Ad
Ad
Ad
Pages: [1]   Bottom of Page
Print
Author Topic: Technical Flash Question  (Read 1909 times)
dwdallam
Sr. Member
****
Offline Offline

Posts: 2044



WWW
« on: October 07, 2012, 12:40:15 AM »
ReplyReply

I may take flack for this,so okay go for it. But I am hoping someone with this information fairly fresh in his or her mind can nail it for me before I have to go do the research and calculations myself, which would take a long time.

To make a long story short, I was using the Pocket Wizard Flex system with my 580EX II flash system. After several years of malfunctions, I gave up on them. One of the malfunctions was that the Canon 580EXs II blew all of their IGBTs and the flash would only dump full power. A really good read for you technophiles: http://photography-on-the.net/forum/showthread.php?t=1125902 

Anyway, I'm now using the Phottix Odin controller and remote and they are truly remarkable. I've not had one misfire or wrong exposure with them.

I have noticed that I cannot turn the flash down low enough at higher ISOs or larger apertures. The Canon 580EXII can go to 1/128th power.
So I'm wondering if the flash is acting up again like it did on the PW Flex system.

My technical question is what would be the distance to subject at any exposure setting where 1/128th on the 580EX II power would not be low enough for a correct exposure?

As always, thanks much for your time and effort.
Logged

Canon Bob
Newbie
*
Offline Offline

Posts: 21


« Reply #1 on: October 10, 2012, 04:16:05 PM »
ReplyReply

I'm not aiming to answer your question directly as I don't know the answer.  I'll look at it in a different way though.

Changing the power output doesn't simply change the light intensity, it changes the duration.  Some figures to peruse
1/1 power gives a light pulse of 1ms (1/1000th) approximately.
1/2 power shortens this pulse to 0.5ms
1/4 power 0.25ms
1/8 power 0.11ms
1/16 power 0.066ms
1/32 power 0.047ms
1/64 power 0.033ms
1/128 power 0.028ms

As you can, it isn't a linear equation and this makes calculation somewhat tedious.

Hope that has helped in some small way.

Bob
Logged
dwdallam
Sr. Member
****
Offline Offline

Posts: 2044



WWW
« Reply #2 on: October 10, 2012, 04:32:37 PM »
ReplyReply

Bob,

Thanks for the reply.

Another way to put this is "For a correct exposure, what is the largest aperture at ISO 800 one can use at 1/128 (580EXII) at a distance of two feet using manual flash, while assuming low enough ambient light so that the ambient light does not contribute (low lit indoors)?"

This will give me a benchmark to test if my flash unit or controller is malfunctioning. If it's too much to try and calculate, perhaps someone with a 580EXII could test using those parameters. Again, this will give me some benchmark to test my own units.
Logged

k bennett
Sr. Member
****
Offline Offline

Posts: 1478


WWW
« Reply #3 on: October 10, 2012, 05:49:44 PM »
ReplyReply

I just tested this. 5D Mark II, ISO 800, 580 EX-II in manual mode at 1/128 power, approximately two feet from the subject (flash to subject distance.) Looks like f/8 is pretty decent. Anything wider is totally blown out. I don't have a tape measure in my camera bag, so this distance isn't exact, but it should be close enough.
Logged

Equipment: a camera and some lenses.
dwdallam
Sr. Member
****
Offline Offline

Posts: 2044



WWW
« Reply #4 on: October 10, 2012, 05:53:38 PM »
ReplyReply

That's about what I'm seeing too. Thanks!
Logged

Ellis Vener
Sr. Member
****
Offline Offline

Posts: 1851



WWW
« Reply #5 on: October 11, 2012, 12:44:29 PM »
ReplyReply

Quote
"I was using the Pocket Wizard Flex system with my 580EX II flash system. After several years of malfunctions, I gave up on them. One of the malfunctions was that the Canon 580EXs II blew all of their IGBTs and the flash would only dump full power. A really good read for you technophiles: http://photography-on-the.net/forum/showthread.php?t=1125902"

Also see http://lpadesign.com/580EXII.pdf for a report on the ControlTL + 580 EX II problems. This report has been out there for about a year and a half. While LPA Design commissioned the study and published the report in the twenty months since it was published Canon has never contradicted the findings as far as I know.
Logged

Ellis Vener
http://www.ellisvener.com
Creating photographs for advertising, corporate and industrial clients since 1984.
hugowolf
Sr. Member
****
Offline Offline

Posts: 639


« Reply #6 on: October 11, 2012, 01:15:23 PM »
ReplyReply

PW Flex system.
My technical question is what would be the distance to subject at any exposure setting where 1/128th on the 580EX II power would not be low enough for a correct exposure?
I am curious as to why you would be using high ISO values when 1/128 power is too much. Basically when about 0.5 Ws is too much. but anyhow ...
The flash has a guide number of 58 metres at f/1, ISO 100, and zoomed to 105 mm
so 29 metres at ISO 400
so about 5.1 metres at 1/128th power, ISO 400
or 1.8 metres at f/2.8

If you insist on high ISO values, you can reduce effective output by zooming the flash head out - at least when used bare. If you are in a softbox it will not help.

The 580ex II does go lower than 1/128th power, but not manually. It only does it in ETTL mode.

Brian A
Logged
dwdallam
Sr. Member
****
Offline Offline

Posts: 2044



WWW
« Reply #7 on: October 11, 2012, 05:14:33 PM »
ReplyReply

Also see http://lpadesign.com/580EXII.pdf for a report on the ControlTL + 580 EX II problems. This report has been out there for about a year and a half. While LPA Design commissioned the study and published the report in the twenty months since it was published Canon has never contradicted the findings as far as I know.

Been through the whole gamut with LPA and the Flex system. They stood behind the product and fixed all of my 580EXIIs plus gave them the RF interior coating for a total of 120.00 USD for three 580s. They also replaced all of the IGBTs. I still had problems using the Flex system and finally gave up in frustration.

I now own the Phottix Odin system and it has proven to be prefect in every way. It's less than half the price of the Flex system too.
Logged

dwdallam
Sr. Member
****
Offline Offline

Posts: 2044



WWW
« Reply #8 on: October 11, 2012, 05:24:15 PM »
ReplyReply

I am curious as to why you would be using high ISO values when 1/128 power is too much. Basically when about 0.5 Ws is too much. but anyhow ...
The flash has a guide number of 58 metres at f/1, ISO 100, and zoomed to 105 mm
so 29 metres at ISO 400
so about 5.1 metres at 1/128th power, ISO 400
or 1.8 metres at f/2.8

If you insist on high ISO values, you can reduce effective output by zooming the flash head out - at least when used bare. If you are in a softbox it will not help.

The 580ex II does go lower than 1/128th power, but not manually. It only does it in ETTL mode.

Brian A

Brian! That's the whole ball of wax! when i first noticed this I was stumped because when i wen to TTL mode, the problem resolved. Thus, I though I had some sort of inconsistency. I was not aware that the 580 would actually shoot below 1/128th in ETTL.

I'll tell you the story so you will understand why I "insisted" on using a high ISO. Actual the situation "insisted" that I do it, or not get the picture I was looking to get. I was shooting indoors and using the crack in the door to light the model. the ambient light in the room wasn't light enough to illuminate the rest of her body, so I wanted a small pop of flash to illuminate her. At the time I was using manual flash because I was using studio strobes with the 580s.  I switched to ETTl and got the image.

Here it is:
Logged

hugowolf
Sr. Member
****
Offline Offline

Posts: 639


« Reply #9 on: October 11, 2012, 07:34:48 PM »
ReplyReply

I thought twice about using 'insist', but decided to go with it anyhow. Thanks for the explanation, so many posts go by without any clear reason for why whatever is being requested.

Brian A
Logged
dwdallam
Sr. Member
****
Offline Offline

Posts: 2044



WWW
« Reply #10 on: October 12, 2012, 01:05:45 AM »
ReplyReply

I thought twice about using 'insist', but decided to go with it anyhow. Thanks for the explanation, so many posts go by without any clear reason for why whatever is being requested.

Brian A


Brian, no worries. I would like to use the ISO that crates the best image, but as we all know, ISO (now more accurately called "gain") always reduces image quality. I would love to use 100 all of the time. However, many times using the  580s on location, I'll bump it to 400 as a baseline for extra flash power, and to make the flashes batteries last longer.
Logged

hugowolf
Sr. Member
****
Offline Offline

Posts: 639


« Reply #11 on: October 12, 2012, 09:34:42 AM »
ReplyReply

I'll bump it to 400 as a baseline for extra flash power, and to make the flashes batteries last longer.
... and much faster recycling too.
Logged
dwdallam
Sr. Member
****
Offline Offline

Posts: 2044



WWW
« Reply #12 on: October 12, 2012, 03:47:05 PM »
ReplyReply

... and much faster recycling too.

Indeed!
Logged

Pages: [1]   Top of Page
Print
Jump to:  

Ad
Ad
Ad