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"New" super-8 camera to market


Lasse Roedtnes
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I'm not sure I understand why C-mount lenses should be regarded as limiting one to "telephoto" shots in Super8.

 

If, for example, the "standard" lens for Super8 is 15mm, then for "standard" shots on Super8 one obtains and uses a 15mm lens. It doesn't matter whether that 15mm lens was designed for larger format cameras. All it means is that on a larger format camera the 15mm gives a wider angle of view.

 

If one wants the same wider angle view on Super8 then one just gets a lens with a shorter focal length.

 

C

Exactly Carl,

 

What we learned in the advanced photographic courses at the university is that: There is a simple math formula, if you want to decide a normal lens for an image format covered, you should take the format's diagonal into account, e.g. normal lens = √a2+b2, where a - width, b - height or vice versa. The results can be fractional, so the numbers are rounded.

 

The focal length never changes in a lens for any format, but the angle of view.

Edited by Erkan Umut
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Exactly Carl,

 

What we learned in the advanced photographic courses at the university is that: There is a simple math formula, if you want to decide a normal lens for an image format covered, you should take the format's diagonal into account, e.g. normal lens = √a2+b2, where a - width, b - height or vice versa. The results can be fractional, so the numbers are rounded.

 

The focal length never changes in a lens for any format, but the angle of view.

 

Yes, that's a good definition of "normal". Using that definition a "normal" lens on Super8 would be:

 

sqrt( 5.69^2 + 4.22^2) = sqrt( 50.1845 ) = 7mm (rounded)

 

However, it doesn't really matter what focal length you call "normal" - the important point is that all lenses of the same focal length will give you the same angle of view on a given camera. So for example, any 7mm lens, whether it was made for Vistavision cameras, or for 35mm cameras, or for 16mm cameras, they will all give the same angle of view on Super8.

 

And if that angle isn't wide enough for what you are after then you just get a wider one.

 

 

Carl

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Exactly Carl,

 

What we learned in the advanced photographic courses at the university is that: There is a simple math formula, if you want to decide a normal lens for an image format covered, you should take the format's diagonal into account, e.g. normal lens = √a2+b2, where a - width, b - height or vice versa. The results can be fractional, so the numbers are rounded.

 

The focal length never changes in a lens for any format, but the angle of view.

Pythagoras was way ahead of his time :)

It is simply the diagonal of the rectangle of the image. Works when it is not too panoramic.

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However, it doesn't really matter what focal length you call "normal" - the important point is that all lenses of the same focal length will give you the same angle of view on a given camera. So for example, any 7mm lens, whether it was made for Vistavision cameras, or for 35mm cameras, or for 16mm cameras, they will all give the same angle of view on Super8.

 

Carl,

 

Are you sure?

I am not.

 

Some years ago, I've rented a Super16 camera package from a house. They have all my selections for the lenses, but one. They offered me a 35mm format lens instead of. The one not available and the offered were the same F/. Then I suspected of that lens giving me the angle of view I want.

 

So I have posted on Cinematography.com and the best answer came from Mr. David Muellen, ASC, who is very knowledgeable DoP and seen on the posts mostly.

 

Any lens made for a format, when used in a smaller format than its created for gives narrower angle of field!

 

Any thoughts?

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Carl,

 

Are you sure?

I am not.

 

Some years ago, I've rented a Super16 camera package from a house. They have all my selections for the lenses, but one. They offered me a 35mm format lens instead of. The one not available and the offered were the same F/. Then I suspected of that lens giving me the angle of view I want.

 

So I have posted on Cinematography.com and the best answer came from Mr. David Muellen, ASC, who is very knowledgeable DoP and seen on the posts mostly.

 

Any lens made for a format, when used in a smaller format than its created for gives narrower angle of field!

 

Any thoughts?

 

 

David Mullen is right, but what he is saying is different from I am saying. We're both correct. What I said is:

 

All lenses of the same focal length will give you the same angle of view on a given camera

 

So by way of elaboration, each of the following statements are true:

 

All lenses of the same focal length will give you the same angle of view on Super8

All lenses of the same focal length will give you the same angle of view on 16mm

All lenses of the same focal length will give you the same angle of view on 35mm

 

The reason why is, as Andries said, due to Pythagorus

 

As a way of getting a handle on this lets look at how angle of view is worked out. As we'll see it doesn't matter what camera we use. Each camera will give you a different angle of view (which is what David Mullen is saying). But for a given camera there are no other variables, other than focal length, which determine the angle of view.

 

The equation for horizontal angle of view is:

 

angle = 2 inverse tan( 0.5 w / F)

 

w - width of film

F - focal length

 

 

That's it. Since the frame width of a given camera remains the same, the only variable here is the focal length. There are no other variables. There is a fixed relationship between focal length and angle of view for a given camera.

 

For a Super8 camera, with a 7mm lens, the horizontal angle of view is (regardless of what camera the lens was designed to mate with):

 

angle = 2 inverse tan( 0.5 * 5.69 / 7)

angle = 2 inverse tan( 2.845 / 7 )

angle = 2 inverse tan ( 0.4064)

angle = 2 * 22.11 degrees

angle = 44 degrees (rounded)

 

Carl

Edited by Carl Looper
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Wow, Carl and S8 Booster thanks a lot!

When it comes to the math formulas and pictures, I am dying for them :rolleyes: .

 

Some years ago I had began to read the Arthur Cox, Sidney F. Ray and D. F. Horne's books, as well as some excellent Russian books but quit. The books are excellent while complicated...

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It is actually Norwegian but it is certainly translated from the book your refer to or another in the category.

Can not remember which one. Too long time since I borrowed it and did this scan to remember. Just thought of it as the "Bible" of film making :)

 

Shoot....

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Note that in the diagram it is a 7mm lens that gives a 44 degree fov on Super8, but a 12.5 mm lens that gives a 44 degree fov on a 16mm camera.

 

Lets check this against the same equation used in previous post. We want to know the angle of view, for a 12.5mm lens (F), on a 16mm camera, ie. where the camera width (w) is now 10.26mm

 

angle = 2 inverse tan( 0.5 w / F)

 

angle = 2 inverse tan( 0.5 * 10.26 / 12.5)

angle = 2 inverse tan( 5.13 / 12.5 )

angle = 2 inverse tan ( 0.4104)

angle = 2 * 22.3 degrees

angle = 44 degrees (rounded)

 

To be understood from this is that a 12.5 mm lens, regardless of which camera it is designed (be it 8mm, 16mm, or 35mm etc), when used on a film with a 10.26mm frame width (ie. on a 16mm camera), will give a 44 degree angle of view.

 

Note that independant of field of view, a lens can vignette, so a 12.5mm lens designed for an 8mm camera, while it will give a 44 degree angle of view on a 16mm camera, may not have enough image area to actually image all of that field of view, ie. the corners of the frame can be empty (black).

 

The equations are not from any book on photography by the way. They are derived from Ancient Greek formulas, the same formulas that camera designers would used when specifying lenses in the first place. We can see why a lens is marked in terms of focal length instead of field of view. The frame width variable belongs to the camera. The focal length variable belongs to the lens. The angle of view is a function of both camera and lens.

 

Carl

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The equations are not from any book on photography by the way. They are derived from Ancient Greek formulas, the same formulas that camera designers would used when specifying lenses in the first place. We can see why a lens is marked in terms of focal length instead of field of view. The frame width variable belongs to the camera. The focal length variable belongs to the lens. The angle of view is a function of both camera and lens.

 

What a simple and yet well enough description... Many thanks!

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The formula for angle of view used was derived from the following.

 

Consider the following description of a triangle, where we can imagine a lens occupying the point A, and half the frame width being the length of the edge labelled a (opposite) and the focal length being the length of the edge labelled b (adjacent)

 

288px-Trigonometry_triangle.svg.png

 

From trigonometry we have the following relation:

 

c0dd18b51a2d4e39c12f9461a485e1b0.png

 

 

Substituting focal length (F) for b and half film width (0.5 w) for a we get:

 

tan A = a/b

tan A = F / 0.5 w

 

Rewriting for A we get:

 

A = inverse tan( F / 0.5 w)

 

And since A is only half the field of view we need to multiply it by 2 to get the full field of view:

 

fov = 2A = 2 inverse tan ( F / 0.5 w)

 

 

C

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So, what I think is, to be able to get the same FoV (AoV) on a S8 camera with a lens designed for 16mm format, that lens could be placed closer to the film/focal plane theoretically (not in practice). (?)

 

Yes that's very true. The focal length of a lens is the theoretical length between lens and film. If the lens were replaced with a pin hole it would also be the length in actual practice.

 

Since the Super8 frame is smaller than a 16mm frame, you would have to move a pin hole closer to a Super8 frame to obtain the same angle of view on a 16mm frame.

 

C

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Yeap, I was thinking the same... :D

 

lj0k.jpg

 

In the diagram there is NO DIFFERENCE in angle of view between what the Super8 images and what the 16mm images.

 

What differs between Super8 and 16mm plane is just the focal length.

 

To obtain the same angle of view in Super8 as you would in 16mm, you would not decrease the angle of view - either in theory or in practice.

 

You would decrease the focal length.

 

A theory that doesn't work in practice would be a theory that is not a very good one. :)

 

Carl

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If one wants the same wider angle view on Super8 then one just gets a lens with a shorter focal length.

 

Yes, but do you know what a 2.5mm C-mount lens costs? 1K and up! *THAT* is the problem.

 

 

So for example, any 7mm lens, whether it was made for Vistavision cameras, or for 35mm cameras, or for 16mm cameras, they will all give the same angle of view on Super8.

 

Wrong. A smaller format will crop to a smaller portion of the same lense's light circle, and thus to a smaller part of the angle of vision, which is "how much you see". The smaller your format, the less you see at the very same focal length. Which is why the format factor is also known as the crop factor. Moving the imaging plane back and forth within the camera won't help you much because the focal plane for a lens is very limited. That's very, very basic optics, easy enough for even me to understand, as it's been the reason for countless years of frustration for me.

 

Allow me to present exhibit A:

 

Format_Factor.gif

(Comparison of field of vision at identical focal length at 35mm Full-Format (above in blue) and a sensor at a size roughly equivalent to DX (below in red). The difference in field of vision (cf. the flowers not being fully imaged within the red rectangle) is due to the different format size, or in other words because the sensor is physically smaller than the 35mm format.)

 

Exhibit B:

 

595px-Full-frame_vs_APS-C.svg.png

(Comparison of field of vision between 35mm Full-Format and APC-C.)

 

Exhibit C:

 

LensCropFactor.png

(Pic that's just beyond me that explains the geometrical math behind the crop factor due to smaller format size. And still even I get what the format aka crop factor is.)

 

QED. I rest my case.

 

You may have been thinking of the common misconception that a wider lens messes with perspective of the overall picture. That's actually wrong because once you crop the picture taken with a wide lens to the area of the image you woulda gotten with a longer lens, you'll see that perspective within the cropped area is the same as if taken with the longer lens to begin with.

 

The reason why people perceive an image with an extremely wide lens as exhibiting a distorted perspective is because if you use an extremely wide (rectilinear) lens, the resulting image will show extremely converging lines the more you get from the image's center to the outer areas, which the human brain perceives as perspectual foreshortening. Once your lens is longer than the human field of vision, humans will perceive it as distorted, although entirely different from the distortion seen in fish-eyes.

Edited by Benjamin Dietze
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Moving the imaging plane back and forth within the camera won't help you much because the focal plane for a lens is very limited (even if you use a focussing ring).

 

That, BTW, goes for the size-decreased side of the lens. It's different for the size-enlarged side, which is why projector-screen distance is much more variable.

Edited by Benjamin Dietze
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Benjamin is right for me, Carl, thou I couldn't open the images he is attached.

 

The perspective never changes if you don't alter the subject to camera distance (for example zooming, you crop from the image size, like enlarging a part of a picture, in contrast to dollying/traveling). I know this good, because its my business, as well as I teach it at the university in cinematography classes. Wide angle lenses tend to create fake perspective visuals. But what changes with wide angle lenses is the closer subjects to camera gets bigger faster relative to the rest. Normal and esp. Telephoto lenses show this very less compared to the W/A.

Edited by Erkan Umut
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By the way, I am tired of this Editing limitation (so short)!!!

 

Maybe, it would be better to move our discussion to the another newly added topic, some people following the post might be angry. They are right, we done it so detailed in optics. Also, by doing this, some other people may even join who doesn't follow this topic...

Edited by Erkan Umut
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Without Benjamin's pictures I have no idea how to correct any mistakes he's made. He's not being very clear in his words.

 

Everything I've said is absolutely 100% correct.

 

What I do suspect is that Benjamin is not taking into account what was said about vignetting. If you use a 7mm lens designed specifically for a smaller format camera it's correspondingly increased angle of view on a larger format camera, can get cropped. The camera/lens combo can't image the entire angle of view.

 

The angle of view is a function of both lens and camera. It is not a function of just the lens.

 

Carl

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