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Formats(65mm,super35mm,super16mm etc.) and space


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#1 Panayotis Ananiadis

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Posted 13 December 2017 - 10:29 AM

Hello everyone!

 

This is my first post here about something that drives me crazy.

 

A lot is written about the three dimensionality of big formats (65mm, medium format still photo cameras etc.), but I can't find anywhere credible explanations of this "hypothesis". Could you help me with that?

 

Extending this question, I would be very grateful if you could explain to me any differences in how different camera systems render space. What are the differences in the way that 65mm/35mm/MFT/16mm cameras render space given the following parameters:

 

- Same distance from the subject

- Same angle of view

- Same depth of field

- Same characteristics/behavior of the lenses used. (hypothetically)

 

(Let's assume that we are talking about digital, because the question is not about film vs. digital differences. I used film measurements ie. 65mm for convenience' sake)

 

Thank you very much!


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#2 Stuart Brereton

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Posted 13 December 2017 - 11:34 AM

Given those parameters, there is no difference in the geometry of the frame. As part of a discussion that is going on on another site, I am in the middle of shooting some tests which should show this.

 

Here are three frames. One shot on an APS-C camera, 18mm lens, another other shot on a FF camera, 28mm lens, and a third shot on a 6x7 medium format camera, 50mm lens. Same camera position, matching depth of field, matching field of view.

FormatTest1small.jpg

FormatTest2small.jpg

 FormatTest3small.jpg

 

Here are two more. APS-C with a 35mm lens. FF with a 50mm lens. Again same camera position, matching DoF, FoV

 

APS-C.jpg

 

 

FullFrame.jpg

 

As you can see, the frames are virtually identical. 

 

There is also a series of tests by Adam Wilt over at ProVideoCoalition which demonstrate this.

 

https://www.provideo...ter-ok-but-why/

 

 

 

EDIT: Post updated to include the 6x7 image.


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#3 Panayotis Ananiadis

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Posted 13 December 2017 - 02:25 PM

Thank you very much!

Actually it was reading this article that triggered me to post here! Great job! But still, it wasn't clear for me, because they were used cameras with "not that much" size difference, that is FF, Aps-c and mft.

What would the findings be if he had compared a 65mm to a super16mm camera?
For example, shooting with the 65mm camera with a 75mm lens and with a 18mm lens on the super16 for an angle of view match, what would happen to the "wideangleshness" of the 18mm?
Does the number 18 indicate any inherent "wideangleshness" or is it just a matter of angle of view?

An hypothetical scenario again for my better understanding;
If the lens manufacturers stopped naming their lenses after their focal lenghts cause of the confusion of all the different sensor sizes that are available now, and instead named them after their angle of views (used on the specific format that are made for), would we lose any valuable information??

Thank you very much once again!
Looking forward to your medium format camera test!

Edited by Panayotis Ananiadis, 13 December 2017 - 02:26 PM.

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#4 Stuart Brereton

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Posted 13 December 2017 - 02:36 PM

FF is 4 times the size of MFT, that's a considerable difference. If there was any difference in spatial rendering, you should be able to see it. There is nothing inherently 'wide angle' about an 18mm lens. It is entirely dependent on the size of the sensor you're using. On Super 16, an 18mm would be considered a 'normal' lens.

 

Naming lenses after their focal lengths makes sense, because the focal length never changes, whereas the angle of view does. I admit it has become confusing with all the different, non standard sensor sizes out there, but you are always going to have to do some sort of mental conversion between formats, so it makes sense to stick with the one constant factor: focal length.


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#5 Panayotis Ananiadis

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Posted 13 December 2017 - 02:49 PM

It's all clear now! Thank you very much!
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#6 Panayotis Ananiadis

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Posted 13 December 2017 - 03:13 PM

I have another related question. Is there any algorithm to calculate the f/T number required to match the dof of different sensor sized cameras without the use of a dof calculator?
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#7 Stuart Brereton

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Posted 13 December 2017 - 03:23 PM

I don't know about an algorithm, but the rule of thumb is that, using s35 as a base, FF needs 1 stop more, 65mm needs 2 stops more, MFT needs 1 stop less, and s16 needs 2 stops less.

 

So:

 

Super 16 f2

MFT f2.8

Super 35 f4

FF f5.6 

65mm f8

 

It's a rough guide, but it works.


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#8 Panayotis Ananiadis

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Posted 13 December 2017 - 03:26 PM

Thanks again for the amazingly quick responses!
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#9 Phil Rhodes

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Posted 13 December 2017 - 03:32 PM

Top one looks like it might have slightly more spherical distortion and slightly more background defocus, but not to a point that I personally feel would make much odds to anyone.

 

As far as I can tell, all tests like these tend to prove that if you're trying to recreate essentially the same setup on different sensor sizes you will be using a different lens and different lenses have different specifics. This is not really a surprise and exhaustive dissection of this reality is not particularly informative or useful.

 

Not to shut down the discussion, or anything. Ahem.

 

P


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#10 Stuart Brereton

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Posted 13 December 2017 - 04:47 PM

Top one looks like it might have slightly more spherical distortion and slightly more background defocus, but not to a point that I personally feel would make much odds to anyone.

The background defocus is more likely down to this being a softer lens generally. It's not so obvious in these small frames, but at original size the whole frame is slightly softer. The spherical distortion could also be down to using a $100 kit zoom against a much more expensive prime. These differences all go make a meaningful comparison rather difficult, as there are all kinds of variables which could be contributing to a different 'look'.

 

I have an identical frame, shot with a Mamiya 6x7 camera, which I will post when I have the negs back from the lab. I suspect I know what it will show... We'll see.

 

 

 

different lenses have different specifics. 

Indeed they do. I have still frames here, from three different 35mm lenses, all on FF. The differences are marked.

 

 

 

This is not really a surprise and exhaustive dissection of this reality is not particularly informative or useful.

There are many people who apparently would be surprised, so I believe that some discussion is necessary to separate reality from the marketing hype surrounding 'large' format digital cinema.


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#11 Phil Rhodes

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Posted 14 December 2017 - 02:29 AM

I'm torn between the attitude that it isn't my job to persuade everyone else out of their dubious obsessions, and the fact that I prefer to live in a world where decisions are made based on rationality. Oh, dear, that's a shame, then...

 

Anyway, to the point at hand, I would expect that anyone making a claim (and "big sensors give more roundness" is a claim) to provide three things:

 

- Details of what the claim refers to and how to measure its effects ("I notice that this image is rounder than that image and here is how I determined that...")

- A hypothesis describing a potential mechanism which would lead to these effects ("I think this is caused by the following factors...")

- Repeatable, documented experiments which would demonstrate the accuracy of the hypothesis ("My hypothesis is accurate because I tried X and Y happened, which could not be plausibly explained by other factors.")

 

This is not a big ask, it is basic investigatory protocol.

 

From what I've seen almost none of the discussion of big-format stuff has done anything except post comparative images and make vague claims about them using terminology that as far as I'm aware is not formally defined anywhere.

 

The closest we've had has been here when we actually talked about defocus and the objective differences between different lenses.

 

I am not very interested in beret-wearing, arm-waving discussion of ill-defined concepts such as "roundness" in a context where that term is essentially undefined and nobody is even attempting to define it, let alone develop a theory about how it works.


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#12 Stuart Brereton

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Posted 14 December 2017 - 06:15 PM

I suspect that eventually tests will be done which will attempt to control for all of the myriad variables, and we'll arrive at the conclusion that it's all down to the lenses. Larger sensors allow for different lens designs which can have a subtle effect on spacial rendering, much as different design s35 lenses can do the same. Whether or not that difference is worth the additional expense of shooting with an Alexa 65 or PV DXL is a question that line producers will be scratching their heads over for years to come.


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