Choosing a lens package

Picking lenses is two choices layered on top of each other. The first is creative: how wide and how tight the story needs to go, and what the glass should look like. The second is arithmetic: what those focal lengths actually frame on the camera and recording mode you are shooting. This guide is mostly about the second, because it is the part that goes wrong quietly.

Start from the frames, then find the focal lengths

Write down the widest and the tightest shots the job needs, and the one or two sizes you will live in. Then convert them into angles, because an angle travels between formats and a focal length does not. A 25 mm is a wide lens on a Super 16 mode and close to a normal one on a large format mode.

The table gives the horizontal angle of common focal lengths on five real recording modes, from a Super 16 crop to large format. Find the angle you want in one column and read across.

The modes, by column: ARRI ALEXA 35 2K 16:9 S16; Blackmagic Design Pocket Cinema Camera 6K Pro 6K 16:9; ARRI ALEXA 35 4K 16:9; Canon EOS C70 Super 35 4K DCI 17:9; ARRI ALEXA Mini LF 4.3K LF 16:9. Figures computed from the recording mode sizes in Cutvey Viewfinder's gear data, counted November 2, 2026, with the app's own rules.

Spacing a prime set

A maker's full series is spaced tightly: the ARRI Signature Prime list in the gear data runs from 12 to 280 mm in 16 lenses, an average step of 1.23x. A package rented for a job takes a subset, with neighbors further apart. In the Super 35 set used below, 18 to 25 is 1.39x, 25 to 32 is 1.28x, 32 to 50 is 1.56x, 50 to 75 is 1.50x. Gaps wider than that leave shots you cannot quite get without moving the camera; a set with every step much closer than that is heavy to carry and slow to change.

Three questions settle the shape of a set:

• What is the widest frame the locations allow? Small rooms push the wide end wider. A scout with a viewfinder answers this better than any rule (how to tech scout).
• Where will you live? Put two lenses close together around the sizes you use most, and leave the extremes thinner.
• What does the long end do? Reaction close-ups across a room need more reach than an interview on a sofa.

Moving a set to another format

A DP who knows a Super 35 set by heart will want the same frames on a large format camera. Scale each focal length by the ratio of the two widths, then take the nearest lens that exists. Here is a Super 35 set on the ARRI ALEXA 35 in 4K 16:9 (24.88 mm wide) moved to the ALEXA Mini LF in 4.3K LF 16:9 (35.64 mm wide), picking from the focal lengths of the ARRI Signature Prime series as the gear data lists them:

The ratio here is 1.43. The 75 mm has no close match: 107.4 mm falls between the Signature 95 and 125, so pick by whether the shot wants the wider or the tighter frame. Matching angles keeps the framing. It does not keep the depth of field: the longer lens at the same stop holds less in focus, which is part of why large format looks the way it does. The depth of field calculator and the crop factor calculator do these sums for any pair of modes.

Primes, zooms, or both

Primes are usually faster and lighter for their stop, and a set from one series matches in color and rendering. A zoom saves lens changes and lets you find the frame by turning a barrel instead of moving the camera; it costs weight and often a stop or more of speed. Plenty of packages are a prime set with one zoom for the days the schedule is tight.

On a scout you can try both. In Cutvey Viewfinder the arrows beside the picture step through a prime kit; on a zoom they turn the barrel, and holding them ramps the zoom. A pinch on the picture gives a fine zoom that is written down with the shot, so a frame found on a 50 mm at × 1.20 is recorded as 50 mm × 1.20, which is 60 mm.

Mixing series

Rental packages often mix: a set of primes plus a macro from another maker, or a long lens the main series does not make. That is fine for framing. Watch two things:

• Coverage. A lens made for Super 35 can vignette on a full frame or large format mode. Check the image circle on the rental house's sheet against the mode you will shoot.
• Matching. Different series render color and contrast differently, so a cut between them can show. Test before the job if the scene cuts back and forth.

The app's kit builder takes primes from different series in one kit (it shows as Mixed primes), and you can add your own series with its own image circle if it is not in the list. Set up a camera, a mode and a lens kit has the steps.

Adapters change the focal length

A focal reducer (a speed booster) between the lens and the camera shrinks the image onto the sensor; an extender enlarges it. Both change the effective focal length, and with it the frame and the depth of field. Here is a 50 mm on the Pocket Cinema Camera 6K Pro in 6K 16:9 (23.1 mm wide), with each of the adapter presets the app offers:

Light is the change in the working stop, 2 × log2(1 ÷ factor): a reducer gathers the image into a smaller area and gets brighter, an extender gets darker. Figures computed from the recording mode sizes in Cutvey Viewfinder's gear data, counted November 2, 2026, with the app's own rules.

In Cutvey Viewfinder the adapter goes under Lens Adapter in Setup; the frame and the depth of field panel both use the result. A clip-on lens over the phone is a different thing and has its own setting. See lens adapters and clip-on lenses.

See the whole kit at once

Choosing between two packages is easier when you can see every lens's frame from one spot. Overview in Cutvey Viewfinder draws each lens in the kit as its own frame line over one picture, taken on the phone camera wide enough for the widest lens. Stand where the camera will be, turn on Overview, and the question "do we need the 21 or is the 25 enough" answers itself.

The figures on this page come from the gear data counted November 2, 2026: 722 camera bodies, 2,309 recording modes, 707 lens series and 3,926 lenses from more than 100 lens brands.

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