Simple Alexa 65 Sensor Questions for the Pro's out here :)

[Iggy Heringa]

Hey guys,

I was reading up on some old saved articles today and came across the following: 

https://www.indiewire.com/feature/large-format-cameras-arri-alexa-65-film-language-joker-roma-midsommar-1202179944/

In my opinion there's a ton of misinformation present in this article and my understanding of the matter fully aligns with Lewis Ward's comment at the bottom of the article stating: 

"Rendering of space does not change across different formats. If you use equivalent focal lengths on s35mm, Full Frame or 65mm, they will all look the same".

Medium Format sensor cams with 65mm lenses have a number of advantages over more traditional combinations but they don't compress space any differently. It's all a matter of field of view. 

The article got me thinking deeper about 65mm and I have the following question: Isn't the biggest differentiating factor of a (Alexa) 65mm camera really the large sized sensor with the unusual wider aspect ratio of about ≈2.1:1 (as opposed to the more common 3:2 sensors)? 

In other words, if I understand correctly, the widest primes that cover the  Alexa 65's image circle will have extra width available that traditional Super35/Full Frame would not be able to achieve, correct?

And thus Alexa 65mm format has some of the horizontal compositional qualities of Anamorphic by means of spherical glass, correct?

Here's a link showcasing common sensor sizes: 

https://www.studiodaily.com/2018/07/download-phil-hollands-digital-film-sensor-chart/

I would love for someone to simply pitch in and let me know wether my thinking on all this is correct. I have no one to talk to about this stuff other than you guys here ?

Thanks so much and best wishes!!

 

 

 

[Albion Hockney]

Most people would say the biggest differentiating factor is depth of field.

A good way to visualize this is to imagine what the image sensor of the camera can see. So lets say you have a 35mm @f2.8 lens that covers a full frame sensor

First you place it on a super 35mm camera, then on a full frame camera. on the full frame camera the only difference is the sensor captures a bigger/wider image utilizing the whole lens. So what you get is the exact same depth of field, BUT a much wider aspect, which in turn gives you the effect of shallower depth of field. on full frame photo cameras the difference is 2 stop of depth of field. Meaning you would need not only a wider lens, but a faster lens to match the look of  35mm F2.8 on a full frame.

As for aspect ratio. Sure if you have a wider sensor you get a wider aspect ratio, but you can of course simply crop on taller sensor as well.

as for width or FOV (field of view) differences. You can always use wider lenses. the widest super 35mm lens I know is the Arri 8R. On full frame there are 12mm lenses (maybe wider?) so maybe you can get a touch wider on full frame. For the Arri 65 I'm not familiar with the options.

At  the end of the day the biggest difference with shooting on larger sensors is resolution, and an easier ability to achieve shallow DOF or extreme shallow DOF effects.

 

[David Mullen ASC]

There are lenses of various focal lengths to achieve a wide range of field of views in all formats. There aren’t fields of view that only a 65mm sensor can achieve.

[David Mullen ASC]

If you like the wide view of the 28mm ARRI DNA lens on an Alexa 65 (about 87 degrees horizontal) you’d just use a 14mm lens on a regular Alexa in Open Gate.

[Dom Jaeger]

There was a lot of somewhat misinformed hype about large format digital cinema cameras when they first arrived, claiming various unique attributes that have since been pretty much debunked. As you say, you can more or less match the same shot with different sized sensors by simply switching focal lengths and there is no discernible difference, outside of the differences inherent in the lenses.

Some people have argued that you can get wide angle shots with less distortion on a large sensor because you use a longer focal length,  but the truth is that wide angle distortion is a function of angle of view, rather than focal length. It’s also a function of individual lens design, so for example an Ultra Prime 8R on S35 will actually distort less than a repurposed medium format 24mm on Alexa 65 and give a wider angle of view. 

There may be certain circumstances where it’s impossible to match a shot created with a fast lens on a large sensor, because to match the depth of field would require opening up the smaller format lens beyond its maximum aperture.  But often large format lenses are slower than S35 lenses, so it’s a moot point. That is starting to change with new lens designs.

The wider aspect ratio of Alexa 65 sensors does lend itself to more widescreen formats, but people crop sensors all the time to get different aspect ratios. And often Alexa 65 footage might be mixed with S35 or IMAX. However most shows using Alexa 65 are probably 2.35 widescreen, or 2:1 which has become a popular streaming format.

As far as allowing for wider angles, as David has just mentioned, any Alexa 65 angle of view can be matched by other formats. Because it’s a pretty niche format that often uses re-purposed medium format glass, there aren’t many extreme wide angle options compared to S35. I think 24mm may currently be the limit for A65, which is not nearly as wide as the Ultra Prime 8R for S35 as mentioned before.

[Dom Jaeger]

I should add, the main difference with larger sensors of course is usually more resolution, but then there are cameras with smaller sensors than Alexa 65 that actually have more photo sites, so that’s not always true.

[Iggy Heringa]

Excellent, excellent! Thanks so much for these answers guys ? They're exactly what I wanted to hear and they confirm what I hoped to be confirmed. As stated in my original message, the author of the article I linked to has no understanding of the matter ?

Some extra notes, research I did in the meantime (and that I should have probably done before my original post) :

 

Here are some quick notes from inputting research into my pCam app:

 

Field of view of widest existing lenses:

Arri S35, Widest 8mm gives a 120 degree horizontal FOV.

ARRI LF, Widest 12mm gives a 113 degree horizontal FOV.

ARRI 65, Widest 21mm gives a 105 degree horizontal FOV.

In other words, the widest achievable field of view on “conventional”  cine lenses appears to be achievable on Super35 designed sensors.

Of course the usage of such wide focal lengths is rare'ish! ?

As for depth of field, the Arri 65mm 1.8 DNA lens would probably be the toughest to find an equivalent full frame or super 35 lens for, to match the depth of field. However,  the 0.7 and 0.95 lenses in super35 for example should not be too far off (don’t know the exact conversion ratio from the Alexa65 sensor to super35 and full frame to calculate more precisely.

Nonetheless, besides field of view and depth of field, there are generally numerous advantageous elements to the larger sensors of course (lower noise, better color depth, resolution, dynamic range, etc) which is the primary reason for using them.

If I write anything incorrect, please be sure to correct ?

 

 

[Iggy Heringa]

38 minutes ago, David Mullen ASC said:

If you like the wide view of the 28mm ARRI DNA lens on an Alexa 65 (about 87 degrees horizontal) you’d just use a 14mm lens on a regular Alexa in Open Gate.

Agreed, I am familiar with quickly doing these conversions in my head. Including matching the appropriate apertures ? 

[Iggy Heringa]

30 minutes ago, Dom Jaeger said:

There was a lot of somewhat misinformed hype about large format digital cinema cameras when they first arrived, claiming various unique attributes that have since been pretty much debunked. As you say, you can more or less match the same shot with different sized sensors by simply switching focal lengths and there is no discernible difference, outside of the differences inherent in the lenses.

Some people have argued that you can get wide angle shots with less distortion on a large sensor because you use a longer focal length,  but the truth is that wide angle distortion is a function of angle of view, rather than focal length. It’s also a function of individual lens design, so for example an Ultra Prime 8R on S35 will actually distort less than a repurposed medium format 24mm on Alexa 65 and give a wider angle of view. 

There may be certain circumstances where it’s impossible to match a shot created with a fast lens on a large sensor, because to match the depth of field would require opening up the smaller format lens beyond its maximum aperture.  But often large format lenses are slower than S35 lenses, so it’s a moot point. That is starting to change with new lens designs.

The wider aspect ratio of Alexa 65 sensors does lend itself to more widescreen formats, but people crop sensors all the time to get different aspect ratios. And often Alexa 65 footage might be mixed with S35 or IMAX. However most shows using Alexa 65 are probably 2.35 widescreen, or 2:1 which has become a popular streaming format.

As far as allowing for wider angles, as David has just mentioned, any Alexa 65 angle of view can be matched by other formats. Because it’s a pretty niche format that often uses re-purposed medium format glass, there aren’t many extreme wide angle options compared to S35. I think 24mm may currently be the limit for A65, which is not nearly as wide as the Ultra Prime 8R for S35 as mentioned before.

Agree entirely with everything you wrote. Thanks so much for writing this out in detail ?  It's crazy how many people (and some filmmakers) are still very misinformed on this topic by the way. 

[Albion Hockney]

there are lots of rare wideangles new and old so I'm not sure your estimates are totally correct.

Here's the widest full frame option I've seen, though its not a "cine lens", I'm sure it could be converted.

https://petapixel.com/2020/06/30/the-laowa-9mm-f-5-6-is-the-worlds-widest-rectilinear-full-frame-lens/

 

[Dom Jaeger]

Yeah there are all sorts of new lenses coming out these days, and there were aspherons and other weird adapters back in the day that allowed for ultra wide (if very distorted and chromatically aberrated) images. Those older ultra wide lenses or attachments were never very rectilinear, which was why the 8R was such a breakthrough. But that’s 20 odd years old now.

That Laowa is full frame, it wouldn’t cover Alexa 65. But that is ridiculously wide!

At a certain point, to keep the image rectilinear, wide angle lenses distort the edges so much that it’s simply a different type of distortion to fish eye. Note how odd the figures look towards the edges of some of those images. I’m sure it’ll be popular with real estate listings though!

[Bonjoe Tom Isaiah]

Correct me if I am wrong I am just a noob, but there is a advantage of using an alexa 65  or bigger sensors from a practical pov I think.

For example if you need to shoot a face, how close the lens is to the face is a huge factor to how the image is perceived so with an alexa 65 you can use a  longer lens than an s-35 to get closer and get the image, but if you are using an S-35 you would have to use a wider lens which would comparatively start bringing distortion, Or else on a S-35 you would have to move back which starts to bring more of a voyuerstic feel.

[Karim D. Ghantous]

19 hours ago, Bonjoe Tom Isaiah said:

Correct me if I am wrong I am just a noob, but there is a advantage of using an alexa 65  or bigger sensors from a practical pov I think.

For example if you need to shoot a face, how close the lens is to the face is a huge factor to how the image is perceived so with an alexa 65 you can use a  longer lens than an s-35 to get closer and get the image, but if you are using an S-35 you would have to use a wider lens which would comparatively start bringing distortion, Or else on a S-35 you would have to move back which starts to bring more of a voyuerstic feel.

I mean this with respect, but everything you wrote is incorrect. Don't worry though, because a lot of people actually believe that longer focal lengths offer a more flattering perspective than shorter ones. That is in fact not true. Focal length does not compress or stretch perspective. Only distance does that. It's a hard fact about optics and geometry.

Bigger sensors bring bigger problems: higher price tags, bigger lenses, longer sensor read-out times, insufficient DOF, possibly more power consumption, and bigger cameras. So, if those are the side effects, the main effects have to outweigh them. And the main effects should be resolution, DR, and sensitivity.

There are certain kinds of lenses called front-telecentric lenses. This means that they take all incoming light in parallel, rather than an angle. So all apparent distance between objects disappears. They are used for industrial applications. They have limitations, though, so there is no free lunch. I have never used one or seen one, but I am told that they exist.

[David Mullen ASC]

On 10/4/2023 at 1:08 AM, Bonjoe Tom Isaiah said:

Correct me if I am wrong I am just a noob, but there is a advantage of using an alexa 65  or bigger sensors from a practical pov I think.

For example if you need to shoot a face, how close the lens is to the face is a huge factor to how the image is perceived so with an alexa 65 you can use a  longer lens than an s-35 to get closer and get the image, but if you are using an S-35 you would have to use a wider lens which would comparatively start bringing distortion, Or else on a S-35 you would have to move back which starts to bring more of a voyuerstic feel.

As Karim points out, you are incorrect. Perspective / distortion / compression of a face has nothing to do with focal length, it had to with the camera to subject distance. Focal length just provides the field of view. So you can match camera distance and field of view between two formats and get the same perspective on a face in close-up, and what you'd mainly see is a difference in depth of field.

 

 

[Benjamin Reece]

Quote

As Karim points out, you are incorrect. Perspective / distortion / compression of a face has nothing to do with focal length, it had to with the camera to subject distance. Focal length just provides the field of view. So you can match camera distance and field of view between two formats and get the same perspective on a face in close-up, and what you'd mainly see is a difference in depth of field.

This is the magic quote and understanding I have been looking for, without knowing it. Mind blown. All these years without this understanding. Totally makes sense now that I hear/see it. 

So if I understand this correctly, it might feel like wider focal lengths distort the face more, but that is simply because the lens/sensor is moved closer to the human face to fill the frame then a more narrow focal length would need to. On a larger sensor with lets say larger resolution and higher pixel pitch, you could crop those between the two and it should almost exactly the same given the same optical design and external conditions. 

Thank you both for this clarity! It makes my 25MM vs 27MM master prime thread/question almost irrelevant given my concerns. 

[David Mullen ASC]

The distortion of facial features from being too close isn't even a camera issue, it happens with your own eyes.  Forget about a face for a moment and imagine being on a hilltop looking at a distant mountain and in the foreground next to you is a medium-sized boulder.  As you kneel down and get closer to the boulder, it gets bigger in your vision relative to the distant mountain.

It's the same with a face, at a distance, the relative sizes of the nose compared to the ears is small compared to their distance to you, but get very close and the distance from you to the nose might be the same as the distance from the nose to the ears, making the nose bigger relative to the ears.

So the sizes of the facial features at, let's say, one foot away, whether the lens is a 10mm or a 1000mm, are the same -- it's just that the 1000mm lens can't hold the whole face in the frame.  However if you panned around with the 1000mm lens and shot pieces of the face and then stitched it together, you'd see the whole face with the same facial distortions as the 10mm lens.

[Benjamin Reece]

Yes. Love that analogy. Fully absorbed and "grokked" as they say in the software engineering world. Thank you David. Such a powerful piece of knowledge.