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Is my lens really 18-35mm help me?

sigma lenses lens fs5 18-35

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#1 Kendrick Gray

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Posted 19 July 2017 - 01:45 AM

So I had a heated discussion today about this topic with other "cinematographers". I had information thrown at me from all sides and I don't know what to believe anymore .Can somebody please clean this up for me once and for all. 

 

Ok I bought a Sigma Art 18-35mm 1.8 lens for my FS5. The lens is a APS-C so it fits well on the camera. A lot of people are using it. 

 

So the question is... Is this really giving me 18-35mm or 28.8-56mm? I was under the impression that the 1.5 crop factor only applied when you were using a full frame lens. A guy then tells me all lenses are for full frame and you have to multiple 1.5 with any lens that you put on it no matter what its for. He was really furious when explaining this to me. Who is right? 


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#2 Mark Kenfield

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Posted 19 July 2017 - 02:18 AM

18-35mm = 18-35mm

The focal length cannot change, only the apperent field-of-view (which is dependant on the format you're shooting: S16mm, S35mm or Vistavision/"Full Frame").

Now the field-of-view of an 18mm lens on a S35mm sensor is going to approximately the same as a 28mm lens on a full frame sensor. But that does not somehow magically transform that 18mm lens into a 28mm lens.
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#3 Kendrick Gray

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Posted 19 July 2017 - 02:23 AM

Is there any lenses made for a particular sensor where the focal length and field of view are identical? Or that just does not happen. 


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#4 Mark Kenfield

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Posted 19 July 2017 - 02:41 AM

Do you mean a lens that maintains its field of view across different sensor sizes? If so, then the answer is no, that's physically impossible.

The new Angieneux EZ zoom lenses are the only lenses be able to provide that feature, and only if you switch out the rear optical groups on the lenses (when switching between formats). but they're not the same lens when you switch the rear optics.

Edited by Mark Kenfield, 19 July 2017 - 02:43 AM.

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#5 Kendrick Gray

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Posted 19 July 2017 - 02:48 AM

I always fine it confusing when cinematographers say they like to do this with a 35mm or that with a 50mm. How are we supposed to know the look they were going for it the field of view always changes depending on the camera? Im assuming if they are using a industry standard camera 35mm and 50mm pretty much would be easy to copy from there look. 

 

In closing... basically even if a lens is aps-c the lens will still never be field of view wise what it says it is. Why on earth does it vignette on a full frame sensor then? So even if its made for the apsc/super35 sensor they still make the field of view change. Ahhh so confusing sometimes. 


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#6 Robin R Probyn

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Posted 19 July 2017 - 02:56 AM

AFAIK ..

 

"A guy then tells me all lenses are for full frame and you have to multiple 1.5 with any lens that you put on it no matter what its for."

 

I think this is wrong .. he probably has only used stills lenses then.. 

 

An APS-C lens will vignette at some stage on a FF sensor .. it cant project an image big enough to cover the larger sensor .. there are some cine lenses around now that are FF.. but the vast majority are s35.. and so no crop factor on a s35 sensor..  


Edited by Robin R Probyn, 19 July 2017 - 02:59 AM.

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#7 Kendrick Gray

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Posted 19 July 2017 - 03:30 AM

So some cine lenses have no crop factor? I knew I wasn't crazy. Whats the point in making a apsc lens and still have crop factor? 


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#8 Brian Drysdale

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Posted 19 July 2017 - 05:01 AM

Crop factor is just a means used to work out the field of view on different sensors compared usually to full frame 35mm. The local length of the lens doesn't change, so you end up with nonsense like the wide angle on a 1/3" video camera being 28mm, when the manufacturer used the equivalent focal length  used on a full frame 35mm camera, rather than the actual focal length.

 

I've found that its better in the end to learn the angle of view for focal lengths on a different sensor/film formats, than start converting to equivalent focal length using a crop factor. You quickly learn the focal length you need, rather than relying on the double thinking required for crop factor.   .  


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#9 Robin R Probyn

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Posted 19 July 2017 - 05:29 AM

So some cine lenses have no crop factor? I knew I wasn't crazy. Whats the point in making a apsc lens and still have crop factor? 

 

 

Tens of thousands have no crop factor if you are using the sensor size they are built for..Well as I know it anyway..for e.g... I have a Canon CN7 17-120mm cine zoom..built for s35mm sensors..  17mm is 17mm field of view..and all through the range.. Im not calculating any crop factor..  if I put this lens on a FF camera.. at some point as I come wide.. it will vignette .. as the rear element is not big enough to cover the FF larger sensor size..  its confusing because people will just say a lens never changes.. true.. but in reality your field of view will change.. depending on the size of the sensor in your camera.. 

The reason a s35 sensor camera has a shallow depth of field "look" compared to 2/3 inch camera.(ok thats simplified but)  is not because the sensor has somehow a magical shallow DoF.. its because, for the larger s35mm sensor camera.. you will be using a longer lens.. to get the same field of view (shot) than the 2/3 ..  and on a FF it will be longer than s35.. for the same Field of view.. 

 

This could be bollocks and if so I,ll be called for it.. but in a nut shell, I think thats the story.. 

 

I guess your friend has possibly only ever used FF stills lenses .. and so is under the impression that all lenses are built for FF.. although as a cameraman its a bit of an odd thing to be thinking TBH.. unless he is direct from being a stills photo only shooting video on 5D or such.. FF cameras.. I mean really this whole crop FF factor thing has only come into being, for most people, since DSLR FF cameras stated shooting video.. 


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#10 Daniel Klockenkemper

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Posted 19 July 2017 - 11:19 AM

Kendrick, 
 
Lenses don't have a crop factor.  A lens has a focal length (the amount of bending it does to light) and an image circle, the size of the circle of light projected behind the lens.  
 
Crop factor is really a way of comparing two different sensor sizes, not lenses.  If lens X on one sensor gives you a certain angle of view, you can calculate what lens Y should be to get the same angle of view on a different sensor.  That's all. 
 
Here's a better way to think about it:  Start with the sensor size of the camera you use - I believe it's 12.7mm x 24mm for the FS5.   The diagonal measurement is 27.15mm.  I'm simplifying a bit, but this diagonal measurement basically tells you what focal length would have a "normal" perspective on this sensor.  Every focal length shorter is a wide angle, and every focal length more than that is a long lens, or telephoto. 
 
If a lens is referred to as APS-C, Super 35, full frame, etc., those are just common ways to talk about the size of the image circle that a lens has. 
 
If a lens has an image circle large enough to cover the sensor you're using, you can use it.  All you need to think about is how that focal length relates to "normal" for the sensor you're using.
 
--
 
Some examples:
 
If you put a 28mm Zeiss Ultra Prime (a Super 35 cinema lens) on your FS5, it will have a basically normal perspective, not wide angle.
 
If you put a 28mm Zeiss CP2 (a full-frame cinema lens) on an A7S, it will be wide angle, because the sensor is much larger - 23.8mm x 35.6mm (42.8mm diagonal). 
 
If you switch the lenses around, the CP2 will have the exact same angle of view as the Ultra Prime on the FS5.  They are both 28mm, and they both have an image circle larger than the diagonal measurement of the FS5 sensor. 
 
When you put the Ultra Prime on the A7S, you would see a circular image in the middle of the frame, and the sides of the frame will be dark.  However, if you compared this circle to the same area on the CP2/A7S combination, you would find that the images inside the circle are the same.  The Ultra Prime has a smaller image circle than the CP2, but they both have the same "bending power" because their focal lengths are the same.
 
You would need to put a 44mm lens on the A7S to get the same angle of view as a 28mm on your FS5.  That's the only reason to think about crop factor. 
 
--
 
I realize this got a bit long, but I hope it makes things more clear for you!
 
Daniel

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#11 Stuart Brereton

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Posted 19 July 2017 - 11:25 AM

Lenses don't have a crop factor. The so called crop factor is just a way of calculating different fields of view with different sensor sizes. A 50mm lens is considered wide angle on medium format, normal on FF35 and short telephoto on s35, but the lens itself doesn't change. It's always a 50mm.


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#12 aapo lettinen

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Posted 19 July 2017 - 02:15 PM

I normally try to avoid talking about crop factors unless I'm discussing with still photographers who are only talking with crop factors instead of actual sensor sizes  :blink:

 

anyways, as others said, a 50mm lens IS a 50mm lens and the used sensor size behind the lens determines the field of view. 

it is best to NOT USE the "35mm equivalent focal lenght" s at all, they just confuse people very much and are not really usable for anything other than comparing some small sensor prosume video cameras with built in zooms :mellow:


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#13 David Mullen ASC

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Posted 19 July 2017 - 11:04 PM

The APS-C size is similar to 3-perf Super-35 so the focal lengths give a similar view in either format.

 

"18mm" is a physical measurement, it's always an 18mm whether it is on a Super-8 camera, an iPhone, or an IMAX camera.

 

"Crop factor" is just a way of discussing field of view issues, and for still photographers, it is all based on the assumption that "no crop" means shooting in Full-Frame 35mm (36mm x 24mm).  But of course that's a strange concept if you are comparing Full-Frame to even larger formats....  Plus a lens projects a circular image, so all rectangular film formats or sensors "crop" the image coming from the lens.

 

Not sure why crop factor issues would lead to a "heated" discussion...

 

Your 18-35mm zoom would be an 18mm-35mm range on either an APS-C / Super-35 camera or a Full-Frame camera but since the image circle was only designed for the smaller APS-C format, it would vignette on a Full-Frame camera.  Plus 18mm is a wider field of view on a Full-Frame camera than on an APS-C camera.

 

If you want to match the view of an 18mm lens on an APS-C camera when using a Full-Frame camera, you'd have to use a lens that is 1.5X longer.


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#14 Kendrick Gray

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Posted 22 July 2017 - 08:21 PM

Ha it lead to a heated discussion because it was a Facebook group full of people who "know everything". Heck, with the right kind of people you'll argue about anything. Thanks for all the replies and giving me an understanding of what exactly is going on. Especially coming from professionals. 

 

The reason I care so much about this is because I'll like to develop a style and come up with a look I can stick with if possible. But its hard to mimic something I see if I don't know what sensor or film they were using. For Instance, It says Ridley Scott uses 75mm+ lenses most of the time and Steven Spielberg 21mm. Even if the lens is what it is I still had no Idea the field of view they were getting. Not necessary trying to copy but to have something to build off of. 


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#15 Kendrick Gray

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Posted 22 July 2017 - 08:28 PM

 

Kendrick, 
 
Lenses don't have a crop factor.  A lens has a focal length (the amount of bending it does to light) and an image circle, the size of the circle of light projected behind the lens.  
 
Crop factor is really a way of comparing two different sensor sizes, not lenses.  If lens X on one sensor gives you a certain angle of view, you can calculate what lens Y should be to get the same angle of view on a different sensor.  That's all. 
 
Here's a better way to think about it:  Start with the sensor size of the camera you use - I believe it's 12.7mm x 24mm for the FS5.   The diagonal measurement is 27.15mm.  I'm simplifying a bit, but this diagonal measurement basically tells you what focal length would have a "normal" perspective on this sensor.  Every focal length shorter is a wide angle, and every focal length more than that is a long lens, or telephoto. 
 
If a lens is referred to as APS-C, Super 35, full frame, etc., those are just common ways to talk about the size of the image circle that a lens has. 
 
If a lens has an image circle large enough to cover the sensor you're using, you can use it.  All you need to think about is how that focal length relates to "normal" for the sensor you're using.
 
--
 
Some examples:
 
If you put a 28mm Zeiss Ultra Prime (a Super 35 cinema lens) on your FS5, it will have a basically normal perspective, not wide angle.
 
If you put a 28mm Zeiss CP2 (a full-frame cinema lens) on an A7S, it will be wide angle, because the sensor is much larger - 23.8mm x 35.6mm (42.8mm diagonal). 
 
If you switch the lenses around, the CP2 will have the exact same angle of view as the Ultra Prime on the FS5.  They are both 28mm, and they both have an image circle larger than the diagonal measurement of the FS5 sensor. 
 
When you put the Ultra Prime on the A7S, you would see a circular image in the middle of the frame, and the sides of the frame will be dark.  However, if you compared this circle to the same area on the CP2/A7S combination, you would find that the images inside the circle are the same.  The Ultra Prime has a smaller image circle than the CP2, but they both have the same "bending power" because their focal lengths are the same.
 
You would need to put a 44mm lens on the A7S to get the same angle of view as a 28mm on your FS5.  That's the only reason to think about crop factor. 
 
--
 
I realize this got a bit long, but I hope it makes things more clear for you!
 
Daniel

 

 

This was gold. Im still trying to comprehend fully. I need to study and understand the science of how lenses work. Thats my issue. 


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#16 Adrian Sierkowski

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Posted 23 July 2017 - 03:23 PM

Generally one can assume both Ridley  and Spielberg are talking about shooting on 35mm Motion Picture film; so you'd roughly be talking about a 21 or a 75mm as they'd appear on APS-C sized sensors (or those close to it). Of course when going into a specific film, as now some shoot digitally (ridley) you'd need to look at the camera used and then the resolution filmed as (as red crops it's sensor for resolutions, as do many other cameras) and you could extrapolate what it would be based on your system. Or, the other way around, if you liked the way a 21mm looked on a Spielberg film, but you're on a 5D, you'd then figure out the "crop factor" to get approximately the same field of view on a 5d.

However, when they are talking about the lenses they like, there is more to that than just field of view. There is the way each lens falls off and out of focus, spatial compression (e.g. how wider lenses exaggerate depth / distance / movement), how a lens flares or doesn't, and it's color reproduction etc etc.

You'll  often times also hear people speaking as such, that they tend to "favor" a certain lens. This is an important distinction as you can "favor" a lens, or style, but often you'll be doing something way off of that for myriad reasons.

I personally "favor" a 32mm when it comes to close ups these days, though in times past I favored an 18 or so for the same thing (i was watching a lot of Gilliam Those days). Further, I favor more "normal" lengths and never particularly go super long; however i'll be on a 300mm and a 16mm for the majority of the next short I'm on this week because we need the specific characteristics beyond Field of View (though the FOV of the 16mm is important for one of our locations)-- notably the compression a 300mm will give us and the expansion the 16mm will.


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#17 Kendrick Gray

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Posted 23 July 2017 - 05:28 PM

Generally one can assume both Ridley  and Spielberg are talking about shooting on 35mm Motion Picture film; so you'd roughly be talking about a 21 or a 75mm as they'd appear on APS-C sized sensors (or those close to it). Of course when going into a specific film, as now some shoot digitally (ridley) you'd need to look at the camera used and then the resolution filmed as (as red crops it's sensor for resolutions, as do many other cameras) and you could extrapolate what it would be based on your system. Or, the other way around, if you liked the way a 21mm looked on a Spielberg film, but you're on a 5D, you'd then figure out the "crop factor" to get approximately the same field of view on a 5d.

However, when they are talking about the lenses they like, there is more to that than just field of view. There is the way each lens falls off and out of focus, spatial compression (e.g. how wider lenses exaggerate depth / distance / movement), how a lens flares or doesn't, and it's color reproduction etc etc.

You'll  often times also hear people speaking as such, that they tend to "favor" a certain lens. This is an important distinction as you can "favor" a lens, or style, but often you'll be doing something way off of that for myriad reasons.

I personally "favor" a 32mm when it comes to close ups these days, though in times past I favored an 18 or so for the same thing (i was watching a lot of Gilliam Those days). Further, I favor more "normal" lengths and never particularly go super long; however i'll be on a 300mm and a 16mm for the majority of the next short I'm on this week because we need the specific characteristics beyond Field of View (though the FOV of the 16mm is important for one of our locations)-- notably the compression a 300mm will give us and the expansion the 16mm will.

 

 

Thanks for this. It should be common sense for me to think that lol. Makes sense. 


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#18 Kendrick Gray

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Posted 23 July 2017 - 05:31 PM

When you come from the DSLR world they compare everything to Full-Frame. I have a new prospective on lenses now. 


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#19 Kendrick Gray

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Posted 23 July 2017 - 09:02 PM

Anybody have any pictures of exactly what is measured to get the millimeter measurement? I want to know exactly what it looks like. Google has not been my friend. 


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#20 Daniel Klockenkemper

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Posted 23 July 2017 - 11:15 PM

Glad it was helpful.  For me, using a variety of different formats has helped me understand better - 8mm, 16mm, Super 35, full frame, medium format, large format (4x5).  It's just so much easier to think about the format than to try to convert everything back to full frame.  
 
As far as picturing what's happening with a lens, it might be helpful to start with the most simple optical device - a pinhole, a hole in a wall that was used before photography to create images in a camera obscura (literally means "dark room"):
 
800px-Pinhole-camera.svg.png
 
The focal length of a pinhole is the distance from the pinhole to the wall.
 
While simple, a pinhole has a lot of disadvantages when it comes to photography, which is why lenses took their place.  A simple lens is one piece of glass: 
 
800px-Lens1.svg.png
 
In the picture above, the light rays in red are entering the lens from infinitely far away, and the distance from the optical center of the lens to the point where light converges to form a sharp image (the focal point) is the focal length (lower case f).
 
Simple lenses still have some drawbacks though, so more complicated lens designs were invented to improve the image: 
 
454px-RR-Aplanat-text.svg.png
 
The above lenses are symmetrical, and conveniently the focal length of these lenses is measured from the central point of the combined elements to where the light converges, which is where the camera's sensor or film would be placed. 
 
Once you get into more complicated lens designs, mentally conceiving exactly how the light rays are moving through the lens starts to get more difficult.  
 
If you want to read more Wikipedia provides a lot of information, but a lot of it gets technical very quickly:  
 
 
I think it's important not to let yourself get too bogged down by technical information though - you only need to understand it as much as you need to in order to advance your craft.  All of us go through repeated cycles of learning and application; you find the limits of your knowledge by putting it into practice.  
 
Best, 
 
Daniel

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