What went wrong here? (Flash / Exposure FAIL)

Hi2all,

I'm not a pro and certainly not a "Wedding photographer" but when friends of mine got stood up by their hired photographer I did my best to bail them out. I'm pleased to say that 2/3rds were keepers (after a bit of Photoshop post-processing, of course), but during the course of the [flash] shooting, I was constantly struggling to "get it right", changing parameters on the fly. One [flash] shot was over-exposed, the next under, etc.

For the most part, I used my Lumiquest Promax diffuser (with white insert) and I would have used it the whole time, but I got caught with a few badly-under-exposed shots which made me resort to:

• changing my 580 EX I's EV to anywhere from +1/3~+1 Stop
  
• abandoning the diffuser. That is, until I couldn't stand the harsh lighting anymore... sigh.
  

It looks to me like the joys of ettl. There are lots of reflective little things on the bride.. or the preflash could have metered with someone else's flash.

Flash didn't recycle fully if you were shooting quickly?

tenoverthenose wrote in post #10453818
It looks to me like the joys of ettl. There are lots of reflective little things on the bride...

This is my first thought. The ETTL saw all that white and reflection and got a bit fooled.

+1 says it thought the scene was more black and needed more light. Flash is for f-stop, shutter for ambient. If it was too bright, you could adjust the fstop down. Can't see your pics with work censors, sorry.

silvrr wrote in post #10453862
This is my first thought. The ETTL saw all that white and reflection and got a bit fooled.

this would mean an underexposure by ettl, if that's true.

buurin wrote in post #10453851
Flash didn't recycle fully if you were shooting quickly?

OMG... didn't think to check that...

Well, I caught the groom at 3min 26sec: properly exposed, but he was also closer to me
The bride came at 4min 07sec: but it was really at the door-frame and at that distance, she did not take up most of the frame. Not to mention she was roughly 4m (13ft) from me at that point... .
Next shot (the one pictured above) came in at 04:12... .

Hmm... I feel kind of silly now, given that 5sec is a bit pushy and the flash was certainly only in "Quick Mode" (green and not red LED).

I guess that was it. Sigh... sorry for the wild goose chase, but thanks for helping me out. I don't know how to beat that problem and I guess the only answer is to "wait for the right shot"; better one good one than three under-exposed shots, heh?

hawk911 wrote in post #10453910
Can't see your pics with work censors, sorry

I'm sorry, but I don't follow what you mean...

Travelller wrote in post #10453964
I'm sorry, but I don't follow what you mean...

The internet filters used by his employer are preventing him from viewing the pics.

The focal length change can be part of the problem too since it increases the distance. Light falls off following the inverse square rule so if you double the distance between the light source and the subject then you will have only 1/4 the light hitting the subject. Combine that with light loss from the diffuser and you can be pushing the limits of what the flash can deliver.

Also, what are you using for power? If you don't already have them, Eneloop batteries in an external power pack may be a good idea since they will greatly speed the flash recycle time.

Travelller wrote in post #10453788
The other downside of the diffuser is that I didn't even manage to finish the the Church ceremony before my fresh set of AAs (Duracell's ultra line) were red-hot and pretty much useless.

Are those alkaline batteries? If they are, NEVER use them in your flash again! Look into rechargeable Nimhs. Eneloops are a good brand to get.

Also, if you bump your ISO up to 400, your flash will only need to fire at half the power. ISO800 would only need 1/4 the power...Likewise you can open up your aperture more.

Bouncing at f/5.6 and ISO200 in a big room is a recipe for dead batteries.

You might also want to look into a battery pack for your 580.

krb wrote in post #10453981
The focal length change can be part of the problem too since it increases the distance. Light falls off following the inverse square rule so if you double the distance between the light source and the subject then you will have only 1/4 the light hitting the subject. Combine that with light loss from the diffuser and you can be pushing the limits of what the flash can deliver...

Thanks, I can appreciate that. I'm so used to the power of the 580EX (without diffuser) that I do believe that its "Quick Flash" mode will be more than satisfactory within, say, 3m (10'). However it's very difficult to factor in the diffuser.

Lumiquest's website indicates a loss of 1-1/3 stops. Canon's User Guide specifies a Quick Flash range of 7.5m (25') minimum* at f/1.4, ISO 100.

So... let's see, f/1.4 -> f/5.6 is a difference of what, ... 1.4,2,2.8,4,5.6 so 4 stops? Let's round off the diffuser to one stop, we're now at a 5-stop difference. But I was at ISO 200, so back to 4 stops. At 50mm (Canon specs), which is also the "bounce" value of the 580EX.

So what's 7.5m (25') less four stops?


*Maximum QF range is 21m (69') and max for normal mode is 30m (100')

egordon99 wrote in post #10454047
Are those alkaline batteries? If they are, NEVER use them in your flash again! Look into rechargeable Nimhs. Eneloops are a good brand to get....

That's funny, someone told me the opposite... sigh. In any case, I always use rechargable Li-ion batteries in one of my other hobbies, but those are rated at 3.7V... probably not a good idea, huh Thanks, I've heard of Eneloops and will give them a go. How's $37 for 4xAAs and charger sound? The batteries alone go for $12. FYI, DX is usually dependable (as long as you don't order during the Chinese New Year...).

Travelller wrote in post #10455066
That's funny, someone told me the opposite... sigh. In any case, I always use rechargable Li-ion batteries in one of my other hobbies, but those are rated at 3.7V... probably not a good idea, huh Thanks, I've heard of Eneloops and will give them a go. How's $37 for 4xAAs and charger sound? The batteries alone go for $12. FYI, DX is usually dependable (as long as you don't order during the Chinese New Year...).

$9.95 for four batteries and a free battery holder is included: http://www.thomasdistr​ibuting.com …98rm8a91donrsll​it8gi3gna7

For the charger, everybody around here says to go for the maha/powerex chargers. I recently ordered a maha 8 battery charger from the site above and it does seem to work well. It's nice to be able to charge 2 sets at a time.


I just noticed there's a current thread that you might find interesting: https://photography-on-the.net/forum/showthre​ad.php?t=893722

krb wrote in post #10455110
...For the charger, everybody around here says to go for the maha/powerex chargers...

Lol, the second I read "Maha" I realized I bought a Maha charger a while back (MH-C204F). Cool! All I need in that case are the batteries. Going directly to Asia saves me a little bit of money. Shipping's [From Thomas Dist.] is not an issue for you (if you live in the States) but it is for us in the Old World (I'm in Austria). DX ships for free.

p.s. Thanks for the thread tip, I'll have a look-see

Travelller wrote in post #10455066
...So what's 7.5m (25') less four stops

I came across a web-tool (in German, however) that although not stellar, does seem to work.

I entered 7m, f/1.4 & ISO 100 and got back a GN of 10. Then I entered the actual Av value I used for the above shot (5.6) and a GN of 10 and it calculated 1.8m (~6'). The bride was at least 6' away from me so I think that I will have to accept the fact that Quick Flash is an iffy proposition (however, not to be ruled out).

Again, the specs define 7.5m as the MINIMUM - which means, as soon as the green LED illuminates. MAX Quick Flash is much higher at 21m (69'), which implies a GN of 29. At full strength (red LED), Canon specifies 30m (100') which equates to a max GN of 42 @55mm. The GN "58" - as in 580EX, is obviously not quite correct and is based on 105mm...

A GN of 29 would have given me up to 5.2M to play with...! With fresh batteries, the difference between min & max Quick Flash must be around 4sec!!! Sigh...

Getting back to the OP.
If you were shooting RAW your stuff-ups are redeemable.