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Camera Sensor Size?


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#1 cogitonz

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Posted 23 March 2014 - 09:07 PM

Hi there

Can anyone tell me what size sensor the moviestorm cameras simulate?

Obviously the angle of view that a particular lens' focal length gives us is totally different depending on the size of the camera's image sensor.

A 20mm lens is completely different when placed on a micro four thirds camera than it is on a super35 movie camera (like a Red Epic), or a full-frame Canon 5D for example.

In order for us to calculate the correct crop-factors and angles of view it would be great to know which camera format the moviestorm cameras are currently.

In the future it would an excellent feature addition to be able choose between different formats of cameras so that we can really know which lenses in the real world match what we have prevized in Moviestorm. Such a list should at least include things like 1/3 inch video camera, 2/3 inch video camera, 16mm film, micro four thords, super35mm film, full frame 35mm stills format, etc. Even better would be to throw some actual real world cameras into the list as well for the slight differences that exist, eg Arri Alexa, Red Epic - MX, Red Epic - Dragon. And of course a custom option so we can define sensor sizes for the future.

cheers

#2 Ben_S

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Posted 24 March 2014 - 01:11 PM

The numbers on the lens slider are the focal lengths that would give that equivalent field of view on a 35mm film.


Edit - supposing whoever wrote this function got their math right:
CODE
    public void setLens35mmEquiv(float length)
    {
        setFOVrads(2 * (float) Math.atan(24 / (length*2)));
    }

It confuses me a little as to how there is no '35' in that function.

Moviestorm's camera fov is vertical, and we use 16:9 screens. I understand that 35mm film was based on width, rather than height, but that still does not make sense to me yet.

Ben Sanders
Moviestorm Ltd

#3 cogitonz

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Posted 24 March 2014 - 08:10 PM

QUOTE (Ben_S @ Mar 24 2014, 1:11 PM) <{POST_SNAPBACK}>
The numbers on the lens slider are the focal lengths that would give that equivalent field of view on a 35mm film.


Edit - supposing whoever wrote this function got their math right:
CODE
    public void setLens35mmEquiv(float length)
    {
        setFOVrads(2 * (float) Math.atan(24 / (length*2)));
    }

It confuses me a little as to how there is no '35' in that function.

Moviestorm's camera fov is vertical, and we use 16:9 screens. I understand that 35mm film was based on width, rather than height, but that still does not make sense to me yet.



Thanks Ben,

Actually that does make some sense, as the 'sensor' size of full-frame 35mm stills format is actually 36mm x 24mm. That's why there is a 24 in the formula and no 35.
It is an interesting choice to go with 35mm stills format as the camera type though. Its not used in professional shoots and until the Canon 5D mk2 came out it wasn't possible to shoot video on at all.

I'd love to see an option to select lenses for a super35mm camera sensor.




#4 cogitonz

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Posted 25 March 2014 - 12:40 AM

QUOTE (cogitonz @ Mar 24 2014, 8:10 PM) <{POST_SNAPBACK}>
Thanks Ben,

Actually that does make some sense, as the 'sensor' size of full-frame 35mm stills format is actually 36mm x 24mm. That's why there is a 24 in the formula and no 35.
It is an interesting choice to go with 35mm stills format as the camera type though. Its not used in professional shoots and until the Canon 5D mk2 came out it wasn't possible to shoot video on at all.

I'd love to see an option to select lenses for a super35mm camera sensor.



Actually, thinking about this further...

Let's assume Moviestorm works by setting the vertical height of the sensor to the traditional 35mm still format vertical height of 24mm. The normal full frame 35mm stills format was a 3:2 aspect ration (36mm x 24mm). But since Moviestorm is (of course) giving us a 16:9 aspect ratio camera, I would assume then that the horizontal measurement is 42.66mm.

Most digital full frame cameras, when taking video, reduce the vertical height of the sensor in order to create a 16:9 format. eg the Canon 5D uses a 36 x 20.3mm sensor.

So there is a crop factor of about 1.19 between Moviestorm's camera and shooting on a full frame DSLR. ie A 50mm lens on a Canon 5D would be the equivalent to a 59mm lens in Moviestorm.

Can anyone confirm this or provide any firmer information?

cheers









#5 Ben_S

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Posted 25 March 2014 - 01:38 PM

That would make sense - I was not aware that the 35mm film was 3:2 aspect ratio.

From that point of view, if set the aspect ratio in the camerawork view (via dropdown from the triangle on the big camerawork button) to 3:2, that will crop the image on the left and right, and should leave you with the 35mm equivalent.

Sadly Moviestorm still only renders in 16:9, so you would need to use a video editor to do similar cropping to get that framing if you wanted your final video to be 3:2.

-----------------------------------------------

HOWEVER, I've noticed that the 'setLens35mmEquiv()' function is not actually used in combination with the lens slider.

The value shown on the lens slider is calculated as:
50 / (2 * Math.tan (framing.getKeyFOV ()))
I'm not convinced that that means anything useful.

The FOV in Moviestorm should be the angle between the top of the frame and the bottom of the frame, and the camera position (ie the lens).
And we should know the lens height for a particular filmstock - then we should have, borrowing a nice wiki page on trig and using it's labeled triangle in the diagram:
A*2 == fov
b == lens length (should be the value shown on the slider)
a*2 == lens height (ie 24mm when using 3:2 35mm film)
b = a / tan (A)
lens length = lens height / (2 * tan (fov/2)

We could also base it on the lens width; lens height = lens width *9/16

Does my trig make sense? I think a failure to divide the angle by two in the current code may mean that the number painted on the lens slider does not actually mean anything useful, I'm afraid.

And if it is just not currently useful, then it would be a good idea for me to fix it. What sort of film/camera sensors would one want to see lens lengths for?
Ben Sanders
Moviestorm Ltd

#6 cogitonz

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Posted 25 March 2014 - 08:24 PM

QUOTE (Ben_S @ Mar 25 2014, 1:38 PM) <{POST_SNAPBACK}>
That would make sense - I was not aware that the 35mm film was 3:2 aspect ratio.

From that point of view, if set the aspect ratio in the camerawork view (via dropdown from the triangle on the big camerawork button) to 3:2, that will crop the image on the left and right, and should leave you with the 35mm equivalent.

Sadly Moviestorm still only renders in 16:9, so you would need to use a video editor to do similar cropping to get that framing if you wanted your final video to be 3:2.


That makes sense, except of course that in practice no body actually wants 3:2 ratio video. 3:2 was only ever a still photography format, never a movie or video aspect ratio. So always rendering 16:9 is absolutely the correct thing for Moviestorm to do, in my opinion.



QUOTE (Ben_S @ Mar 25 2014, 1:38 PM) <{POST_SNAPBACK}>
-----------------------------------------------

HOWEVER, I've noticed that the 'setLens35mmEquiv()' function is not actually used in combination with the lens slider.

The value shown on the lens slider is calculated as:
50 / (2 * Math.tan (framing.getKeyFOV ()))
I'm not convinced that that means anything useful.

The FOV in Moviestorm should be the angle between the top of the frame and the bottom of the frame, and the camera position (ie the lens).
And we should know the lens height for a particular filmstock - then we should have, borrowing a nice wiki page on trig and using it's labeled triangle in the diagram:
A*2 == fov
b == lens length (should be the value shown on the slider)
a*2 == lens height (ie 24mm when using 3:2 35mm film)
b = a / tan (A)
lens length = lens height / (2 * tan (fov/2)

We could also base it on the lens width; lens height = lens width *9/16

Does my trig make sense? I think a failure to divide the angle by two in the current code may mean that the number painted on the lens slider does not actually mean anything useful, I'm afraid.

And if it is just not currently useful, then it would be a good idea for me to fix it. What sort of film/camera sensors would one want to see lens lengths for?


Your trig is over my head, but it all sounds good:)

Basing the calculation on sensor height rather than width may be a good idea, as that usually holds constant on a camera, and just the vertical crops when switching between 16:9 and 2.35:1 (for example).

If you were to add actual film/camera sensors into the moviestorm camera, then my first recommendation would be to start by only listing 16:9 formats. Most cameras only shoot that these days, we can always mask to something else (like 2.35) and that's what we want for editing anyway. More formats can always be added later. (And lets ignore the pain of anamorphic for now)

In terms of which cameras to list, my suggestion is to start with:


Super35 - pretty much the professional standard these days. Only headache is that no two 'super35' sized cameras actually have the exact same sized sensor. They are all slightly different. No one could blame you for just picking an average and using that. It is also close enough the 'crop sensor' (APS-C) sized DSLR cameras that it could represent them as well (even they differ in their sensor sizes between cameras). Later if you wanted to offer really accurate options, then instead of just a generic 'super35' you could break it down into its most popular members: eg. super35mm film, APS-C sized DSLRs, Arri Alexa, Red Epic-MX, Red Dragon etc (there are even sub formats within the one camera too...)

Full Frame Stills 35mm (36mm x 20.3mm) - for the DSLR crowd.

micro four thirds - becoming very popular

2/3 inch video chip - used to be the professional video format back before 'digital cinema'

1/3 inch video chip - consumer video cameras

16mm film - for the legacy hipsters and the digital bolex modern hipsters



hope that is of some help,

cheers













#7 Ben_S

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Posted 27 March 2014 - 06:27 PM

Right, been having a bit of a read, and found some reasonable looking explanations here:
http://cvp.com/index...size comparison

Do these look like the dimensions you might expect for different lenses? Are there ones missing that you would expect to be there?
Ben Sanders
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#8 cogitonz

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Posted 28 March 2014 - 09:18 AM

QUOTE (Ben_S @ Mar 27 2014, 6:27 PM) <{POST_SNAPBACK}>
Right, been having a bit of a read, and found some reasonable looking explanations here:
http://cvp.com/index...size comparison

Do these look like the dimensions you might expect for different lenses? Are there ones missing that you would expect to be there?



That list looks pretty good to me, in fact no one would blame you for not doing the entire list. If you wanted to ever go further I think it would just be a matter of added more specific formats in the Super35 subcategory, and perhaps the APS-C categories. Those are terms that are hiding a few minor variations. For example the Red Epic has several recording formats available, all of which use a different size piece of the sensor. But its probably simpler to stick with these measurements.

Just remember that these sensor sizes listed are not necessarily 16:9, when cameras are put into video mode they crop the vertical measurement to create a 16:9 image. So keep the horizontal number constant and just adjust the vertical to get our desired 16:9

cheers


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