The Properties of Camera Lenses
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The Properties of Camera Lenses

Hi John Hess from – with a
grounding in the science and history of lenses, let’s explore the features of the modern
day lenses and explain what focal length, aperture, the features of prime and zoom lenses,
and some specialty lens equipment you may run into as a filmmaker. The first and most fundamental property of
a photographic lens is it’s focal length. Recall that the focal length on a simple thin
lens is the distance from the point where collimated rays of light converge into a single
point. With photographic lenses being a series of different elements, the focal length is
slightly more complicated. When talking lenses we’re talking about the distance between
the imaging plane and the optical center point when the lens is focused with collimated light
– in other words focused at infinity. Without getting too much deeper into optical
science let’s just cover the key take away here – The focal length is the one of the
factors that determines your field of view – that is the angle that your shot covers.
Using the same sized sensor a shorter focal length means you’ll have a wider field of
view – a longer focal length means you’ll have a narrower field of view – more zoomed
in. Using this simplified animation you can visually understand the relationship between
field of view and focal length. But focal length is only one aspect of field
of view – there’s that other bit I mentioned earlier – the sensor size. To demonstrate
the effect of sensor size on the field of view I built this simple mock camera out of
a wood box, a lens cap and a piece of diffusion paper. This diffusion paper mimics the imaging
plane – I tried to get this imaging plane about the same distance from the lens – using
a Nikon flange distance of about 46.5mm. Looking on the diffusion we see a circle of
light put down by the lens. This is the image circle. Now using pieces of foam board, I’ve
cut out the window to show what a 35mm stills camera would see. Because of the popularity
of 35mm in the stills world, this is also called “full frame” Full frame cameras are popular as DSLRs but
building sensors of that size that are free from errors in the manufacturing process is
is very difficult and potentially very expensive. Since these sensors are manufactured on a
single silicon wafer, you could produce more sensors and have fewer defective sensors if
you made them smaller. Here’s one example of a smaller standard
– the Canon APS-C Sensor. This is actually closer to Super 35mm motion picture film which
runs the film vertically through the camera rather than horizontally like on still photography
or the process called VistaVision. Notice that even though the lens did not change
on our model, we have a different angle of view because of the sensor size. For comparison,
here’s another smaller popular format – micro four thirds. Micro four thirds is relatively
close to the look of 16mm motion picture film. Associated with each sensor size is something
called the crop factor which is basically the magnitude of the crop as compared to a
35mm horizontal standard. A Full Frame sensor has no crop factor – it’s 1:1. APS-C is
about 1.6 – that means the image will appear about 1.6 times larger. Micro four thirds
is about 2. We’ll get into more detail on lens equivalency
in another course. But people all over get really hung up over this topic when there’s
really just no need to. Remember that the field of view is determined by both the focal
length and the sensor size – but since we can’t change the sensor size on most cameras
– it’s the focal length we adjust to get a wider or more telephoto shot. So how do we classify focal length ranges?
Let’s start in the middle with what’s called a normal lens – a normal lens delivers
an image that’s natural – the kind of dimensionality that we’re used to with our own eyes when
viewing a normal sized print from a normal distance – I realize that’s wishy washy
that but this is all subjective. Now as I just said, the sensor size plays a key role
– so in order to know what a normal lens is we have to know the the size of the sensor.
For photography and shooting for television screens or web, a normal lens is equal to
that of the diagonal dimension of your sensor – get out old the Pythagorean theorem. According
to the ASC – for a cinema – because the viewer is watching on a big screen from far away,
the normal lens would be twice the diagonal. So If you are shooting on a 35mm full frame
camera, the diagonal is 43mm. A lens that is around 43mm – a 50mm lens would be appropriate
for television and computer viewing whereas an 80mm lens would be more “normal” for
a cinema experience. On a smaller sensor like APS-C which is closer to Super 35mm the diagonal
is 26mm so your normal for small screen could be a 24mm lens or a 50mm for cinema. For micro
four thirds we’re looking at 22.5mm diagonal which is not that far off from APS-C for your
normal lens choices. The definition of “normal lens” sits in a sort of gray area – you
don’t have to be absolutely precise here. So above the “normal range” are the Telephoto
lenses. These lenses have a smaller field of view resulting in a higher zoom factor.
Smaller field of view tends to compress spatial dimension and make things look closer together. Below the normal range are the wide angle
lenses which you might have guessed have a larger field of view. Larger field of view
will exaggerate spatial dimension – make things feel farther apart – if you get down to really
small focal lengths you can start getting some fisheye effects as we’re compressing
an unnaturally wide angle of view into a small space. These kind of distortions can be corrected
for with really high end optics but you do pay the price. Now we come to the second most important feature
of the modern lens – the aperture. Sometimes in video the aperture is called the iris – but
they function the same way. In order to make lenses sharper, lensmakers
in the 19th century began to introduce apertures into their designs. What the aperture does
is restrict the angle of light that travels through the system – a smaller aperture reduces
the light rays to those that are closer to being collimated – that is more parallel – resulting
in a sharper and more deeply focused image. The drawback to a smaller aperture is less
light actually makes it to the lens. To demonstrate this property, let’s use
a single lens model. Here I have light from a bare bulb traveling through a lens and onto
an imaging plane. Using lids from a tennis ball container, I created a simple aperture
– notice that as the hole in the lid gets smaller, the image on the paper gets sharper
but at the cost of getting dimmer. But there is a cost to reducing the size of
the aperture and it comes in the form of light defraction. As the aperture gets smaller the
light rays passing through the aperture begin to diverge and add and subtract with one and
another. The result is something called an Airy Disk named after mathematician and astronomer
George Biddell Airy. With large apertures, this Airy discs appear very small – smaller
than even a single pixel on the camera’s photoreceptor, but as you decrease aperture,
the airy disc grows bigger and bigger. Once the disk is the width of a pixel, you’ll
start seeing decreased sharpness even as you make the aperture smaller. How do we measure the size of the aperture?
For that lensmakers use something called the F-number sometimes called F-ratio or most
commonly just F-stop. The Fstop of a lens is a dimensionless number that is the focal
length divided by the diameter of the of the aperture. So a 50mm lens with an aperture that has a
diameter of 25mm would be at F2. But lets say we want to double the light that
goes through the lens – we do this by doubling the area of the aperture. A little bit of
high school geometry here – if we want to double the area of a circle which is pi times
radius squared – we need to increase the radius by a factor of square root 2 which is about
1.4. Now this math carries over to the Fstop value
– if we want to double the light, we need to divide the Fstop value by 1.4. So to double
the light a 50mm lens gets from an F2 lens we need to set to F1.4. To halve the amount
of light we need to multiply the Fstop by 1.4. So to get half the light of an F2 we
need an F2.8. Halving or doubling light is called a full
stop. Let’s continue with our series. A stop down from F2.8 is F4. A stop down from
F4 is F5.6 then F8, F11, F16 and F22. Most lenses will have these stops on the lens as
well as some half stops in between these. On photography lenses, these values are notched
into either a manual ring or part of the electronic aperture servo – you are limited to just those
preset values which really is good enough for almost all photography work. But on Cinema Lenses, the aperture is often
“declicked” meaning the aperture can smoothly adjust all the way up and down the fstop scale. Now notice that this is a dimensionless value.
A 100mm f2 lens means the aperture’s diameter is 50mm where as a 35mm f2 means the aperture
is only 13mm in diameter. The idea here is that in a perfect world both f stops would
let in the same amount of light and therefore create the same exposure. But that’s not quite the case as those lenses
are designed differently – they may have different number of glass elements which can reduce
performance. To counter this cinematography lenses feature something called T-stops – for
transmission stops. T-stops are essentially the F-stop corrected for the amount of light
absorbed or reflected by the glass in the lens – basically how much light actually gets
transmitted through the lens. In the days before specialized glass coating, the T-Stop
was crucial for cinematographers shooting a scene with different lenses of different
focal lengths. A 50mm lens at F5.6 might have a completely different exposure than a 24mm
lens at F5.6. This is where the T-stop is useful – a 50mm at T5.6 would expose the same
way as a 24mm at T5.6 even if the actual Fstop numbers may be a little different between
the two lenses. As glass coating technology has improved dramatically since the 30s and
40s, the differences are not as pronounced today as they used to be. Still high end cinema
glass does retain the T-Stop nomenclature – but the function is very similar to F-stops
if that’s what you’re familiar with. One of the biggest decisions when picking
out a lens is deciding between prime lenses and zoom Lenses. A prime lens is a lens with
a single focal length. One aspect of prime lenses worth discussing
focus breathing. When focused is set to infinity the rear nodal point of the camera and the
imaging sensor are separated by the focal length. When focused on a closer object, the
nodal point must be moved further away from the imaging plane. The result in some cheaper
lenses is the image will slightly zoom in or out as you rack focus. For photography
– this is not an issue, but for cinematography this can be a little distracting although
it may be a look that people are getting familiar with. High end cinema primes lenses shift the focal
elements in a way that eliminates this focus breathing. Now as you probably already imagined, a zoom
lens is capable of a range of focal lengths – this is done by shifting a variety of lenses
inside the housing as we demonstrated in a very crude model in our science video. Zoom lenses can suffer from focus breathing
as well but they have another issue with maintaining focus throughout the zoom range. Cheaper photography
zoom lenses are called “Varifocal lens” – that means if you change the focal length
of the lens, you must re-establish the focus. More expensive Parfocal lenses will maintain
the focus throughout the zoom. A common practice among video and ENG shooters is to zoom all
the way, set critical focus, and then reframe the shot. That’s something you can only
do on a Parfocal lens but it’s a good way to make sure you focus is sharp where you
want it to be when looking at a small viewfinder. So why would you choose a prime lens over
a zoom lens? Well it’s really a matter of quality vs ease of use and cost. A prime lens
is one focal length so the lens designers can design a precise instrument to suit that
one specific task. A zoom lens requires sacrifice in terms of design and cost in order for it
to function throughout the zoom range. For that reason, primes are generally cheaper
than their zoom counterparts and have better quality. But with a zoom lens, what you sacrifice
in quality, you make up for ease of use. Instead of carrying around a 24, 35, 55 and 70mm lens,
you can carry around a single 24-70mm zoom lens. That can save a lot of time on set and
cost of buying or renting a set of lenses. Cinema and Video zoom lenses are often geared
for servo control which allows for mechanical zoom operation which is critical for getting
a smooth zoom in or zoom out shot – this is certainly a handy feature of ENG style lenses. There is one drawback on some zooms worth
pointing out. Because of the design of the lens, you may not have a continuous aperture
– that is you could have an F2.8 on the wide range of the lens but be an F4 when zoomed
all the way in. This is just a design limitation as you can find continuous Fstop lenses if
you’re willing to pay more. There are zoom lenses that over a $100,000 which can easily
serve all your needs – but at that point you start have to start to ask whether it would
be cheaper to just get a set of primes. So between zooms and primes there’s a lot of
factors to consider. A popular feature among DSLR camera lenses
is Optical image stabilzation or OIS or just IS. First introduced by Nikon in 1994, an
optical image stabilization system works by floating the rear lens element on magnets
and using two piezoelectric angular velocity sensors (often called gyroscopic sensors)
to detect vibration – in other words – they use magic. Image stabilization is especially
important in really long focal lengths as even the slightest movements can cause jitters
in a shot. For cameras with smaller than 35mm sensors
such as APS-C or micro four thirds there is a tool called focal length reducers – sometimes
called telecompressor. A popular brand is of this device is the Metabones speedboosters.
Basically these devices operate in the the opposite fashion of a magnifying glass – they
make the light image circle created by the lens smaller. In doing so they concentrate
more light on the image sensor resulting in about one stop of light increase while increasing
the field of view of a lens. Now if you’re specific about the the shape
of the bokeh in your shots – bokeh is the shape of the blur of out of focus background
– you may want to consider the type of shutter blades on the lens. If you want to get really
creative you could put cutouts on the end of your lens to act as an additional aperture
and create custom bokeh shapes. Speaking of bokeh – a popular look developed
in the widescreen wars of the 50s utilized the anamorphic lens – a look that’s still
very much in use in Hollywood today. Anamorphic lenses squeeze the image horizontally creating
a wider field of view than a spherical lens would provide. Anamorphic lenses come in different
strengths and will give boken and lenses flares a signature look. For getting up close and personal to your
subject you’ll need a macro lens. Macro lenses allow for extremely close focusing.
Luckily lots of photography zoom lenses have a macro toggle for such shots – but they won’t
have the extreme close up focus of a dedicated macro lens. If you’re on the cheap, you
can use Extension tubes which add distance between the camera and the lens making really
close up focusing possible. The farther away the lens is, the closer you can focus at the
expensive of loss of light. This will throw the focus of your lens way off but it’s
an inexpensive way of getting the macro shot. While we’re on the subject of moving the
lens – there is a class of lenses called tilt shift lenses that actually move the glass
off the optical center. This tilts the focal plane so which allows for selective focus
even with deep depth of field. The result is often used for creating the miniature look
in timelapses. If you want to just experiment with the shifting the focal plane there is
a technique called lens whacking where you disconnect the lens and then hold it askew
in the camera’s lens housing. And finally there is one type of lens which
has pretty much fallen out of fashion but has an interesting role in the history of
filmmaking – that is the split diopter. A split diopter is almost like a bifocal for
a lens – it’s a half piece of convex glass that allows half the lens to have a different
focus distance from the other half. Brian De Palma experimented with this type of lens
throughout the 70s but nowadays with sensors with better low light capabilities, creating
a deep depth of field sort of negates the advantage of split diopters. So hopefully now you have a deeper understanding
of how lenses work. Still there’s nothing like actual first hand experience – take your
lens out and just give it a try. On the next video we’ll dive into the complicated world
of depth of field and lens equivalency but until then just get out there and experiment
and learn – that’s all part of the journey to making something great. I’m John Hess
and I’ll see you


  • Michael Reed

    Coming from a 34 yo with ZERO exp with film or cinematography, these videos have been an absolute God send with bringing me up to speed with how to play around with this unexpected interest in film. Thank you sir, you are a scholar and a gentleman.

  • Achilleas Labrou

    At 1:25 Field of view isn't the angle that the shot covers. The angle that the shot covers is the angle of view.
    Field of view is usually used as the minimum area a lens can shoot at the closest distance it can focus.
    Focal length is a very misunderstood topic because it has different properties with different image sensor sizes. Nearly professionals shot with full format sensors, so they don't care.
    However for amateurs who don't know about the impact of the image sensor size to photos, focal length is very confusing. The angle of view of a lens is a more clear lens characteristic for amateurs.

  • Wudy Ng

    OMG! your video is ****ing awesome! I love it!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! make more videos!!!!!!!!!

  • Jonathan Furtado

    Do you have a link of where to purchase these resources so we can use them to create a lesson plan as a companion to your video?

  • 1096 bimu

    I love how you talk about larger and smaller field of view. Not like the idiots who keep talking about 50mm without mentioning sensor size. As if the 50 is a magical focal length regardless of what camera you're using.

  • Nguyễn Hoàng

    Thank you, the video is so great!
    I can understand about DOF, FOV, Aperture, ISO, Shooting Speed, etc… But one thing I not understand yet is: Focus point adjusting.
    I have prime lens Sony SEL 16mm f/2.8 on Sony A6000
    When I change mode to Manual, and Focus mode to Manual Focus too.
    The Aperture I fix to F3.5, so DOF is fix.
    The Speed I fix to 120.
    The ISO is 200.
    Certainly, the Focus Length of lens is 16mm.
    Total, all parameter is fixed.
    And I can use Focus Ring on lens to manual change what distance I want to focus (Move DOF forward or backward).
    So what is happening on Lens or Camera when I do it? I search many on Internet but not get this point yet. Would you please to teach me?

  • javier astudillo griffiths

    At 5:30 you mentioned of normal lens is twice de size of the diagonal and for Full Frame sensor is 43mm , so the companies they sell the 50mm as a normal lens like field of view of the human eye, why not just sell at 43 mm or better, just say that the normal size start at 43mm in a FF camera .
    Pd: the ASC is for the America Society of COmunication?, im from chile and im making my Thesis and you videos are perfect for my proyect and some thimes is hard to translate to spanish. i will apriciated if you respond thanks 🙂

  • Omar Hassan

    At 6:08 you said that the normal lens for APS-C sensor is 26 mm for televisions and computers. is this a 26 mm calculated after adjusting for the crop factor? or we need to consider the crop factor that turns the 26 mm into 40 mm??

  • Ramon Lopez

    I wish I would have watched a video like this many years ago. All the possible doubts one can have about photography nicely explained in 20 minutes. You are the best dude. Eres la caña! (spanish idiom) Thanks a million.

  • Tony tFuntek

    WOW….great video. Learned a lot. Question is how do they design lens smaller and keep the F number the same i.e. 50mm f1.8 full frame V 50mm f1.8 on a smaller sensor like m4/3's ? How can they both transmit the same amount of light with a smaller diameter ?

  • lamenamethefirst

    I must say your videos are really great. Packed with information, very well presented and detailed. However there was always something about your videos that was a little odd to me. For a long time I couldn't really understand why. But I think I know now. It sounds ridiculous but your videos feel a bit…lonely. It's probably because you do all the work yourself. You ARE your channel and you're always in front of an artificial (usually black) background. I'm not saying that you should change your format because it works perfectly. But maybe occasionally show us a little bit of the outdoors to prove you are indeed a human and not an angel of film knowledge sent forth into this world for our benefit.

  • Martin Gomez Santiago

    Hey! So, what about the 70mm or 65mm cameras. They do really have a bigger sensor than 35mm. Would they have a bigger angle size? And the lenses?

  • Larys Lubowicki

    All right!
    Let's say I have 24-70mm lens setted up to f2.8,
    I zoom it from 24mm to 70mm, f/ number remains 2.8…
    According to given definition of f value (focal lenght/diameter of amerture), the diameter of aperture should change, but blades of aperture don't move while zooming…
    So I believe this definition was unnecessarily simplified. Am I right or wrong? 🙂

  • Omar Awany

    This channel is very important to all people who want to become cinema I thank you very much for this information and I wish you continued .. I am Omar from Syria I wish you the best

  • Virginia Li

    These videos are so awesome lol. My film class at USC is so much less clear than this. One suggestion is to up the focus and saturation on your face, it seems a little fuzzy and unsatisfying to me.

  • FinalLugiaGuardian

    Me hearing John Hess: "Here's how image stabilization works. Science, Science, Science, Tech, Tech, Tech. In other words they use magic."
    I guess it really is true that any sufficiently advanced technology is indistinguishable from magic.

  • Superbustr

    @Filmmaker IQ You're smarter, more knowledgeable and more educated on cinema then any of my academic university film teachers…

  • Hector Ramirez

    Man!!!! No jokes, I could have spent a whole month in school for this same info? thank you so much!!! Awesome explanation and Visual aid!

  • Steven Watchorn

    This was pretty much exactly what I needed. I am a film buff, but also work in physics with a specialty in optics (interferometry, though geometric or ray optics is something I am pretty well versed in). So I had all the science basis, but I did not know the lingo used in photography/cinematography. With this video introducing that in plain terms, I can match up the jargon with what I know from the optics side. Thanks very much for such a lucid video!

    A couple questions:

    1. When the word "sensor" is used here, does it refer to one picture element of the chip, or the the entire chip? In another video, when comparing chip sizes, there was a "number of sensors" listing in the figure that seemed to match up with the number of pixels. This also seemed to be the meaning when talking about the "circle of confusion" in the hyperfocal distance video. But here, when talking about normal lenses as such, the sensor seems to refer to the entire chip. Is there one meaning, or can it vary?

    2. When talking about normal lenses and saying they need to be "about the same size as the sensor," does that refer to the diameter of the lens being about the same size? This is what it looks like, but I just want to be sure.

    Many thanks again!

  • panda4247

    It's funny how "lens" is singular so it's "lens -> lenses", not something like "len -> lens"
    I always think of hobbitses when he says lenses

  • Jaco van Lith

    It is not correct to mention Full Frame, it must be Double Frame. The ( Single) Frame of
    18 x 24 mm was the standard. The standard of the frame shot on a perforated film with
    a width of 35 mm. It is the size of the ( professional) cine camera, like the one made bij Arri..

  • typograf62

    A split diopter was also used in Das Boot.
    Years ago I experimented with macrophoto using extension tubes. It turned out that some extension tubes from my grandfathers large camera (he had used that for making stereo photographies) fitted my modern camera (a Praktica), still using 42 mm thread.

  • Mauricio Moreno

    Is it just me, or does someone else see Dr. Marvin Monroe from The Simpsons in this video? 😀

  • Keith Rayner

    These lectures are just awesome. Just the thing I need to see from the professionals to help me with my C100c and follow focus lenses " Fantastic"

  • AnthonyDavidPhoto

    Hey John! Your videos are amazing! They've taught me many things that for so many years I knew the wrong way! If you can please tell me, does the aperture width changes on crop frame lenses? I've searched a lot on the internet but couldn't find a solid answer. I am asking so that I know if I should convert the aperture of a crop frame lens when I want to make comparison tests. Thank you in advance!

  • Omar Quintana

    hello, im huge fan of your videos. at the 5:40 minute you said the ASC indicate the normal lens is 2x the diagonal for theatrical . I couldn’t find this data at asc manual neither at google. could you be kind of point me on the right direction

  • Michael Rapp

    Hi guys, I really enjoy your videos, kinda geeky- nerdy, but quite entertaining for me (yes, definitely some nerdiness in my pedigree… )
    I have one question: what software do you use for the infographics/ blackboard stuff; doing the equations and "blackboard drawings"? (like at 13:18)
    Cheers, and keep up your good stuff,

  • Babu.G.S Rao

    kudo's to the modren day technology…..because of which the gaints of photography are watchable in my living room….thanks for sharing the knowledge sir….

  • Omar Quintana

    at 7:00 you say telephoto compress spacial dimension and wides exaggerate spacial dimension, but in other occasion you say the compression is because the distance camera-subject (focus distance) not because the focal length
    i did a test: same photo of a ball with a telephoto and wide. after I enlarged the central area of the wide angle to match the telephoto and with the telephoto I got a flat disc and with enlarged section of the wide angle photo no compression at all
    so I’m lost here on the matter

  • Evtim Stefanov

    That was realy great! Thank you. Just wanna ask: Would a Nikon stabilisation (talking about that gyrodcopic effect with floating element in the lens) work with a mirrorles camera without using those expensive electronic adapers? Thank you very much in advance!

  • Steve Moran

    very informative, My focus is on camera usage for aerial photography and map making. This information is helpful in determining the best camera and lens for the job.

  • Cornelius Dobeneck

    Just one thing … yes, I know, everybody got used to it but "Crop Factor" is still technically wrong! It should be named "Zoom Factor". Just walk through your own video and you see why. Let me point out the "FOCAL LENGTH REDUCER!" Why isn't it called "Crop Reducer"? And another thing. Everybody constantly compares any whatsoever sensor to the most common PHOTAGROPHY 35mm sensor while in film history 35mm filmstock DOES NOT always captured the same frame size. In other words, when it comes to film 35mm film is NOT 35mm film! 35mm filmstock/silent era = aspect ratio (AR) 1:1.33; 35mm film stock/early sound film AR = 1:1.2; 35mm Academy film stock (aka STANDARD) AR = 1:1.33; 35mm US widescreen film stock AR = 1:1.85; 35mm EU film stock AR = 1:1.66; 35mm Anamorphic AR 1:1.2 (projected 1:2.35)! All of these are 35mm Film so why in hell does noone talk of "Crop Factor" when it comes to film stock? Because its idiotic! BUT what has been filmstock in the anolog world is now SENSOR SIZE in the digital world. As we can see above … there is NO "standard" in image size and I didn't even started to talk about IMAX and or 70mm filmstock. So NO, a sensor does NOT crop an image BUT a sensor has an effect on the lens if you use unpropper gear. A full frame lens is NOT designed to be used on a M4/3 sensor! Just as you wouldn't put a 70mm filmstock into a 35mm filmcamera and talk about "entagling factor"! And why the hell did you NOT point out that there are lenses especially designed to be used on none 35mm sensor cameras? I'm sorry but when someone is using an APS-C designed LENS on a fiull frame camera NOONE will speack about a fucking "Crop Factor" despite the fact that the image taken will most likely BE croped … if you get that nonsense to work anyway! All the talk about "Crop Factor" is technically mambo-jambo and makes no snese AT ALL! All you can do is talk about IMPROPPER use of gear and how this effects your work. The camera sure as hell does nothing with your image but recording the image that the camera records that the camera records that the camera records ….. 😀

  • syousef

    Overall an excellent comprehensive video good but while I realize your focus is video, here are a couple of caveats/corrections for stills photography:
    1. Focus breathing can be an issue for stills photography. It makes the lowers the magnification/reproduction size of closer objects. If you're trying to get as many pixels on a bird a couple of meters away that is an issue. If you're shooting people it means you'll want to get closer as well.
    2. Varifocal lenses are also a problem for stills photography for fast action sports (e.g. motor sports or an airshow). You don't get this wrong but you don't go into it either. Whene you want to zoom while you're shooting a sequence, even if the lens is very fast focusing you're still going to miss some shots with a varifocal lens that you'll get with a parfocal lens. On Nikon compare the Older 70-300VR (parfocal) to the newer AF-P DX VR (faster focusing but varifocal). You're going to want the older lens.
    Keep up the excellent videos.

  • WildWestHikes

    Thanks for another fantastic video. I'm of the "buy once cry once" philosophy. This information is indispensable when it comes to not wasting money on additional lenses that may be unnecessary for a beginning photographer.

  • Old Video Geek

    Great video I'm a longtime videographer and already understood 95% of what you were talking about, thanks a lot for clearing up that other 5%.

  • Colin Robertson

    A little late to this channel, but this is serious gold, even for a (primarily) stills photographer. Great summary John.

  • amanieux

    do you have a video explaining why is image getting sharper/more contrast/less CA/less bloom at smaller apertures ? as the sensor is a rectangular shape, would not the image be better with a rectangular aperture rather than a circular aperture ?

  • Zach Turner

    These are all the best informative videos on cinema and photography you can find. I'd say ten out of ten except I have to deduct points for consistently referring to silicon as "silicone".

  • rs232boy

    Man, those are the absolute best explanations I have seen on the subject in my whole life. You have amazing pedagogy and a genuine talent for technical explanations. Keep up this work!

  • paul sullivan

    APS-C crop factors: Canon: 1.6 (as stated…) Nikon (whose APS-C sensors are slightly larger than Canon's…) crop factor is 1.52

  • Pete Long

    Honestly the best. I've learned more from you than I did in my entire college career. The hardest part about it is choosing which video to watch next! and learning when to stop for the day!

  • Kennynva

    New here…but at 4:15 in the video, talking about crop size they show full frame, then show APS-C and say you get 1.6 X LARGER…where to me the diagram is shrinking, which to me means smaller. I dont understand that…what is getting larger?

  • Barmaley_bl

    I am surprised you didn't mention teleconverters as they are a cheap way to widen or tighten the focal length of a prime lens or zoom.

  • wado1942

    I always wondered why traditional cinematographers considered 50mm lenses "normal" even though their frames are 1/2 the size of still photographers'. Now I know! Thank you for yet another great video.

  • Kevy D.

    Hi John, again great video! My question is about the normal lens and the diagonal part, especially when we consider about aspect ratio, the normal aspect ratio for photography is 1.33:1 but the sensor size is 36:24 that is 1.5:1, therefore does that mean based on same formula the normal lens for a 4:3 photo would be 40mm instead of 43mm? Let me know if I am wrong. Even though the changes looks small however when it comes to cinematography a normal lens for super 35mm camera from aspect ratio of 1.33:1 to 2.39:1 could be changed from about 31mm to 25mm that is a lot. Also when you talk about for cinema the diagonal needs x2, is there any deeper research about it? Like how the distance and screen size influence the normal lens look, because ACS seems not given much detail about it.

  • Nick Giles

    Absolutely amazing content throughout this and in fact all their videos!
    One question though: Why does the sensor size affect FOV? I understand how focal length does, but why exactly do we get a crop factor with a smaller sensor? Is there another sort of inverse triangle behind the lens that makes FOV larger or smaller based on the sensor?

  • stupedrandomname

    I love that that home made camera! It is wonderful to see the light coming through the lens like that with absolutely no tech babble around it. Just light and the image. Thanks for putting that together.

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