# Thread: Is there a way to calculate how much light I will need?

1. ## Is there a way to calculate how much light I will need?

I am shooting an Egg on an 8x10.
I am looking to rent a light but am not sure what light to use. I do know it will need to be powerful.

My film stock is iso 50.
I want to shoot at 125th of a second.
At aperture F 32

I also know I need a bellows draw compensation of 5 stops

Is there math to figure out how much light I will need?

2. ## Re: Is there a way to calculate how much light I will need?

The bellows calculation comes from shooting on a 240mm lens with 1222mm of bellows

3. ## Re: Is there a way to calculate how much light I will need?

Hmmm white or brown egg?

4. ## Re: Is there a way to calculate how much light I will need?

How much light depends upon exposure time. I've made LF close-up shots with ambient window light where I opened the shutter, left for work, and come back 6-8 hours later and closed the shutter. If you're using hot lights or ambient light and long exposures, you just need to get a handle on the reciprocity corrections for such long exposure times (of course, I'm assuming B&W film; with color you'll want to aim for shorter exposures to avoid color shift).

If you are looking at flash, remember that, when shooting a still life (which stays still...), you can use multiple pops of the flash to arrive at your needed exposure.

If you have access to the light (flash unit) you want to rent, take your (flash) meter with you and measure. Maybe someone will come up with a formula for determining how many lumens or candles per square foot you need, but I imagine it will be rather complicated. Measuring the actual light source is likely faster and easier.

Edit: I've just seen in another thread that you're likely shooting an "action" shot, i.e., not a still life. So, long exposures won't work in this case. So, just go in to your lighting rental place with your meter and do some measuring of light intensity. Keep in mind that the distance from the light to the subject is critical (inverse square law and all that), so measure with an incident meter at the working distance or take a reading from a lit object at the working distance (or adjust the light-to-subject distance to get the intensity you need).

Best,

Doremus

5. ## Re: Is there a way to calculate how much light I will need?

Originally Posted by AnselAvedon

Is there math to figure out how much light I will need?
Here you have a table, use the studio reference entry at 1000 lux, this for 1/50 exposure, ISO 100, f/2.8, so you just need multiply/divide the 1000 Lux properly for your shutter speed, aperture, ISO, and bellows compensation.

You can also use math:

Know how many lux x second you want on film, from exposure you know how many lux you want on film, from f stop, bellows compensation, and subject reflectiveness you know howm many lux should receive you subject, and from the area you light source illuminates and the power to light convension efficiency you know the watts of your light. It would be nice if somebody can show the exact formula...

For exact exposures, a good choice for precision is using "the view's camera TTL metering feature": place a DLSR or SLR (Nikon F65...) in the back of the view camera (need a DIY attachment, made with a macro extension ring), focus to the same point you are to focus and measure... with shift/rise you can explore all the framing, or you can use camera orientation for it if fall off is not a concern.

6. ## Re: Is there a way to calculate how much light I will need?

To get your answer requires a radiometric calculation. Actually, it requires a series of calculations and assumptions. Very heavy stuff. I've been doing radiometry for work for years and I still have to pull out notes I wrote for myself in the past.

Easier to set up a test.. *much easier*.

Meter off the egg with an available light set at your desired distance from the egg. Determine how many stops down you are. Doubling the light output adds a stop.

When you get your actual light in, you can fine tune with lighting distance. Halving the distance adds roughly 1-2 stops depending on the characteristics of your source (baffling vs bare bulb, etc).

7. ## Re: Is there a way to calculate how much light I will need?

I think your initial requirements are impossible.

50 ISO and 1/125 shutter at f32 is a problem. As it seems you want to use hot lights. Strobes will get you there and not melt everything, but shutter speed then is irrelevant. Your shutter speed will become strobe speed. Very fast.

This is a scan from 11X14" X-Ray ISO 80. The ashtray is about 4" in diameter. I didn't keep all records. I think I shot with a 300mm Sironar stopped down to f22. We can prpbably calculate my distance to object and bellows extension. Object to lens maybe 1 foot. I bet Dan could figure the details.

I use 3 Einstein strobes full blast at very close range, fitting them around the Deardorf S11 was tight. Multiple pops of all 3 strobes. I used a flash meter and got a good exposure in a couple shots. I developed each film then adjusted from examination.

Just an exercise/experiment. I got what I wanted to know.

I do know magnification was about 2.5. The 11X14 neg doesn't fit on my V700 so the image here is cropped.

Watergate 2.5-1 Macro by moe.randy, on Flickr

8. ## Re: Is there a way to calculate how much light I will need?

you will need a whole lot of light to shoot at 1/125

maybe get an arri 500 right up close to the egg... like within a foot... maybe use some frosted glass between to even the light out?

but with f32... and then tossing 5 stops on top of that..... at 1/125?

oy

9. ## Re: Is there a way to calculate how much light I will need?

Why use continuous light? Flash will do it. The trick is to use a short flash-to-subject distance. At close distances a flash acts like a large light source, not like a point source. No kidding.

OP, its time for you to learn how to use flash guide numbers.

10. ## Re: Is there a way to calculate how much light I will need?

Originally Posted by Dan Fromm
Why use continuous light? Flash will do it. The trick is to use a short flash-to-subject distance. At close distances a flash acts like a large light source, not like a point source. No kidding.

OP, its time for you to learn how to use flash guide numbers.

If subject is static, continous light is convenient, it has the advantage that we can see/control the illumination effects. We can meter easily key vs fill...

With flash we should use the modeling light, meter the continous light and adjust strobes with flashmeters to get the right balance.

But today we have DSLRs to preview the illumination effects, it is really useful to preview the effect of the modifiers, the light nature, the light fall... a bit like when in the past instant film was used to preview a result for the LF negative.

I found that a DSLR is a very good tool to adjust illumination for LF in studio conditions.

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