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F0.74 - new Metabones Speed Boosters break boundaries


Andrew Reid
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Yes, I think it becomes a ~55mm F1.2 lens - and thus a 110mm equivalent to full frame. But now I'm starting to get confused as well when it comes to equivalent depth of field. I usually don't think about it because I don't personally care what the DOF is equivalent to full frame.

 

For depth of field just multiply the aperture by the crop factor vs full frame.

 

So APS-C has a crop factor of 1.5x over photographic full frame.

 

Therefore a F1.4 aperture X 1.5 crop = F2.1

 

There's two ways to think about the Speed Booster effect...

 

You can either multiply the lens aperture and focal length by the Speed Booster factor, say 0.58x for the pocket camera version...

 

That turns a 50mm F1.2 into a 29mm F0.74.

 

Then apply the normal Super 16mm sensor crop of roughly 3x on top of that. So in full frame terms you have a 87mm F2.22 - very shallow DOF in other words.

 

In terms of actual BRIGHTNESS - a F0.74 is an F0.74 regardless of crop factor though.

 

And the other way to think about the Speed Booster is to apply the 0.58x, 0.64x or 0.71x to the sensor. So 2.39x crop on the BMCC  becomes 1.53x and then multiple your 50mm lens by that.

 

Forgetting all the maths, all you really need to know is that the aperture brightens up over 1 stop and your field of view changes to become APS-C on the BMCC and 1.76x crop just a bit wider than GH2 on the Pocket.

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Great to have new options, but the inability to use on regular m4/3 cameras seems a bit of a disadvantage to me.  It may not be as future proof because a new camera - even from black magic - may have a different crop factor or a larger shutter or built in NDs.   

 

Also one thing to bear in mind is that - even with these current cameras - because the rear element is close to the sensor a mosaic anti aliasing filter may not be able to fit behind it.

 

For those who already have the original on the cinema camera I think its good to understand exactly what the difference will be.  The native crop of the bmcc is 2.2777  (36mm/15.81mm)  (I don't know where 2.39 comes from. perhaps it doesn't account for aspect ratio).

So with the current speed booster you have an effective 1.617 crop (which is pretty much equal to canon apsc) and with the new one you will be getting a 1.457 crop.  So its a noticeable difference but nothing earth shattering.  Although 1.457 is wider than the 1.5 crop that apsc lenses are designed to cover, I think most lenses will have enough leeway in their image circle for this not to be an issue.

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Ah, yes, the physical shutter must be the reason why it doesn't work on regular MFT cameras. I totally forgot about that. I really can't blame Metabones or Blackmagic, apparently there is no way to get something smaller than 0.71x for regular MFT.

 

So theoretically the BM speed boosters could be put on Lumix cameras, as long as you don't take any photos?!

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Guest c2dd7b52878779b55f43cc8c269267c1

For depth of field just multiply the aperture by the crop factor vs full frame.

 

So APS-C has a crop factor of 1.5x over photographic full frame.

 

Therefore a F1.4 aperture X 1.5 crop = F2.1

 

There's two ways to think about the Speed Booster effect...

 

You can either multiply the lens aperture and focal length by the Speed Booster factor, say 0.58x for the pocket camera version...

 

That turns a 50mm F1.2 into a 29mm F0.74.

 

Then apply the normal Super 16mm sensor crop of roughly 3x on top of that. So in full frame terms you have a 87mm F2.22 - very shallow DOF in other words.

 

In terms of actual BRIGHTNESS - a F0.74 is an F0.74 regardless of crop factor though.

 

And the other way to think about the Speed Booster is to apply the 0.58x, 0.64x or 0.71x to the sensor. So 2.39x crop on the BMCC  becomes 1.53x and then multiple your 50mm lens by that.

 

Forgetting all the maths, all you really need to know is that the aperture brightens up over 1 stop and your field of view changes to become APS-C on the BMCC and 1.76x crop just a bit wider than GH2 on the Pocket.

 

Thanks Andrew, this clarifies everything I was confused about, I think

 

Though I am still unsure about the brightness. I get that, as you say, F0.74 remains so regardless of crop factor. But then a smaller sensor always gathers less light than a larger sensor doesn't it? So doesn't that mean that, all other things being equal, an F0.74 lens on a Super 16mm sensor will not result in as-bright an image as a 0.74 lens on a Super 35 sensor? And won't that difference in brightness be mathematically relative to the crop factor (i.e. the same multiplication the other things)? Again, I hope I've made this clear … it's perfectly possible I'm missing something.

 

Amazing low-light footage btw - certainly gives a different angle on "the camera discussion that shall not be named"

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Thanks Andrew, this clarifies everything I was confused about, I think

 

Though I am still unsure about the brightness. I get that, as you say, F0.74 remains so regardless of crop factor. But then a smaller sensor always gathers less light than a larger sensor doesn't it? So doesn't that mean that, all other things being equal, an F0.74 lens on a Super 16mm sensor will not result in as-bright an image as a 0.74 lens on a Super 35 sensor? And won't that difference in brightness be mathematically relative to the crop factor (i.e. the same multiplication the other things)? Again, I hope I've made this clear … it's perfectly possible I'm missing something.

 

Amazing low-light footage btw - certainly gives a different angle on "the camera discussion that shall not be named"

 

An F0.74 lens will give the same exposure on any size of sensor.  The exposure is unconnected to the sensor size.  A bigger sensor collects more light energy (more photons or whatever you want to call it) for a given f number but the photons are spread over a larger area so it isn't brighter.   The speed booster concentrates this light energy into a smaller area like a magnifying glass burning an ant, so the exposure is increased but the noise will be the same if both sensors are equally good.

 

The easiest way to think of the speed booster is by acting like it modifies the sensor.  Giving the BMCC an APSC crop factor. Giving the same depth of field and noise as an APSC camera, but giving a brighter image for a given iso.

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So theoretically the BM speed boosters could be put on Lumix cameras, as long as you don't take any photos?!

 

The BMPCC adaptor has a large protruding element which might foul a Lumix shutter, however the BMCC adaptor doesn't, and looks like it would physically fit fine.  However as Metabones is not recommending it for the 18x13 M43 sensor I would assume it vignettes pretty badly.  

The BMPCC adaptor might just work on the Digital Bolex too, they are similar sensor sizes and anyone using a Digital Bolex will love a bit of authentic vignette ;)

BMPCC sensor - 12.48 x 7.02

D Bolex sensor - 12.85 x 9.64

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The BMPCC adaptor has a large protruding element which might foul a Lumix shutter, however the BMCC adaptor doesn't, and looks like it would physically fit fine.  However as Metabones is not recommending it for the 18x13 M43 sensor I would assume it vignettes pretty badly.  

The BMPCC adaptor might just work on the Digital Bolex too, they are similar sensor sizes and anyone using a Digital Bolex will love a bit of authentic vignette ;)

BMPCC sensor - 12.48 x 7.02

D Bolex sensor - 12.85 x 9.64

Yeah vignetting would of course be a problem. Didn't think of that ...

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Expressing the increase in brightness via F-stops ("turns your lens into a f0.74!!!!") is what's so confusing for people, because people tend to think of DOF in terms of F-stops. I think people have a better grasp of differences in DOF if they are expressed via sensor sizes:

 

The easiest way to think of the speed booster is by acting like it modifies the sensor.  Giving the BMCC an APSC crop factor. Giving the same depth of field and noise as an APSC camera, but giving a brighter image for a given iso.

 

Exactly. For FOV and DOF, think of the Speedbooster as attaching to and modifying the camera, not the lenses. Meaning, think of your camera as now having a larger sensor (exactly how much larger depending on which SB model you're mounting to it).

 

For exposure (brightness of image), think of the Speedbooster as giving your camera a "free" improvement in ISO (meaning a brighter image but with no additional noise/grain). So you think of any given ISO on your camera as one stop (or 1&1/3 or 1&2/3 stops, for these new SB's) brighter, but with the same noise.

 

 

 

So, if I have a Pocket, and get the new Pocket-specific Speedbooster, I will think of it as turning my sensor into a 1.74x crop/slightly-smaller-than-Canon-APSC/slightly-larger-than-GH2 size, and making the ISO performance 1&2/3 stops better.

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Guest c2dd7b52878779b55f43cc8c269267c1

The easiest way to think of the speed booster is by acting like it modifies the sensor.  Giving the BMCC an APSC crop factor. Giving the same depth of field and noise as an APSC camera, but giving a brighter image for a given iso.

 

Hence its name! I get it now! Wow, these things really are awesome.

 

I was probably getting confused with large sensors having superior low-light performance because of larger pixels (better signal-to-noise ratio). But of course the Blackmagic cameras are different to hybrid cameras because they aren't downsampling. Their pixels are probably quite chunky.

 

Thanks.

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Guest c2dd7b52878779b55f43cc8c269267c1

Expressing the increase in brightness via F-stops ("turns your lens into a f0.74!!!!") is what's so confusing for people, because people tend to think of DOF in terms of F-stops. 

 Right on the money - this is exactly where I was getting confused.

 

Very good explanation too - thanks.

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Hence its name! I get it now! Wow, these things really are awesome.

 

I was probably getting confused with large sensors having superior low-light performance because of larger pixels (better signal-to-noise ratio). But of course the Blackmagic cameras are different to hybrid cameras because they aren't downsampling. Their pixels are probably quite chunky.

 

Thanks.

 

 

 

 

 

Unfortunately the comment is slightly wrong.  the effect is actually changing the lens focal length.  the ratio between defocused infinity and an 'in focus' subject in the foreground will indeed be the same as on a bigger sensor without the speed booster, but the actual look can be quite different.  

 

assuming you took a 50mm f1.2 lens on full frame, and put it against a 80mm f2.8 lens on medium format, the ratio of 'maximum defocus' to 'in focus' and the fov would be similar, but the actual rendered image would be drastically different in terms of depth of field.  the medium format image will have more ping to the in focus subjects.  assuming the point of focus were the eyes of a model, the medium format setup would capture a deeper depth of field while still creating as strong maximum defocus.  Therfore the medium format image will render a greater amount of the face in focus than the faster lens on a smaller sensor.

 

the same differences will be seen when comparing a boosted pocket vs an aps-c sensor.  both will have the same ratio of defocus to focus, and the same fov.  but the aps-c will render its depth of field in a more sectioned off and 3 dimensional fashion.  the pocket will be over a stop brighter though.

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Unfortunately the comment is slightly wrong.  the effect is actually changing the lens focal length.  the ratio between defocused infinity and an 'in focus' subject in the foreground will indeed be the same as on a bigger sensor without the speed booster, but the actual look can be quite different.  

 

assuming you took a 50mm f1.2 lens on full frame, and put it against a 80mm f2.8 lens on medium format, the ratio of 'maximum defocus' to 'in focus' and the fov would be similar, but the actual rendered image would be drastically different in terms of depth of field.  the medium format image will have more ping to the in focus subjects.  assuming the point of focus were the eyes of a model, the medium format setup would capture a deeper depth of field while still creating as strong maximum defocus.  Therfore the medium format image will render a greater amount of the face in focus than the faster lens on a smaller sensor.

 

the same differences will be seen when comparing a boosted pocket vs an aps-c sensor.  both will have the same ratio of defocus to focus, and the same fov.  but the aps-c will render its depth of field in a more sectioned off and 3 dimensional fashion.  the pocket will be over a stop brighter though.

 

Interesting. I'm imagining what you're saying in terms of a kind of DOF "roll-off".

 

In terms of explaining the basic principles simply, without complicating it too much to begin with, I think the other guys were still "right" though. I'd be interested how visible the difference is in real world images - hard to do a controlled test though.

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The BMPCC adaptor has a large protruding element which might foul a Lumix shutter, however the BMCC adaptor doesn't, and looks like it would physically fit fine.  However as Metabones is not recommending it for the 18x13 M43 sensor I would assume it vignettes pretty badly.  

The BMPCC adaptor might just work on the Digital Bolex too, they are similar sensor sizes and anyone using a Digital Bolex will love a bit of authentic vignette ;)

BMPCC sensor - 12.48 x 7.02

D Bolex sensor - 12.85 x 9.64

 

I hope it does work on the Digital Bolex. Bmpc without rolling shutter !

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Unfortunately the comment is slightly wrong.  the effect is actually changing the lens focal length.  the ratio between defocused infinity and an 'in focus' subject in the foreground will indeed be the same as on a bigger sensor without the speed booster, but the actual look can be quite different.  

 

assuming you took a 50mm f1.2 lens on full frame, and put it against a 80mm f2.8 lens on medium format, the ratio of 'maximum defocus' to 'in focus' and the fov would be similar, but the actual rendered image would be drastically different in terms of depth of field.  the medium format image will have more ping to the in focus subjects.  assuming the point of focus were the eyes of a model, the medium format setup would capture a deeper depth of field while still creating as strong maximum defocus.  Therfore the medium format image will render a greater amount of the face in focus than the faster lens on a smaller sensor.

 

the same differences will be seen when comparing a boosted pocket vs an aps-c sensor.  both will have the same ratio of defocus to focus, and the same fov.  but the aps-c will render its depth of field in a more sectioned off and 3 dimensional fashion.  the pocket will be over a stop brighter though.

 

There are two questions at hand here.

 

1. does this (the effect you mention) happen

 

2. Does this happen with the speed booster.

 

 

1.  I have always had a feeling that this happens.  Smaller sensors with faster lenses never seem to give as strong a subject isolation.

However, I have never seen someone prove this, either with a demonstration or with scientific theory.  If you have more info on this I would love to hear it to confirm my suspicions.  I would also love to see you try and present your case in the dpreview open talk forum.  Particularly with a provocative thread title. There are some hardcore equivalency crusaders there, and you would really get their hackles up

 

2.  I don't actually think it is happening with the speed booster.  It isn't actually changing the focal length at all.  The booster cant change the properties of the lens. Its just taking the image that comes out of the back of the lens and squeezing it into a narrower image circle.  besides any distortion or refraction or whatever that the booster ads, the image will look the same apart from minor variations in the crop.

 

 

(incidentally, for the people saying the speed booster increases iso performance.  It depends.  increasing it compared to what?

Compared to using the same lens on the BMCC without the speed booster? Yes.

Compared to using the same lens on a native apsc sensor camera? No.  The image will be brighter at a lower ISO, but the noise will be the same as the apsc camera at a greater ISO.   The signal to noise ratio is the same, because the signal is the same. It cant get any extra signal from somewhere.)

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Compared to using the same lens on a native apsc sensor camera? No.  The image will be brighter at a lower ISO, but the noise will be the same as the apsc camera at a greater ISO.   The signal to noise ratio is the same, because the signal is the same. It cant get any extra signal from somewhere.)

 

Would you mind explaining this a bit further please, or putting it a different way? I can't quite get my head around what you're saying …  :unsure:

 

EDIT: Don't worry, I just got it ...

 

No, actually I didn't, lol  :lol:

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Would you mind explaining this a bit further please, or putting it a different way? I can't quite get my head around what you're saying …

 

EDIT: Don't worry, I just got it ...

 

OK. cool. Although I think I have another way to explain it if you need.

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