Can anyone explain this?

The weather is awful and I've had a brutal week. I needed to take a few photos so I put the K20 on a (naff) tripod (no weights this time :wink and fired off a few with my DA* 16-50 and DFA 100. No adjustments to camera settings, little PP other than cropping and re-sizing.

1/. 16-50

[IMG]http://i217.photobucket.com/albums/cc222/Oggy3323/16-50.jpg[/IMG]

2/. 100

[IMG]http://i217.photobucket.com/albums/cc222/Oggy3323/100-2.jpg[/IMG]

3/. 100 again

[IMG]http://i217.photobucket.com/albums/cc222/Oggy3323/100-1.jpg[/IMG]


When I took the second picture I was amazed at the difference in tint/colour cast. I looked at the two for a while and worked out that the second picture was taken at a different angle relative to the light source (a 150 W eq low energy bulb) so I moved the camera to a similar position to the first picture and took the third.

Would people expect the angle of the light to make this much difference to the colour?

Might be a white balance thing, or they all the same?

As I said - camera settings all the same.

The only differences I am aware of are that in 1 and 3, the light source was directly behind me and in 2, it was about 45degrees to me.

I know but auto white balance is also a setting

It appears that the second shot is less exposed when you look at the background.
Strange I must say that.

They were all exposed on the "Tungsten" setting (the one I find best for low energy bulbs).

Same applies, the tungsten setting will vary slightly unless you stop the camera doing that.

The light may reflect differently off the flowers at different angles. The same way that grass ends up in stripes after mowing.

At the risk of being a geek and not getting invited to your Christmas party can you explain the physics behind that John?

Changing the angle of the lighting changes the reflection and makes the exposure slightly different. A polarizing filter might have mitigated the difference.

An extreme example would be to take a photo of an object on a sunny day, once from the front-lit position and once from the back-lit position. The colour would be totally different.

Some more on reflectance.

link

Regards

Oggy - which camera body are you using?

On my K10D I can set 'Fine tune when using AWB' and 'Auto EV compensation' (both are turned off btw) but I don't know if (for example) the K10D tungsten setting varies as John describes above?

John - can you advise? I have also noticed variable exposure and colour issues in almost identical shots.

Thanks!

I understand it does, but have yet to look into it closely. AWB is IMHO the one to avoid, unless of course it happens to give you exactly the results you want.

If the main light source was a 'low energy' bulb you have the same issues as when shooting using fluorescent strip lights. The light output is changing 50 times a second (60 in US), therefore the colour temperature (WB) is also changing 50 times a second.

When you press the button half way, the (Auto) WB is set. Some time later when you make the exposure the chances are that the light colour (WB) has changed.

If you have WB set to something specific like 'Tungsten', you'll experience the same problem. Only when the lght is full on will the WB be correct'ish in camera.

Tungsten filament lamps have a more constant light output because a hot wire can't cool down and heat up that fast. Hot gas, as in a fluorescent bulb/tube, can and does.

That said, I believe that there are some 'low energy' bulbs that have a more constant output.

Good point Peter.

Proper photographic cold continuous lighting is one thing, but domestic bulbs are really quite poor.

Tungsten light actually had quite a lot of advantages which are now being withdarwn from availability!