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Thread started 01 May 2015 (Friday) 03:18
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Trying to determine if my 10-stop filter has a color cast

 
trale
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May 01, 2015 03:18 |  #1

I recently bought a 10-stop ND filter for my 5D3. It works beautifully, and from normal shooting I'm not detecting any noticeable color cast, which is great. Here's a quick test I did outside:

Without filter:

IMAGE: https://dl.dropboxusercontent.com/s/whf5zowfqqdyspo/C_outdoors_nofilter.jpg

With filter:
IMAGE: https://dl.dropboxusercontent.com/s/5uei13p2lv428vy/C_outdoors_10stop.jpg


But I'd like to be a bit more thorough, so I did a few controlled indoor test shots with a color-checker, and I need some help to analyze the result.

The first scenario is set on Auto-white-balance (which is what I normally shoot with anyway).
The no-filter test case resulted in a normally exposed shot at a shutter speed of 1/30s, Temp=4250, Tint=+21:
IMAGE: https://dl.dropboxusercontent.com/s/zjdwupnn9e8l6o9/E_AWB_noFilter.jpg

With the filter, I get an shutter speed of 25s, Temp= 4150, Tint=+8
IMAGE: https://dl.dropboxusercontent.com/s/riwhcihrkszl7q2/E_AWB_10stop.jpg

My first impression is that they look very similar, the filtered shot perhaps a tad warmer. A slight tweak will make them look identical. But then I noticed that the Temp and Tint values are not the same as the control shot. The control has a slightly higher Temp (4250 vs 4150), and a significantly higher tint toward magenta (+21 vs +8). So even though the resulting shot looks pretty similar, their Temp and Tint values are different to reach a similar output.

So the 2nd scenario is to use manual white balance so the temp & tint stays the same in both shots, and here's what I got:

Control shot (no filter): WB set to 4300 (and apparently a tint of +8):
IMAGE: https://dl.dropboxusercontent.com/s/nhu2tqo467brgzw/F_4300k_noFilter.jpg

With filter: Same Temp =4300, tint=+8
IMAGE: https://dl.dropboxusercontent.com/s/u6u80ddsxt77nfe/F_4300k_10stop.jpg

My reaction is that the filtered shot looks better white-balanced, but what really matters is that clearly it doesn't look the same as the no-filter control shop. The temperature doesn't differ much between the shots, but the no-filter shot has a green tint compared to the filtered shot's magenta tint.

So does this mean that my 10-stop filter does have a color-cast toward magenta? Even thought with Auto WB the shots look nearly the same, and sliding the tint slider in post can eliminate any perceived differences.

What conclusions should I draw?



  
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MalVeauX
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May 01, 2015 03:31 |  #2

Heya,

All filters of this magnitude have a color cast.
The real question is to what degree and if it's acceptable and easy to deal with in post.

The conclusion to draw here is that your filter has a near unnoticeable color cast, which is very good for a 10 stop filter and you should be very happy with this filter.

Very best,


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GeoKras1989
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May 01, 2015 05:48 |  #3
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That little difference would not have bothered me on film, where you are pretty much stuck with it. In the digital age, the difference is quite meaningless.


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AJSJones
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May 01, 2015 12:16 |  #4

MalVeauX wrote in post #17539311 (external link)
Heya,

All filters of this magnitude have a color cast.
The real question is to what degree and if it's acceptable and easy to deal with in post.

The conclusion to draw here is that your filter has a near unnoticeable color cast, which is very good for a 10 stop filter and you should be very happy with this filter.

Very best,

Wrong!!! It is EXCELLENT for a 10-stop filter:D:D


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brucea
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May 01, 2015 14:04 |  #5

the question nobody has asked: what is the brand of the filter??




  
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saea501
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May 01, 2015 16:01 as a reply to  @ brucea's post |  #6

If the filter is that good, why does it matter?

Maybe so you can go out and buy one? :-)


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trale
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May 01, 2015 16:18 |  #7

MalVeauX wrote in post #17539311 (external link)
Heya,

All filters of this magnitude have a color cast.
The real question is to what degree and if it's acceptable and easy to deal with in post.

The conclusion to draw here is that your filter has a near unnoticeable color cast, which is very good for a 10 stop filter and you should be very happy with this filter.

Very best,

Yes, I am very happy with this filter. And in my normal flow of post-processing, I'm not seeing any kind of cast that's tricky to get rid of. It's as easy to work with as normal shots without the filters.

I suppose my OP is more an academic question: What should be the process/methodology for determining whether any filter has a cast or not, and to what degree?

Theoretically speaking, if a filter is absolutely color neutral, then when shot under the same Temperature and Tint settings (with the appropriate shutter-speed to achieve the same exposure), it should look exactly the same as a shot without the filter, right? Or is there something wrong with that reasoning?


And for anyone that is curious, this filter is from a brand new company that I helped kick-start:
http://breakthrough.ph​otography/ (external link)

This is their X3 10 stop ND filter. It is their premium line, and certainly commands a premium price. And so far, it's living up to that claim. Certainly better than my previous Hoyas NDs. I didn't include this in my OP, to avoid biased responses.




  
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scotchtape
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May 01, 2015 16:36 |  #8

Nice. My cheap ND filters (that I never use) have terrible color cast.
I have one of those expensive Tiffens that got good reviews but haven't made any tests with that one yet - the variable ND one.

Someone should do a comp




  
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MalVeauX
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May 04, 2015 00:16 |  #9

Heya,

The very nature of things, you have to expect SOME change to the light as it passes through a medium of some kind, especially a crystalline matrix like what you find in a filter. The fact that they found a better way to make a strong 10 stop filter and reduce the color cast that is associated with them to a much lesser degree is fantastic. Granted, we can fix color casts quite easily in post, so it's not that big a deal to me. I do like the idea of one less thing to adjust in post. Maybe if they ever produce square plate filters, I'll get interested in one of their products. As it is, I have no want/need for a 10 stop circular screw on. That said, again, they have done wonderful engineering to achieve such a low degree of color cast. But again, you have to expect a slight bit of change to light passing through a filter.

If there was no measurable difference, I would question authenticity, you know? It's not possible to have "absolute" neutrality. Again, the light is passing through a medium. It will change. It must. It's just a question of "to what degree."

Great filter. If they go square, it will make Lee re-think things.

Very best,


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Canon_Lover
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May 04, 2015 16:38 |  #10

That's pretty damn impressive color accuracy for a 10 stop filter. I would be thrilled to have that little of color change.




  
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Trying to determine if my 10-stop filter has a color cast
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