How do you....

[cdifoto]

...precisely measure how many stops of light you lose when using a flash diffuser? I'd like to know how Sto-Fen and Gary Fong and others determine how much light is lost when their products are mounted.

I'm wondering not only whether they're comparing their product to others or without diffusers at all, but also the actual method to test.

[jamison55]

I would think you could set the flash to Manual, then fire it at a flash meter with and without the diffuser...

Wait a minute, I have a flash meter (blows the dust off his flash meter)

...10 minutes later...

So I took my 550ex and set it to Manual (1/4 power). I then set the flash meter to 1/125 second and placed it across the room. I am now ready for my test.

First I fired the flash directly at the meter. It told me that the appropriate aperture was f4.

Then I put an Omnibounce on, pointed it forward, and fired it at the meter. It told me the appropriate aperture was f2.8.

So based on this test, the omnibounce reduces the flash output by 1 stop when pointed forward.

[Rhys]

It'dbe interesting to know what difference gold and silver reflectors make as opposed to white. Alas, my flash meter is graded in single stops and is currently on the wrong side of an ocean.

[cdifoto]

I would think you could set the flash to Manual, then fire it at a flash meter with and without the diffuser...

Wait a minute, I have a flash meter (blows the dust off his flash meter)

...10 minutes later...

So I took my 550ex and set it to Manual (1/4 power). I then set the flash meter to 1/125 second and placed it across the room. I am now ready for my test.

First I fired the flash directly at the meter. It told me that the appropriate aperture was f4.

Then I put an Omnibounce on, pointed it forward, and fired it at the meter. It told me the appropriate aperture was f2.8.

So based on this test, the omnibounce reduces the flash output by 1 stop when pointed forward.


Damn...and I don't have a flash meter. I wanted to see how much light my bounce card loses or gains versus standard bouncing and the lightsphere.

Do you think using manual and whatever power is required for proper exposure without the card on, and then just using FEC to get as close to indentical histograms as possible with the card would be a decent alternate method?

[jamison55]

Just another reason to come to Boston...

Actually, I bought my flash/incident meter because I thought I would need it with the studio strobes, but the histogram tells me what I need so I never use it.

I picked it up for $35 on EBay.

[cdifoto]

Just another reason to come to Boston...

Hah yeah...speakin' of Boston...how's the ice up there? We're getting a nice downpour of it...

Actually, I bought my flash/incident meter because I thought I would need it with the studio strobes, but the histogram tells me what I need so I never use it.

I picked it up for $35 on EBay.

Hmm...I've been blowing a lot of cash on minimal and single-use stuff lately (scanner, Better Beamer, beer :D ). Maybe I should add "cheap light meter" to that list. Sadly I haven't got a clue how to use one. Are they pretty much self-explanatory (or easily figured out)?

Any particular brand? Should I at least avoid an old one? Etc etc etc...

[jamison55]

Do you think using manual and whatever power is required for proper exposure without the card on, and then just using FEC to get as close to indentical histograms as possible with the card would be a decent alternate method?

Actually, yes. If you had an identical histogram at +1 FEC you'd know that the diffuser eats a stop. The flash set to manual is the key so the output is the same...

[cdifoto]

Actually, yes. If you had an identical histogram at +1 FEC you'd know that the diffuser eats a stop. The flash set to manual is the key so the output is the same...

Right because of the E-TTL compensation. Output would vary.

[jamison55]

Hah yeah...speakin' of Boston...how's the ice up there? We're getting a nice downpour of it...

6 degrees with half a foot of snow on the ground from the last storm. It's supposed to snow again tomorrow...

Hmm...I've been blowing a lot of cash on minimal and single-use stuff lately (scanner, Better Beamer, beer :D ). Maybe I should add "cheap light meter" to that list. Sadly I haven't got a clue how to use one. Are they pretty much self-explanatory (or easily figured out)?

Any particular brand? Should I at least avoid an old one? Etc etc etc...

Mine is a little older (early 90's or so) and took a little while to figure out. You choose a shutter speed between 1/30 and 1/500, then press a button to set it. If you are taking an incident reading you hit the button again, if a flash reading you fire the flash at it. A number appears in the LCD. When you turn the dial to match the number, the other side of the dial shows the appropriate aperture.

The newer (expensive) meters are much easier to use...

[cdifoto]

6 degrees with half a foot of snow on the ground from the last storm. It's supposed to snow again tomorrow...

Yuck. I hate cold. I haven't even been outside for more than 5 minutes at a time since we got this batch! lol. I love workin' from home. Heck I dunno if my car would even start in this stuff. As a fail-safe I parked my van and car side by side (battery to battery) and keep cables in the car. :eek: :D



Mine is a little older (early 90's or so) and took a little while to figure out. You choose a shutter speed between 1/30 and 1/500, then press a button to set it. If you are taking an incident reading you hit the button again, if a flash reading you fire the flash at it. A number appears in the LCD. When you turn the dial to match the number, the other side of the dial shows the appropriate aperture.

The newer (expensive) meters are much easier to use...

Ok that sounds do-able. I'll try to save myself a few bucks and match histograms first. Then if that fails I'll buy a meter and play. Sure as heck don't wanna spend the big bucks on something I'll rarely ever use.

Thanks! http://www.dcresource.com/forums/images/icons/icon14.gif

[cdifoto]

...because DUH! It's not available in Manual Mode! I didn't think about that when assuming it would be feasible. In-camera FEC has no effect when flash is in manual either.

I used manual flash 1/8th power and adjusted the aperture accordingly for these two shots. They're not perfectly identical...but I attribute that to the way the card filled the scene a little more than straight up bouncing did. In both cases I had the head bounced 90 degrees and swiveled 90 degrees as well. I did overexpose a little according to the Photoshop histogram...on the camera neither end fell off. Not sure what's up with that.


This is with the card: (f/4)
http://i14.photobucket.com/albums/a304/cdifoto/bouncecard/ScreenShotCard.jpg

This is without the card: (f/2.8)
http://i14.photobucket.com/albums/a304/cdifoto/bouncecard/ScreenShotNoCard.jpg

So the card actually gained a stop of power over bouncing bare flash. It makes sense since I'm throwing light forward in addition to up when the card is mounted.

Next test is Lightsphere vs Card. Same 1/8th. Something flawed in my test though it seems. I know the histograms aren't identical...and I do have falloff (blown highlights in both) but it appears they falloff pretty close to one another. What I don't get is that the Lightsphere and *bald* bouncing both lost the same amount of light...even in manual flash (unless there's more/less falloff on the histogram than I believe).

Lightsphere: (f/2.8)
http://i14.photobucket.com/albums/a304/cdifoto/bouncecard/ScreenShotwLS.jpg

Card: (f/4)
http://i14.photobucket.com/albums/a304/cdifoto/bouncecard/ScreenShotwCard.jpg

BTW this is the best test I could think of without having a light meter for precision.

And try not to mind the mess!