How to use a grey card with a Lee Big Stopper

[batmura]

I have recently bought a Lee Big Stopper and am very pleased with it except for the blue colour cast it gives the photos. I was wondering if using a grey card would solve this problem. If so, how would I take a reading from it with the filter on? Or would I simply take a normal shot with the grey card in the frame and then do my white balance selection using the tool in Lightroom? In other words, my question is would the white balance be different with and without the filter?

Thanks!

 

[480sparky]

Including a gray card in your image will make changing the WB a one-click option in post, and would work best when shooting in raw.

Another option would be to find how much you need to correct for when using the 10-stop filter, then creating a profile for it so you wouldn't even need the gray card. For instance, my B+W 10-stop (which is actually 10 1/3) needs the red channel set to 0.90 and the blue to 1.11 to correct for the color cast.

When I stack it and my Singh-Ray VND, those numbers change to 0.87 and 1.24 respectively.

 

[batmura]

I understand the one-click ease of grey cards, but I would like to know how to use it. Can I take a picture holding the grey card in the frame and then another one with the filter attached? Opening in Lightroom, I would click on the image with the grey card, copy the settings and apply them to the image with the filter. Is that the easiest method? Or would I have to hold the grey card in the frame while the filter is attached? That would mean holding it for minutes at a time.

I hope I have made my question clear now.

 

[Josh66]

I understand the one-click ease of grey cards, but I would like to know how to use it. Can I take a picture holding the grey card in the frame and then another one with the filter attached? Opening in Lightroom, I would click on the image with the grey card, copy the settings and apply them to the image with the filter. Is that the easiest method? Or would I have to hold the grey card in the frame while the filter is attached? That would mean holding it for minutes at a time.

I hope I have made my question clear now.

Yes, but you would want the grey card image to also be taken with the filter on. Lay the grey card on the ground or something if it's going to be a long exposure.

Take a picture of it using the filter, in the same lighting that you will be shooting in. Then just use that image to set the WB of the following images in PP.


EDIT
You'll also want to take a new picture of it if the lighting changes significantly. You want it to be taken in identical conditions to the photos you want to use it as a reference on. Or as close to that as you can get. If it's not 100% "perfect", there probably won't be much real-world difference.

 

[batmura]

Why would I have to take a picture of the card using the filter? Isn't it a neutral density filter after all? Would the outcome be different if taken without a filter? I'm just tryint to understand the logic here. Thanks!

 

[Josh66]

Why would I have to take a picture of the card using the filter? Isn't it a neutral density filter after all? Would the outcome be different if taken without a filter? I'm just tryint to understand the logic here. Thanks!

Didn't you say the filter was causing a color cast? Not very "neutral", IMO...

The color cast is why you need to take the grey card shot with the filter on. You want it to be in the same conditions as the photos that you will use it to correct.

If you take the grey card picture with the filter off, and the filter cause a color shift, the grey card isn't going to do anything for you. If the filter does NOT cause a color shift, it should be fine to take the grey card picture without the filter.

 

[batmura]

Josh, thanks a lot! Clears things up perfectly for me

 

[480sparky]

Didn't you say the filter was causing a color cast? Not very "neutral", IMO... ...........

Most 10-stop NDs create a color cast. Rare is the one that has consistent density across the spectrum.

 

[Josh66]

The grey card will be your 'point of reference' - your datum point. If there is a color cast, you want that color cast to also be on the grey card, so you can correct it. The grey card is a known value - when you select it in PP and set that as the WB, the software will adjust the colors as required to bring that to the proper levels.

That's like, the whole point of using a grey card in this manner - put it in the same light that the photos will be in. In this case, it's the filter, not the lighting, causing the change in color, so the grey card needs to experience that change too. Imagine that instead of the filter causing a color cast, there was a colored gel over the light source. Same problem. Since it's the filter, and not the light - the only solution is to take the reference photo with the filter on.

I think you "get it" now, but if there's anything you're still not sure about - ask away.


I wasn't really aware that most 10-stop ND filters do cause a color cast, but it makes sense. That's a lot of light to block, lol.