Haze inside an IR filter?

[Vcotea]

Hello!


I've just noticed a sort of hazing inside my IR filter. It's not affected by me cleaning (rinsing with high-proof alcoholic solution and then wiping with optical tissue) either side of it. The filter has been screwed on one of my lenses and has been sitting for the last week in a drawer, which is cool and dry. The filter is a B+W 46mm UV/IR Cut (486M) MRC Filter, for what it's worth.


Here is a link to where I uploaded some images of the said haze on the filter: http://imgur.com/a/zxz1R#jfb0At9

Does anybody know what this might be?


Thanks!

 

[sevo]

That is a piece of solid clear glass with dichroic coatings - unless you melt it or expose it to levels of radiation that would kill you on the spot, it will be impossible to create internal haze in it.

What you see must be either on the surface (cleaner etched into coating?), or you are observing internal cross-reflection effects by looking at an angle through the filter coatings - the latter is irrelevant, this filter does all kinds of odd and highly undesirable things at that shallow an angle, and is explicitly specified as being unsuitable even for moderate wide angle lenses.

 

[bsdunek]

Many filters are laminated, that is, a piece of polorized material between two pieces of glass. I moisture or fungus creeps between the layers, this can happen. You might try disassembling the filter, if possible, and cleaning everything. If it doesn't work, the filter was bad anyway. Be careful of the center, polarizing layer, as it's probably plastic.

 

[sevo]

Many filters are laminated,

This one is not.

 

[Vcotea]

Thanks for the replies.
Maybe it's because of the alcohol solution leaving marks. Should I try to buy a fluid for cleaning camera lenses instead?

Apparently, some others may have run into similar issues with this kind of filters, some time ago: http://www.l-camera-forum.com/leica-forum/leica-m8-forum/180384-how-clean-ir-cut-filter.html

 

[sevo]

Cleaning can be difficult as the filter effect is due to the coating strength - just a tiny deposit or erosion might alter the optical properties.

But as I said, the filter is strongly angle dependent by design - if anything odd is observable outside its working range (i.e. at angles where you can also see a colour change), you may ignore it.

 

[rlouzan]

I've seen it happen with some old 1970s Canon glass filters, stored in their original plastic cases. Sometimes the haze can be cleaned but comes back. Probably due to plastic outggasing of cases and cheap lens caps. The worst case I've seen was a lens with cheap lens caps stored in a leather case.

Regards,
Robert