Lens Magnifcation Factors

[Ed Watkins]

Hi all,

I have been working out some Lens Magnification/ Crop Factors for different formats on the RED. I know some people don't find them useful, but I do conceptually.

Using the following measurements (I think they are Brook Willard's) for the RED sensor:
4K: 22.12 x 12.44 (16:9 useable)
3K: 16.59 x 9.33 (16:9 useable)
2K: 11.06 x 6.22 (16.9 useable)

EDITED to Reflect discussion below, I got it arse backwards:

For Nikon full frame SLRs 36 x 24mm (36 x 20.5mm 16:9 cropped) the lens magnification factors are:
4K: 1.63
3K: 2.18
2K: 3.27

So a 100mm lens on a RED will have the same apparent FoV as a 163mm Lens on a Nikon DLSR.

For for Nikon DX 23.7 x 15.7mm (23.7 x 13.33mm 16:9 cropped) LMF:
4K: 1.07
3K: 1.43
2K: 2.14

So a 100mm lens on a RED will have the same apparent FoV as a 107mm lens on a Nikon DX.

For Canon lenses manufactured for APS-H 28.7 x 19.1mm (28.7 x 16.14mm 16:9 cropped) LMF:
4K: 1.30
3K: 1.73
2K: 2.60

So a 100mm lens on a RED will have the same apparent FoV as a 130mm lens on a Canon APS-H .

For Canon APS-C 22.2 x 14.8mm (22.2 x 12.49mm 16:9 cropped) LMF:
4K: 1.00
3K: 1.34
2K: 2.01

So a 100mm lens on a RED will have the same apparent FoV as a 100mm lens on a Canon APS-C .

For 2/3" sensors 8.8 x 6.6mm (8.8 x 4.95mm) LMF:
2K: 0.8 (16:9 will be cropped)

For s16mm film 12.5 x 7.4mm (12.5 x 7.03mm) LMF:
2K: 1.13

For s35mm film 24.9 x 18.7mm (24.9 x 14.00mm) LMF:
4K: 1.13
3K: 1.5
2K: 2.25

I'll be adding these as presets on my iPhone App in the near future.

 

[Nicholas Shields]

Very interesting. Well summed up.

 

[Brian D. Goff]

Hi all,


So a Nikon/Canon 100mm SLR lens will have the same apparent FoV and focal length as a 171mm native PL lens on the RED body.

I don't quite get it - my Leica 50mm is almost exactly the same fov as the RED zoom at 50mm. I thought focal length is a fixed measurement (within certain tolerances), so that let's say a 50mm lens remains a 50mm lens no matter if it is on a SLR, RED, 35mm, 16mm or HD cam). The only thing that changes is that a 50mm lens on a full frame SLR will appear wider, but that is only because the frame is larger. I just had this conversation with a DP, and I don't think he believed me as I tried to convince him that my Leica lenses focal length are nearly just the same rating as the RED lenses. Correct me if I am misunderstanding something.

 

[Anders Holck]

goffb you are indeed correct. A 50 mm is a 50mm no matter if it comes from Leica, ARRI/Zeiss, Canon, Pentax, Fuji or Nokia.

 

[Ed Watkins]

I don't quite get it - my Leica 50mm is almost exactly the same fov as the RED zoom at 50mm. I thought focal length is a fixed measurement (within certain tolerances), so that let's say a 50mm lens remains a 50mm lens no matter if it is on a SLR, RED, 35mm, 16mm or HD cam). The only thing that changes is that a 50mm lens on a full frame SLR will appear wider, but that is only because the frame is larger. I just had this conversation with a DP, and I don't think he believed me as I tried to convince him that my Leica lenses focal length are nearly just the same rating as the RED lenses. Correct me if I am misunderstanding something.

Focal length is a fixed measurement on a lens.
It does not change depending on the sensor, hence the optical properties of the lens (its DoF etc.) are the same independent of sensor size.

BUT the difference in sensor size to film size does affect the way the image looks (if the sensor is smaller some of the lens's FoV will be cropped).
Thus a 50mm lens designed for an SLR 35mm film camera will not give the same image when it is put on a RED; i.e the FoV will change.

Lens magnification factors /crop factors are one way of accounting for the change in FoV when using lenses designed for different sensor sizes.

<<edit: I was wrong... Ignore.>>
If you want to get the same FoV as a 100mm PL lens on a RED you would need to use a 57mm Nikon lens on the RED (56 x 1.76 = 100mm).

Of course the 57mm Nikon would have the optical characteristics of a 57mm lens not a 100mm lens so you would have to adjust the aperture accordingly if you wanted to match the DoF of a 100mm as well as its FoV. (which is why some people don't like to use LMF's)
</edit >>

I hope that helps clear it up a bit.

As for your Leica lenses having almost the same FoV as RED PL lenses I can't comment, I do not have the relevant figures for Leica lenses/film size.

 

[Stephen Williams]

I don't quite get it - my Leica 50mm is almost exactly the same fov as the RED zoom at 50mm. I thought focal length is a fixed measurement (within certain tolerances), so that let's say a 50mm lens remains a 50mm lens no matter if it is on a SLR, RED, 35mm, 16mm or HD cam). The only thing that changes is that a 50mm lens on a full frame SLR will appear wider, but that is only because the frame is larger. I just had this conversation with a DP, and I don't think he believed me as I tried to convince him that my Leica lenses focal length are nearly just the same rating as the RED lenses. Correct me if I am misunderstanding something.

Hi Brian,

You understand it perfectly, the crop factor relative to 35mm still frame(Vistavision) just causes confusion, the sooner people know what a 28mm lens or 50mm lens looks like on a Red the better.

Best wishes,

Stephen

 

[Stephen Williams]

Thus a 50mm lens designed for an SLR 35mm film camera will not give the same image when it is put on a RED; i.e the FoV will change.

If you want to get the same FoV as a 100mm PL lens on a RED you would need to use a 57mm Nikon lens on the RED (56 x 1.76 = 100mm).

.

Hi,

A 50mm Nikon Lens on a Red One will match a 50mm Zeiss or Cooke PL lens on a Red, it's very simple a 50mm lens is always a 50mm lens.

You are totally incorrect a 100mm PL lens will NOT match a 57mm nikon lens when fitted on a Red camera.

Stephen

 

[Ed Watkins]

Hi,

You are totally incorrect a 100mm PL lens will NOT match a 57mm nikon lens when fitted on a Red camera.

Stephen

Please explain.

Are you saying a 100mm PL lens and a 100mm Nikon lens will have the same physical FoV on a RED?
I'm not talking about matching DoF or focal length (I know that a 100mm lens from any brand will be the same in this respect as DoF is a factor of lens focal length, which is determined by the lens optics). I'm talking about the visible FoV which is what LMF tries to account for.

Maybe I'm missing something...
A RED PL lens' optics are designed to resolve its full FoV image to a 22.12 x 12.44mm area.
The Nikon lens is designed to resolve its full FoV image to a 24 x 36mm area.
Clearly the Nikon lenses' image when focused on the RED sensor will be cropped.
Are you saying this has no affect on the apparent FoV visible in the recorded image?

For example that both Nikon and a RED 100mm lens when used on a RED will have the same dimensional field of view.
e.g 2.21m x 1.24m at a distance of 10m?

I'm not trying to start an argument about whether LMF is useful (I was asked by a client to work these out, and add them to my app), what I am trying to work out is if I have the whole concept ass backwards.

 

[Ed Watkins]

O.k,
Having talked to a number of different DP's this evening this is what they had to say:

1) Putting a lens designed to resolve on one sensor/films size onto a camera with a different film/sensor size changes the images field of view. See the example I was sent below:
The outer, red box displays what a 24×36 mm sensor would see, the inner, blue box displays what a 15×23 mm sensor would see.

Therefore the apparent FoV of a lens differs based on the sensor it is used on and the sensor it was designed for.

2) I overlooked something important.
For a meaningful LMF, (i.e one that relates a Nikon lens to a RED PL lens with an equivalent FoV) I should have been using 16:9 cross sections of the original format size, not the full frame format size, as LMF is established by using the horizontal measurement of a format not it's actual dimensions.

3) Once again, I am not talking about matching two lenses optically I am talking about matching two lenses FoV's.
The DoF of a 50mm lens will be the same no matter what sensor/film it is used on, <<edit: ignore this, i was wrong>> it's FoV however will not.<</edit>>

I'll update the LMF's accordingly.

 

[Daniel Browning]

So a Nikon/Canon 100mm SLR lens will have the same apparent FoV as a 163mm native PL lens on the RED body.

A 100mm lens, when used on a RED body in 4K, will have the same apparent FoV as when a 163mm lens is used on a Nikon FX DSLR.

That's how I would have written it. What you wrote had some irrelevant and mistaken information.

The brand, mount, and other lens details don't matter. All that matters is the focal length and two sensor sizes you're comparing. (FoV carries connotations of the viewfinder, but since that varies so wildly I'm sure everyone will assume that we're not talking about the viewfinder but the image from the sensor itself.) The part about lenses "manufactured for" is misleading as well.

 

[Ed Watkins]

A 100mm lens, when used on a RED body in 4K, will have the same apparent FoV as when a 163mm lens is used on a Nikon FX DSLR.

That's how I would have written it. What you wrote had some irrelevant and mistaken information.

The brand, mount, and other lens details don't matter. All that matters is the focal length and two sensor sizes you're comparing. (FoV carries connotations of the viewfinder, but since that varies so wildly I'm sure everyone will assume that we're not talking about the viewfinder but the image from the sensor itself.) The part about lenses "manufactured for" is misleading as well.

I'm more confused now.

What I want to do is have a useful comparison between the recorded image of a Nikon lens on a RED vs. a RED PL lens on a RED (both of which have the same Focal length).

Can some one tell me straight out if the recorded image produced by both lenses (both with the same focal length, set to the same focal distance, and aperture) on the RED exhibit exactly the same recorded FoV or not?

If so, I apologize, stand corrected, and have got everything ass backwards.

If not, then how does one meaningfully describe the difference between the two images, if LMF and FoV are the wrong terms what are the correct ones?

I'm not trying to cause an argument, I'm just trying to get my head round a concept.

Any help is greatly appreciated.

 

[Daniel Browning]

Can some one tell me straight out if the recorded image produced by both lenses (both with the same focal length, set to the same focal distance, and aperture) on the RED exhibit exactly the same recorded FoV or not?

Yes. Exactly the same.

There's no need to apologize. You're doing a useful service.

If not, then how does one meaningfully describe the difference between the two images, if LMF and FoV are the wrong terms what are the correct ones?

I like the terms FoV or crop factor, used like the example sentence in my last post.

 

[Ed Watkins]

Yes. Exactly the same.

There's no need to apologize. You're doing a useful service.



I like the terms FoV or crop factor, used like the example sentence in my last post.

In that case, my bad, sorry.
Ignore my initial logic, and use the LMF's if it helps.

 

[Brian D. Goff]

Hi Brian,

You understand it perfectly, the crop factor relative to 35mm still frame(Vistavision) just causes confusion, the sooner people know what a 28mm lens or 50mm lens looks like on a Red the better.

Best wishes,

Stephen

Ok, so thst what I wanted to konw - thanks Stephen. So if we're only talking lens, a 50 is a 50

Now, what about the sensor. RED sensor covers S35mm, BUT records less - am I right? So a DP used to shooting S35mm asking for a 50mm FoV on RED will need a wider lens?

 

[Alexander Christ]

50mm is 50mm is 50mm... I hope David does not read this thread :biggrin:

Now, what about the sensor. RED sensor covers S35mm, BUT records less - am I right? So a DP used to shooting S35mm asking for a 50mm FoV on RED will need a wider lens?

Yes, 4K is about Academy 35 and the upcoming 4.5K 2.40:1 recording mode is like S35. So a DP used to S35 would need about a 10% wider lens. Those Primes do not exist so give him a 50mm (and move the camera a little backward).

Ed, check your PM.

 

[Stephen Williams]

Ok, so thst what I wanted to konw - thanks Stephen. So if we're only talking lens, a 50 is a 50

Now, what about the sensor. RED sensor covers S35mm, BUT records less - am I right? So a DP used to shooting S35mm asking for a 50mm FoV on RED will need a wider lens?

Hi Brian,

In practice give the DP the lens he asks for, it's his job to know what lens he wants on the format he is shooting. Even if you have all 18 lenses that Cooke make in the S4 range you won't be able to give him an exact equivalent in any case, so don't even worry about it.

Be aware that a physically long zoom will seem to be a slightly longer focal length than is written on the barrel, this is because the front nodel point of the lens is well in front of the camera. This is also the DOF calculation point. This is one of the reasons why the dof charts of Primes & zooms vary slightly. (The other being DOF is based on F stops not T stops). If you move the camera back so the image size is identical then the DOF will also be identical at the same F stop.

Stephen

Edit The only difference with an old Manuel 50mm Nikon lens v a Cooke 50mm lens is the area covered by the lens, ie the circle of image that the lens produces is larger. The glass lenses need to be physically bigger (& thicker)for a given 'F' stop. As the light has to go through more glass lens theory would suggest lower quality. As the Optimo Zooms are enormous & produce very sharp images on a par with primes one can probably ignore lens theory! (The best lenses out resolve both film & digital sensors)

 

[Sanjin Jukic]

I do have chance to swap lenses very fast between Nikon, Laica and Cooke with IMS on RED.

The test between Nikon Nikkor AF 50mm f1.8 D, Leica Summicromn -R 50mm f/2 and old Cooke Cine Varotal 25-500mm f3.6 T4 Zoom (a vintage zoom).

Maybe there are not the best lenses to show this difference but its just to give you an idea.

Here below are results all at f.T5.6, no any ND, Pola-Circ, etc...

Leica Summicron-R 50mm f 2 at f/5.6, ISO/ASA 320.

Nikon AF Nikkor 50mm f1.8 at f/5.6, ISO/ASA 320.

Cooke Cine Varotal 25-250mm on 50mm f3.6 T4 at T/5.6, ISO/ASA 320.

Leica, Nikon, Cooke comparison at 50mm f/T5.6

 

[Ed Watkins]

Thanks Sanjin,

Looking at Sanjin's images the Cooke (set at 50mm) records an image on the RED that is cropped/magnified compared to the Nikon/Leica 50mm.

How does one account for that difference mathematically if you wanted to replicate the same image (in terms of field of view, not depth of field) on a RED with two different lenses. Or is that simply a pointless exercise?

I keep being told "a 50 is a 50 is a 50" and I understand why, but still, the images the different lenses produced on the RED in Sanjin's test are not the same.

Is this because as Steven says:

Be aware that a physically long zoom will seem to be a slightly longer focal length than is written on the barrel, this is because the front nodel point of the lens is well in front of the camera...

or because

...The only difference with an old Manuel 50mm Nikon lens v a Cooke 50mm lens is the area covered by the lens, ie the circle of image that the lens produces is larger. The glass lenses need to be physically bigger (& thicker)for a given 'F' stop. As the light has to go through more glass lens theory would suggest lower quality. As the Optimo Zooms are enormous & produce very sharp images on a par with primes one can probably ignore lens theory! (The best lenses out resolve both film & digital sensors)

If it is because the circle of the image the lens produces is bigger, then is there a useful way to compare the circle of image produced by different lenses so that one could meaningfully compare the recorded FoV a given lens would produce when used on the RED?

I really appreciate all the help on this thread,
I just want to get the concepts nailed so that I don't feel confused about it in the future.

 

[Sanjin Jukic]

Ed,

Sorry I forgot to write but Cooke was on 50mm.

When you want to match the size you should try out to set Cooke approximately between 42mm-43mm.

Above is corrected.

 

[Stephen Williams]

Ed,

Sorry I forgot to write but Cooke was on 50mm.

When you want to match the size you should try out to set Cooke approximately between 42mm-43mm.

Above is corrected.

Hi,

Moving the camera back about 20 cm would be better, then the front nodel points would match up. DOF & FOV would then be identical.

Stephen