Dark images in Manual mode with 2 Broncolor strobes

[alisadeghy]

Hi

I'm trying to shoot some products with my Canon 70D and 2 Broncolor strobes (firing in full power) in camera Manual mode.
These are my exposure settings:
Shutter speed 1/100 sec.
ISO-100
f/16
I use my internal camera flash to trigger strobes and they fire correctly.
But my photos get dark randomly in same setting!!! For example in these images I use the exact same setting but only in different distances from product!

The exposure level indicator shows a small arrow downside -3 mark.
The other problem is that camera does not allow me to adjust shutter speed more than 1/250 sec. and I'm so confused!
Is there anything wrong with my camera or evaluation system? Or it's just me doing things wrong?
.
.
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FYI I know I can use other modes and you know, any other things you would advice, but please just answer my questions!
Thanks

[kvbarkley]

You can't go above 1/200 because that is the flash sync speed. Any faster and the flash will fire when the shutter is partially closed.

How are you syncing the flash?

[alisadeghy]

Actually my strobes are kinda old and they are in constant speed and as I said I use my camera flash just to trigger them, you're right, that's why I can't adjust my shutter speed more than 250. Thank you.
But I hope someone can solve my main problem here!

[RobertTheFat]

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@alisadeghy wrote:
Actually my strobes are kinda old and they are in constant speed and as I said I use my camera flash just to trigger them, you're right, that's why I can't adjust my shutter speed more than 250. Thank you.
But I hope someone can solve my main problem here!

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An optical slave usually needs a clear line-of-sight path between its sensor and the triggering flash. Since moving things around seems to have an effect, is it possible that the strobes sometimes can't see the trigger? Or don't recognize it soon enough and fire late?

[Waddizzle]

Is it possible that flickering,ambient lighting could be causing the inconsistent exposures?

[alisadeghy]

Robert, I don't think so, because the distance between flash and strobes is something like 1 meter and nothing is blocking the sight and the fire immediately and seems they're working well!
Waddizzle, there is no flickering or something like that in studio, just strobes modelling lights and usual lights.

[Waddizzle]

"Waddizzle, there is no flickering or something like that in studio, just strobes modelling lights and usual lights. " 

The human eye would not notice the flickering, no more than the eye can detect 24 fps of a flickering moving image.  Most flourescent lights exhibit flicker at line voltage frequenceies, which the human eye cannot detect, but is easily picked up by your DSLR.

I would suggest dimming the ambient lights, or using an enclosure with controlled lighting, to shoot your images.

[cicopo]

Like any situation where you use strobes that only fire at full power you'll need to experiment & based on your settings mentioned you've got lots of room to get what you need done.

use a wider F stop, f16 is pretty small

use a slower shutter speed, (I assume you're using a tripod so slower shouldn't be a problem)

raise the ISO, a bit at a time

OR ANY combination of the above until you find settings that work.

AND be sure you give the strobes enough time to be fully charged for each shot.

[kvbarkley]

Does your flash trigger understand the Canon Pre-flash?

[RobertTheFat]

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@kvbarkley wrote:

Does your flash trigger understand the Canon Pre-flash?

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That's an interesting point. The E-TTL protocol assumes, I believe, a fixed interval between the preflash and the main flash. If the strobes don't understand E-TTL, they might misinterpret the preflash as the main flash and fire before the shutter opens. Of course that leaves open the question of why it sometimes happens and sometimes doesn't. Conceivably the (relatively weak) preflash is misconstrued only if the strobes are too close to the camera or have an unusually direct sight line to the camera's flash. In any case, the first thing to check, if it hasn't been done already, is that the camera and the strobes are on the same page with respect to the protocol being used.

P.S.: E-TTL and TTL are not the same thing. Given that the strobes are old, it's conceivable that they understand TTL but not E-TTL. Also, there's both an E=TTL and an E-TTL II; exactly how they differ, I'm not sure.