Home of Professional Cinematography since 1996

Exposure Compensation

Published : 19th November 2003


Ramping from 36 fps to 24 fps ... correcting with the shutter ... starting at 180 degrees ... what should your shutter be at 24 fps ... and WHY is that your answer?

Mako Koiwai



Mako writes :

>Ramping from 36 fps to 24 fps ... correcting with the shutter ... starting at >180 degrees ... what should your shutter be at 24 fps?

OK, I'll bite.

120 degrees

> And WHY is that your answer?

Shutter speed (exposure time) = shutter degrees/360 x frame rate

180/360 x 36 = X/360 x 24 X = 120

Is there a prize?

Brian Heller
IA 600 DP



The angle is = 120'

Why = It's what my palm pilot told me to say... I swear.

Joe Zovko
AC
LA, CA



Joe Zovko wrote:

> The angle is = 120'

> Why = It's what my palm pilot told me to say... I swear.


No calculator required -- easy head math.

180 degrees = 36 fps

2/3 of 36 fps = 24 fps
2/3 of 180 degrees = 120 degrees

Jeff Kreines



Solving the equation both times indicates that the shutter angle for the 24 fps should be 270 degrees not 120 degrees.

Do the math 180 divided by 360 = .5 X 36fps = 18
120 divided by 360 = .3333 x 24 = 8

In a speed ramp the exposure time is to remain consistent.
Solving the equation for 18 means the angle is 270

270 divided by 360 = .75 X 24 = 18.

I am no math wiz but if the equations are correct the algebra you did is incorrect.

Robert Goodman
Photographer/Author/Producer
Philadelphia, PA
www.stonereader.net



Robert Goodman wrote :

>Solving the equation both times indicates that the shutter angle for the >24 fps should be 270 degrees not 120 degrees.

Your equations are wrong - you've inverted them. Frame rate is the inverse of the shutter period.

Willi Geiger
Technical Director
Industrial Light + Magic



Robert Goodman wrote :

>Solving the equation both times indicates that the shutter angle for the >24 fps should be 270 degrees not 120 degrees.

Um, no... first, there aren't any cameras with 270 degree shutters.


Second, since you're setting the exposure for 36 fps using a 180-degree shutter, you need to cut exposure when you slow the camera to 24 fps -- ergo close the shutter a bit to compensate.

Jeff "bad at real math, but quick at rough calculations" Kreines



Robert Goodman wrote :

>...Do the math 180 divided by 360 = .5 X 36fps = 18
>120 divided by 360 = .3333 x 24 = 8....


Indeed. If ramping to a slower frame rate, the effective shutter speed is going to drop, so you can't possibly go to a wider shutter angle to keep the exposure constant.

The correct shutter angle for 24fps would be 120.

36x360/180 = 72

24x360/120 = 72

Both angles will provide 1/72 sec. at their respective frame rates.

Jeff Kreines



>O.K. ... now ... what is the "half way" fps between 24 and 48 fps ?

36 fps.

>What is the "half way" shutter between 180º and 90º ?

135º.

Doubles and halves, baby, doubles and halves...

Art Adams, DP
Mountain View, California - "Silicon Valley"
http://www.artadams.net/



O.K. ... now ... what is the "half way" fps between 24 and 48 fps ?

What is the "half way" shutter between 180º and 90º ?

Mako, Makofoto, Glendale



I get a different answer. If you are going from 24fps to 36fps you need to open up half a stop. Therefore, if you are going the other way, you need to close down half a stop. By changing the shutter from 180" to 135" you are effectively closing down half a stop.

So I get the answer as 135" for 24fps.



>O.K. ... now ... what is the "half way" fps between 24 and 48 fps ?36 fps.

I don't agree. There's a more complicated answer (so it must be better).

Halfway between 24 and 48 ( a factor of x2) would be a factor of root 2 -familiar to everyone who recognises the sequence 2, 2.8, 4, 5.6 etc.

So the halfway speed is 24fps x 1.414, which is nearly 34 fps.

And the halfway angle would be 180 / 1.414 which is 127 deg

Dominic Case
Atlab Australia



Very Good Dominic ...

Yet most of us dummies out in the field think the half way fps between 24 and 48 is 36 fps ... and that the in between shutter angle is 135º.

Interestingly enough ... it seems that many of the exposure charts in our manuals are also off ...

This examination came about because a techie AC friend of mine, Matt Petrosky, was wondering why the read-out of the remote ramp device for his Panavision Millennium was showing the shutter correction for 36 fps/180º to 24 fps was 120º instead of 135º.

Now we know that if he had inputted 34 fps/180º ... the correction would have been 127º at 24 fps.

In order to end up with a 135º correction, at 24 fps ... one would have to start at 32 fps/180º.

So the "proper" sequence of speeds between 24 fps and 48 fps, that is 1/4, 1/3 and 2/3rds, would be ... (we've learned 1/2 = 34 fps) ...

Mako Koiwai, Makofoto, always curious ... always learning ...



28 fps is a .2 stop correction
30 fps is a .3 stop correction
32 fps is a .4 stop correction
34 fps is a .5 stop correction
36 fps is a .6 stop correction
38 fps is a .7 stop correction
42 fps is a .8 stop correction

Of course ... we need to find the "new" correct in-between'ies for all the other speeds ...

My apologies to all of you who already knew these basics .... Especially David Eubank ... who's PCine/PCam Palm program always had it right to start with …cheers ...

Mako Koiwai, Makofoto

... the glass is now half full, but I've got too much time on my hands ...



Mako Koiwai wrote:

>This examination came about because a techie AC friend of mine, Matt >Petrosky, was wondering why the read-out of the remote ramp device for >his Panavision Millennium was showing the shutter correction for 36 >fps/180º to 24 fps was 120º instead of 135º.

This is really quite simple. The confusion arises with the term "exposure compensation".

You don't want to compensate the exposure when ramping; you want constant exposure. You achieve this in ramping by varying the frame rate or the shutter angle inversely to one another. Higher frame rate means a narrower shutter, lower frame rate a wider shutter angle. The speed and the shutter angles are compensated to maintain constant exposure.

The formula is as follows: exposure time in fractions of a second = (equals) shutter angle in degrees / (over) 360 degrees x (times, as in multiply by) the frame rate. Palm Pilots with cinematography programs are programmed to solve for any unknown in this formula. No alchemy is involved.

Thus for a 180 degree shutter at 24 fps, the exposure time is 1/48 second.

At 36 fps the shutter speed becomes 1/72 second.

At 48 fps the shutter speed becomes 1/96 second.

Whether or not 36 fps is the midpoint between 24fps and 48 fps, seems to be a question of semantics or philosophy.

Brian Heller
IA 600 DP



Jeff Kreines wrote :

>No calculator required -- easy head math.

Hello there –

“Easy” and “Math” are two words for me that never go together, especially when mixed with the word “Head”. If I wasn’t so interested in drawing as a child, maybe I would have paid more attention to school work; then all of that "math junk" would have been easier, but of course I would probably have gone into physics as opposed to concentrating on the arts my whole life. That’s why I always keep that little electronic nerd (Mr. Palm Pilot) in my pocket while working.

Joe Zovko
AC
LA, CA



Wade Ramsey writes :

>I believe you meant to say that higher frame rate means (needs) a >wider shutter, lower frame rate a narrower shutter, unless you meant that >the higher frame rate affects exposure the same as a narrower shutter

Thanks Wade. Cutting and pasting, I thought I was making it clearer, but
managed to get it exactly backwards. Duh.

Brian "Ran out of coffee this AM'" Heller
IA 600 DP



Wade Ramsey writes:

>IF you have the Palm and the program! If you are just using an ordinary >calculator, you'll find that using the above formula (shutter >angle/360xfps) results in a 24fps shutter speed with a 180 deg. shutter >angle of .020833333 secs.

Wade, I think I'm missing something.
180 over 360 (180/360) = 1 over 2 (1/2). 1 over 2 times 24 (1/2 x24) = 1 over 48 (1/48) If your calculator is giving you a different result, it's time for a new calculator.

Brian "prefers pencil and paper" Heller
IA 600 DP



Mako Koiwai wrote :

>This examination came about because a techie AC friend of mine, Matt >Petrosky, was wondering why the read-out of the remote ramp device for >his Panavision Millennium was showing the shutter correction for 36 >fps/180º to 24 fps was 120º instead of 135º.

Mako, the flaw in the logic is that although 36 is half way between 48 and 24 fps, 24fps is not half way between 36 and 18. Half way between 36 and 18 fps is 27 fps (18 Frames difference, half of 18 is 9 36 minus 9 is 27) The math says your exposure time for a 180º shutter at 36 FPS =1/72. The Exposure time for a 120º shutter at 24 FPS is 1/72. The exposure time for a 135º shutter at 27 fps is 1/72

BUT If you are ramping from 36 fps to 18 fps ( a one stop increase in exposure), then at 18 fps your shutter would have to close to 90º to keep the exposure constant. Along the way at 27 FPS (The actual halfway point) the Shutter is at 135º, and at 24 FPS it is 120º. Or in 18 frames you would closedown 5º per frame.

Now "Stop" all this fun and games, and git back to work

Steven Gladstone
Cinematographer - Gladstone Films
Cinematography Mailing List - East Coast List Administrator
Better off Broadcast (B.O.B.)
New York, U.S.A.



>Brian - for your math to be correct the formula is Exposure Time >(fractions of a second) = (360 degrees/shutter angle in degrees) X >Frame Rate.

Not to labor this issue, since I have to put this formula to work soon....

Your version results in a whole number, which you then say is expressed as a fraction. The traditional formula (I didn't invent it.) -- not that it matters much in practice -- does result in a fraction, i.e., 1/48.

The confusion is due in part to trying to write a formula in words with a program that does not allow for mathematical expression. I guess I am too used to doing it in my head and assumed everyone on this list is familiar with the math.

Brian Heller
IA 600 DP



First, I merely solved the equation Brian Heller posted not examining the rationale.

Now, I'm intrigued of course, so what is the correct formula to maintain a constant exposure?

Obviously something with the square root of 2 in it.

Robert Goodman
Author/Photographer/Producer



Robert Rouveroy writes :

> Sorry fellas, I came a bit late in this discussion.

Just a little.

>But does anyone take into account that there are cameras that have a >much faster pulldown? Or slower?

Would these be the models with the electronic shutters or with the ramping motors

So, start over again :

Not bloody likely.

Brian Heller
IA 600 DP



Wade Ramsey writes :

>It would probably help a lot if our email systems would accurately >transmit formulas, rather than our having to explain them.

Alas, yes.

Brian Heller
IA 600 DP



Brian Heller wrote :

>...Higher frame rate means a narrower shutter, lower frame rate a wider >shutter angle. The speed and the shutter angles are compensated to >maintain constant exposure...

I believe you meant to say that higher frame rate means (needs) a wider shutter, lower frame rate a narrower shutter, unless you meant that the higher frame rate affects exposure the same as a narrower shutter, etc.

>...The formula is as follows: exposure time in fractions of a second >=(equals) shutter angle in degrees / (over) 360 degrees x (times, as in >multiply by) the frame rate.

IF you have the Palm and the program! If you are just using an ordinary calculator, you'll find that using the above formula (shutter angle/360xfps) results in a 24fps shutter speed with a 180 deg. shutter angle of .020833333 secs. Find that on your meter! It's much simpler to turn that formula over: 360xfps/shutter angle, to find for the denominator. With a 180 deg. shutter and 24fps you get 48. Even us math challenged folks can then figure out that the shutter speed is 1/48 sec. (You can even do this on paper without a calculator using long division.)

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614



>The formula is as follows: exposure time in fractions of a second = >(equals) shutter angle in degrees / (over) 360 degrees x (times, as in >multiply by) the frame rate. Thus for a 180 degree shutter at 24 fps, the >exposure time is 1/48 second.

Brian - for your math to be correct the formula is Exposure Time (fractions of a second) = (360 degrees/shutter angle in degrees) X Frame Rate.

360 divided by 180 = 2 multiplied by 24 fps = 48 expressed as a fraction 1/48

Your formula results in 1/12 (180/360 = .5)

Not a speed ramping guy but can do simple math. And Wade dividing a simple number by a simple number is easier to do in your head than multiply 24X360 and then divide by etc.

Robert Goodman
Author/Photographer/producer



>Wade, I think I'm missing something. 180 over 360 (180/360) = 1 over 2 >(1/2). 1 over 2 times 24 (1/2 x24) = 1 over 48 (1/48) If your calculator is >giving you a different result, it's time for a new calculator

Sorry fellas, I came a bit late in this discussion. But does anyone take into account that there are cameras that have a much faster pulldown? Or slower?

The Bell&Howell 70DR gives an exposure of 1/42 at 24 frames. The Pathe Webo is 1?60 at 24.

So, start over again :

Robert Rouveroy
The Hague, Holland

I plan to live forever. So far, so good.



Brian Heller wrote :

>Wade, I think I'm missing something. 180 over 360 (180/360) = 1 over 2 >(1/2). 1 over 2 times 24 (1/2 x24) = 1 over 48 (1/48) If your calculator is >giving you a different result, it's time for a new calculator

Yeah, me too! The formula you gave was shutter angle divided by 360 times fps. When I enter 360 x 24 I get 8640; when I divide that into 180 the calculator shows .020833333. If the calculator has a reciprocal function hitting that will give you 48. But my way works easily on your preferred pencil and paper!

But if, as Robert Goodman points out, you use your formula exactly as stated and divide 180 by 360 = .5, then multiply that by 24 you get 12, or 1/12 sec., which is obviously wrong. (It would probably help a lot if our email systems would accurately transmit formulas, rather than our having to explain them.)

Us mathematically challenged types, who barely made it through high school algebra, need simple calculations!

My calculator can beat your calculator any old day...!

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614



>Whether or not 36 fps is the midpoint between 24fps and 48 fps, seems >to be a question of semantics or philosophy

hmmm ... not quite what I meant this discussion to centre on ..

I was just trying to point out that the popular notion that 36 fps and 135º are the midpoints .... is incorrect ... contrary to our many charts... but supported by the auto corrections offered up by both Arri and Pana cameras ... and various cine computer programs.

We are only talking a tenth or two of difference ... and perhaps in the "old" days it didn't make any difference ... it hardly makes any difference now ... but with our computer read outs ... it's nice to know what is accurate and correct.

If you know that the mid point is 34 fps ... you won't be surprised that your 435 is showing 120º compensation for 36 fps ... and you will know that manually you need to select 120º and not 135º.

These changes obviously effect our entire scale ... the mid point between 48 and 96 fps is 68 fps ... not 72 fps ... etc. The faster the fps ... the more dramatic the change will SEEM, without actually changing the stop very much.

Mako Koiwai



So let me get this straight: instead of the doubles/halves rule of photography I learned various places at various times in my formative years, I really needed to learn how to multiply and divide by the square root of 2? Or does this really only apply to "in-betweenies?"

Art "I never learned Calculus; I couldn't handle the Latin" Adams, DP
Mountain View, California - "Silicon Valley"



360 deg. over shutter angle multiplied by 1 over fps. divide resulting numerator into denominator for shutter speed.

360/180 x 1/24 = 180/8640 = 1/48
360/200 x 1/24 = 200/8640 = 1/43(.2) (but who's counting)
360/90 x 1/48 = 90/17280 = 1/192 (round it off)

Believe me, math was not my strong suit. But this was one of the first things my mentor Morry Bleckman taught me at 14.

I still have to try it a couple of times to be sure I'm correct.

Steven Poster ASC



Mako writes :

>Yet most of us dummies out in the field think the half way fps between >24 and 48 is 36 fps ...

But none of the above-mentioned people would suggest that midway between f/8 and f/16 is f/12.

At least I hope not

(to be accurate it would be f/11.3, but what's the point)

Dominic Case
Atlab Australia



>to learn how to multiply and divide by the square root of 2 We haven't >mentioned logarithms recently have we

Seriously, you are quite familiar with the scale of root 2.

Instead of 2,4,8,16,32 etc it goes 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 etc (close enough). "Stop" now!

It simply fills in the gaps between the doubles and halves.

Dominic Case
Atlab Australia



>(to be accurate it would be f/11.3, but what's the point)

Or 2 x 5.6, roughly. I like how you can find out what's two stops ahead or behind by doubling or halving a selected f-stop.

When I was an assistant I worked with a couple of DP's who worked in quarter and third stops. Once, when I was day-playing as B camera first assistant on a TV series in the early 90's the DP told us the stop was 9.5. I was flummoxed. I guessed it was halfway between 8 and 11 but I didn't know for sure. So I asked the A camera first where he set his aperture, and he responded, "I'm guessing it's right around halfway somewhere." I just matched his stop. I guess it worked out, but now I'm not so sure we were dead on. (We couldn't have been far off, though.)

I prefer the simple method: fractions, always added to a base stop.

Art Adams, DP
Mountain View, California



Worse is 5.6 (5.66) instead of 5.7 ...

Mako, Foto, Glendale, CA



>the DP told us the stop was 9.5. I was flummoxed. I guessed it was >halfway between 8 and 11 but I didn't know for sure.

It is in between, actually 9.5137. Of course we do some rounding off in our estimates of t-stop, but not necessarily in the right direction. So a 5.6 is really 5.6569 and a 22 is really a 22.6274 which should be a t/23. The higher you go from t/1.4 the more inaccurate since we derive the other numbers from adding the 1.4 which is really 1.4142 including a couple of decimals.

Walter Graff
Producer, Director, Creative Director, Cinematographer
HellGate Pictures, Inc.
BlueSky, LLC
www.film-and-video.com



Brian Heller wrote :

>Would these be the models with the electronic shutters or with the >ramping motors

Hilarious indeed !

I thought this was a theoretical discussion on accurate or not so accurate shutter openings at various speeds... If you operate with electronic shutters and ramping motors, why worry about exposure, n'est ce pas?

Robert Rouveroy
The Hague, Holland



Jessica Gallant writes :

> I've always measured stops by thirds. Is this considered unusual?

Apparently by some … But you're in very good company

Everything relating to exposure in motion picture photography is calibrated to 1/3 stops. Spectra meters were calibrated to 1/3 stops.

However, with the advent of digital meters that read out in 10ths of a stop, some people carry this perceived accuracy beyond what it is possible to reliably adjust an aperture to.

In everyday practice it is common to say a "half stop" or to "split 8 and 11". Since the difference between half a stop and a third of a stop is 1/6th of a stop, with modern negative film it's not much of a problem.

Brian Heller
IA 600 DP



Art Adams wrote :

>...I prefer the simple method: fractions, always added to a base stop.

But that can be more confusing. If you have a T-2.4 lens how does its maximum aperture relate to the next one, T-2.8? Then when you need to figure DOF for T-8, what f/stop is that? If your DP is calling out f/numbers and you work in base plus fractions what are you going to do when he asks for T-2.5? (That's one-third stop down from T-2, not one-half.) And T-3.5, and 4.5?

BTW, quarter stops are nonsense. We can't see exposure differences closer than third stops (and then usually only in side by side comparisons), which are the minimum steps of the ASA/ISO system.

Having learned during the old ECO reversal days, I find myself carefully incrementing third stop settings on the lens (I even have charting tapes on the Super Speeds indexing the third stop positions), then realize that I'm shooting negative...

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614



>When I was an assistant I worked with a couple of DP's who worked in >quarter and third stops.

I've always measured stops by thirds. Is this considered unusual?

Jessica Gallant
Los Angeles based Director of Photography
West Coast Systems Administrator, Cinematography Mailing List
http://www.cinematography.net



Jessica Gallan writes :

>I've always measured stops by thirds. Is this considered unusual?

Not at all Jessica.

International standards are stated as +/- 1/3 of a stop for aperture and meter tolerances. I believe thirds are the natural division nomenclature for exposure. Even so, I use tenths to express stops and to do calculations ever since digital meters came around. My longstanding and trusty and crusty assistant, Norman knows that .3 are about one third of a stop. And when I ask him to open up a tenth, he knows I'm just wanking. But he does nudge it. It's nice to be indulged.

But let's think about the difference between exposure when we were working with ASA25 at f5.6 as opposed to EI 500 at f1.4.
At 25ASA for a 5.6 you would need 3250 Foot Candles.
At 500EI for a 1.4 you need 5 Foot Candles.
Changing the lighting by 2 FC at 500EI is significant.
Changing the lighting by 100 FC at 25ASA doesn’t mean much....

Don't know exactly why I brought that up. But it always blows me away to think about it.

Maybe that's why some of the old masters didn't need a meter and would judge exposure by the "heat" of the light.

Steven Poster ASC



Quoth Mr. Poster :

Changing the lighting by 2 FC at 500EI is significant.
Changing the lighting by 100 FC at 25ASA doesn’t mean much....

This reminds me of one of the things that I miss about my analog spectra candela and Pro meters...since I came up with these moving coil movement meters, I feel that I have a visceral understanding of the logarithmic nature of light because of the spacing of the footcandle measurements on the dial. With modern digital readout meters, there is not that sense - with my old meters the needle travels the same distance to go from 4 fc to 8 fc as it does to go from 125 fc to 250 fc...but with a digital meter, it is just numbers.

I still have my analog pros and candela, but I only use my newer digital meters now...the reminder is not enough of a plus to make up for the mouthful of spectra slides that were always in my mouth as I searched for the right slide for the moment...and the electronic meters survive bumps and drops much more readily than the old moving coil meters do.

Mark Weingartner
LA based
(and bought Mr. Poster's old analog color meter for a song)



>...and the electronic meters survive bumps and drops much more >readily than the old moving coil meters do.

I used to like the way you could tip the old Spectra one way and get one reading and then tip it another way and get a different reading just from the weight of the needle.

Steven Poster ASC



Mark H. Weingartner wrote :

> With modern digital readout meters, there is not that sense - with my old >meters the needle travels the same distance to go from 4 fc to 8

Well, the spectra electronic pro shows a scale, but it's so small that it doesn't really seems as useful or immediate. I like seeing a scale, it's like the difference between an analog and digital clock.

There's really no reason why a needle and scale couldn't be properly displayed large on a meter readout.

I'm surprised no one has done this yet with a PDA or a pocket PC - written a program to work with a sensor adaptor. Seems like a natural.

Maybe someone has done it already?

Steven Bradford
One eye going nearsighted, the other going far....
Seattle



Steven Bradford wrote :


>There's really no reason why a needle and scale couldn't be properly >displayed large on a meter readout.

What a strange coincidence. I visited the offices of Spectra about 2 weeks ago looking to see if they possibly had an old Combi 500 sitting around since they don’t make them new any more. Well a group of employees were in a meeting and seemed quite surprised and happy that I asked that question.

Asking me why I wanted an old meter like that (and probably surprised that some one as young as me was asking for it), I said since I have always been looking through the viewfinder of my old Canon AE-1 for so long, I’ve grown used to watching a needle and actually prefer it to reading numbers on a screen. They told me that they are now making a new meter that will have a digital screen that simulates the style of an analog meter. So maybe there will be a revival of sorts.

Joe Zovko
AC
LA, CA



Mark H. Weingartner wrote :

>I still have my analog pros and candela, but I only use my newer digital >meters now...

I still keep my Spectra Combi in my kit as a back up, dependable and lives in a cool, heavy-duty, tooled leather belt case.

Mike Evans
DoP
www.i25productions.com



>This reminds me of one of the things that I miss about my analog >Spectra candela and Pro meters...

A few days ago I got out my Spectra Combi II which I never trust, did a comparison with my Sekonic spot which I always trust (within reason) and... they matched exactly, incident to grey card.... on 2 of the scales. over an I dunno, a 7 or 8 stop range.

Maybe the thing just needed to hibernate ?

Sam Wells



>Well, the spectra electronic pro shows a scale, but it's so small that it >doesn't really seems as useful or immediate. I like seeing a scale, it's >like the difference between an analog and digital clock.

Me too, and I always liked to see the needle moving as you moved an analog meter through light & shadow.

I remember driving a rental car with a digital speedometer once - truly evil !

Sam Wells



Sam Wells wrote :

>Me too, and I always liked to see the needle moving as you moved an >analog meter through light & shadow.

I still like my old Minolta Autometer II -- it was analog, and used a motor to drive the readout dial. But it weighs a lot.

>I remember driving a rental car with a digital speedometer once - truly >evil !

I've gotten used to one -- my car has it. Not as bad as you might think... though I also like analog gauges.

Jeff Kreines



>At 500EI for a 1.4 you need 5 Foot Candles. Changing the lighting by 2 >FC at 500EI is significant.

Yes that's right on the money and shooting a few night exteriors with super speeds and fast stock will help one understand that concept very quickly. Not only are the exposure footcandles low but the shadow exposures are really low. That's when the ambient light and light coloured objects in and out of frame become very significant in affecting exposure densities in the toe. 1/2 footcandle or less could determine if it's on the neg or not.

Best Regards,

Jim Sofranko
NY/DP



>They told me that they are now making a new meter that will have a >digital screen that simulates the style of an analog meter. So maybe >there will be a revival of sorts.

Excellent. I think that current digital meters give almost too much information. I love my Spectra IV-A but I've learned never to use it in footcandle mode because it's just too much information. I'd love to see a meter with a digital needle that hovers here and there and gives you a much more organic feel than an F-stop with tenths flickering back and forth next to it.

Tenths are fun, and footcandle readings with decimals can be quite impressive, but give me something that reads in 1/3 stop increments and in fractions and I'm as happy as can be.

I haven't found anything quite as film-friendly as that Spectra. I've got a Minolta Autometer 4 as a backup incident meter and a Spotmeter F and it frustrates me that they won't go lower than ASA 12. I was working at ASA 3 and 4 last week; the Spectra was fine, as was my old Pentax Spot V, but the Minoltas wouldn't have anything to do with it. One can always tell the meter to compensate in other ways but eventually one loses track in the rush of the moment and mistakes are made.

Art Adams, DP
Mountain View, California - "Silicon Valley"



>...I'd love to see a meter with a digital needle that hovers here and there >and gives you a much more organic feel than an F-stop with tenths >flickering back and forth next to it...

Amen to that! I'm farsighted (visually, at least!) and have to pull off my glasses to view find a film camera. I often jump from camera to subject to make a reading without putting my glasses on and find that 2.8.8 and 2.8.0 look pretty similar when not in focus. Even when I see the tenths number clearly, I end up translating it back into the nearest third T-number to set the lens (2.8.8 would be 3.5.) It's irritating to have such precise measurements that then have to be translated into other numbers to use. If I have my glasses on, I look at that small analog scale (Spectra IVA) to see where it really is!

I, too, have wondered why no one has come up with an LCD "needle". It just makes sense. We need to view the way exposure works--logarithmically.

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614



Wade Ramsey wrote :

> I, too, have wondered why no one has come up with an LCD "needle". It >just makes sense. We need to view the way exposure works-->logarithmically.

Some racing motorcycles on the professional level have had tachometers that were digital bar graph displays arranged in a sweep like an analog needle would make . I have often admired these and thought about how they would make lovely light meter scales.

Mark Smith
Oh Seven Films



>I would really love if one of you out there knows of a link to an easy to >carry around chart with this info. Exposure Compensation for Shutter >angle and for SlowMo. It would save me a lot of headaches.

If you compute exposure by shutter speed, that is if you read your light meter by shutter speed, the following formula will give you the answer to your question and then you can make your own chart.

Shutter angle in degrees / 360 x the reciprocal of the frame rate = shutter speed thus for normal frame rate with a 180 degree shutter :

180/360 x 1/24 = 48th sec

90/360 x1/24 = 96th second.

5/360 x 1/24 = 1/1728th sec. or 72 times normal speed

If you are using a 180 degree shutter then the shutter speed is always twice the frame rate. 96 fps = 1/192 sec (1/200th is close enough.)

Hope this helps,

Brian Heller
IA 600 DP



>I, too, have wondered why no one has come up with an LCD "needle".

I've wondered about this too.

>Some racing motorcycles on the professional level have had tachometers that were >digital bar graph displays arranged in a sweep like an analog needle would make .

Yeah and you could have a peak hold option like an audio meter etc.

Sam Wells



>Some racing motorcycles on the professional level have had >tachometers that were digital bar graph displays arranged in a sweep >like an analog needle would make.

And you could have a redline to warn you the light was going to blow your highlights!

Wade K. Ramsey, DP
Dept. of Cinema & Video Production
Bob Jones University
Greenville, SC 29614



I would really love if one of you out there knows of a link to an easy to carry around chart with this info.

Exposure Compensation for Shutter angle and for Slow Mo. It would save me a lot of headaches.

Thanks a bunch.

Maurice Jordan



Wade Ramsey wrote :

>And you could have a redline to warn you the light was going to blow >your highlights!

I was thinking more of a programmable high light limiter, that you could connect to your lamps and keep them from going over your preset limits.

Mark Smith
Oh Seven Films



Mark Smith wrote :

>I was thinking more of a programmable high light limiter, that you could >connect to your lamps and keep them from going over your preset >limits.

And a governor (remember those?) to keep unauthorized personnel from trying anything risky...

Jeff Kreines