How Does a DP Choose Lenses?

May 16, 2022May 16, 2022 neilosemananamorphic, bokeh, iris, lens flare, lenses, prep, spherical

There is a huge range of glass available to filmmakers today – everything from vintage cinema lenses from the 60s to modern stills glass made for DSLRs. How can a DP choose which is right for their production?

Mount

The first thing to take into account is the lens mount on your camera. If it is PL mount you will have access to a huge range of cinema lenses, some of them with decades of movie history. Other mounts such as Canon EF also provide plenty of choice, but mainly glass aimed at stills rather than cinematography. Some lenses can be mount-converted, some cameras can switch mounts, and adapters are available too, but it’s important to know upfront which lenses are going to be ruled out by your camera choice and which aren’t.

Spherical or Anamorphic

Test of a 30mm Cooke Xtal anamoprhic lens

Anamorphic lenses squeeze the image horizontally, to be unsqueezed in post-production. The results are a wider picture, distinctive oval bokeh (out of focus areas) and often lens flares with horizontal streaks in them. This look is very cinematic, but anamorphic lenses tend to be bigger, heavier, more expensive, need more light than and don’t focus as close as their spherical counterparts, so think carefully before you choose them.

Speed

The speed of a lens – i.e. its maximum aperture – is one of its most important characteristics. A fast prime lens might open to T1.4, while a zoom or anamorphic prime might only go to T4. That’s three stops’ difference, equating to eight times more light required by the T4 lens. That can have a big impact on the size and number of lights you need. The ISO you plan to shoot at will also factor into this, of course.

Also consider how deep or shallow a depth of field you want. If you’re after super-blurry backgrounds, only a fast lens will give you those (though shooting on a large-format camera will help). This brings us to…

Bokeh

Bokeh is the appearance of out-of-focus areas in your image. It is most noticeable in small highlights such as fairy lights, which generally turn into big circles when they’re out of focus. Just how big and how smoothly circular depends on the lens and the aperture settings. Some lenses will have more geometric bokeh, octagons for example, which is a result of the shape and number of iris blades within. The bokeh may look rounder when the lens is wide open and more geometric when it is stopped down, or vice versa. It will also have a different shape at the edges of frame. What this comes down to is what look you feel is most aesthetically pleasing or appropriate for your story.

Lens Flares

Testing the flare of a Cooke Century 32mm

Another aesthetic choice. How much does the lens flare when light shines straight into it? What about when the light is just out of frame? Is there much veiling flare – an overall milkiness to the image? Do you like the colours and shapes of the flare? Do they feel natural or intrusive, and which is most fitting for the tone of your piece?

Sharpness

This is an important factor with the resolutions of cameras ever increasing. Any decent lens will be sharp at T5.6, but the more you open the iris the more you might start to see the image softening, especially when it is wide open (or conversely when it is stopped down to its minimum aperture). Check also the edges of frame, which may be less sharp than the centre, especially on a vintage or anamorphic lens. If you plan to do a lot of central framing then soft edges may not matter, or may even help to draw the viewer’s eye to the subject, but if you plan to put your subjects at the extreme sides of the frame then you should be careful what lenses you select.

Breathing

A lens is said to breathe when pulling the focus makes the image zoom in or out slightly. It is most noticeable with zoom lenses, some stills lenses and older glass. If you are racking back and forth between the characters in a deep two-shot, lens breathing can become very distracting.

Other Considerations

Other things to look out for are diffraction spikes, the star effect that happens around bright light sources, and colour rendition, which can vary slightly from lens to lens. If you expect to be physically close to your subject you should note the minimum focus distance of the lenses, which will be different for each length in the series. Also consider what focal lengths your chosen lens series contains – are there enough different lengths to cover everything you hope to shoot, especially at the shortest and longest ends of the range?

If you’re still not sure where to start, test footage and comparison videos of different lenses can be found online, like this one I made in 2017:

Better still, ask a rental house if you can come in for a day and shoot your own tests.

See also:

5 Things You Didn’t Know About the Iris in Your Lens

January 10, 2022January 9, 2022 neilosemanaperture, bokeh, depth of field, exposure, f-stop, focus, focus pulling, iris, lenses, VFX

Inside a lens, amongst the various glass elements, is an ingenious mechanism which we call the iris. Just like your biological iris, it controls the amount of light passing through the pupil to form an image. I’ve written about the iris’s use to control exposure before, and its well-known side effect of controlling depth of field. But here are five things that aren’t so commonly known about irises.

1. f-stops and the entrance pupil

This image shows the exit pupil because it’s seen through the rear element of the lens. A view through the front element would show the entrance pupil.

The f-number of a lens is the ratio of the focal length to the diameter of the aperture, but did you know that it isn’t the actual diameter of the aperture that’s used in this calculation? It’s the apparent diameter as viewed through the front of the lens. A lens might have a magnifying front element, causing the aperture to appear larger than its physical size, or a reducing one, causing it to appear smaller. Either way, it’s this apparent aperture – known as the entrance pupil – which is used to find the f-number.

2. No-parallax point

The no-parallax point of a lens is located at its entrance pupil. Sometimes called the nodal point, although that’s technically something different, this is the point around which the camera must pan and tilt if you want to eliminate all parallax. This is important for forced perspective work, for panoramas stitched together from multiple shots, and other types of VFX.

3. Focus

If you need to check your focal distance with a tape measure, many cameras have a handy Phi symbol on the side indicating where the sensor plane is located so that you can measure from that point. But technically you should be measuring to the entrance pupil. The sensor plane marker is just a convenient shortcut because the entrance pupil is in a different place for every lens and changes when the lens is refocused or zoomed. In most cases the depth of field is large enough for the shortcut to give perfectly acceptable results, however.

4. Bokeh shape

The bokeh of a 32mm Cooke S4 wide open at T2 (left) and stopped down to T2.8 (right). Note also the diffraction spikes visible in the righthand image.

The shape of the entrance pupil determines the shape of the image’s bokeh (out of focus areas), most noticeable in small highlights such as background fairy lights. The pupil’s shape is determined both by the number of iris blades and the shape of their edges. The edges are often curved to approximate a circle when the iris is wide open, but form more of a polygon when stopped down. For example, a Cooke S4 produces octagonal bokeh at most aperture settings, indicating eight iris blades. Incidentally, an anamorphic lens has a roughly circular aperture like any other lens, but the entrance pupil (and hence the bokeh) is typically oval because of the anamorphosing effect of the front elements.

5. Diffraction spikes

When the edge of an iris blade is straight or roughly straight, it spreads out the light in a perpendicular direction, creating a diffraction spike. The result is a star pattern around bright lights, typically most visible at high f-stops. Every blade produces a pair of spikes in opposite directions, so the number of points in the star is equal to twice the number of iris blades – as long as that number is odd. If the number of blades is even, diffraction spikes from opposite sides of the iris overlap, so the number of apparent spikes is the same as the number of blades, as in the eight-pointed Cooke diffraction pictured above right.

Undisclosed Project: Experimentation

March 15, 2021June 30, 2021 neilosemanAlexa, Angenieux, Arri, blog, bokeh, cinematography, Cooke, focus, lens flare, lenses, lighting, Panchro, Red, Red Gemini, Sony, Sony F55, spherical, Superspeed, testing, Varotal, video, Zeiss

The main event of last week’s prep was a test at Panavision of the Arri Alexa XT, Red Gemini and Sony F55, along with Cooke Panchro, Cooke Varotal, Zeiss Superspeed and Angenieux glass. More on that below, along with footage.

The week started with Zoom meetings with the costume designer, the make-up artist, potential fight choeographers and a theatrical lighting designer. The latter is handling a number of scenes which take place on a stage, which is a new and exciting collaboration for me. I met with her at the location the next day, along with the gaffer and best boy. After discussing the stage scenes and what extra sources we might need – even as some of them were starting to be rigged – I left the lighting designer to it. The rest of us then toured the various rooms of the location, with the best boy making notes and lighting plans on his tablet as the gaffer and I discussed them. They also took measurements and worked out what distro they would need, delivering a lighting kit list to production the next day.

Meanwhile, at the request of the producer, I began a shot list, beginning with two logistically complex scenes. Despite all the recces so far, I’ve not thought about shots as much as you might think, except where they are specified in the script or where they jumped out at me when viewing the location. I expect that much of the shot planning will be done during the rehearsals, using Artemis Pro. That’s much better and easier than sitting at home trying to imagine things, but it’s useful for other departments to be able to see a shot list as early as possible.

So, the camera tests. I knew all along that I wanted to test multiple cameras and lenses to find the right ones for this project, a practice that is common on features but which, for one reason and another, I’ve never had a proper chance to do before. So I was very excited to spend Wednesday at Panavision, not far from my old stomping ground in Perivale, playing around with expensive equipment.

Specifically we had: an Arri Alexa – a camera I’m very familiar with, and my gut instinct for shooting this project on; a Sony F55 – which I was curious to test because it was used to shoot the beautiful Outlander series; and a Red Gemini – because I haven’t used a Red in years and I wanted to check I wasn’t missing out on something awesome.

For lenses we had: a set of Cooke Panchros – again a gut instinct (I’ve never used them, but from what I’ve read they seemed to fit); a set of Zeiss Superspeeds – selected after reviewing my 2017 test footage from Arri Rental; a couple of Cooke Varotal zooms, and the equivalents by the ever-reliable Angenieux. Other than the Angenieux we used on the B-camera for The Little Mermaid (which I don’t think we ever zoomed during a take), I’ve not used cinema zooms before, but I want the old-fashioned look for this project.

Here are the edited highlights from the tests…

You’ll notice that the Sony F55 disappears from the video quite early on. This is because, although I quite liked the camera on the day, as soon as I looked at the images side by side I could see that the Sony was significantly softer than the other two.

So it was down to the Alexa vs. the Gemini, and the Cookes vs. the Superspeeds. I spent most of Thursday and all of Friday morning playing with the footage in DaVinci Resolve, trying to decide between these two pairs of very close contenders. I tried various LUTs, did some rough grading (very badly, because I’m not a colourist), tested how far I could brighten the footage before it broke down, and examined flares and bokeh obsessively.

Ultimately I chose the Cooke Panchros because (a) they have a beautiful and very natural-looking flare pattern, (b) the bokeh has a slight glow to it which I like, (c) the bokeh remains a nice shape when stopped down, unlike the Superspeeds’, which goes a bit geometric, (d) they seem sharper than the Superspeeds at the edges of frame when wide open, and (e) more lengths are available.

As for the zoom lenses (not included in the video), the Cooke and the Angenieux were very similar indeed. I chose the former because it focuses a little closer and the bokeh again has that nice glow.

I came very close to picking the Gemini as my camera. I think you’d have to say, objectively, it produces a better image than the Alexa, heretical as that may sound. The colours seem more realistic (although we didn’t shoot a colour chart, which was a major oversight) and it grades extremely well. But…

I’m not making a documentary. I want a cinematic look, and while the Gemini is by no means un-cinematic, the Alexa was clearly engineered by people who loved the look of film and strove to recreate it. When comparing the footage with the Godfather and Fanny and Alexander screen-grabs that are the touchstone of the look I want to create, the Alexa was just a little bit closer. My familiarity and comfort level with the Alexa was a factor too, and the ACs felt the same way.

I’m very glad to have tested the Gemini though, and next time I’m called upon to shoot something great and deliver in 4K (not a requirement on this project) I will know exactly where to turn. A couple of interesting things I learnt about it are: (1) whichever resolution (and concomitant crop factor) you select, you can record a down-scaled 2K ProRes file, and this goes for the Helium too; (2) 4K gives the Super-35 field of view, whereas 5K shows more, resulting in some lenses vignetting at this resolution.

Anamorphic Lens Tests

August 7, 2017August 18, 2017 neilosemanAlexa, anamorphic, Arri, aspect ratio, bokeh, cinematography, Cooke, focus, Hawk, Kowa, lens flare, lenses, testing, video

Anamorphic cinematography, first dabbled with in the 1920s, was popularised by Twentieth Century Fox in the fifties as CinemaScope. Television was growing in popularity and the studios were inventing gimmicks left, right and centre to encourage audiences back into cinemas. Fox’s idea was to immerse viewers in an image far wider than they were used to, but with minimal modifications to existing 4-perf 35mm projectors. They developed a system of anamorphic lenses containing elements which compressed the image horizontally by a factor of two. By placing a corresponding anamorphosing lens onto existing projectors, the image was unsqueezed into an aspect ratio of 2.55:1, or later 2.39:1.

Since those early days of CinemaScope, anamorphic cinematography has become associated with the biggest Hollywood blockbusters. Its optical features – streak flares, oval bokeh and curved horizontal lines – have been seared into our collective consciousness, indelibly associated with high production values.

I’ve not yet been fortunate enough to shoot anamorphic, but I was able to test a few lenses at Arri Rental recently, with the help of Rupert Peddle and Bex Clives. Last week I wrote about the spherical lenses which we tested; our anamorphic tests followed the same methodology.

Again we were shooting on an Alexa XT Plus in log C ProRes 4444 XQ, this time in 4:3 mode, a resolution of 2048×1536. Since all of the lenses had a standard 2:1 anamorphosing ratio, the images unsqueezed to a super-wide 2.66:1 ratio. (This is because the lenses were designed to be used on 35mm film with space left to one side for the optical soundtrack.) You can see the full width of this ratio in the first split-screen image in the video, at 2:08, and in the second image below, but otherwise I have horizontally cropped the footage to the standard 2.39:1 ratio.

We tested the following glass:

Series	Length	Speed	CF*	Weight
Hawk V	35mm	T2.2	30″	5.6kg
Cooke Xtal	30mm	T2.8	?	3kg
Kowa Mirrorscope	40mm	T2.2	36″	1.15kg
Kowa Mirrorscope	30mm	T2.3	?	?

* CF = close focus

For consistency with the spherical lenses, we used lengths around 32mm, but in the anamorphic format this is a pretty wide lens, not a mid-range lens. We shot at T2.8, again for consistency, but I hear that many anamorphics don’t perform well wider than T4.

We were only able to test what Arri Rental happened to have on the shelves that day. The biggest and presumably most expensive was the Hawk V-series. Next in size and weight was the Cooke Xtal – pronounced “crystal” – a 1970s lens based on the much-loved Speed Panchros. The smallest and lightest, was the Kowa Mirrorscope, with a list price of £1,200 per week for a set of four. (Sorry, I couldn’t find any pricing info for the others online.) Note that there isn’t really a 30mm Mirrorscope; to get this length you put a wide angle adapter on the 40mm. As this extra element decreases the optical performance, we tested it with and without, hence the two lengths.

Here’s the video…

Skin tones

Click on the image to see it at full quality.

To my eye, the Hawk has a fairly rich, warm skin tone, while the Cooke – as with the spherical S4 tested last week – seems a little grey and flat. The Kowa is inexplicably brighter than the other two lenses, which makes it hard to compare, but perhaps it’s a little cooler in tone?

Sharpness

Focus is more critical with anamorphic lenses than spherical ones. From a forum posting by Max Jacoby:

Anamorphic lenses have what is known as a “curved field of focus” that works similarly to the curved movie screens in some large Cinerama theatres. This is one reason that one needs to expose these lenses at a deeper stop. If one doesn’t, the curved field will not be covered by depth of field and either the edges or centre of the frame will be soft.

One day I’d like to re-test these lenses at a lower stop, T4 or T5.6, where they will all undoubtedly perform much better. But in this T2.8 test, on Bex’s face in the centre of frame, the Hawk V and the Kowa Mirrorscope 40mm – both almost a full stop from their maximum apertures – are clearly the sharpest of the bunch. The Cooke Xtal, which is wide open, is unsurprisingly softer. The 30mm adapter on the Mirrorscope completely destroys the image, not only making it very soft but also introducing colour aberration.

Now let’s look at the checkerboard at the side of frame and see if we can spot any differences in sharpness there…

It seems to me that the Kowa, both with and without the adapter, has a greater difference in sharpness between the centre and edges of frame than the the Hawk and Cooke. With the latter two lenses, the checkerboard is reasonably sharp, at least on the lefthand side, with some ghosting/blur visible towards the righthand side. The same thing can be observed on the chart in the flare tests at the end of the video.

Breathing & Bokeh

All of these lenses have a noticeable degree of breathe, which I suppose is to be expected from anamorphics. The Hawk V has roughly oval bokeh, the Cooke’s is more circular, while the Mirrorscope has interesting D-shaped bokeh.

Flare

The Hawk V doesn’t flare much at all, which is apparently due to the anamorphic element being in the middle of the lens, rather than at the front. The Kowa has a nice streak and glow around the light source, with a funky purple artefact on the opposite side of frame. But it’s the Cooke Xtal which provides the most classic lens flare, with a horizontal line across most of the frame and a partial star pattern around the source, despite the lens being wide open.

At the end of the video you can see how the flares develop on each lens as the light source moves horizontally across frame.

Distortion

A bulging effect is very obvious on all of these lenses, due to the focal lengths being quite wide for anamorphic. Notice how at 40mm on the Kowa Mirrorscope this curvature of the image is significantly reduced.

It’s hard to compare the levels of distortion because none of the focal lengths are exactly the same, except for the Cooke Xtal and the Kowa Mirrorscope with the 30mm adapter on. The Cooke’s top right and bottom left corners appear to be stretched away from the centre relative to the other two corners. I suppose that strange and funky stuff like this is exactly why you choose vintage glass.

Interestingly, the Cooke’s image appears a little tighter than the Kowa’s, which combined with my inability to find any evidence online of the existence of a 30mm Xtal, leads me to suspect we may have been given a mislabelled 32mm.

Conclusions

When we got to the end of our spherical tests and started putting the anamorphics on, I was shocked by the drop in sharpness. But as noted earlier, this is because anamorphics really need to be used with a smaller aperture than the T2.8 I often shoot at. If I learnt nothing else from this test, I learnt that anamorphic needs more light!

I would love to put the Cooke Xtal’s lovely flares and general vintage look to good use on a period movie one day. The Hawk V would be a good choice if I wanted the anamorphic look with warm, dynamic skin tones. The Kowa system seemed a little cheap and cobbled-together, but could well be a good solution for anamorphic on a budget, as long as I stayed away from the 30mm adapter!

I hope you’ve found these tests useful. Thanks again to 1st AC Rupert Peddle, 2nd AC Bex Clives and Arri Rental UK for making them possible.

Spherical Lens Tests

July 31, 2017August 18, 2017 neilosemanAlexa, Arri, bokeh, Canon, cinematography, Cooke, focus, Leica, lens flare, lenses, spherical, testing, video, Zeiss

The other week I spent a day at Arri Rental in Uxbridge, in the Bafta Room no less, conducting various camera and lens tests. I’ve done a number a productions now where I wanted to test but there wasn’t the time or money, so for a while I’ve been meaning to go into Arri on my own time and do some general tests for my education and edification. An upcoming short provided the catalyst for me to get around to it at last.

Aided by 1st AC Rupert Peddle and 2nd AC Bex Clives, I tested a dozen lenses, some spherical, some anamorphic. Today I will cover the spherical lenses; next time I’ll look at the anamorphics.

Method

We shot on an Alexa XT Plus in log C ProRes 4444 XQ at 3.2K. In the video the image has been downscaled to 1080P and a standard Rec.709 LUT has been added.

I set the Alexa to ISO 800 and lit Bex to a T2.8 using a 650W tungsten fresnel bounced off poly. For fill I caught a little of the spill from the fresnel with a matte silver bounce board on the opposite side of camera. I placed fairy lights in the background to observe the bokeh (out of focus areas) and turned on a 100W globe during each take to see what the flare did.

We shot all the lenses at 2.8 – the stop I most commonly use – and also wide open (compensating with the shutter angle), but the direct 2.8 comparison proved most useful, so that’s mainly what you’ll see in the video. We tested a single length: 35mm or the closest available to it.

What we didn’t do was shoot grey-scale or colour charts, or do any testing of vignettes or distortion. (The day after doing these tests, Shane Hurlbut, ASC published an Inner Circle post about how to tests lenses, so I immediately learnt what my omissions were!)

We tested the following lenses:

Series	Length	Speed	CF*	Weight	Price
Leica Summilux-C	29mm	T1.4	18″	1.7kg	£27K
Arri/Zeiss Master Prime	35mm	T1.3	14″	2.2kg	£16K
Cooke S4	32mm	T2	6″	1.85kg	£14K
Leica Summicron-C	35mm	T2	14″	1.3kg	£13K
Zeiss High Speed (a.k.a. Superspeed Mk III)	35mm	T1.3	14″	0.79kg	£12K (refurb)
Arri/Zeiss Ultra Prime	32mm	T1.9	15″	1.1kg	£10K
Zeiss T2.1	32mm	T2.1	24″	0.45kg	£4K (used)
Canon	35mm	T1.5	12″	1.1kg	£3K

* CF = close focus

Here’s the video…

Skin tones

Click the image to see it at best quality.

The Arri/Zeiss Master Prime and the two Leicas seem to have the most vibrant skin tones. To my eye, the Leicas have a slight creaminess that’s very pleasing. The Canon looks just a little cooler and less dynamic. I was surprised to find that the Cooke S4, the lens I’ve used most, appears to have a grey, flat skin tone compared with the Master Prime, Leicas and Canon. I would rank the Ultra Prime and Superspeed next, on a par except that the Ultra Prime has a noticeable magenta cast. My least favourite skin tones are on the Zeiss T2.1, which comparatively makes poor Bex look a little bit ill!

Some of the nuances will be lost in the YouTube and Jpeg compression, but this is a very subjective assessment anyway, so feel free to completely disagree with all of the above. Any of the differences noted above could be corrected by grading, to some extent . But remember that the lens is at the very start of the light’s journey from set to screen, and any wavelengths that don’t get through it are lost forever. It’s like fluorescent lamps with colours missing from the spectrum; you can’t put those back in in post.

Sharpness

I have to say, I’m unable to detect any difference in sharpness between the Master Prime, Cooke S4, Canon and Leicas. The Ultra Prime and Superspeed both look a hair softer, while the T2.1 is very soft.

Breathing

Breathing is the slight zooming effect that you get with some lenses when you pull focus. Looking at 4:44 in the video you can clearly see the differences in breathing between the eight lenses. Because this part of the video is showing a crop of the bottom left corner of the image, the breathing manifests as a shift to the left (zoom in) as the lens is racked closer (goes soft) and a shift to the right (zoom out) as it’s racked deeper (goes sharp).

All the Zeiss lenses except the Master Prime have a significant amount of breath when seen in isolation like this, but not enough to be noticeable to an audience in most real-world situations. The Cooke S4 has a little bit of breathe, and the Canon a hair less. The Master Prime and the Leicas are rock solid.