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Old 16-05-2017, 12:10 PM
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Adjustable IR filters

While browsing on ebay, I found this filter:
http://www.ebay.com.au/itm/Adjustabl...torefresh=true

I will buy it for sure... in the meantime, did anybody try to use it and what were the results?
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Old 16-05-2017, 12:41 PM
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Could not find much about them apart from this forum post and not so favourable reviews here.

To quote:
Quote:
Although the concept is intriguing in reality though the results are quite poor and itís all due to physics. The way these filters are made is by taking a simple variable ND filter, which is a sandwich of 2 types of polarizers and adding a red longpass filter on top of the stack. At this point some of you may already have figured out the issues just from reading the previous sentence. Thatís right, all the problems you experience with variable ND filters transfer over and are made worse with the capture of two different light spectrums, visible and infrared.

The dreaded cross pattern is just as bad here, gets progressively worse the stronger IR effect you dial in. Also, because of the qualities of stacked polarizing filters you also induce a lot of softness to the image, washing out fine detail considerably. I guess if these effects is what you are after then great, this is a perfect filter for you but for the general photographer who is seeking the finest image capture possible this filter just isnít a good idea.
What do you plan using them for?
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Old 16-05-2017, 12:55 PM
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Idea was to use it for AP in IR... IR spectroscopy as well.
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Old 16-05-2017, 01:38 PM
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You can probably get rid of the cross pattern using flats in AP.
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Old 16-05-2017, 01:53 PM
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Merlin66 (Ken)
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Bojan,
For IR spectroscopy, besides having a suitable sensitive camera all you need is a Red sorting filter - something like a Wratten 25 - this will suppress any overlap with the 2nd order at higher wavelengths (>7500A)
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