Looking for resources on filters: how they work, when to use and why

Hi,

I was recently asked a series of questions that I don’t know answers to and in todays world is a bit hard to find sensible resources for…

The questions are:
How do the polarization (CPL) filters work? How do the ND filters work? How do the Variable ND filters work?
When and how to use polarization filters? When NOT to use them? What to look for when using them to know they are performing as expected or not doing much? What are the trade-offs?
When to use ND filters? When not to use them?
When Variable ND make sense to use instead of ND filters?
Are there any other “interesting” filters that one might want to look into?

Then there are square filters which I personally got burned with (low quality filter + demanding shooting condition = pretty much unusable result :/).

Are there any sensible materials I could read and watch about those? All that I could find was vids/materials in the style of “look at how cool is polarizing filter and now buy my presets” or “filters from this company are the best, the other are garbage” with very little practical info or knowledge :frowning_face:

Thanks for all the help!

https://www.cambridgeincolour.com/ is a good resource

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There are some good and easy readings on the NISI Filters site: A guide to using filters to their maximum potential - NiSi Filters Australia They explain and do showcases on their filter products. But basically you can use all of the major brands in a similar way. The only thing which I found important when buying filters is that they differ in color cast magnitude.

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Pt. 6 at Roger Clark’s website has a couple of articles on evaluating filter quality which might be of interest:
https://clarkvision.com/articles/index.html#part_6

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Yes, I had the same problems (as expected) when I bought some cheap rectangular ND filters. Especially when trying higher grades you get all kinds of color shift. So better stay with major brand filter glass.

As an upside there and the main reason I bought these filters: they came as a set, complete with a nice cover for 6 or 8 filters, and - the best - about 10 lens thread adapters (49 to 92 mm I think) for a major brand filter carrier system. Whole set for 8 or 10 Euro, when the brand adapters are 8 to 12 each. Real good fit, work like a charm, a real bargain.

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One thing which I find import is that the filter holder should allow the CPL to be as close as possible to the lens. This reduces vignetting in the end if you have an ultra-wide angle lens. And keep in mind that each filter reduces the sharpness of the image. That’s a trade-off you need to keep in mind.

Tell me about it, I decided to change my filters because of this. After a bit of research I bought Nisi square filters. I haven’t regretted it. The ND filters are particularly good, with very little colour cast.

One that I have found useful, also from Nisi is their “Natural Night” filter. This reduces street lights and helps with astrophotography.

This is a useful page if you are trying to find compatible filters for various wide angle lenses:

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