BMPCC Crop factors

I confess to being somewhat confused by ref to specific crop factors at various resolutions in BMPCC manual. (Wish BMD had included a column on this detail in their 'Sensor Frame rates' table.)
Thought I was getting there until I saw BMPCC 4K table listing 4K DCI as 'Full'... Ultra HD as 'Window'... so far so good... but then HD 1920 X 1080 as 'Scaled from Full'...?!
(Confused because of UHD and HD being same aspect ratio.)
When I'm clearly not understanding Window / Scaled properly I reckon time to give up and ask for help...
Anyway, for now I am mainly trying to find an answer to the following...

Can some kind soul tell me what effective 'crop factors' are for:
1. BMPCC 6K / 4K DCI 4096 x 2160/ ProRes / Scaled from 5.7K
2. BMPCC 6K / 2.8K 2868 x 1512 / B RAW / Window
3. BMPCC 4K / Ultra HD 3840 x 2160 / B RAW / Window
3. BMPCC 4K / HD 1920 x 1080 / B RAW / Window

Thanks!

The BM PCC6K is approximately a APS/C sensor (S35), and the Picket 4K a MFT 16:9 Sensor.
I find crop factors a waste of time, trying to compare a 16:9 or 17:9 Cinema aspect ratio sensor with a still camera 135 sensor, why

Get pCAM or other similar app like ViewFinder, and you can see the differences between the two cameras directly p, without trying to use a confusing intermediate format. If yiu are trying to match the angle of view on the two cameras, pCAM will do a better job.
Cheers

Stephen, you are close to understanding the options. You are asking about this with regard to both the BMPCC6K and BMPCC4K. Let me try to summarize with a simple example.

Any sensor or film gate can be considered a crop compared to the film gate for 135 film (36x24mm). That is often referred to as ‘full frame’ if you are coming to cinematography from a background in photography.

Digital sensors vary significantly in size and aspect ratio. The ‘traditional’ Micro Four-Thirds sensor has a physical width of 17.3mm so its horizontal crop compared to ‘full frame’ is roughly 2x; let’s pretend the actual photosites available were 3840x2160 UHD. And this camera can record either 3840x2160 or 1920x1080.

If you recorded 1920x1080 HD as a ‘window’ your crop would be roughly 4x compared to 135 film. You know all this.

But many cameras will downscale in camera so that your field of view uses the full sensor but the image is scaled down by the camera to fit the HD window. If you recorded HD physically, you would still see the larger UHD FOV so the crop then is 2x instead of 4x.







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...
Can some kind soul tell me what effective 'crop factors' are for:
1. BMPCC 6K / 4K DCI 4096 x 2160/ ProRes / Scaled from 5.7K

5.7K 17:9 is 1.7x so any window you can scale it to will still be 1.7x roughly; if you scale from the full sensor, crop is 1.6x roughly

2. BMPCC 6K / 2.8K 2868 x 1512 / B RAW / Window

2.8K 17:9 windowed crop is 3.3x roughly

3. BMPCC 4K / Ultra HD 3840 x 2160 / B RAW / Window

UHD window crop is 2x

4. BMPCC 4K / HD 1920 x 1080 / B RAW / Window

HD window crop is 4x



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The BM PCC6K is approximately a APS/C sensor (S35), and the Picket 4K a MFT 16:9 Sensor.
I find crop factors a waste of time, trying to compare a 16:9 or 17:9 Cinema aspect ratio sensor with a still camera 135 sensor, why

Get pCAM or other similar app like ViewFinder, and you can see the differences between the two cameras directly p, without trying to use a confusing intermediate format. If yiu are trying to match the angle of view on the two cameras, pCAM will do a better job.
Cheers

I guess 'crop factor' is still useful for a lot of people who start with standard full frame 35mm still photography, then move into 35mm movie and other cinematographic formats. So, regardless of formats' precise aspect ratio, they find it helpful to be able to make a quick calculation of equivalency to the field of view reference scale that they 'see' best in their mind.
(I am reminded that I do need to get a more recent viewfinder app than the one I have now though!)

In fact I'm not so much looking for info on the broad difference between the 6k and 4k, since I do understand the (rough) equivalencies of APS-C / 'S35' and MFT pretty well, but I really would appreciate verification of the 'windowed crop factor' for the four specific examples mentioned.

Thanks.

Thanks rick.lang for answers on 1, 2, 3, 4.
Crystal clear and very useful!

And cheers to all.

Yes, but the field of view on a 135mm Camera is going to loom different that a 16: or 17:9 image, and more so on a 2.3:5 aspect ration, even on a 35.9mm wide sensor. You need a tool that can help,you visualize this. Crop factors are just meaningless numbers, that most people can not relate to. They are only sort of useful when trying to arch an angle of view between two different size cameras. Anyway, Rick gave you the answers and how to compute them.

That said, two different 35mm lenses on the same camera/sensor can have two different angles of view. Crop factors are only a starting place, prefer lens tables, like the ACS tables based on standard filming formats, gives you instant view of the differences in focal lengths needed to get the approximate shot you want. You still need to test camera/sensor lens combination to be sure.
Cheers

Many thanks Denny - understood.
You mention 'Viewfinder' app...
Can you please confirm exact name? I am seeing a few similar. (Android user)
Many thanks!
Stephen.

I use an IOS application called Artist Viewfinder MkII, their should be similar Android apps also. another is pCAM, which also offers more options, and is excellent.
Cheers

Hope this helps for an idea of crop factor.

Nice illustration showing different aspect ratios and sensor crops...
Cheers

Here is one for BMPCC 4K as well.

You need to add the 2.6K S16 and 2.8K Anamorphic Windows as well, since they are coming soon in FW 6.6 update.
Cheers

You need to add the 2.6K S16 and 2.8K Anamorphic Windows as well, since they are coming soon in FW 6.6 update.
Cheers

Hey Denny,

Because these are linked images from my site https://www.braw.info these will automatically update when I ad the new detail there. Which I will do very soon after the exact specs are made public.

Or if they are public, let me know where I can see them.

Regards

Grant mentioned this in his IBC update and several shots from IBC of the Pocket 4K running the beta 6.6 FW show this in the camera’s new menu. Also, Nofilm school released note about the 2.8 Anamorphic window coming in FW 6.6. But, yes, waiting until the FW release is formally announced by BMD is a good idea. I was just giving a heads up it could be coming soon.
Cheers

I shot 2kDCI by mistake and clearly it is cropped. Can anyone tell me the crop factor and is it the DCI that governs the crop? Fortunately I was shooting birds so it worked rather well. Thanks. So much to learn! ) and this forum is certainly a huge help.

Which camera? Do you mean 2.8K on the BMPCC6K? That’s 2868x1512 and the horizontal ‘crop’ compared to 135 film is 3.34x. If you were using a lens with a focal length of 100mm, that would have the angle of view of a 334mm lens on a ‘full frame’ camera. That’s going to bring those birds in flight pretty close!

Hi Rick;
No it was my Ursa GR with a Nikkor 200-400 at 400mm. Sorry, I should have said so. Looks like a significant crop ie from just over full body on a Chukar to head shot. And, they were not in flight.

Hi Rick;
No it was my Ursa GR with a Nikkor 200-400 at 400mm. Sorry, I should have said so. Looks like a significant crop ie from just over full body on a Chukar to head shot. And, they were not in flight.

I think you’re looking at a horizontal crop of about 3.2x then so you’re shooting the equivalent of 1280mm!

No wonder it was hard to hold. I had some tripod issue so was in my truck holding on the window. Clip to come.
I don't understand why this is a crop? I can find nothing in the manual about it. So this crop is because the format is DCI?

I don’t have the camera, but I think it depends on your camera settings. If you were shooting raw, then it’s always a crop.

But if you are shooting ProRes you may have the ability to shoot in a cropped window or downscaled from the 4K DCI window. Downscaled in camera, the ‘crop’ would be 1.6x or equivalent to 640mm in ‘full frame.’

Do you recall what settings you had?

Hi Rick;
I missed this post.
I was in ProRes 422 4k 16.9.
My fat finger hit 2k DCI when I noticed the crop so decided to shoot a couple of clips with the crop and see what the result was.
Nikon 200-400.
Yesterday I posted the clips on my FB page: www.facebook.com/richardtwrightphotography if you want to have a look.

Thanks for the feedback.

Thanks, Richard. Definitely tripped, not downscaled. ProRes gives you the option in the second page of the Record tab. Still that closeup was impressive. I’d try to stabilize that shot which is going to pull you in a little closer but you’ll get a steady shot out of it. Great job overall!

Thanks Rick;
Good catch. I thought I had stabilized all the clips but just looked at the original and stabilized it and you are right - much better. I do not find what you mean on page 2. Page 2 on mine is chgoices for film or video and speeds.
Thanks

Richard, in the upper right corner or Menu / Record / page 2, there is a box that shows the sensor area the camera is using. If you are recording ProRes HD for example, you will see the sensor area could be 4K (UHD) or HD. If you want the crop, you would select HD; if you want it to downscale in camera, you would select 4K (UHD) in my example. If you are recording raw, that sensor area box is greyed out since raw is always a window.

On the BMPCC4K recording ProRes HD, the sensor area gives me the option to select 4K (UHD) or 2.6K or HD. So I could have no crop or some crop or full crop.

The 2.6K is particularly interesting as a choice for ProRes as 2.6K is a raw sensor cropped window that is not available to record in ProRes. But you can record ProRes HD with the angle of view of 2.6K if you want a mild crop. Very thoughtful of the BMD camera team to have that option.

Besides the saving in media space with HD, the mild crop of 2.6K with in-camera downscaling gives you a 1.4x downscaled factor which will help the camera determine better colour and detail than if you were recording HD in a window without downscaling.

Hi Rick;
Thanks for the lessons. On the g2 the window you are describing un shows on or off. I cannot seem to find a window that shows the sensor area the camera is using. I will recheck the manual but seems this has changed on the g2.Cheers Richard

Okay - I'm getting it. Sorry and thanks.
On is windowed sensored, so a crop, and off is not a window so not cropped. Duh!
Reading up again as each time I read I know a bit more and have a bit more shooting experience.

Perhaps the wording of the box is different on the Pro G2. Having the sensor Window either On for a crop or Off for full sensor readout sounds right. Sorry about the misinformation!

I was just going by the wording on the BMPCC4K. Too lazy to check my URSA Mini 4.6K as I’d have to get it out of the storage closet. The BMPCC4K is always powered up and ready by my desk.

Hello,
I saw a table comparing sensor crop [or windowing] for various BRAW and ProRes Resolutions.
I recall it saying that BRAW cropped the sensor at less than 6k resolutions, but ProRes used the full sensor, even for HD, downsampling it.
Can anybody confirm and/or point me to a comparison table?
Thanks
Nigel

BMPCC6K Pro specs:

“Recording Formats

Blackmagic RAW 3:1, 5:1, 8:1, 12:1, Q0, Q1, Q3 and Q5 at 6144 x 3456, 6144 x 2560, 5744 x 3024, 4096 x 2160, 3728 x 3104 and 2868 x 1512 with film, extended video, video dynamic range or custom 3D LUT embedded in metadata.
ProRes at 4096 x 2160, 3840 x 2160 and 1920 x 1080 with film, extended video or video dynamic range or custom 3D LUT.”

BRAW is open gate or a sensor crop.

ProRes can record in the listed resolutions as a sensor crop or using the field of view of the corresponding sensor but downscaled to a smaller dimension. So HD can be downscaled from the field of view of UHD 3840x2160 or cropped to HD sensor crop 1920x1080.

BMPCC6K Pro specs:

...ProRes can record in the listed resolutions as a sensor crop or using the field of view of the corresponding sensor but downscaled to a smaller dimension. So HD can be downscaled from the field of view of UHD 3840x2160 or cropped to HD sensor crop 1920x1080.

I'm not saying that you're wrong, but the April 2021 Installation and Operation Manual Blackmagic Pocket Cinema Camera says on page 22 for Maximum Sensor Frame Rates for the 6K that all the ProRes 1920 x 1080 resolutions are scaled from either full, 5.7K or 2.7K.

2.7K? Really?

...the April 2021 Installation and Operation Manual Blackmagic Pocket Cinema Camera says on page 22 for Maximum Sensor Frame Rates for the 6K that all the ProRes 1920 x 1080 resolutions are scaled from either full, 5.7K or 2.7K.

2.7K? Really?

Since Kodak's 1923 16mm film standard is 10.262 x 7.493mm, a 2.7K crop (2729/6144 = .444173 x 23.1 = 10.26mm) of the BMPCC 6K sensor would fit a lot of old 16mm lenses.

Did the technical writer of the Pocket manual have access to an unreleased firmware update that has a 2.7K resolution for the BMPCC 6K?

I have a nice 16mm Zeiss Vario-Sonnar 10-100mm F/2.8 lens that does not fully cover Super 16. It was popular and shown on all the publications for the 1965 ARRI 16BL film camera that was the staple for news gathering and documentaries in it's day. Although they were crazy expensive in their heyday ($2,600 or $22,219 USD today), it is cheap and plentiful on the used market. It produces excellent images. It would vignette at 2.8K on the BMPCC 6K.

I want my 2.7K!

D’oh! I should have checked so my bad! Sounds very familiar when you mentioned it. Thanks.

The 2.7K though probably refers to the actual 2.8K sensor window. I’m not going to check that now but I seem to recall noticing that reference too previously and just assumed they meant the 2.7K window.

Thanks Rick
"ProRes can record in the listed resolutions as a sensor crop or using the field of view of the corresponding sensor but downscaled to a smaller dimension. So HD can be downscaled from the field of view of UHD 3840x2160 or cropped to HD sensor crop 1920x1080."

So PRoRes HD can make use of the full [almost] S35mm sensor for DOF purposes?

Yes you have that option. I don’t have that camera but you can experiment on your camera to see which ProRes resolutions can be downscaled from a larger resolution in camera.

I do have the BMPCC4K and that can do ProRes HD cropped or downscaled. Sorry all the options are not described in the specs, but easy to see when you have the camera and toggle the settings.

The 2.7K though probably refers to the actual 2.8K sensor window.

Yes, I confirmed this. When you shoot in ProRes HD on the BMPCC 6K, you have the sensor area (scaled from) options of 6K, 5.7K or 2.8K.

When you shoot in ProRes UHD or 4K DCI you have the sensor area option of 6K (16:9) or 5.7K (17:9).

I've heard that when it does this downsampling, pixel binning is not used, so moire is not a problem.

The BM PCC6K is approximately a APS/C sensor (S35), and the Picket 4K a MFT 16:9 Sensor.
I find crop factors a waste of time, trying to compare a 16:9 or 17:9 Cinema aspect ratio sensor with a still camera 135 sensor, why

Get pCAM or other similar app like ViewFinder, and you can see the differences between the two cameras directly p, without trying to use a confusing intermediate format. If yiu are trying to match the angle of view on the two cameras, pCAM will do a better job.
Cheers

The crop factor is useful to know when buying lenses! I bought a 16mm and 35mm assuming x2 crop because its a M4/3 mount and the 16 is not 32 and the 35 is not 70, these are quite important if trying to match shots or swap lenses with other M4/3 cameras, I also have the magic cinema app and the difference is way off as well.

The crop factor is useful to know when buying lenses! I bought a 16mm and 35mm assuming x2 crop because its a M4/3 mount and the 16 is not 32 and the 35 is not 70, these are quite important if trying to match shots or swap lenses with other M4/3 cameras, I also have the magic cinema app and the difference is way off as well.

It depends on the lens format you're coming from as I showed you on a different thread. Also if you are using an SB, then it's different there too.

So many sensor sizes....
Easier if we all moved to horizontal FOV which is easy to calculate using the focal length + sensor size and the trigonometry you learnt at school (or take a refresher lesson on youtube)

a 35mm lens is always a 35mm lens!

only the field of view (FOV) is different.
the crop factor is the difference of a full frame lens on different sensors.

and the FOV depends on the sensor size for which the lens is built:

FOV_FFvsS35.jpg (459.47 KiB) Viewed 8781 times

picture: @2022 CVP


.

Just bear in mind that the 135 format itself was originally created as a sort of crop format of the then common 645/6x6 format cameras which we now typically refer to as medium format, which in turn were much smaller than the formats of the even older view cameras and the like, which we now tend to call large format cameras (for which the film came in sheets the size of a typical print).

When the 135 format came out people generally regarded it as a lower-quality format for the consumer market as it was considered sub-par compared to the medium format cameras that the pros were using.

If a 135 camera is "full frame", does that make a medium format camera "fuller than full"?

In the end these are just numbers - it is all relative to what you are accustomed to. Be careful not to think of the smaller formats as somehow inferior or sub-par simply because they are being labeled as a "crop" of the 135 format which is mismarketed as "full frame" to make you think you need something bigger to be a "pro" (thus promoting sales of more expensive equipment than many people really need or would benefit by) - there are benefits to the smaller sensors too. Pros and cons both ways.