paco_rosso

July 23, 2023

Think this. The illuminance (lux) is:
E = k * 2^EV

Where k is a 270 / S and S is the ASA sensitivity (the firs number in the ISO sensitivity, the ISO value cameras adjust). 270 is for international units, and only god knows what it can be in those medieval units used in the US.

So you are adding an illuminance E1 to another illuminance E2. Let's go:
First, lets call n to difference beetween E1 and E2. So E2 = E1 * 2^n.
Now add both illuminance:

Etotal = E1 + E2

Et = E1 + E1 * 2^n.

Et = E1 (1+2^n).

In the case you say, both E are the same, so n = 0. Then Et = E1 * 2. Et is 1 stop greater than E1. As E1 was the illuminance with EV1 = 8 then EVtotal = 9.

We can build a sum table if we think in the difference in stops beetween both EV. This is:
dEV      EVt
0,0   1,0
0,3   1,2
0,5   1,3
0,7   1,4
1,0   1,6
1,3   1,8
1,5   1,9
1,7   2,1
2,0   2,3
2,3   2,6
2,5   2,7
2,7   2,9
3,0   3,2
3,3   3,5
3,5   3,6
3,7   3,8
4,0   4,1

July 23, 2023

9 EV.

Think this. The illuminance (lux) is:
E = k * 2^EV

Where k is a 270 / S and S is the ASA sensitivity (the firs number in the ISO sensitivity, the ISO value cameras adjust). 270 is for international units, and only god knows what it can be in those medieval units used in the US.

So you are adding a illumination E1 to another illumination E2. Let's go:
First, lets call n to difference beetween E1 and E2. So E2 = E1 * 2^n.
Now add both illumination:

Etotal = E1 + E2

Et = E1 + E1 * 2^n.

Et = E1 (1+2^n).

In the case you say, both E are the same, so n = 0. Then Et = E1 * 2. Et is 1 stop greater than E1. As E1 was the illuminance with EV1 = 8 then EVtotal = 9.

July 23, 2023

When mixing ambient light with flash we get two exposures. So you need to guess what is the exposure the ambiente gives when shooting at 1/250. If ambient light is f:11 at 1/250 and your flash gives about the same f... then what "stops" the movement is the ambient light no the flash. It is: blurry image. ¿How hight should be the flash exposure over the ambiente one to "stop" the move? ¿3, 4, 5 stops?
So: no, with sunlight flash do not stop the motion.

December 23, 2018

No!

¿Why?

December 23, 2018

Is there any DSLR or MILC with a flash guide number mode? That is once you have determine the true GN of the flash you simply enter the GN into the camera and it would automatically set the aperture based on the focus distance and ISO?

Some flashes says in its screen the f number once you have focused the lenses ¿Does it not help?

December 6, 2016

a soft light in front of the face and slightly under the nose. (See the shades and the lights in her cheeks).

July 28, 2016

About the PI factor. When a light beam arrives at a surface can do two things: bounce or splash.

The light can bounce as the balls of billiard game. We call this "specular reflection". The light beam comes, and the light beams goes. Now think in a stream of water from a hose pipe against a fence. The stream of water do not "bounce" but "splash. When the light splash we call it "scater" or "diffuse reflection". So, a beam of light (a ray) arrives and change its distribution to a sphere. The change in energy is from a ray to a sphere. This is what the 1/PI factor explain, the change in intensity from the ray of light arriving to the figure to the sphere of light departing from the figure.

July 26, 2016

The relationship between illuminance and luminance is: L = (r*E)/PI

Where L is the luminance, in cd/m2. (Candles per square meter).

E is illuminance in lux. r is the reflection coefficient (The ratio between the luminance of a sample of the material divided by the luminance of the reference). PI is PI, it is, 3.141599...

July 16, 2016

The link you provide to the data says the unit give 3010lx at 1 meter.

It is a ISO 100, t:1/60, f: 4.3 at 1 meter from lamp. ¿What is the f, t you get with your current lamp?

May 31, 2016

I shoot dance with a profoto B1. When I set the flash at power 7 (from 10 maximum) I can shoot 4 frames per second. With power set at 6 or 5 I can shoot more framse per second. Other solutions are: profoto B4, broncolor move 1200j, broncolor siros L. All them with batteries.

(www.behance.com/pacorosso)

June 20, 2015

Stop thinking in "incident" and "reflected" reading. Think in "ilumination" and "brillance" reading. The incident what read is the light falling on the stage, it is, the "illumination". If youknow shat amount of light fall on the stage you should not be bored by the place the tones in the gamut: each of the light values fall in his correct place, shades in shades, medium tints in medium tints, lights in tlights.

June 20, 2015

Stop thinking in "incident" and "reflected" reading. Think in "ilumination" and "brillance" reading. The incident what read is the light falling on the stage, it is, the "illumination". If youknow shat amount of light fall on the stage you should not be bored by the place the tones in the gamut: each of the light values fall in his correct place, shades in shades, medium tints in medium tints, lights in tlights.

March 28, 2015

I see a big big softbox in front and some high position.

And a background ligt, of course. The rim in the face I think is by the reflected light ("reverbered") by the background.

March 16, 2015

If you wants to sum f numbers:

f1 PLUS f2 = sqrt (f1*f1 + f2*f2)

June 23, 2014

I have some problems with the luminous data of several lamps makers companies. This table resume the situation: http://pacorossofoto.files.wordpress.com/2013/08/par641.jpg

(Commas are used in the way it is used in Europe, as decimal separator, not as thousands, so 11,00 is 11.00 not 11 000). <img src="http://pacorossofoto.files.wordpress.com/2013/08/par641.jpg" alt="" width="979" height="449" /> The first column "grados" is the plane anle of emmision in degrees. (From catalogue) Second column is the solid angle, calculated from w = 2 * PI * (1-cos (a/2)) where PI is 3.141599, w is the solid anle in stereorradians and a is the plane angle. Third column "candela" is the light intensity in candles (data from catalogue). (This lamps are PAR 64). Fourth column "lumen" is light flux in lumen. It is calculated multiplying the light intensity (3th column) for the solid angle (2nd column) because the light intensity is J = F / w Where F is the flux, J is the intensity and w is the solid angle. This data (flux) is calculated from catalogue data. Fifth column "W" is the electric power in watts (from catalogue). Sixth column "R" is the luminous efficacy calculated dividing the lumen (fourth column) over the power (fifth column). R = F / w. It is, R is lumen per watts. Seventh column is the lamp. OSR stands for Osram, Phil stands for Phillips. The lamps are PAR64 conceived for stage lighting and photographic studio (in wide sense: cinema, TV, etc).

My problem... See the R number. About 11lm/w. In the bibliography it is said the typical R for tungsten is about 25lm/w... ¿What do you think about it?

(If we talk about flash lamps (strobes, not lanterns) the R is as low as 14) I think I am wrong but do not know where I fail.

(Another day we'll talk about why the real BCPS is much lower than the catalogue says).

May 4, 2014

The design rule for a vertical parament is to locate the lamps at half the distance than the lenght you want to illuminate.

It is: for each 1 meter (foot) of vertical background, the height should be 1/2 meter (foot). And for each 1 meter (foot) of horizontal background the distancia from lamp to wall should be 1/2 meter.

With a 5 meters long the locate the lamps at 2,5 meters.

April 16, 2014

The relation beetwen BCPS and f number readed with a photometer is this: First: you have to read the f provided by the flash at a distance d with a flashmeter. Never read the flash at less than 2 meters. Distance recomended is 3.16meters. BCPS = 270*f^2 * d^2 / s Where f is the f number readed in the photometer. f^2 is f*f. d is the distance in meters from flash to photometer. d^2 is d*d. s is the sensitivity in ASA number, it is, the ASA part of the ISO number. If you use feets, then must change the constant 270 to another suitable to imperial units. Recomendations: set the photometer at 3,16meters, it is the square root of 10. Use ISO 100/21. In this conditions the equation is: BCPS = 27 * f^2

BCPS is a magnitude, not a unit. The unit of BCPS is candles per second: cds . And is the light intensity (candles) which produce the same exposition in 1 seconds that the lamp we are measuring. The relation with the guide number is when the distance is 1 meter. As we cannot measure the f number at so short distance we can change the equation in this way: BCPS : BCPS = 2.7*f^2*d^2 f=GN / d So: BCPS = 2.7*GN^2 GN = SQRT (BCPS / 2,7) GN = 0.608 SQRT( BCPS )

April 16, 2014

Ok but ¿What happens with the BCPS? Tonight I have measure the BCPS of a Profoto B1 without any lightshaper and have read a 230lxs at 3,16m, so the BCPS is 2300 js. Tonight I have illuminated the front of an hotel in a place bouncing the B1 (nude, without lightshaper) in the wall in front off the hotel. It is: I have illuminated one side of the place bounthing the light in the opposite wall. I was almost in 1/3 of the lenght of the place, near the bouncing wall. So it was about 15 meters from the B1 to the wall and about 50 meters fom this wall to the opposite. In this, I get a f:2,8 for a ISO 640/29.

With a 1/1000 emission time the illuminance provided by the bouncing in the final wall was about 3300lx.

BUT: if the BCPS of the B1 is 2300js ¿Why I cannot get the same light with a Metz 45 with a BCPS of 4400js? I am not talking about the allyouknowwattssecondsisnottheamountoflight. I am talking about BCPS wich is the intensity of the light (candles) in the exposimeter system (per second).

My thinking is I: BCPS in the fabricants data is a marketing number not a physic measurement. Maybe the angle of emmision has things to say in the actual intensity and we do not must be confident with the numbers in the specifications table.

February 26, 2014

¿Can you show some sample? ¿Some youtube link?

December 7, 2013

Each day I think I know less than the day before.

Profoto says its new B1 (500ws) provide 10 times more light than a camera flash. I have made this measurements: At 2 meters, a profoto D1 500 (500ws) provide 700 lxs (lux second). So the BCPS is 700 x 4 = 2800 js (jules second)... but my metz 45 claim to have a BCPS 4.500 js...

I measure a Bowens gemini 500 at 2 meters with the normal reflector (S) and have 1100 lxs, so it is a BCPS 4400 js.

¿What is the ws in a camera flash?

¿What is the photometric render in a camera flash? ¿35lm/w? ¿11lm/w? The broncolor data in their catalogues seems to be around 40lm/w.

¿Can a camera flash (a nikon SB900 for example) equal the light power of a 500ws studio strobe?

July 26, 2013

Handheld flashes ("speedlites") are under 150js power while compact flashes ("monlight") are from 200 to 1500js.

I think the best is a kit with 2 compact with 400-600js and one handheld.

(Bowens gemini, elinchrom BX or Dlite, profoto D1, etc).

July 23, 2013

Rules of thumb to sum lights:

You have two lights.

See the difference in stops.

1 If difference is 0 stop, both are equal, then the sum is 1 stop higher: f:8 + f:8 = f:11

2 If difference is 1 stop, then sum is 2/3 stops greater than the higest of them: f:8 + f:11 = f:11 + 2/3.

3 If difference is 2 stops, the sum is 1/3 greater than the hisget. f:8 + f:16 = f:16+1/3

4 If difference is 3 or greater, then the lowest of them has no effect: f:8 + f:22 = f:22

(Actually, when the difference is 3 stops the sum is only 1/6 greater than the highest).

So:

If the difference beetween ambiente light and flash light is 1 stops, this is the flash is at the same power than ambient light.

If the difference is 1,5 (1+2/3) stops, then the flash is 1 stop greater than the ambient.

If the difference is 1 stops (1+1/3) the power of the flash is twice the ambient.

If the difference is 3 or greater then the exposure of the figure is due only to the flash.

ONE WAY TO CALCULATE THE ADJUST OF POWER.

So ¿How can you deal with this?

Mesaure the light in the face without flash. This is Eb (b from base)

Measure the light in the face with flash, this is Et (t from total). This is the sum of base light (ambient) and your flash. It is: Et = Eb + Ef.

You know Eb and wants to know how to adjust your flash to get than unknown Ef.

Let's talk in illuminance, Lets write illuminances over the base (all light wrote in ratios over Eb):

Eb / Eb = mb = 1.

Et/Eb = mt = 2^nt

Ef/Eb = mf

Now:

Et = Eb + Ef

Divide all by Eb and then:

Et/Eb = Eb/Eb + Ef/Eb

So:

mt = 1 + mf

Then the light your flash must produce is:

mf = mt-1

And this is the adjusto in power (ratio of lights is the same as ratio of power).

mf is how many times the flash is greater than the ambient light (in the face).

mt is the how many time the light measured by your photometer (with flash) is greater than the ambient light.

For example:

You have a face read (without flash) f:4.

You wants the face will be 1 stop over ambient, then:

The total light is 2:1 (mt = 2)

So the flash must be adjusted to give a mf = 2-1 it is a mf:1.

Shoot your flash and read the ligth. It is mt. ¿How many is mf? (the light aported by the flash)

First write the photometer read in ratio over the ambient light.

For example, you read a f:4 in ambient and a f:11 with flash.

The amount of light submited by the flash is:

f:11 is 3 stops greater than f:4, so the ratio is 2*2*2 = 8:1

mt=8

Then: mf = mt-1 = 8 - 1 = 7.

You want mf =1 so you need to reduce the power to 7:1, this is 2+8/10 stops.

(Remember: from 100 asa to 200 there is 1 stop, from 200 to 400 there is 1 stops -this sums 2 now- and one third over 400 is 500 and 2/3 is 640, 1 stop is 800 and you wants 700 (this is 700:100,, 7/1) so from 100 asa to 700 there is more than 2+2/3 but less than 3 stops, you can suppose 8/10). ASA sensitivity numbers are the same relation than lights.

So, set the power of your flash to maximum and then reduce 2 + 8/10 its power to achieve a face with 1 stop over ambient.

ANOTHER WAY:

The to reduce the contras in a figure from a value mi (initial contrast in ratio) to another me contraste (final, end, contrast, in ratio) the flash must give a light ma with is:

ma = (mi-me) /(me - 1)

(ma stands for light added).

And procedure is the same: read the flash at max power, read the ambient light. writedown the numbers in ratio over the ambient light. Rest 1 to the read of the flash.

Divide the ma calculated over the mf and this is the amount of power reduction you must adjust in your studio light.

This second procedure is what I use to control the contrast in a chiaroscuro composition with a lateral light to the figura (the bride at the window).

July 3, 2013

There are other solutions, for exemple: http://www.elinchrom.com/product/Ranger-RX-Speed-AS.html

1100ws

In profoto I know the b2, b3 and b4, but not a B7 with batteries.

May 9, 2013

Only one ligght, at 6, high, maybe a beautydish or a little umbrella near the head.

in the firs photo, see there is no dark lines in the cheek bones neither in the nose, so there is no two lights crossing on the head. See the way the side of the face is shadowed. If there is two lights one is frontal and soft, maybe a reflector, but I would light this set with only one beauty dish, high, at 6, and close to the forehead.

February 27, 2013

Forget about "diagrams". Learn the effects of light in the figures and in the space and decide the position of the lamps from the shades you want.

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