Blackmagic 4.6K vs. Arri Alexa Comparison and Review

[Kenneth C Merrill]

Hi Guys! Here is the comparison and review that I did with my friend Jay P Morgan who hosts The Slanted Lens channel on YouTube.

As stated at the beginning of the video, we did run into a speed bump :\ The EF mount lens we used on the Ursa Mini was not mechanically sound (unknown to us at the time), and I had to later rate the T-stops on the lens by hand, using my good ole' Scarlet MX to compare the witness marks between the EF mount lens and the PL mount lens we used. It wasn't too hard once I got the process down.

As stated at the very end of the review, the shots you see compare ProRes from both cameras. We shot the scene in raw on the Ursa Mini as well, and I actually anticipated showing a comparison with Ursa Mini ProRes, but the differences were negligible, and we didn't want to drag out the comparison too long.

I think for the price, the Ursa Mini 4.6K is an incredible camera. It does fall short of the touted specs in some ways, I think, but it's more than capable of making gorgeous images. As I mention at the end of the review, the only hesitation I have about the camera is reliability and QC. I'm sure John Brawley will have something to say about that (and Red has its own checkered history), but for me its a deal breaker until production ramps up and the cameras are proven to work consistently and reliably.

https://www.youtube.com/watch?v=Rk7ZFx7j8f8

Feel free to ask any other questions. I've already talked a bit about the test over on the other thread about Ursa Mini footage too.

 

[Marc Wielage]

Link?

 

[Kenneth C Merrill]

Link?

I'm an idiot.

 

[luigivaltulini]

What difference!!


Excuse but as you shot? 709 in camera or you have graded log in Davinci?
You can have 2 DPX, ALexa and URSA at -4 stop not graded?

 

[Fabricio Morato]

What difference!!


Excuse but as you shot? 709 in camera or you have graded log in Davinci?
You can have 2 DPX, ALexa and URSA at -4 stop not graded?

From what I understood from the video, both cameras were captured in log and slightly graded (contrast and saturation).

 

[Ryan Hamblin]

I've personally been able to pull back about 5 stops over on skin. But still hold detail that was at least two stops over that. And then under about 6 under and pull it back. So all in all with proper exposure there is detail held around 14 stops. I would for sure say Alexa gets a stop more on the top end. It's probably a 15 stop cam. It's a great time for cameras for sure

 

[Kenneth C Merrill]

What difference!!


Excuse but as you shot? 709 in camera or you have graded log in Davinci?
You can have 2 DPX, ALexa and URSA at -4 stop not graded?

All shot in log and graded in Resolve. I'm out of town now, but I might be able to host some files later.

 

[Kenneth C Merrill]

I've personally been able to pull back about 5 stops over on skin. But still hold detail that was at least two stops over that. And then under about 6 under and pull it back. So all in all with proper exposure there is detail held around 14 stops. I would for sure say Alexa gets a stop more on the top end. It's probably a 15 stop cam. It's a great time for cameras for sure

I would love to see a demonstration of this! I got no where near those numbers, and I'm wondering how you did it!

 

[Hans von Sonntag]

The interesting part of this test is how well the Alexa holds colour when under and over exposing things. The BM changes colour enormously when changing exposure. I have seen that often with the little BM Pocket cam but see now the similar behaviour with the new 4.6k camera. I think BM has still to work on their colour science.

BTW: Red Dragon behaves similar to the Alexa in this regard. Besides pleasing skin tone colour rendition and rich blacks, a convincing colour balance trough out a fairly large exposure range is the main focus point of a good camera.


Hans

 

[M.Halsell]

The modern sensor is expected to have a little more reach during periods of illumination duress. We are constantly peeking at the sensor behavior above the recommended base ISO to see the possibilities. The more expensive cameras are able to punch thru, generally with usable results.

The Exposure Index tests hints, but doesn't tell the complete story. The in-the-field, bare knuckle tests with constantly changing light levels and color temperatures will normalize the professional reputation of the camera. The greater the sample size, the quicker the feedback.

 

[luigivaltulini]

I would love to see a demonstration of this! I got no where near those numbers, and I'm wondering how you did it!

Kenneth, I think Ryan is right.

What I'm seeing now, I had a doubt!
John I think he said something about the recovery of Highlight in Davinci Resolve, DNG mode only.


If you use a ProRes files'm losing nearly 2 stops on the high lights and probably something below.! if DNG use and highlight Recovery able to recover well ..
UMM need to ask John if he had this problem too.
If this were true then the gap with ALexa is really minimal.

Prores:

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DNG

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[Ryan Hamblin]

I'll try and get around to editing something together. It will just be of the 4.6k but I spot metered everything to know levels and if I remember right I had 5 over and still held skin tone color and some detail in highlights that were 2 stops over. Color got a little sideways at that much over but I notice the 4.6k seems to try to keep skin colors correct as you go over but highlights get desaturated...On the under side it was like 6 under I think but could have went more, but for sure got some desaturation

 

[Kenneth C Merrill]

Kenneth, I think Ryan is right.

What I'm seeing now, I had a doubt!
John I think he said something about the recovery of Highlight in Davinci Resolve, DNG mode only.


If you use a ProRes files'm losing nearly 2 stops on the high lights and probably something below.! if DNG use and highlight Recovery able to recover well ..
UMM need to ask John if he had this problem too.
If this were true then the gap with ALexa is really minimal.

Prores:

[/URL][/IMG]


DNG

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I also shot in uncompressed raw and got the exact same response as ProRes.

 

[Ryan Hamblin]

I agree I feel like prores gives me almost exactly what's there in raw. I do see a little more retained in blacks but it's minimal

 

[luigivaltulini]

I agree I feel like prores gives me almost exactly what's there in raw. I do see a little more retained in blacks but it's minimal

ok so it's not the same thing as converting DNG RAW log default mode (without -100 highlight recovery) to ProRes log, and grade this prores. !!
Well, I was worried.


Kenneth good, then you can also share DNG, fantastic. I'm waiting

 

[Sam Taylor]

a convincing colour balance trough out a fairly large exposure range is the main focus point of a good camera.
Hans

This is so important, and often over looked.

 

[Jacek Zakowicz]

This is so important, and often over looked.

What do you mean?
This is just another definition of a dynamic range- the more dynamic range, the better color rendition in wider exposure range- same thing. Are you saying dynamic range is overlooked?

 

[Hans von Sonntag]

What do you mean?
This is just another definition of a dynamic range- the more dynamic range, the better color rendition in wider exposure range- same thing. Are you saying dynamic range is overlooked?

Dynamic range is mostly seen as the exposure range a sensor can handle regarding usable information. If you define colour consistency/balance over a exposure range as a measure of usable information you are right, of course (and I absolutely agree). But many see/measure dynamic range only in terms of luminance values. How one defines colour consistency as balanced or "good" is subjective like we experience with noise.

It depends a lot of the user how much colour-shift is acceptable or not. For me the colour shifts that can be seen in this tests are severe and not acceptable for most stiff I do. Others will have a different view on things, different application, see the price-tag, the client's expectations, other advantages of the particular camera.

Hans