Light loss shooting through and bouncing in an umbrella

[Stradawhovious]

Another dumb-ass rookie question here......

Just finally got around to taping my guide chart to the side of my SB-600, and had a couple of questions.....

How much light am I going to lose shooting through say...... a 42" umbrella, and shooting into (bouncing) the same umbrella.

Some of the sources I have seen say I will lose as little as one stop off the chart, and others say as much as 63%. Is there some sort of formula I can use, or am I best off just redoing the chart for the umbrella?

Thanks for putting up with yet another drastically rookie question from Strad.

 

[Stradawhovious]

Nothing at all?

 

[480sparky]

Wouldn't it depend on the umbrella and the material it's made of?

 

[OrionsByte]

Why not do some tests?

Shoot at say f/8 with the flash on manual, bare, and adjust it to get a proper exposure on some subject.

Put it behind a shoot-through umbrella, keep the same power setting on the flash, and open the aperture up until you get a proper exposure again. The difference in aperture will tell you how much light you're losing.

 

[Big Mike]

As with everything....it depends.
The size/shape/material will all play a factor. The zoom setting and position of the flash will make a difference.

If you had a flash meter, you could check this very accurately. If you don't have a flash meter, you can take shots with each and compare the results...this might not help with your charge, but it would tell you which set up gives you the most/least light.

 

[Stradawhovious]

If you had a flash meter, you could check this very accurately.

If I had a flash meter, I'd meter in the morning.

Id meter in the evening.

Hell, I'd meter all over this land!


As it stands, I don't.

Thanks fellas, This confirms my assumptions that I will more than likely have to just make a new chart. Which is fine, I just didn't want to go through all the work if there was a simple general formula I could use to get me in the ballpark.

Thanks!

 

[mjhoward]

I was just looking at this same sort of thing last night. Here's a good read/test:

TEST: Umbrella Spill - Bounce vs. Shoot Through vs. Umbrella Softbox - Canon Digital Photography Forums

 

[Stradawhovious]

I was just looking at this same sort of thing last night. Here's a good read/test:

TEST: Umbrella Spill - Bounce vs. Shoot Through vs. Umbrella Softbox - Canon Digital Photography Forums

Good read. Thanks!

 

[KmH]

It's worth noting that the language used to quantitatively describe the amount of light at the various points in the scene was f/stops, and 10ths of f/stops.

 

[shmne]

Alright I'm just going to ask a question:

Why does it matter?

There is an extraordinary amount of factors that will alter the numbers one way or another. I think it is better to concentrate on how the umbrella shoots, document and take note of it. Then move on from there. You don't need a chart, just learn it by using it. It reminds me of the old saying "Analysis paralysis"

 

[Josh66]

Just test it. Once you know, you'll know.

It will always be the same. Say it's 1 1/3 stops - it'll be 1 1/3 stops every time, so just compensate by that amount.

 

[Stradawhovious]

Alright I'm just going to ask a question:

Why does it matter?

My brain works funny. Once I kow the mechanics of things, I can put them into a sort of working kowledge.

For example...... I see how the guide chart works for my bare SB-600 flash. After reading through the chart, and doing a couple simple tests to see how it works out in real life I understand the principle, and no longer need the chart. I can get reasonably close the first time by just understanding the mechanics.

I never would have been able to do it without the chart.

Same goes for the umbrella. If I can say to myself, "well, I'm going to lose 1 2/3 stops of light by shooting though the umbrella" Then I can easily pick my flash settings knowing my aperture and distance from the subject and get reasonably close the first time.

Without a constant, I will need a chart to look at once or twice just to get the math straight in my head

Like I said, my brain works funny.

 

[Village Idiot]

If you had a flash meter, you could check this very accurately.

If I had a flash meter, I'd meter in the morning.

Id meter in the evening.

Hell, I'd meter all over this land!


As it stands, I don't.

Thanks fellas, This confirms my assumptions that I will more than likely have to just make a new chart. Which is fine, I just didn't want to go through all the work if there was a simple general formula I could use to get me in the ballpark.

Thanks!

You can find cheaper ones. You don't have to spend $300 or more on a meter.

Alright I'm just going to ask a question:

Why does it matter?

There is an extraordinary amount of factors that will alter the numbers one way or another. I think it is better to concentrate on how the umbrella shoots, document and take note of it. Then move on from there. You don't need a chart, just learn it by using it. It reminds me of the old saying "Analysis paralysis"

It could be especially important if you're using small low powered strobes that need every ounce of juice they can get.

 

[Stradawhovious]

You can find cheaper ones. You don't have to spend $300 or more on a meter.

For example............

 

[cgipson1]

I bought a Wein flashmeter about 25 years.. sold it to a friend about 10 years ago... it was still working at that time. They are a little crude compared to todays meters, but they do work.. and are accurate. Amazon has them.. as do other places. Under $120. They make a cheaper one too. apparently.. but have never used it.

Amazon.com: Wein 950-020 WP-1000 Flash Meter: Camera & Photo