Very Odd Pentax Red/Blue Filter, but for what use?

[doug_stemke1]

I was digging through a bin at a camera show and came across a most

unusual filter. If you turned it one way it was red (the whole image

was red); if you turned in around the other way it was blue.

Therefore in an odd sort of a way it was like a polarizer, just that

the choices were blue or red rather than polarized or not. I didn't

buy it because it was very expensive but it peaked my curosity.

 

1) What kind of optical glass would they make that would do something

like that?

 

2) What use would one have with this combination? Like I said, it

was very expensive; I assume owning one red and one blue filter, even

coated, would be cheaper.

 

It was an 'oldish' kind of filter, I don't see it in any new

catalogs. Other than the "golly-gee-whizz" factor I can't imagine

there was much use for a filter like this.

 

Just wondering. Thanks.

[steve_levine]

There must have been some letters or numbers on this thing?Red & Blue combined wont let much thru.It sounds like an IR filter possiblly?

[keith_van_hulle1]

I think that's what some call an enhancing filter. Punches up certain colors (reds/browns) when used on foliage, especially in conjunciton with a polarizer. The word didymium comes to mind in conjunction with this but I can't remember where. Try a search with that.

[todd peach seattle, washi]

Sounds like a red/blue polarizer. It's not typically used 'all red' or 'all blue', but adjusted so that the polarized light in the scene reacts with one half of the filter or the other (I'm not sure technically what's happening). Cokin has them.

 

They're a tool for making psychedelic / Mitchell Funk / cross-processed looking photos. I used to have a photo in my 'brag book' (the book camera salespeople turn to in order to convince you to buy more equipment) with a red/blue. Deep purple sky and and pink desert rocks. Didn't sell many........

[solja]

For what it's worth, last month's issue of Outdoor Photographer had a 'gold/blue' polarizer in it that sounds very similar to what you described, except turned one way it enhanced the gold tones in an image, turned the other way it enhanced the blues.

[canon man]

Yeah, sounds lik another one of those filters tha tyou buy for one price carry it in your bag for a year or two, use it once then sell it for less than half of what you paid for it!