenses, which is a pretty big fad in video now. Doesn't look like a earthshaking difference though. But every bit helps.

https://www.lensrentals.com/blog/2015/01/a-thinner-sensor-stack/

i guess if you can afford one of those lenses you can afford to have the sensor stack fixed as well, if its an issue for you . Although i dont think its the manufacturers fault for not making exotic, expensive, fast, wide, adapted glass work at 100 % on their camera. I swing the other way, cheap, old glass adapted 😉

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5 minutes ago, leslie said:

i guess if you can afford one of those lenses you can afford to have the sensor stack fixed as well, if its an issue for you . Although i dont think its the manufacturers fault for not making exotic, expensive, fast, wide, adapted glass work at 100 % on their camera. I swing the other way, cheap, old glass adapted 😉

(Cheap) old glass is the most affected it seems, because they didn't have any sensor stacking back then!

I am sure there will be some tests soon. Can't wait for the results.

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Just now, Kisaha said:

(Cheap) old glass is the most affected it seems, because they didn't have any sensor stacking back then!

shouldn't the adapter take that into account ? its not like the sensor stack moves around very much

edit : my understanding is flawed i guess, sorry if i antagonize you. I don't know how bm could get it wrong with the sensor on the  first pocket camera but i remember vaguely that there was some issue back then. i presume that most manufactures build mounts so that they sell more of their own lenses rather than have those dollars go else where. which is a bit of an oddity for bm as they dont make lenses do they ? perhaps we should consider ourselves lucky if we can get adapted lenses to work at a reasonable   level of performance

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18 minutes ago, leslie said:

shouldn't the adapter take that into account ? its not like the sensor stack moves around very much

That's exactly the point Metabones does with this adapter. Most sensors are close to 2-2.5mm, the m43 are 4-4.5mm so they need special construction.

BM is m43 but unlike the other m43 sensors, their sensors are close to 2.5mm. That changes..well, something.

"1. The difference in sensor-stack thickness between the camera the lens was designed for and the camera actually being used.

2. The maximum aperture of the lens. Wide-aperture lenses are going to be more sensitive than narrow aperture lenses.

3. How telecentric the lens is. (More specifically, how far forward the exit pupil of the lens is.) A lens with the exit pupil far away from the sensor is not affected by the thickness of the sensor stack very much. A lens with the exit pupil very close to the sensor is affected a lot."

So, a combination of those 3 can yield specific undesired results.

The worst case scenario could be an ultra fast wide angle rangefinder lens.

As I said, it can be nothing in practice, in theory definitely is something, so we need an independent test to learn what we are missing, or not, in real life.

For those who want the best performance out of their cameras, these adapters are going to sell, no question about it.

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Finally got around to buying and testing these mini-XLR adapters.

1263900453_MiniXLR001.thumb.jpg.beaf1b31e6ba80490bae62742aa0829f.jpg

They are the official Blackmagic ones that they sell for the VideoAssist but obviously work fine with the Pocket4K as well.

Decent build quality, very practical length of 40cm and they come in a pack of 2 for £30 so a good value as well.

More to the point they are actually available, as mini-XLR to XLR is generally still a tricky cable to track down.

https://cvp.com/product/blackmagic_bmd-hyperdaxlrmini2

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24 minutes ago, BTM_Pix said:

Finally got around to buying and testing these mini-XLR adapters.

1263900453_MiniXLR001.thumb.jpg.beaf1b31e6ba80490bae62742aa0829f.jpg

https://cvp.com/product/blackmagic_bmd-hyperdaxlrmini2

+1

These are the ones I have spoted myself. I have a pair for my Zoom F8, but I want to have backupa anyway.

How do they sound? I remember people complaining for weak signal and/or hiss and stuff. 

Have you tried a phantomed power mic or any kind of mic?

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6 hours ago, webrunner5 said:

Kind of a bit outdated article, but I think you get the point. Should help with wide angle lenses, which is a pretty big fad in video now. Doesn't look like a earthshaking difference though. But every bit helps.

https://www.lensrentals.com/blog/2015/01/a-thinner-sensor-stack/

Thanks @webrunner5 for this article. This was fascinating reading.

So, here are my big picture conclusions:

  1. This is only an issue at really wide apertures (1.4+)
  2. The sensor stack on the P4K is 1.5mm thinner than normal M4/3, so if you are using an adapter without optics, the P4K should perform better than other M4/3 cameras because its sensor stack is close to the same thickness as a normal SLR. 
  3. The Sigma 18-50 f/1.8 lens is pretty much immune from the problem because it has an exit pupil distance of 150mm. 
  4. MOST importantly (and unexpectedly) the P4K may show problems with *native* M4/3 lenses at very wide apertures because those lenses were designed to use a 4mm filter stack but the P4K uses one that is 2.5mm.

Luckily, I have a Voigtlander 25mm f/0.95 lens and P4Ks + GH5/GH5s cameras. When I get time, I will compare the P4K vs. the GH5s wide open and look for differences. If there are differences, it will probably be on the edges of the images. I would bet that the differences would be most visible in photos, but obviously the P4K doesn't do very good photos... :) 

So, Blackmagic designed in a difference (filter stack = 2.5mm instead of 4mm) that would likely make the P4K perform better with adapted lenses, but also likely caused it to perform worse with native M4/3 lenses...weird. 

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4 hours ago, Yannick Willox said:

What does this actually mean for the new PL 10-25 mm native m43 lens ? Does it also suffer, as it has been designed for thicker sensor stack ?

I would think on the wide end it will be distorted at the edges without the new Metabones on it, Especially wide open, which sad to say is the main reason you would buy it, for the speed. I would imagine BMD does this to get a bit sharper image, which is probably happening in the middle on a "normal lens", but really wide angle lenses take a hit on the edges. I don't think it effects telephoto lenses at all or much at all.

The steeper the angle of light hitting the sensor the worse it is going to be. If you look at old Manual Lenses the wide angle ones tend to have the rear glass nearly at the lens mount. The mid Teles and up the glass is way up in the barrel. That means the closer the glass is to the rear mount the more radical the light bend is.

Now on my Sony FE FF lenses even the wide angle ones were recessed a fair bit in and were more of a rectangle than a round exit on the lens. I think Sony probably has some of the best designed lenses for Mirrorless cameras out. I am not saying the RF, or Z mounts are bad, but I have never used or even seen a lens they use. But I bet the older EF, Nikon F lenses have the same old designs for the old DSLR bodies, even the newer versions of them.

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48 minutes ago, Kisaha said:

How do they sound? I remember people complaining for weak signal and/or hiss and stuff. 

Have you tried a phantomed power mic or any kind of mic?

Well its difficult to say anything definitive about noise and signal loss really as I can't A/B them against anything as these are the only ones I have and the Pocket4K is the only piece of equipment I have that has mini XLR inputs.

Yes, have tried with phantom powered and dynamic mic.

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I use the BM mini to XLR cable with phantom powered boom mic ...

Signal is very strong ... if you adjust levels without hiss and no appreciable noise.

Adequate for the weekly blog that I record ... I no longer use an external recorder.

The camera continues to address a wide variety of needs ... it is very well designed and implemented.

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18 hours ago, webrunner5 said:

Sounds to me you could use the old one on the new one if there is that little difference? Maybe it protrudes further into the sensor box though?

I have one, but am afraid to try it.

6 hours ago, docmoore said:

I use the BM mini to XLR cable with phantom powered boom mic ...

Signal is very strong ... if you adjust levels without hiss and no appreciable noise.

Adequate for the weekly blog that I record ... I no longer use an external recorder.

The camera continues to address a wide variety of needs ... it is very well designed and implemented.

I've been happy with the audio through XLR on the P4k as well.

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On 8/1/2019 at 5:54 AM, drm said:

The Sigma 18-50 f/1.8 lens is pretty much immune from the problem because it has an exit pupil distance of 150mm

That is great information.  Here's link that contains other lens exit pupil distances. It also mentions the Blackmagic 2.5k as having an optical sensor stack of 2.4mm so assuming the Blackmagic Pocket 4k's sensor stack is 2.5mm, an older used metabones speed booster made for the BMCC maybe a cheap alternative with caveats like vignetting and corner sharpness to be considered.

https://www.lensrentals.com/blog/2014/06/sensor-stack-thickness-when-does-it-matter/comment-page-1/

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50 minutes ago, majoraxis said:

That is great information.  Here's link that contains other lens exit pupil distances. It also mentions the Blackmagic 2.5k as having an optical sensor stack of 2.4mm so assuming the Blackmagic Pocket 4k's sensor stack is 2.5mm, an older used metabones speed booster made for the BMCC maybe a cheap alternative with caveats like vignetting and corner sharpness to be considered.

https://www.lensrentals.com/blog/2014/06/sensor-stack-thickness-when-does-it-matter/comment-page-1/

At 35mm is 70 FYI.

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