Overcoming ambient light problem?

[beyond the blue]

I've recently got myself a SB 910 so thought I would try out some high speed sync stuff. Trying to overcome the ambient light with my Nikon D90 I set the speed to 1/4000 (being the max speed the flash will sync at) and F22 (max for the lens) and ISO 200 but these settings still wasn't enough to overcome the light.
I went into the ISO settings and tried Lo 0.3 / Lo 0.7 / Lo 1 but none of these made any difference compared to ISO 200. Why would that be?

 

[Phil V]

Forget settings per -se, they don't mean anything.

If you want the flash to overpower the ambient, you need two things; to underexpose the ambient (easy?) and then to have enough flash power to light your subject at those settings (less easy).

So you might have a problem overpowering a bright sunlit afternoon with a speedlight on high speed sync (the sun is more powerful than the speedlight and by using high speed sync you're reducing the flash power further). Try again late evening.

It's the equivalent of knowing that a telephoto lens makes distant things larger and then wondering why a 200mm lens won't let you read a newspaper that's half a mile away.

It's Physics innit.

 

[beyond the blue]

If you want the flash to overpower the ambient, you need two things; to underexpose the ambient (easy?)

Phil
Thats what the problem is I could'nt underexpose the ambient light. Really my query was more to do with why would'nt the "low ISO settings make a difference to the exposure.

 

[Phil V]

Phil
Thats what the problem is I could'nt underexpose the ambient light. Really my query was more to do with why would'nt the "low ISO settings make a difference to the exposure.

No idea, I'm not a Nikon shooter, but are you absolutely sure of those settings, because that's an awful lot of light?
In the bright sunshine outside my house now, those settings got me an almost entirely black image - In fact in aiming for a high shutter speed, 1/1000 got me f3.2 (about 7 or 8 stops lower?).

So 1/1000 at f6.3 gets me 2 stops under.

 

[Steve Smith]

Thats what the problem is I could'nt underexpose the ambient light. Really my query was more to do with why would'nt the "low ISO settings make a difference to the exposure.

The ISO setting will most certainly affect the exposure.

And at ISO 100, there isn't ever enough ambient light that you can't under expose with the right combination of shutter and aperture.

On the brightest day, f16 and 1/125 will be very close to correct so stop down a bit or increase the shutter speed and the ambient will be under exposed.


Steve.

 

[beyond the blue]

Maybe I'm not explaning the the problem well enough, let me have another go.
When I used the settings as described in my OP ie; 1/4000, F22, ISO 200 the exposure very nearly underexposed the ambient light to give me a totally black image (but not quite) so I needed to reduce the ISO further, now on a Nikon D90 you don't have the option to go below ISO 200 without going into what they call LO ISO, these low ISO setting are named Lo 0.3, Lo 0.7, Lo 1
neither of these three settings affected the exposure further ie didn't darken the exposure further. I was wondering if anyone could explain why.

 

[beyond the blue]

Confession time!!! I still had auto ISO switched on, which was defaulting to ISO 200 and wouldn't allow the lower settings to take affect. :bang: All day wasted.:bang:

 

[Steve Smith]

That would explain it!

Although if 1/4000, F22 very nearly underexposed the ambient light it wasn't anywhere near as low as ISO 200.

For those settings to be one stop underexposed on a bright day, it would have to be at around ISO 6400.


Steve.

 

[beyond the blue]

When I used the settings as described in my OP ie; 1/4000, F22, ISO 200 the exposure very nearly underexposed the ambient light to give me a totally black image (but not quite)

That would explain it!

Although if 1/4000, F22 very nearly underexposed the ambient light it wasn't anywhere near as low as ISO 200.


Steve.

This was 1/4000, F22, ISO200

 

[TG.]

Why not just use your flash in manual mode ? ie underexpose the subject then try different settings on your flash in manual, till you get the sort of exposure you want.

 

[Steve Smith]

This was 1/4000, F22, ISO200

I don't doubt it. On a bright sunny day, those settings would be five stops under exposed.

In your previous post you said that these setting produced an image which was "very nearly under exposed". the reality is that it is very under exposed.

I would consider the term "very nearly under exposed" to mean very close to correct rathr than almost totally black.


Steve.

 

[Phil V]

I don't doubt it. On a bright sunny day, those settings would be five stops under exposed.

In your previous post you said that these setting produced an image which was "very nearly under exposed". the reality is that it is very under exposed.

I would consider the term "very nearly under exposed" to mean very close to correct rathr than almost totally black.


Steve.

That would explain it!

Although if 1/4000, F22 very nearly underexposed the ambient light it wasn't anywhere near as low as ISO 200.

For those settings to be one stop underexposed on a bright day, it would have to be at around ISO 6400.


Steve.

Which is probably what the camera chose.

Confession time!!! I still had auto ISO switched on, which was defaulting to ISO 200 and wouldn't allow the lower settings to take affect. :bang: All day wasted.:bang:

It's worth noting though for those people who believe they're taking control and shooting Manual with Auto ISO on, the last thing you are is actually 'in control'.