Sounds to me like a quick tutorial and some practice with cementing glass, filter, lens elements together is in order. Get some scrap glass and filters and some lens cement and "go to school" and figure out the technique. Some here will likely be able to help. Once you have the technique down, you've solved the problem for life.
Doremus
Expert in non-working solutions.
Polyester filter are optically quite poor. With true Wratten gel filters you have to be careful about how old they are and how they've been stored. They can fade.
You might try looking up C Kenneth Mees (?) and the Wratten & Wainwright company... They invented gelatine filters (later sold to EKC, where Mees became chief scientist)... I have seen old photo tech books that described the process of cementing gels between cover glasses... (I don't have access to my library now...)
Another tip would be to call the engineering dept at one of the filter manufacturers... They take calls about custom designs and might help... in the US, I would call Tiffen...
In the (not very) old days in Hollywood was Harrison & Harrison would allow walk-ins for one on one consulting of filter problems...
Just don't use a process that uses moisture, as it damages the coating...
Steve K
No, they will fade from light and time. When Kirin was distributing B+W filters they placed a very large order for screw in glass wratten filters sandwiched in glass to the old Helix in Chicago. After a few years we took over the distribution their inventory print outs showed that they had sold very few of them and wanted us to take them back on a 2 for 1 stock balance. These were new filters in sealed B+W boxes stored in filter drawers for a few years. B+W refused our request to return them as they were special order items and all had faded over time.
The official Wratten filter publication broke down the specific nature for fade risk of every single filter number with respect to three different key variables. But the problem with deep tricolor examples is that they can fade a fair amount and still look the same deep color. That means that over time they will fall out of balance and become unpredictable, without the problem possibly even being suspected except for increasingly uncooperative negatives over time. For example, with a 25, 58, 47 combination, the 25 red is rated AAA, the 58 green BBC, and the 47 blue BBB. This mean that the blue filter is likely to fade faster than the red, and the green potentially faster than either of the other two. But with old inventory, as if often the case when people purchase gel filters these days, even the starting point might be suspect.
The filters I'm looking at (and will try) are newly made gelatine filters. The green is out of stock and will take some time for new to be made.
Can someone point me to measurements/articles that show that polyester films are "poor"? I'm sorry, but I have far more doubts about gelatine then polyester.
Expert in non-working solutions.
Just try using them. They're cheapo for a reason. I have a big set of Lee polyester filters than I use for mockup purposes, light balancing tests, or non-image-forming applications, never for actual photography unless the scale of reproduction is very modest, like a small casual ad picture. You'll lose image sharpness with them. Some of these are way out of whack in terms of rated density. You should really get ahold of people who have done this before and have prior experience refitting new filters, but it wasn't cheap.
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