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Blackmagic Pocket Cinema Camera 4K

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3 hours ago, mercer said:

So a P4K specific speedbooster may be introduced to reflect the exact mount and filter thickness of the camera.

@Brian Caldwell

Can we get you to weigh in on this?

As far as I understand, filter stack thickness varies between m43 cameras, yet no m43 camera has problems focusing native lenses to infinity.

Which leads me to believe the camera manufacturer offset the distance of the mount to account for their filter stack to prevent this issue from ever occuring.

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EOSHD Pro Color for Sony cameras EOSHD Pro LOG for Sony CamerasEOSHD C-LOG and Film Profiles for All Canon DSLRs
1 hour ago, andrgl said:

@Brian Caldwell

Can we get you to weigh in on this?

As far as I understand, filter stack thickness varies between m43 cameras, yet no m43 camera has problems focusing native lenses to infinity.

Which leads me to believe the camera manufacturer offset the distance of the mount to account for their filter stack to prevent this issue from ever occuring.

It’s not to do with getting focus at infinity at all.

its about optimising performance with very fast lenses when shooting wide open. 

Previously it meant making a specifically optimised BMD SB variant to account for the different IR cover glass thickness. 

You can still use a regular SB and it will still hit infinity. It’s just less optimised to work with faster than F2 lenses. 

JB

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@John Brawley - Really interesting discussion!  If you use a faster lens wide open without a speed booster will the performance change based on sensor stack thickness?  Does a manufacturer like Sony stay will the same sensor stack thinness year over year? or if Sony makes it thinner generation to generation, does performance increases generation to generation with the same native lenses?

Thanks!

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54 minutes ago, majoraxis said:

@John Brawley - Really interesting discussion!  If you use a faster lens wide open without a speed booster will the performance change based on sensor stack thickness?  Does a manufacturer like Sony stay will the same sensor stack thinness year over year? or if Sony makes it thinner generation to generation, does performance increases generation to generation with the same native lenses?

Thanks!

The sensor maker doesn’t necessarily make the sensor stack. The very fact that the sensor stack thickness is consistent with BMD cameras should tell you this.  

Wide open lenses with shorter cover glass isn’t the issue. It’s because we’re adding another optical formula in between the rear of the lens and the sensor.

The thickness isn’t important to performance either. Obviously or we’d have noticed major problems by now !

It changes the optics performance of what a speed booster is doing though. And THATS the issue.

It’s not worse.  Or better. It’s just different to other MFT cameras and that means to fully optimise the optics design of the SB you have to change the formula and that makes it less optimal for other MFT cameras.  

This is about making a correction to get the most from a lens.  

Many cine lenses that have rear filters for example always have to have a clear filter in because the optical formula is calculated with that exact thickness of refractive index always being there, no matter if it’s clear or ND.  

This is my “lay” understanding.  It gets reported as “non standard” MFT cover glass, but there isn’t an actual standard ! 

Olympus and Panasonic both use a different thickness, it’s just that they’re close enough together that the same speed booster works fine for both of them. (One is 2.3mm I think and one is 2.5mm)

They are also using OLPFs as well as being IR. BMD only have the IR filter, no OLPF.  

This is about economics.  They don’t want to have to make a BMD specific speedbooster, they want the same MFT speedbooster to work on all MFT cameras.

 

JB

 

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3 hours ago, John Brawley said:

It’s not to do with getting focus at infinity at all.

See this is why I'd like to have @Brian Caldwell reply. I was forced to study optics for a semester specifically for microscopy.

Brian could maybe tell us what specifically changes quantitatively. Instead of just "performance".

Can't really fathom what else would change besides the angle of refraction.

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@andrgl Here's an interesting article about RX and non-RX lenses for Bolex.

http://cinetinker.blogspot.com/2014/12/rx-vs-non-rx-lenses.html

I'm pulling some quotes from the section about the aberrations caused by using non-RX lenses (designed with no glass prism) on an RX camera (which has a 10mm glass prism between the lens and the film).

Quote

The problem is that the prism causes the outer light rays from a lens to be bent at different angles to the central ones, so they don't converge at the same point, creating blurry images at the film plane. These aberrations are what the RX lenses have been designed to counteract.

Quote

The aberrations are more pronounced at wider apertures, because this is when the light rays pass through the edges of the lens elements as well as the centre, exhibiting the most variation in how they are bent.

 

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6 hours ago, andrgl said:

See this is why I'd like to have @Brian Caldwell reply. I was forced to study optics for a semester specifically for microscopy.

Brian could maybe tell us what specifically changes quantitatively. Instead of just "performance".

Can't really fathom what else would change besides the angle of refraction.

He’s posted a few times on the BMD forum about this issue. Some others have tested his assertions as well. 

My takeaway is that the edges are “softer” and have more aberrations with fast primes because the design isn’t optimised for the different thickness in cover glass (not made by Sony)

https://forum.blackmagicdesign.com/viewtopic.php?f=2&t=71899

and

https://forum.blackmagicdesign.com/viewtopic.php?f=2&t=26122

JB

 

EDIT and actually this post and the video below it demonstrates the differences visually.  https://forum.blackmagicdesign.com/viewtopic.php?f=2&t=26122#p162887

 

 

 

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23 minutes ago, matthere said:

In the top video ^^ they seem to mention waveform a lot?  Is this a confirmed feature?

Think they showed us focus peaking when talking about 'waveforms'. Think they have little idea what they're talking about. They also called the 4/3" sensor inside slightly bigger than the Micro Four Thirds sensor... which... is not a thing. xD

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When using waveforms in an NLE it does add a performance hit on the CPU/GPU so maybe this is a factor. I'd like to see an RGB parade as well for the very reason it makes ETTR easier. Zebras are usually linked to the green channel so it's quite possible to be clipping red or blue channels and not be aware of it.

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A bit of basic math:

1. Weight: BMPCC4K 722 + Oly Zuiko 12-100 IS 561 + Sammy T5 USB-C 51 = approx. 1,3 Kg

2. In $: 1300 + 1200 + 280 = 2700$

Then other things (a rig or a cage, or a gimbal, cables, etc.) come. Not bad in 1 nor 2.

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