Photoshop help with colour cast and overexposure

Started Aug 26, 2014 | Discussions thread
tony brown Veteran Member • Posts: 4,146
Re: Photoshop help with colour cast and overexposure
1

Nick1020 wrote:

tony brown wrote:

Nick1020 wrote:

Hi..

I recently purchased a couple of cheap ND filters off eBay. I wasn't expecting amazing results due to the cost and so far, my expectations have been met.

I took a few photos of some waterfalls in the hope of being able to have longer exposures during the day. The results were mixed. Some photos had quite bad purple colour cast as well as overexposed whites on the water. I've managed to improve the quality of some of the photos which were affected with colour cast in Photoshop. I used a new adjustment layer with Photo Filter and another editing hue/saturation but some photos are proving to be a little tricky to improve.

Here's an untouched photo which is typical of the purple colour cast and overexposed whites issue:

When you say you bought a couple of ND filters, were thay by any chance a pair of adjustable twin polarising filters? They give a huge variable range of densities but even the best types (e,g, Hoya) warn of a purple colour cast at the darker settings. It is inherent in the light reduction of crossed polarisers.

By the way, a circular polarised filter is just a normal linear polariser on the front followed by a bi-refringent rear element which splits the light into two outputs at right angles to each other, which then appear unpolarised to the camera. If you place two circular polarisers together and look through them, you only get a reduction as you rotate one, if the two linear sides are adjacent to each other. In other words they act like a normal linear polariser wth a scatterer on the back so as not to interfere with the auto-focussing systems on some digital cameras.

If they were just normal single ND filters, I can't imagine why they resulted in the image you show unless you could also see the same on the screen?

I am not used to camera phones but if you wanted ND filtering, f/2.2 seems a very big aperture. Could you not have got considerably lower illumination by just using a smaller aperture?

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Cheers, Tony.

Thanks for the reply Tony. I'm afraid much of what you said is lost on me though.

The filters didn't come with much information. There's no manufacturer markings on them. They came in boxes very similar to this one:

The filters themselves just have ND4 and ND8 plus 72mm on them.

As for the cast, it was only that bad when I used both the ND4 and ND8 filters at the same time. Using just one at a time let too much light through so I had to compromise by using both of them.

Unfortunately the aperture is fixed on the 1020 so I'm unable to do anything about that.

Thanks again for the reply. Very helpful info, although I will have to read it a few times to understand it properly

Thank you for the reply. No, it doesn't look like they are a pair of cross polarised filters. You might play with those sometime. They too, can be bought on E-bay for very little like this example links:- (N.B. I have not checked their diameters, just the type of ND filter.)

http://www.ebay.co.uk/itm/3in1-67mm-Variable-Neutral-Density-Fader-ND-Filter-ND2-ND8-ND16-to-ND400-LF306-/161360446317?pt=UK_CamerasPhoto_CameraAccessories_CameraLensesFilters_JN&hash=item2591d5036d

or this:-

http://www.ebay.co.uk/itm/Slim-58mm-Fader-Variable-ND-Filter-Neutral-Density-Adjustable-ND2-to-ND400-/310792822322?pt=UK_CamerasPhoto_CameraAccessories_CameraLensesFilters_JN&hash=item485cb21e32

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Cheers, Tony.

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