Figuring out wattage...

ChristopherCoy · Sep 22, 2014

I have a question about figuring out lighting wattage. I know what I want to do, I just dont know how to get there.

I want to use my Hassy in a studio type setting with hot lights. I know that I want to shoot Tri-X or HP5 at box speed, at 1/160th or better, around f/4.

So I've got my exposure triangle, but if I were to buy hot lights, how do I figure out how many watts of light I need to reach that set triangle?

I'm hoping that my question is understandable.

wildbill · Sep 22, 2014

look up the photometrics for the lights you're interested in buying and then look up the stop loss for any diffusion you plan on putting in front of them.
here's the chart for arri units:
Dead Link Removed

RalphLambrecht · Sep 23, 2014

ChristopherCoy said:
I have a question about figuring out lighting wattage. I know what I want to do, I just dont know how to get there.

I want to use my Hassy in a studio type setting with hot lights. I know that I want to shoot Tri-X or HP5 at box speed, at 1/160th or better, around f/4.

So I've got my exposure triangle, but if I were to buy hot lights, how do I figure out how many watts of light I need to reach that set triangle?

I'm hoping that my question is understandable.

I'm afraid, this is a trial and error exercise.however a lightmeter can help you choose the wattage for the next trial.

John Koehrer · Sep 23, 2014

Your question has quite a few variables besides wattage. The size & color of the room you're in and size and efficiency of the reflectors will all have some effect.

MattKing · Sep 23, 2014

Are there any sources around you where you can rent or borrow lights?

Or do you know someone who has a similar setup, that you can visit.

If so, do so, and take measurements and record specifications.

Then extrapolate from there.

Failing all that, buy from a source that allows returns or exchanges.

wiltw · Sep 23, 2014

A problem with hotlights is that in order for you to use the desired ISO film, shutter speed and f/stop, you may need to put in so many lights that

your models have to squint from the intensity of the lights
your models sweat under the heat
it is impossible to shoot except in the coolness of winter (assuming your models wear sunglasses to avoid squinting)

wildbill · Sep 23, 2014

wiltw said:
A problem with hotlights is that in order for you to use the desired ISO film, shutter speed and f/stop, you may need to put in so many lights that

your models have to squint from the intensity of the lights

your models sweat under the heat

it is impossible to shoot except in the coolness of winter (assuming your models wear sunglasses to avoid squinting)

I find this to be totally untrue and I do lighting for a living. Photometrics don't lie. Yeah models sweat, that's why they get paid well.

Arklatexian · Sep 23, 2014

Whatever you buy, get them all the same power. Then you can move the reflectors away from or toward the subject to get the lighting you want. The physics of light will never let you down....regards

ChristopherCoy · Sep 24, 2014

wildbill said:
I find this to be totally untrue and I do lighting for a living. Photometrics don't lie. Yeah models sweat, that's why they get paid well.

well not to mention that todays flourescent/LED lighting technology doesn't put out nearly the heat that halogen/incandescent bulbs did.

And my subjects are/will be dogs so I'm figuring they wont care much.

MattKing · Sep 24, 2014

ChristopherCoy said:
well not to mention that todays flourescent/LED lighting technology doesn't put out nearly the heat that halogen/incandescent bulbs did.

And my subjects are/will be dogs so I'm figuring they wont care much.

The flourescent/LED lights don't generally put out as much light either.

ChristopherCoy · Sep 24, 2014

I'm thinking about this one as a cheap starter/tester kit.

http://www.cowboystudio.com/product_p/s1200wkit.htm

wildbill · Sep 24, 2014

MattKing said:
The flourescent/LED lights don't generally put out as much light either.

for the power consumed, they sure as hell do. Yeah, many of them don't but there are plenty of very high output led& flourescent fixtures on the market available in tungsten/daylight and variable color temp. Maybe you haven't used them. Here are a few to check out:
Arri led fresnels
Arri L7 led's
kino flo vista beams (flourescent)
kino flo celebs (led)
mole richardson led fresnel retrofits
Aadyntech (led)

MattKing · Sep 24, 2014

wildbill said:
for the power consumed, they sure as hell do. Yeah, many of them don't but there are plenty of very high output led& flourescent fixtures on the market available in tungsten/daylight and variable color temp. Maybe you haven't used them. Here are a few to check out:
Arri led fresnels
Arri L7 led's
kino flo vista beams (flourescent)
kino flo celebs (led)
mole richardson led fresnel retrofits
Aadyntech (led)

Bill:

You are, of course, right.

My post was coloured by an assumption - that the OP was looking for something toward the budget end of the spectrum - like the kit he linked to in the post before yours.

ChristopherCoy · Sep 24, 2014

MattKing said:
My post was coloured by an assumption - that the OP was looking for something toward the budget end of the spectrum - like the kit he linked to in the post before yours.

We've never met, but it's scary how well you know me... LOL

polyglot · Sep 24, 2014

As everyone else said, the gain between your lights and subjects also matters. Distance between light and subject, size of subject, etc, they all matter. Remember that light falls off as distance squared so if you want uniform light through the depth of a scene, the light needs to be far away, which means it needs to be more powerful.

You need to read the Wiki page on Luminous Efficacy.

That kit you linked is very crappy but your exposure requirement is pretty low. There is nothing about it that is 1200W, it has four of 85W bulbs, which together might be expected to put out about 20,000 lumens assuming about 60lm/W because they're compact fluorescents. They also have poor colour quality, so are suitable ONLY for B&W.

Running some very approximate numbers with some very big assumptions:
- if I put a decent battery powered hot-shoe flash (100J = 4000lm-s) in a 60cm softbox, it will do about ISO100 f/16 at 1m. For a 1/2-length portrait of a person, it wants to be about 2m away, so that's ISO100 f/8 = ISO400 f/16
- so you can key-light half a person with about 4000lm-s to get f/16 ISO400; you only want f/4 so that's 250lm-s
- one of those lights (two bulbs in reflector) does probably 10,000lm
- to get 250lm-s you need 250/10000 = 0.025s seconds of exposure, or 1/40

So if you assume the umbrellas have the same efficiency as a softbox (they should be slightly better, but they're so cheap that they're probably not), you can expect very approximately f/4 1/40 ISO400 with one light about 2m from the subject. Assuming you want separate key and fill lights, these are not bright enough to get the 1/160 you want. If you put all four bulbs in a single fixture, you'd get about f/4 1/80 ISO400.

Hopefully the above numbers show you why flashes are far preferable to continuous lights for still photography. Just one good AA-powered hot-shoe flash will give 4000lm-s and let you shoot a person at ISO400 f/16 1/250; to get the same quantity of light from 350W of CFLs requires an exposure of 1/5 second. And the little flash runs cooler and doesn't need power cables and is light and tiny and and and...

ChristopherCoy · Sep 24, 2014

polyglot said:
As everyone else said, the gain between your lights and subjects also matters. Distance between light and subject, size of subject, etc, they all matter. Remember that light falls off as distance squared so if you want uniform light through the depth of a scene, the light needs to be far away, which means it needs to be more powerful.

You need to read the Wiki page on Luminous Efficacy.

That kit you linked is very crappy but your exposure requirement is pretty low. There is nothing about it that is 1200W, it has four of 85W bulbs, which together might be expected to put out about 20,000 lumens assuming about 60lm/W because they're compact fluorescents. They also have poor colour quality, so are suitable ONLY for B&W.

Running some very approximate numbers with some very big assumptions:
- if I put a decent battery powered hot-shoe flash (100J = 4000lm-s) in a 60cm softbox, it will do about ISO100 f/16 at 1m. For a 1/2-length portrait of a person, it wants to be about 2m away, so that's ISO100 f/8 = ISO400 f/16
- so you can key-light half a person with about 4000lm-s to get f/16 ISO400; you only want f/4 so that's 250lm-s
- one of those lights (two bulbs in reflector) does probably 10,000lm
- to get 250lm-s you need 250/10000 = 0.025s seconds of exposure, or 1/40

So if you assume the umbrellas have the same efficiency as a softbox (they should be slightly better, but they're so cheap that they're probably not), you can expect very approximately f/4 1/40 ISO400 with one light about 2m from the subject. Assuming you want separate key and fill lights, these are not bright enough to get the 1/160 you want. If you put all four bulbs in a single fixture, you'd get about f/4 1/80 ISO400.

Hopefully the above numbers show you why flashes are far preferable to continuous lights for still photography. Just one good AA-powered hot-shoe flash will give 4000lm-s and let you shoot a person at ISO400 f/16 1/250; to get the same quantity of light from 350W of CFLs requires an exposure of 1/5 second. And the little flash runs cooler and doesn't need power cables and is light and tiny and and and...

I was trying to stick to hot/continuous lights because dogs dont freak out as bad. I used to use AB400's in a 4x6 box... I could always go back to them I guess.

But I guess I can try some cheap manual hot shoe flashes instead. My plan is to use my hassleblad with the 80mm 2.8. which I think will only sync at 1/160th or so.

MattKing · Sep 24, 2014

ChristopherCoy said:
I was trying to stick to hot/continuous lights because dogs dont freak out as bad. I used to use AB400's in a 4x6 box... I could always go back to them I guess.

But I guess I can try some cheap manual hot shoe flashes instead. My plan is to use my hassleblad with the 80mm 2.8. which I think will only sync at 1/160th or so.

Is your Hasselblad one of the relatively less common focal plane shutter models? Unless it is, it will synch at all available speeds.

And unless you are working in conditions with unusually bright ambient light, the shutter speed won't matter much, because the flash will supply the light, and exposure at the film will depend only on the light from the flash, the aperture of the lens, and the sensitivity of the film.

ChristopherCoy · Sep 24, 2014

500c/m

MattKing · Sep 24, 2014

ChristopherCoy said:
500c/m

Then the leaf shutter in the lens will synch at all speeds.

mweintraub · Sep 25, 2014

ChristopherCoy, So where is this "armpit of Texas" you live in because Cowboy Studios is based in Allen (north of Dallas) and have a show room where they might have this on display. I've got a light meter.

ChristopherCoy · Sep 25, 2014

mweintraub said:
ChristopherCoy, So where is this "armpit of Texas" you live in because Cowboy Studios is based in Allen (north of Dallas) and have a show room where they might have this on display. I've got a light meter.

I'm down in the SE part of Houston, where all the chemical plants and refineries are. It smells like an armpit all the time...

ChristopherCoy · Sep 25, 2014

MattKing said:
Then the leaf shutter in the lens will synch at all speeds.

That I did not know, but I was just reading that after seeing your post. Interesting.

Why can it sync at all speeds, when modern cameras are limited to like 1/250th?

MattKing · Sep 25, 2014

ChristopherCoy said:
That I did not know, but I was just reading that after seeing your post. Interesting.

Why can it sync at all speeds, when modern cameras are limited to like 1/250th?

Those so-called "modern" cameras are the ones that have a focal plane shutter. Those shutters use two curtains - the first starts opening the film/sensor to the light at the beginning of the exposure, while the second starts closing the film/sensor to the light at the end of the exposure time.

If you watch such a shutter in action, it will look like a travelling slit.

The most important thing to understand about such a shutter is that for speeds above the maximum synch speed, the second curtain starts closing before the first curtain finishes its travel - i.e. there is no time when the light from the flash can get to all of the film/sensor.

Leaf shutters work differently. They use the aperture of the lens. They start closed, then a small hole opens up at the centre, they proceed to open to the aperture you have set and then, after the time chosen, they reverse the process and begin to close, ending up fully closed at the end.

If you watch such a shutter in action, it will look like an opening and closing hole.

As a result, as long as the flash goes off at some time close to the time that they are fully open, the leaf shutter will synch with the flash at any speed.

Hope this helps.

Figuring out wattage...

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