Need to know : why is did the sky change colour

[gordon77]

hey ppl i was taking some shots at a place up north from me in the morning after the sun had rised. first of all i acknowledge the tilt on the horision (i swear it was straight) i was still stumbling from an 'all nighter' anyways i wanted to capture the movement of the water coming in over and around some seaweed so i slapped on my ND (4stops) to slow the shutter down and this worked well. ive only just uploaded them onto my comp and i now see that the difference in the colour of the sky is amazing!!!!

i would liketo know why this has happened when the only difference i have made is shutter and appeture changes - these shots were taken at most 10-15 mins apart however the sky had not changed to my eye in that time

these were taken on my humble 400d with 17-85 IS USM (and UV filter but we all know that )

Mods NB: i really hope this is in the right section if not fell free to move :thumbup:



without filter filter:

ISO:100 Shutter speed:1/250 App: 8

with Cokin P ND8

ISO:100 Shutter speed: 0.5 App: 22

 

[LAW2]

I can't answer your question definitively, but my guess would be the tinting of the filter is not a true grey. Much like car window tint that looks purple. Just a guess, but I really like the photo. Inspired me to try it myself. I hope someone can help you.

 

[karissa]

Well, I'm taking a bit of a stab at this but... in my experience, long exposure night shots end up with very interesting colors. Could this be part of the issue? The longer exposure is causing lighting differences? Maybe someone can be more technical than I have been.

 

[Digital Matt]

It could be an auto white balance issue, with regard to the neutral density filter, but also, at 1/2 second, time is passing in front of your lens, and a lot of things you don't see with your naked eye are recorded to the sensor.

 

[gordon77]

thanks for the replys ppl i have forgotten to mention something but both the shots were taken with an ND4 grad aswell so the sky is stoped down by 6. maybe this could be something to do with having 2 filters??? but yes - im beggining to enjoy the ND filters - you can get some interesting shots with them by the looks

 

[Steph]

In my experience, Cokin ND grad filters are not trully neutral and sometimes give a pink/purple cast to skies, exactly as shown on the second picture. I guess with a digital camera you can corect the colour of the sky in post-processing but it is more problematic with film. Alternatively, Hitech and Lee (and probably othes) make trully neutral filters.

 

[Garbz]

Well, I'm taking a bit of a stab at this but... in my experience, long exposure night shots end up with very interesting colors.

If you are talking about long-exposure colour casts, this happens only on film. And the cast usually tends towards the green side. Other than that all lighting staying equal the images should be identical. I blame the filters.

 

[gordon77]

If you are talking about long-exposure colour casts, this happens only on film. And the cast usually tends towards the green side. Other than that all lighting staying equal the images should be identical. I blame the filters.

aha i see thanks for the info Garbz/Steph this is what i needed to know. filter issues asside - what image do you ppl prefer??? i kinda like the effect of the diffrent coloured sky but the 'cleanlyness'
(compared to the second shot) of the first is allso appealing

 

[Sw1tchFX]

these shots were taken at most 10-15 mins apart however the sky had not changed to my eye in that time

The human brain is an amazing thing. We can auto white balance with incredible speed and accuracy. Take flourecent lights for example, if you're in an office they're white, right? No, they're very green, our brains just adjust to it. It's eiasier to see the difference if you're outside, looking in.

Camera's don't work like that. Just because you see the lights in the office you're in as white, your camera sees them as green, you need to tell it to use more magenta to balance it and make it white.

 

[gordon77]

ahh yes this something i was intrested in doing later on when i got more familiar with the camera but i guess i can start fiddling round with the custom white ballance now lol,do i need an 18% grey card to take a shot of or can this be ajusted in the cameras raw edit software?