Shooting High Speed – Further Information

Hi ,

I am about to start a shoot next week with a DP I've been warned about.

We will be shooting high speed frame rates and I've been told the DP in question will only give me a 'T-stop basic' shortly before we turn over thus not giving me much time to work out the stop.

How much time is reasonable to expect for this?

We are using a Photosonics 4B which goes up to 2082 fps and an Arri 435.

Now I understand if we are shooting 50fps and the 'T-stop basic' is T5.6 then I would just open up 1 stop to T4. Am I correct in this assumption?

If we are to shoot 800fps, 1000fps or 1500fps (as examples ) and the 'T-stop basic' was T22 what's the new adjusted stop? Is there a quick way to calculate this and are there any charts out there to assist me?

Any help greatly appreciated.

Best regards,

Lancelot Smith
Focus puller/camera assistant
London UK (recently relocated)

Why not make up a quick reference table of likely speeds and compensations.

J. Bucknall
1st AC
London

>>Regarding how fast or what is the time one should have to do this >>calculation is in my opinion irrelevant.

Agreed. The important thing is to get it right. But you don't want to take so long that people wonder if you know what you're doing.

I also agree with an earlier poster who said to make up a chart or get some sort of calculator. PCam and PCine are great for this if you have a Palm device. Maybe Photosonics offers such a thing.

Are you getting your information about the DP second hand or have you actually talked to the DP to find out what he/she wants?

You probably don't have to have depth of field discussions with the DP on set unless he/she asks. I don't know many DP’s who don't keep depth of field in mind when they calculate a stop.

Just remember that f-stops double or halve the light coming in. That should allow for some quick calculations. For example, if your basic stop was T22, then :

25 -> 50 = 1 stop
50 ->100 = 2 stops
100 -> 200 = 3 stops
200 -> 400 = 4 stops
400 -> 800 = 5 stops

So, at 800 fps your stop would be T4. At 1000 fps, open up a quarter stop or so (T3.8). 1500 fps, open up a full stop (T2.8 or, if you really want to nitpick, blow on the ring a little to get T2.7). When in doubt, err on the slightly wider open side.

Personally I would never give a "basic" stop. It's my responsibility to make sure that I've got the right shooting stop, and my assistant's job to make sure it's on the lens and to help me with my math if I ask.

Art Adams
Director of Photography
Film | Hidef | Video

San Jose, CA, USA
www.artadams.net
415.760.5167
Skype: ArtAtoms

Hi Lancelot!

Well I'm wondering that you don't have a highspeed technician with the 4B...

Shooting highspeed is something very special in the business. You have to find out what are the technical specifications of the camera and their cleaning procedures.

The Photosonics 4B is a so called "prism camera". This means that instead of a mirror a beamsplitter is placed in front of the image plane. And no highspeed camera will have a full 180° shutter. The 4B has a "K5" Shutter which is similar to 72°. So you will not only have a compensation for the frame rate, also for the shutter angle and for the beamsplitter!

If you want to shoot on 2.100 fps it's a total compensation of 8 stops!

Calculations and more information can also be found on "www.highspeedfilm.de" - this site belongs to Dedo-Weigert-Film in Germany

And now all the best for your shooting - and don't forget to maintain the camera on Set!!!

Best regards,

Marco

>>How much time is reasonable to expect for this?

A freelance cinematographer assistant will be faced with working procedures that differ from a group of cinematographers to another. So to avoid any misunderstanding talk to him prior to the shoot, as exactly what he means and how he sets up his lightmeter. There are many ways in calculating and announcing a T-Stop, but talk to him and whatever another person said still get it right with your guv.

If you are several assistants than the first so to speak should inform you about that. There is nothing unusual about that on the contrary.

Nevertheless nothing stops you from preparing some notes or make up little charts. Your post is already the right way to go. The Kelly and the Samuelson Calculator, just two examples will give you some conversion but not beyond 300 some frames, which is more than what you need on an Arri 435. Unfortunately for the Photosonics this is not the case but you can easily calculate this yourself. Just write them down. There is probably some pocket pc program, e.g. pcam or cinecam but I rarely use this. However it is not just a matter of opening up the aperture, cause there is a certain depth of field to take into account.

Make sure that the cinematographer is also informed about this, that is part of your job, informing, reminding or pointing this out.. On a recent HS commercial,

I had multiple cameras set up.

The highest frame rate we could get was actually decided by the amount of light that was available in relation to a wanted depth of field. The 435 was then set up in such a way to match the depth of field close to the HS cameras, by the use of ND, and shutter. Normally the cinematographer will have taken that into account prior to the shoot anyway.

25, 50, 100, 200, 400, 800, 1600 fps equals
1, x2, x3, x4, x8, x16, x32 each increment is equal to one stop.

Regarding how fast or what is the time one should have to do this calculation is in my opinion irrelevant. I mean the quicker the better of course but most important of all is to get it right and to be sure.

In case of doubt calculate again. You might not be popular then but they will forget this. A mistake will not be popular at all and that they will not forget and most likely not forgive.

Hope this helps, good luck.

Regards

SUYS Emmanuel

Assistant Caméra - Camera Assistant - Kamera Assistent
35mm-16mm-HD
BVK- European based Mobil# Munich +491608036889 - London +447910034443
(please use German number)
cml-listmum, CinematographyMailingList

>>The Photosonics 4B is a so called "prism camera". This means that >>instead of a mirror a beamsplitter is placed in front of the image plane.

Any time you are faced with these calculations, make yourself a chart. It only takes a minute, and is much better than trying to calculate in your head.

Since you will be using the Photosonics 4B, with its 72 degree shutter, use the chart for the 4B on the website, as Marco suggested, but for other cameras with 180 degree shutters, make a chart for yourself :

frame rate t/ stop (at 180 degree shutter)

24/25 fps 16 22 32
48/50 fps 11 16 22
100 fps 8 11 16
200 fps 5.6 8 11
400 fps 4 5.6 8
800 fps 2.8 4 5.6
1600 fps 2 2.8 4
3200 fps 1.4 2 2.8

Add as many more columns and/or frame rates as necessary.
When the DP gives you the 25 fps exposure, find that stop on the top row and go down that column to your frame rate.
Tape the chart on the side of the camera, and you are ready to go. (Give a copy to the DP!)

You'll have to estimate the in between speeds and stops, but that should be simple with this reference chart available.

Check your chart against a printed chart, or pCam/pCine, or other calculator to make sure the first few entries are correct (and that you are going in the right direction!), then it's just a matter of simple math, open one stop for every time you double the frame rate.

For frame rates SLOWER than 24/25 fps, extend the chart upwards, closing one stop for every time you cut the frame rate in half.

Just make sure the shutter angles are correct and consistent.

Doug Hart
1AC, NYC

Art Adams wrote:

>>You probably don't have to have depth of field discussions with the DP >>on set unless he/she asks. I don't know many DP’s who don't keep >>depth of field in mind when they calculate a stop.

In the majority of cases you are right of course. It is not about having a discussion so to say but I would call this double checking.

Most people I work with of course keep the depth of field in mind but they also expect me to follow than do just the mechanical aspect of the job. As a focus puller it is not just about getting the focus right but also about keeping a constant eye on the depth of field. I found myself in quite a few situations over the years where the "remark" was very much appreciated. I believe that one should point out or double check with the cinematographer when a certain stop might have a less attractive outcome as far as depth of field is concerned. Of course this, I think, very much depends on the working relation between the cinematographer and his assistant, on the type of work, the pace of the shoot and the mood on the set that day. There is a time for this and this has to be discreet as any other exchange between the assistant and the cinematographer.

On a high speed shoot a couple of weeks ago there was such a situation, as one of the cameras had a depth of field to long according to my calculations, we could not get the background softer any further by the means of ND filters. That camera's setup was modified accordingly.

There are times where there is just so much happening on a set and that little extra awareness is very welcome. Nothing wrong with the people I work for and this does not take away their merit whatsoever. It is the way I usually work and one of the reasons why I work for some on a regular basis. Again this is something that is more than often well discussed prior to shooting on how the cinematographer expects me to work alongside him.

My two rupees,

SUYS Emmanuel

Hi all,

Just a quick note to thank everyone for their helpful comments recently

- Doug, Art, Bill et al.

Apparently there will be a Photosonics tech. on site as well which should make my job a little easier.

I have spoken to the DP re: basic stops and been informed that's just the way he likes to work - perhaps he enjoys keeping his 1st. AC on their toes.

Best,

Lancelot Smith
Focus puller/camera assistant
London UK (recently relocated)

The guy sound like an idiot, is he trying catch you out by pressuring you into shooting at the wrong stop?

His funeral. Be calm, polite, firm and take as much time as you need to calculate the correct stop. I always give a basic stop to my focus puller, get him to calculate the shooting stop and then I check against my calculation.

The only reason for not giving you the stop until the last minute would be that he doesn’t know what it is until the last minute. I hope he reads this post.

Dan Bronks
DP
UK