recently I asked “what lenses do you like” and pretty much ignored zooms, because the idea was do help define my (your) eye without the redundancy of the any focal length available zoom dynamic.
How about I contradict that now, go fully hypocrite even.
When shooting video, a zoom may be the better option.
I am going to assume that at least two focal lengths are required in most videographers kits.
Video has different needs, some of which can be hard or expensive to service, but also has some handy mitigations for the negatives zooms can bring.
Changing focal length in video is the same as for stills except it can interrupt your “rig” setup. Balance of cages, follow focussing attachments, filters etc can all be changed, but not fast and sometimes not fast enough. You could argue that the more contemplative nature of video production makes this irrelevant, but let’s be real, modern content creation is not that space.
Cinema prime lenses are designed to match each other and often come in sets (size, weight, ring placement, filters and even colours), but they are not cheap and often, to be consistent, each weighs as much as the heaviest of them. There are zooms available and often for less than a full set of primes, but these are at the top end of the range, quite rare and often massively proportioned.
Without a matching set of cinema glass, you may need to adjust to;
changing filters and re-set their rotations (or buy duplicates of the same),
re-balancing a gimbal/cage centre point,
different focus throw and even direction if changing brands,
shifting ring placement, especially with a follow focus,
a different aperture range,
changing rig balance,
matching colours in post. Only cinema matched glass avoids this.
Some of these still need doing even with with matching glass.
A zoom fixes all or many of these issues. The only thing that may need some, but often not much adjustment is gimbal balance (or don’t zoom when using one!), but again, all the other stuff is fixed, so this is the only problem.
Situations that stretch stills cameras are sometimes less problematic for video.
For video, a slower aperture zoom may be a blessing and is certainly less of a problem.
For stills, movement in low light may need a minimum shutter speed of 1/250th or higher pushing your ISO into less pretty places, or forcing a wider aperture/shallower depth of field if available, but with video 1/50th or 1/60th usually tops you out (180 degree rule at 24/25/30fps).
These shutter speeds with a maximum aperture of f2.8 and ISO’s up to 3200 handle most situations and are available to most camera and lens systems.
Depth of field? Even a MFT camera at f2.8 has decent shallow depth rendering for many practical purposes, especially if you are a manually focussing, enough room for smooth transitions without “more out than in” often being the case. Super shallow depth in video is desirable, but less so and often less practical than for stills.
The Oly 12-40 f2.8 on my G9’s provides (in 1080), a 24-215* equivalent range using the loss-less tele converter mode, takes the one filter set (62mm), with full time linear manual focus and good close focus. The colour and overall look matches obviously because it is the one lens.
If I want very shallow depth, some of the prime’s available match well enough with the added bonus of having their own set of 46mm filters.
The S5, 20-60 and 50mm are similar except (ironically), they do share the same filters so duplicates or some switching is needed. The variable aperture zoom is used at f5.6, giving me effectively the same depth as the f2.8 MFT lens.
Tricky for a stills camera, this is much easier to achieve and suitably “cinematic” in video.
My intention for the work G9 rig (or non-rig I guess) is to carry the Olympus 17 with ND filter mounted for video which gives me two focal lengths in video (FF 35 and 90mm), the 25mm as a low light stills lens indoors. This means really only having one very light weight lens more in the bag that can be used for stills in good light, but video in any light (bright light being the problem for video).
The fully rigged video G9 on the other hand gets the 12-40. It is a heavy lens, but one that works well for video with all the advantages highlighted above. This has the matt box ring, any filter needed and like the 17mm has linear manual focus that turns the same way and a fixed aperture. I have also grown to appreciate the light and bright Panasonic sensor and organic Olympus lens combination.
That kit also gets an EM1x and the Sigma 30mm, Leica 8-18 and 12-60 and the Oly 40-150 f2.8 for stills, any of which could be used for video also.
*The other zoom. There is another option available with a few catches. The G9 and other cameras I assume have some form of built in teleconverter or format change (the S5 has full to APS-c switch), that can “zoom” your lens providing two focal lengths. Limited to 1080 usually, because it is using a 4k sensor to crop without loss to 1080 (same as in post), this allows you a two step zoom.