Question regarding on-camera flash

[Digital]

I recently took a pic of a blue eyed subject. I used a on-camera flash mounted on the hotshoe. The flash was not bounced. When editing in LR, and looking at the proofs the subject's eyes were no longer blue.
Can anyone explain this. I do not even have a theory.
Any assistance will be greatly appreciated.



Bruce

[rpcrowe]

On camera flash projects its light along the axis of the lens. The flash will hit the retina and bounce back into the lens usually causing red eye in humans and ghostly blue-green eye in dogs...

Elevating the flash away from the lens axis will prevent the reflection from bouncing back into the lens. Obviously, bouncing the flash will also prevent that!

[Manfred M]

Bruce - it would be great if you could post that image to give us a better look at the eyes. My first guess is that that part of the eyes got blown out a bit.

[Shadowman]

Also, how close are other surfaces, any other light sources in range?

[dennybeall]

You say "not blue" but not what color they are. In any case, it's the flash right in their face. Time for Photoshop.....

[Dave Humphries]

Bruce - you are Mr. Sleuth, not us

Please show us a picture.

[RBSinTo]

Often, on camera flash is employed indoors because of low light levels, resulting in the subject's pupils being wide open, so that when the flash is fired, there is a larger area of blood-rich retina exposed resulting in the effect in humans commonly known as red-eye. Another way to mitigate the effect if using bounce flash or the flash off-camera is not possible, is either to have the ambient light level as high as possible so that the subject's pupils are smaller, or to use a pre-flash burst before the shot to accomplish the same effect (smaller pupils) before the picture-taking shot.
Robert

[Digital]

Bruce - it would be great if you could post that image to give us a better look at the eyes. My first guess is that that part of the eyes got blown out a bit.

Manfred, here is the pic. If this is red eye, it is the funniest red eye I have ever seen. I failed to mention that I was using a Lumi-Quest diffuser over the flash.

Bruce

[george013]

Manfred, here is the pic. If this is red eye, it is the funniest red eye I have ever seen. I failed to mention that I was using a Lumi-Quest diffuser over the flash.

Bruce

White balance? The white isn't white either.

George

[Manfred M]

I think George is on the right track. The skin tones in the image look quite yellow in the shot. Yellow is the complementary colour to blue, so if I start removing yellow (by adding blue) from the image, we start getting more blue in the image, including the eyes..

So the question is what colour temperature setting did you use?




This is a screen print from the close up of the eyes in Photoshop after I removed some of the yellow. The predominant colour of the eyes seems to be blue, but of course I don't know how close this blue is the the real eyes.

Did you have one of the coloured reflectors on the LumiQuest when you shot this image?

By the way, on-camera flash is not going to give you are particularly attractive image. The modifier you are using is still going to leave you with a small, hard light source. Bounce flash or off camera flash work a lot better for this type of shot.

[Digital]

Manfred, the WB on the camera was set to auto. After George's comment, I went into LR and changed the WB to fluorescent. The yellowish cast disappeared, and the subject's eyes appeared more blue. My guess is that the ambient light overpowered the light from the flash which resulted in the effect that I got. The ambient light was, as you can guess fluorescent.
As far as your comment about bouncing the flash, I now employ this method for a variety of reasons. This goes to show my ignorance of using speedlights in relation to portraiture. I have a lot to learn.
Thanks to you, and George for commenting, and both of you feel free to correct me if I am wrong on my assumptions.

Bruce

[Manfred M]

Manfred, the WB on the camera was set to auto. After George's comment, I went into LR and changed the WB to fluorescent. The yellowish cast disappeared, and the subject's eyes appeared more blue. My guess is that the ambient light overpowered the light from the flash which resulted in the effect that I got. The ambient light was, as you can guess fluorescent.
As far as your comment about bouncing the flash, I now employ this method for a variety of reasons. This goes to show my ignorance of using speedlights in relation to portraiture. I have a lot to learn.
Thanks to you, and George for commenting, and both of you feel free to correct me if I am wrong on my assumptions.

Bruce

Normally the appropriate setting while using flash is either flash or daylight. Unless you were "dragging the shutter", the default speeds on a flash generally overpower the ambient light. One way to check to see how much influence the ambient light had on the image is to get the ISO, shutter speed and aperture setting for that image. Set the camera to Manual mode and use those settings to shoot where you took the original image. You don't need a model there, but whatever illumination you see in the image will give you a very good indication of how much or how little the ambient light influenced your shot.

[Digital]

Manfred, the aperture for this photo was f/8, SS-1/60, and ISO-200. Given my recent experience with SS influencing the ambient light, it seems that the one factor that sticks out is that the SS is to slow for the amount of ambient light in the room where the pic was taken. Based on a previous thread on CiC, I believe that if I had bumped the shutter speed to 1/100, and possibly increase the ISO to 400, I may have gotten better results.

Bruce

[Manfred M]

Yes - that shutter speed of 1/60th definitely could be the issue. If you want to minimize the risk of ambient light, then shooting at whatever the synch speed is for your camera; typically in the 1/200th to 1/250th range. That would likely resolve that issue.

By the way, if you read about "dragging the shutter", that is exactly what you were doing. There are times that we want the ambient light affecting our exposure.

[Dave Humphries]

Manfred, the aperture for this photo was f/8, SS-1/60, and ISO-200. Given my recent experience with SS influencing the ambient light, it seems that the one factor that sticks out is that the SS is to slow for the amount of ambient light in the room where the pic was taken. Based on a previous thread on CiC, I believe that if I had bumped the shutter speed to 1/100, and possibly increase the ISO to 400, I may have gotten better results.

Hi Bruce,

A key point to clarify:

The flash exposure will not be changed by shutter speed changes from 1/60s to say 1/100s, or even 1/200s.

Therefore; you do not want to increase the ISO upwards because it will affect is the fluorescent ambient light too, bringing it back to the same absolute level as it is in the shot above.

You want the flash to be the more dominant source of illumination and you do that (in these circumstances) by increasing the shutter speed, which reduces the effect of ambient light in the scene.

So there's no need to change the ISO.

If you do increase the ISO, it will just bring the ambient exposure up again (compensating for the faster ss) and, depending how the flash is configured, either over expose the subject, or more likely if shooting TTL; the flash power will be reduced (automatically) and achieve a result that will look very similar to the above.

There is a lot to learn - and I'm no expert; just a block or two further up the street

Cheers, Dave

[Digital]

Dave, when using flash you are dealing with two exposures: light from the flash, and the light that is external to the flash (e.g. light from fluorescents). The ambient light. For the most part the SS influences the ambient light. I proved that (to myself) about a year ago when I changed the SS to a shorter duration or to put it more simply I increased the SS. The exposure on the flash stayed the same in this experiment while the ambient light had less influence, depending on the SS. I have viewed videos that did this same thing using an outdoor setting. The only difference was the ambient light was from the sun. Now this same video indicated that for the most part the exposure from the flash was influenced by the aperture setting.
My question to you is, if the ambient light in a photo is mostly influenced by the SS, and the flash exposure is mostly influenced by the aperture setting, what does the ISO setting mainly influence? Does it mainly influence the flash exposure or the ambient light. ?
Or both.
In my thread I used the word "possibly increase the ISO...". I used the word possibly because there was a little voice going off in my head that said if you increase the ISO you are "telling" the camera to be more sensitive to light that it receives. Logic would dictate that a higher ISO setting would allow you to set your SS at faster speeds, and be able to stop down (do we still use that term?) your aperture when photographing a particular subject in a particular light.
So, to use your example, setting a higher ISO would allow the camera to be more influenced by the ambient light, hence would offset the faster SS you are using to control the ambient light. In a way this is all relative.
Any suggestions you have will be greatly appreciated.


Bruce

[Manfred M]

Bruce - the duration of the flash is in the order of 1/1000th sec, so as long as the shutter speed is at or below the synch speed of your camera (the synch speed is the highest shutter speed where the first shutter blade is at the bottom of the gate before the top blade starts to decend). This is why changing the shutter speed has no impact on flash exposure, but can have a significant impact on the contribution of the ambient light.

When it comes to ISO and you are shooting with iTTL mode, the flash intensity will drop, as you increase ISO (assuming you are not changing the aperture). If your flash is running at full power and there is still not enough light and you are shooting wide open on the aperture, then increasing the ISO will have an impact on the exposure.

[Digital]

Bruce - the duration of the flash is in the order of 1/1000th sec, so as long as the shutter speed is at or below the synch speed of your camera (the synch speed is the highest shutter speed where the first shutter blade is at the bottom of the gate before the top blade starts to decend). This is why changing the shutter speed has no impact on flash exposure, but can have a significant impact on the contribution of the ambient light.

When it comes to ISO and you are shooting with iTTL mode, the flash intensity will drop, as you increase ISO (assuming you are not changing the aperture). If your flash is running at full power and there is still not enough light and you are shooting wide open on the aperture, then increasing the ISO will have an impact on the exposure.

Manfred, thanks for commenting. From what you said I gathered that the ISO setting has " more" of an influence on the flash exposure as opposed to the exposure for the ambient light. Thanks for the clarification.

Bruce

[Manfred M]

Manfred, thanks for commenting. From what you said I gathered that the ISO setting has " more" of an influence on the flash exposure as opposed to the exposure for the ambient light. Thanks for the clarification.

Bruce

It's not quite that straight forward. If you shoot at a lower shutter speed and at a higher ISO, the ambient light will make a higher contribution to the image. If you want to you can test this yourself by doing test shots.

If your camera settings are such that you are using primarily ambient light to take the exposure, and all you use the flash for is to fill in the shadows (this is called fill flash), the ambient light component will be the main light source in the image. This technique is used a lot in outdoor portraiture work.


I used heavy duty fill flash on this Himba woman sitting under a tree in dappled light at mid-day, in Namibia get a better image. of her face.

[Digital]

Manfred, I think understand your point. In an indoor setting using iTTL setting on the flash, the ISO setting will "mainly" influence the flash exposure: however I am not saying that that the ISO setting does not have some influence on the ambient light. Just not as much as the SS.

In regards to outdoor shoots, you are dealing with the sun as the ambient light, hence as you stated the ambient light is the primary light source, hence the flash becomes a secondary source to fill in shadows. I have no problems with fill flash.

Correct me if I am wrong.

BTW nice photograph.


Bruce